JP3984211B2 - Optical head device and signal reproducing device - Google Patents

Description

The present invention relates to an optical head device and a signal reproducing device effective for an optical disc apparatus capable of high-density recording / reproduction having lower read / write compatibility.

  Optical disks are attracting a great deal of attention as the next-generation storage memory because they have high density and large capacity and can be replaced in the same way as floppy disks. However, the disk exchange function has a great merit in expanding the use of the memory, but it is an obstacle to increase the density and capacity of the disk. That is, in a memory capable of exchanging disks, read / write compatibility with an already widespread disk is always required for a disk with high density and large capacity. This is because it is necessary to take over the already popular software property from the past to the future.

  As the recording light source, a semiconductor laser having a light emission wavelength of 830 nm and 780 nm and a 50 mW class is used in an actual optical disc apparatus, and a red laser beam of 690 nm and a 30 mW class has begun to be shipped.

  As other short wavelength light sources, green and blue light sources using SHG are attracting attention. YAG or YVO is oscillated using a semiconductor laser as an excitation light source, and this near-infrared light (1.06 μm) is doubled in wavelength by an SHG element such as KTP installed in a resonator to create a green light source of 530 nm, Alternatively, a blue light source is made by directly doubling the semiconductor laser light.

  As a method for reducing the light beam spot diameter, there is a method of increasing the NA of the objective lens in addition to shortening the wavelength. NA is 0.45, which is the recommended value for CD, and is currently increased to 0.55 in a device using a magneto-optical (MO) medium capable of recording / reproducing. If the value of NA is increased, the beam spot can be reduced at this ratio. However, there is a limit to increasing this value due to problems in manufacturing the objective lens at a low cost (depending on the lens load) and coma due to the tilt of the disk substrate. When a conventional plastic substrate with a thickness of 1.2 mm is used, NA is limited to about 0.55. To increase the NA, it is necessary to attach a tilt correction mechanism to the head or reduce the substrate thickness. is there. When the substrate thickness is changed from 1.2 mm to 0.6 mm, the allowable value for the tilt is increased, and the NA can be increased to about 0.65.

  As the rewritable optical recording medium, an MO medium and a phase change recording medium (PC) have been put into practical use. The PC medium has recently attracted attention because it can be overwritten, and recording and erasing can be performed by phase change between crystal and amorphous. This medium includes a GeSbTe medium whose reproduction signal is a negative signal and an InSbTe medium whose positive signal is a positive signal. The former is erased by solid phase, and the latter is erased by melting. The latter is better for the erase ratio because it melts, but on the other hand, the stress due to heat is large, and the former is better for the number of rewrites. For this reason, practical use has started from the latter.

In an optical disk apparatus, an optical head having two light sources having different wavelengths has been developed for the purpose of increasing the number of functions. As the light source, a laser light source is usually used. In such an optical head, for example, one of the two light sources is used for reproduction and the other is used for recording / erasing. In this case, since a light beam with high power is used particularly for recording or erasing, it is important for obtaining a stable operation of the light source to prevent the reflected light of this light beam from entering the light source as return light. Become.
Japanese Utility Model Publication No. 4-93922 JP-A-2-168447 Japanese Patent Laid-Open No. 2-310837 Japanese Patent Laid-Open No. 4-258821

  When recording / reproducing with respect to a medium for high density and reproducing with respect to a medium for low density are realized by one optical head device, it is necessary to avoid complication.

  In addition, since the optical discs have different thicknesses for high density and low density, it is necessary to easily cope with the disc.

It is an object of the present invention to provide an optical head device capable of recording / reproducing with respect to a high density medium and reproducing with respect to a low density medium without complicating the configuration .

An optical head device according to the present invention is an optical head device that selectively irradiates a high density medium or a low density medium having different information recording densities with first and second light beams. a first light source for emitting the first light beam having a wavelength, a second light source for emitting the second light beam of the second wavelength longer than the first wavelength, said first light beam Alternatively, the objective lens for condensing the second light beam as the first light spot or the second light spot on the high density medium or the low density medium, respectively, and the first light source. A first optical path for guiding the emitted first light beam to the objective lens; and a second optical path for guiding the second light beam emitted from the second light source to the objective lens. In the first optical path, the objective lens The incident light is parallel light, and the first light spot is set so as to be compatible with the high-density medium. In the second optical path, the light incident on the objective lens is a point light source. The second light spot is set so as to be compatible with the low density medium, and the high density medium is lighter than the recording layer compared to the low density medium. The thickness of the substrate located on the beam incident surface side is small.

According to the present invention, reproduction on high-density media and low-density medium without complicating the configuration, recording is possible.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, in the following description, the first embodiment to the 28th embodiment are reference embodiments, and the present invention will be described as a specific embodiment from the description of the 29th embodiment after FIG. Is done. That is, the first to twenty-eighth embodiments are meant to supplement the lack of explanation of the embodiments of the present invention.

  (First Embodiment) FIG. 1 is a diagram showing an optical system of an optical head device according to the first embodiment, and FIGS. 2 and 3 show the polarization states in the respective parts of light of the first and second wavelengths. FIG. In the following, the terms “high density” and “low density” used for an optical disc as a medium relatively indicate the degree of areal density defined by track density (TPI) and linear density (BPI). . In other words, the high density optical disc has a higher surface density than the low density optical disc.

  The optical head device shown in FIG. 1 includes objectives disposed opposite to first and second light sources 1 and 2, a beam splitter 3, a collimator lens 4, beam splitters 5 and 6, a quarter-wave plate 7, and an optical disk 9. The lens 8 includes a detection system lens 10, a photodetector 11, a collimator lens 12, and a beam shaping prism 13.

  The light sources 1 and 2 are semiconductor lasers, for example, and oscillate at different wavelengths λ1 and λ2. The light source 1 emits a p-polarized light beam whose polarization direction is the x-axis direction, and is used for reproducing information recorded on the optical disk 9. The light source 2 emits a p-polarized light beam whose polarization direction is the y-axis direction on the incident surface of the beam splitter 5 and is used for recording information on the optical disk 9 and erasing the recorded information. Is done. Therefore, the power of the light beam emitted from the light source 2 is sufficiently higher than that of the light source 1.

  The beam splitters 5 and 6 and the quarter-wave plate 7 synthesize light beams with wavelengths λ 1 and λ 2 emitted from the light sources 1 and 2 and guide them to the optical disc 9, and reflected light with wavelengths λ 1 and λ 2 from the optical disc 9. This constitutes a synthesis / separation optical system. As shown in FIGS. 4 and 5, respectively, the beam splitters 5 and 6 have wavelength characteristics of transmittance of p-polarized light and s-polarized light, respectively. For the wavelength λ2, the p-polarized component is transmitted and the s-polarized component is reflected.

  1 will be described with reference to FIGS. 2 and 3. FIG.

  First, the operation of the optical system when reproducing from, for example, a high-density optical disk using the light source 1 having the wavelength λ1 will be described. The light beam having the wavelength λ1 emitted from the light source 1 is transmitted through the beam splitter 3 and then collimated by the collimator lens 4 to become a parallel beam. The beam splitter 3 has characteristics as a polarizing beam splitter that separates the p-polarized component and the s-polarized component.

  The light beam having the wavelength λ 1 collimated by the collimator lens 4 enters the beam splitter 5. As shown in FIG. 4, the beam splitter 5 reflects both the p-polarized component and the s-polarized component for the wavelength λ1, transmits the p-polarized component for the wavelength λ2, and reflects all the s-polarized component. Has characteristics. Therefore, the light beam having the wavelength λ 1 is reflected by the beam splitter 5 and guided to the beam splitter 6. The characteristic of the beam splitter 5 with respect to the wavelength λ2 may be a characteristic of transmitting a part of the p-polarized component.

  As shown in FIG. 5, the beam splitter 6 reflects both the p-polarized component and the s-polarized component for the wavelength λ1, transmits the p-polarized component for the wavelength λ2, and reflects the s-polarized component. Have Accordingly, the light beam reflected by the beam splitter 5 and incident on the beam splitter 6 is reflected again by the beam splitter 6 and guided to the quarter-wave plate 7. In FIG. 4 and FIG. 5, the characteristics of the beam splitters 5 and 6 are the same. However, the characteristics are not necessarily required as long as the characteristics satisfy the above conditions.

  The quarter wave plate 7 is a wave plate optimized for the wavelength λ2. Therefore, for example, if the difference between λ1 and λ2 is small, the light beam having the wavelength λ1 after passing through the quarter-wave plate 7 becomes an elliptically polarized beam close to a circle. The light beam having the wavelength λ1 that has passed through the quarter-wave plate 7 is narrowed down by the objective lens 8 and applied to the optical disk 9.

  The reflected light of wavelength λ 1 reflected by the optical disk 9 passes through the objective lens 8 in the direction opposite to the incident light beam, and is then converted by the quarter wavelength plate 7 into elliptically polarized light whose major axis is the x-axis direction. The reflected light beam having the wavelength λ 1 that has passed through the quarter-wave plate 7 is reflected by the beam splitter 6 and further reflected by the beam splitter 5. The major axis of the elliptically polarized light of the reflected light beam when emitted from the beam splitter 6 is in the z-axis direction, passes through the collimator lens 4 and enters the beam splitter 3. Since the beam splitter 3 has a characteristic of reflecting only the s-polarized light component, a part of the reflected light beam having the wavelength λ 1 is reflected by the beam splitter 3. The light beam reflected by the beam splitter 3 enters the photodetector 11 through the detection system lens 10.

  The photodetector 11 is for performing reproduction of an information signal recorded on the optical disc 9, focus error detection, and tracking error detection. For example, the photodetector 11 includes a divided photodetector in which a light receiving surface is divided into a plurality of light receiving surfaces. An output signal corresponding to the above is subjected to current-voltage conversion and amplification by an amplifier (not shown), and then input to an arithmetic circuit, whereby a reproduction information signal, a focus error signal, and a tracking error signal are generated. The detection system lens 10 is provided especially for focus error detection. When the astigmatism method is used for focus error detection, a cylindrical lens is used as the detection system lens 10.

  Next, the operation of the optical system when performing recording or erasure on the low density optical disk or the high density optical disk using the light source 2 having the wavelength λ2 will be described. The light beam of wavelength λ2 emitted from the light source 2 is collimated by the collimator lens 12 to become a parallel beam, and the beam shape is shaped into a circle by the beam shaping prism 13. The light beam shaped by the beam shaping prism 13 is incident on the beam splitter 5 as p-polarized light whose deflection direction is the y-axis direction, and is transmitted in accordance with the p-polarized light transmittance Tp shown in FIG. According to the example of FIG. 4, since the transmittance Tp is almost 100% at the wavelength λ2, the light beam having the wavelength λ2 is almost transmitted.

  The light beam having the wavelength λ 2 that has passed through the beam splitter 5 enters the beam splitter 6. Since the beam splitter 6 has the characteristics shown in FIG. 5, the light beam that is p-polarized light in the y-axis direction that is incident from the beam splitter 5 is reflected by the beam splitter 6. The light beam having the wavelength λ2 reflected from the beam splitter 6 is converted into circularly polarized light by the quarter wavelength plate 7 optimized for the wavelength λ2, and then narrowed down by the objective lens 8 to be irradiated onto the optical disk 9. Record or erase.

  Next, the reflected light of wavelength λ 2 reflected by the optical disk 9 passes through the objective lens 8 in the direction opposite to the incident light beam and becomes linearly polarized light in the x-axis direction by the quarter wavelength plate 7. Transparent. Therefore, the reflected light of wavelength λ2 from the optical disk 9 does not return to either of the light sources 1 and 2.

  As described above, in the present embodiment, the reflected light from the optical disk 9 of the light beam having the wavelength λ2 having a large power emitted from the light source 2 does not return to the light sources 1 and 2. 2 can be stably recorded / reproduced / erased without being unstable.

Next , another embodiment will be described. In the following embodiment, the same parts as those in FIG. 1 are denoted by the same reference numerals, and only differences from the first embodiment will be described.

  (Second Embodiment) FIG. 6 shows an optical head device according to a second embodiment, in which convex lenses 21 and 23 and photodetectors 22 and 24 are added to stabilize the output of the light sources 1 and 2, and the photodetector. Based on the output of 22 and 24, it has the structure which performs the output control of the light sources 1 and 2 via the light output control circuit which is not illustrated.

  Here, in order to surely detect a part of the light beam having the wavelength λ2, a beam splitter 14 having a characteristic of transmitting part of the p-polarized light is used instead of the beam splitter 5 in FIG. The wavelength characteristic of the beam splitter 14 is shown in FIG.

  Further, in FIG. 6, instead of the beam splitter 3 in FIG. 1, a beam splitter 15 having the characteristics of a polarization beam splitter that separates p-polarized light with a predetermined intensity ratio with respect to the wavelength λ1 and reflects all s-polarized light is used. Yes. The wavelength characteristic of the beam splitter 15 is shown in FIG.

(Third Embodiment) FIG. 9 shows an optical head device according to a third embodiment, which can reproduce information recorded on the optical disk 9 and detect a servo error signal even with a light beam of wavelength λ2 from the light source 2. As described above, a detection system lens 31 and a photodetector 32 are added to the configuration of FIG. That is, as in the first embodiment, the beam splitter 6 transmits only the light beam having the wavelength λ 2, so that the reflected light of the wavelength λ 2 from the optical disk 9 that has passed through the beam splitter 6 is detected through the detection system lens 31. By guiding the signal to the device 32, the reproduction information signal, the focus error signal, and the tracking error signal are detected.

  As described above, according to the present embodiment, information reproduction, focus error detection, and tracking error detection can be performed independently for each of the light beams having the wavelengths λ1 and λ2.

(Fourth Embodiment) FIG. 10 shows an optical head device according to a fourth embodiment, which is a combination of the second and third embodiments.

(Fifth Embodiment) FIG. 11 shows an optical head device according to a fifth embodiment, in which the positional relationship between the light sources 1 and 2 and the beam splitters 5 and 6 in FIG. Along with this, mirrors 41 and 42 are added.

(Sixth Embodiment) FIG. 12 shows an optical head device according to a sixth embodiment, in which convex lenses 21 and 23 and photodetectors 22 and 24 are added to the fifth embodiment in the same manner as in the second embodiment. Based on the outputs of the detectors 22 and 24, output control of the light sources 1 and 2 is performed via a light output control circuit (not shown).

(Seventh Embodiment) FIG. 13 shows an optical head device according to a seventh embodiment. A detection system lens 31 and a photodetector 32 are added to the fifth embodiment as in the third embodiment, and the beam splitter 6 is added. In this example, the reproduction information signal, the focus error signal, and the tracking error signal are detected by guiding the reflected light of the wavelength λ2 from the optical disk 9 that has passed through the optical system 9 to the photodetector 32 through the detection system lens 31. .

(Eighth Embodiment) FIG. 14 shows an optical head device according to an eighth embodiment, which is a combination of the sixth and seventh embodiments.

(Ninth Embodiment) FIG. 15 shows an optical head device according to a ninth embodiment, in which the beam splitter 6 in the first embodiment is rotated by 90 ° about the x-axis, and 1 between the beam splitters 5 and 6. This is an example in which a / 2 wavelength plate 16 is inserted. In this case, since the polarization direction of the light beam traveling from the beam splitter 5 to the beam splitter 6 is rotated by 90 ° by the half-wave plate 16, this is equivalent to the rotation of the beam splitter 6 by 90 ° around the x axis. In the present embodiment, even if the mirror 42 is omitted, there is essentially no change, only the positional relationship between the optical disc 9 and the optical system is changed.

(Tenth Embodiment) FIG. 16 shows an optical head device according to a tenth embodiment. Similarly to the second and sixth embodiments, the ninth embodiment includes convex lenses 21 and 23 and photodetectors 22 and 24, respectively. In addition, output control of the light sources 1 and 2 is performed through a light output control circuit (not shown) based on the outputs of the photodetectors 22 and 24.

(Eleventh Embodiment) FIG. 17 shows an optical head device according to an eleventh embodiment. A detection system lens 31 and a photodetector 32 are added to the ninth embodiment in the same manner as the third and seventh embodiments. The reproduction information signal, the focus error signal, and the tracking error signal are detected by guiding the reflected light of wavelength λ2 from the optical disk 9 that has passed through the beam splitter 6 to the photodetector 32 through the detection system lens 31. It is an example.

(Twelfth Embodiment) FIG. 18 shows an optical head device according to a twelfth embodiment, which is a combination of the tenth and eleventh embodiments.

(Thirteenth Embodiment) FIG. 19 shows an optical head device according to a thirteenth embodiment. Similarly to the ninth embodiment, the beam splitter 6 in the fifth embodiment is rotated by 90 ° about the x-axis, In this example, a half-wave plate 16 is inserted between the splitters 5 and 6.

(Fourteenth Embodiment) FIG. 20 shows an optical head device according to a fourteenth embodiment. Similarly to the second, sixth and tenth embodiments in the thirteenth embodiment, convex lenses 21 and 23 and a photodetector 22 are shown. , 24 are added, and output control of the light sources 1 and 2 is performed based on the output of the photodetectors 22 and 24 via a light output control circuit (not shown).

(Fifteenth Embodiment) FIG. 21 shows an optical head device according to a fifteenth embodiment. In the thirteenth embodiment, as in the third, seventh and eleventh embodiments, a detection system lens 31 and a photodetector 32 are provided. In addition, the reproduction information signal, the focus error signal, and the tracking error signal are detected by guiding the reflected light of wavelength λ2 from the optical disk 9 that has passed through the beam splitter 6 to the photodetector 32 through the detection system lens 31. This is an example.

(Sixteenth Embodiment) FIG. 22 shows an optical head device according to a sixteenth embodiment, which is a combination of the fourteenth embodiment and the fifteenth embodiment.

(Seventeenth Embodiment) FIG. 23 shows an optical head device according to a seventeenth embodiment, in which the beam splitters 5 and 6 and the beam shaping prism 13 in the first embodiment are integrated. According to this embodiment, the optical system can be further downsized.

  Note that the second to sixteenth embodiments can also have a configuration in which two beam splitters and a beam shaping prism are integrated. In the first to seventeenth embodiments, when the first light source can emit a light beam sufficient for recording, the first light source is independently used for both recording and reproduction with respect to the high-density optical disc. In addition, the second light source can be used independently to perform both recording and reproduction on the low density optical disc. At this time, one of the first and second light sources is preferably turned off when the other is used, thereby preventing the light beam from one from affecting the beam from the other, Reliable recording / playback can be performed.

Further description will be given of an embodiment of an optical disk device. The following eighteenth and nineteenth embodiments have two light beam axes shifted from each other and a mechanism for adjusting at least one of the axes. However, this adjustment mechanism is also applicable to the above-described first to seventeenth embodiments having a coaxial light beam axis.

To (18th Embodiment) FIG. 24 shows an engagement Ru implementation form the optical disk apparatus. In this embodiment, as the high-density light source 51a, for example, a green SHG having a wavelength of 532 nm that emits a low-power constant DC light, and as the low-density light source 51b, a red semiconductor laser having a wavelength of 690 nm capable of direct optical modulation with high power, an optical disk A case where a phase change medium (PC medium) is used as 56 will be described as an example.

  First, the configuration of the optical system will be described. Light beams that are linearly polarized divergent light are emitted from the light sources 51a and 51b. Hereinafter, the light beam emitted from the high-density light source 51a is referred to as a high-density light beam, and the light beam emitted from the low-density light source 51b is referred to as a low-density light beam. These high-density light beam and low-density light beam are first collimated by the collimator lens 52 to become parallel light beams. Each light beam that has become a parallel light beam is transmitted through the polarization beam splitter 53, further circularly polarized by the quarter-wave plate 54, and then condensed on the optical disk 56 by the objective lens 55.

  The collimating lens 52 and the objective lens 55 are designed so that the aberration becomes a specified level at each wavelength in order to pass the high-density light beam and the low-density light beam, that is, two light beams having different wavelengths. (This is generally called chromatic aberration correction). The wavelength setting of the polarization beam splitter 53 and the quarter wavelength plate 54 is arbitrary as long as the optical signal level can be obtained at each wavelength. In this embodiment, from the viewpoint of S / N, the spectral sensitivity of the photodetector is used. Is matched with the lower wavelength, that is, the emission wavelength of the high-density light source 61a.

  Since the size of the light spot formed by condensing by the objective lens 55 is proportional to the wavelength of the light source, the light beam from the high-density light source 51a becomes a small light spot 140 on the optical disk 56 as shown in FIG. The light beam from the low-density light source 51b is collected as a large light spot 141. In FIG. 25, reference numeral 142 denotes a prepit in which ID information or the like is recorded, and reference numeral 144 denotes a tracking groove. Data information is recorded in this groove. Such a method of recording data information in the tracking groove is called an in-groove recording method.

  Next, the light beam collected on the optical disk 56 is reflected. The reflected light of the high-density light beam passes through the objective lens 55 and the quarter-wave plate 54 optimized for the wavelength of the high-density light beam in the direction opposite to the direction of incidence, compared with the case of incidence. As a result, the polarization direction is linearly polarized light rotated by 90 °. Therefore, the reflected light of the high-density light beam from the optical disk 56 is reflected by the polarization beam splitter 53 and guided to the focus error generating element 57.

  On the other hand, the reflected light of the light beam for low density from the optical disk 56 similarly passes through the objective lens 55 and the quarter wavelength plate 54 in the opposite direction to the incident time, but the quarter wavelength plate 54 is light for high density. Since it is optimized for the wavelength of the beam and does not function as a quarter-wave plate for the wavelength of the light beam for low density, the reflected light of the light beam for low density does not rotate by 90 °, and is elliptically polarized. And enters the polarization beam splitter 53.

  Since a part of the reflected light from the optical disk 56 passes through the polarization beam splitter 53 and returns to the light source, the level of the reproduction signal is lowered by that amount. However, when the optical disk 56 is a PC medium, the reflected light is large. In addition, the decrease in the reproduction signal level is not particularly problematic. If the ratio of the emission wavelengths of the high density light source 51a and the low density light source 51b is about 1.2 to 1.4, 80% or more of the reflected light from the optical disk 56 is reflected by the polarization beam splitter 53. . If the return light to the semiconductor laser used as the low-density light source 51b becomes a problem, the polarizing beam splitter 53 and the quarter-wave plate 54 can be designed according to the emission wavelength of the low-density light source 51b. good.

  Next, the reflected light from the optical disk 56 that has been reflected by the polarizing beam splitter 53 and passed through the focus error generating element 57 is incident on the dichroic prism 58, where the light beams for high density and low density having different wavelengths are transmitted. The separated high-density light beam reflected light is guided to the photodetector 59a, and the low-density reflected light is guided to 59b. As the focus error generating element 57, for example, an astigmatism optical system, a double knife edge, or a mixed aberration HOE (hologram element) is used. For the photodetectors 59a and 59b, for example, a two-divided photodetector is used.

  The detection outputs of the photodetectors 59a and 59b are branched into three and input to the servo system switching circuit 60, the relative position deviation detection circuit 67, and the preamplifiers 71 and 72. The servo system switching circuit 60 selects one of the detection outputs of the photodetectors 59a and 59b. Based on the selected detection output, the focus error calculation circuit 61 and the tracking error calculation circuit 62 generate a focus error signal and a tracking error signal. Generated. The generated focus error signal and tracking error signal are supplied to a focus actuator 65 and a tracking actuator 66 through a focus drive circuit 63 and a tracking drive circuit 64, respectively, and the objective lens is supplied by these actuators 65 and 66. 55 is servo-controlled in the focus direction and the tracking direction.

  Which detection output of the photodetectors 59a and 59b is used for the focus and tracking control is selected by the servo system switching circuit 60 according to the discrimination result of the disc discrimination circuit 81 for discriminating the type of the optical disc 56 set in the optical disc apparatus. Is done. The disk discrimination circuit 81 will be described later.

  The optical system of the optical head in this embodiment scans the same track (guide groove 144) with the light spot 140 by the high-density light beam and the light spot 141 by the low-density light beam shown in FIG. Thus, the position in the disk radial direction (also referred to as the tracking direction) is adjusted to coincide. However, if there is a change in temperature / humidity or aging, the two light spots 140 and 141 exceed the relative permissible displacement (about ± 0.05 μm when the track pitch is 1 μm), and the radial direction of the disk May be misaligned. Therefore, it is necessary to align the two light spots 140 and 141 in the disk radial direction by some method.

  That is, since the spatial positions of the high-density light source 51a and the low-density light source 51b cannot be matched with respect to the track direction, the position of the light spot 140 by the high-density light beam and the low-density beam The position of the light spot 141 has a certain distance in the track direction. This distance varies depending on the positions of the light sources 51a and 51b and the magnification of the optical system (generally 1 or less), but is about several tens of μm. Depending on the distance between these two light spots 140 and 141 in the track direction, both spots 140 and 141 cause a relative positional shift in the tracking direction, and it is necessary to correct this.

  On the other hand, the relative defocus of the two light beams 140 and 141 is also caused by the misalignment of the light sources 51a and 51b in the optical axis direction due to temperature / humidity and aging. The magnitude of this focus shift is determined by the magnification of the optical system (generally 1 or less), and can be made substantially the same or less than the depth of focus. There is no.

  Therefore, in the present embodiment, automatic adjustment is performed as follows with respect to the relative positional deviation of the light spots 140 and 141 in the disk radial direction, which is a particular problem. As shown in FIG. 26, consider a case where the light spot 141 by the low-density light beam is relatively displaced on the optical disk 56 by the distance Δy in the disk radial direction with respect to the light spot 140 by the high-density light beam.

  Initially, the high-density and low-density light beams on the photodetectors 59a and 59b are respectively divided into photodetectors 59a and 59b, which are two-split photodetectors, as shown in FIG. It is adjusted so as to be positioned in the center with respect to the dividing line of the light receiving surface. However, as shown in FIG. 26, when the light spot 141 by the low-density light beam shifts in the disc radial direction with respect to the light spot 140 by the high-density light beam, the light spot 141 is changed as shown in FIG. Although it is located at the center of the dividing line on the photodetector 59a, the light spot 140 is located off the center of the dividing line on the photodetector 59b.

  Therefore, in the present embodiment, the relative displacement detection circuit 67 detects the displacement in the disk radial direction from the detection outputs of the photodetectors 59a and 59b, and the position of the light source 51b in the disk radial direction so as to eliminate this displacement. Adjust. Specifically, the low-density light source 51b is attached to the piezo element 68 so as to be movable in the disk radial direction with respect to the high-density light source 51a, and the piezo element drive circuit 69 is used as the output of the relative displacement detection circuit 67. The element 68 is driven. As a result, it is possible to always automatically align the position of the light spot 141 by the low-density light beam with the position of the light spot 141 by the high-density light beam with respect to the disk radial direction.

  FIG. 28 is a diagram showing a specific configuration example of the relative positional deviation detection circuit 67, and includes subtracters 151, 153, 157, adders 152, 154, and dividers 155, 156. The dividing lines of the photodetectors 59a and 59b are set so as to divide the incident light beam into two equal parts when the light spot is not displaced with respect to the disk radial direction. In this case, the subtracters 151 and 153 determine the difference between the detection outputs of the divided regions of the photodetectors 59a and 59b, and the detection outputs of the photodetectors 59a and 59b obtained by the adders 152 and 154 determine these difference signals. Is normalized by dividing by the dividers 155 and 156. Then, if the difference between the normalized output signals of the dividers 155 and 156 is obtained by the subtractor 157, the relative positional deviation amount Δy between the light spot 140 and the light spot 141 shown in FIG. It will be possible.

  Next, the handling of the positional deviation of the light spot 140 by the high-density light beam and the light spot 141 by the low-density light beam in the track direction (direction perpendicular to the disk radial direction) will be described. As described above, since the amount of positional deviation of the light spots 140 and 141 in the track direction is several tens of μm or more, it cannot be absorbed by the sector format GAP (gap portion) in the optical disk. However, the displacement due to temperature / humidity and secular change can be made extremely small and can be generally absorbed by GAP. Since a fixed positional deviation can be measured at the time of head adjustment, it is one method to move the timing of the recording pulse for each track number using this value. As a more practical method, in the present embodiment, as described below, a method of detecting a positional deviation of the light spots 140 and 141 in the track direction on the time axis and delaying the timing correspondingly during recording is used. .

  Now, assume that the light spot 140 and the light spot 141 read the reference pit 160 as shown in FIG. The reference pit 160 is a pit having a shape (size) such that a sufficient detection output can be obtained from the photodetectors 59a and 59b even when the light spot 141 is read by the light beam for low density. The detection output waveform obtained by reading the reference pit 160 is as shown in FIG. 30, and the detection output (solid line) of the photodetector 59a and the detection output (dashed line) of the photodetector 59b are centered on the reference pit 160. The corresponding position is shifted by time Δt. This time shift Δt is detected by the time shift detection circuit 73 of FIG.

  FIG. 31 is a block diagram showing a specific configuration example of the time shift detection circuit 73. The binarization circuit 82 calculates the sum of the detection outputs of the photodetectors 59a and 59b obtained by the preamplifiers 71 and 72. 83, a binary level signal is input to a time interval measuring circuit 84 configured using a counter, and the change point of the output signals of the binarizing circuits 82 and 83 (of the reference pit 160 in FIG. 30). The time interval (time position corresponding to the center) is obtained as a time shift Δt.

  Next, the positional deviation compensation operation in the track direction of the light spots 140 and 141 based on the output of the time deviation detection circuit 73 will be described using the time chart at the time of recording shown in FIG. The signal processing circuit 74 in FIG. 24 receives this signal from the reproduction signal obtained by the light spot 140 by the high-density light beam, that is, the output signal of the binarization circuit 82 (see FIG. 31) in the time shift detection circuit 73. 30 is generated at a time position corresponding to the center of the reference pit 160 of FIG. 30 and is supplied to the recording timing correction circuit 75. FIG. The recording timing correction circuit 75 delays the recording timing pulse by the time lag Δt obtained by the time lag detection circuit 73 (output of the time interval measurement circuit 84 in FIG. 31) and corrects it as shown in FIG. A recording timing pulse is generated, and the recording signal pulse shown in FIG. 32C is sent to the light source drive circuit 76 for the low density light source 51b as a gate signal. As a result, data is correctly recorded on the optical disk 56 without a time shift (Δt) caused by a positional shift of the light spots 140 and 141 in the track direction.

  As the reference pit 160 used for measuring the time shift Δt, an optical disk apparatus that records and reproduces data in units of sectors can use a sector mark, or a test zone track is provided in advance. It is also possible to record the reference pit 160 and determine the time shift in another track from the time shift Δt measured using this.

  In this embodiment, the reproduction signal of the data recorded on the optical disk 56 is signal-processed by the signal processing circuit 74 on the output signals of the binarization circuits 82 and 83 (FIG. 31) in the time shift detection circuit 73. can get.

In the above apparatus, when the set optical disk 56 is a high-density disk, recording is performed using the low-density light source 51b, and reproduction is performed using the high-density light source 51a. When the optical disk 56 is a low density disk, recording and reproduction are performed using the low density light source 51b. Therefore, it is determined whether the optical disk 56 is a high-density disk or a low-density disk, and the recording / reproducing operation is switched.

  First, the recording / reproducing operation when the optical disk 56 is a high density disk will be described.

  Whether or not the optical disk 56 is a high-density disk is determined based on, for example, a sensor hole 79 provided in the disk cartridge 78, a sensor hole detector 80 for detecting this by an optical method, and the output of the detector 80. This is performed by the above-described disk discriminating circuit 81 connected. As another discrimination method, first, the servo system of the optical disk apparatus is switched so as to be suitable for a high density disk, and information on a predetermined track is read. If it can be read correctly, it is determined as a high density disk and cannot be read correctly. In some cases, it may be possible to determine that the disk is a low-density disk and switch the servo system so as to be compatible with the low-density disk.

  When a high-density disk is set as the optical disk 56, focus and tracking servo is performed using reflected light of the high-density light beam. That is, the light detection output of the light detector 59a is selected by the switching circuit 60 and input to the focus error calculation circuit 62 and the tracking error calculation circuit 62, whereby a focus error signal and a tracking error signal are obtained. Signals are supplied to the focus actuator 65 and the tracking actuator 66 via the drive circuits 63 and 64, respectively.

  When reproducing from a high-density disk, only the high-density light beam is used for both reproduction and servo. At this time, the switch circuit 70 is turned off according to the determination result of the disk determination circuit 81. On the other hand, at the time of recording on the high density disk, the optical spot 56 is simultaneously irradiated with the light spot 140 by the high density light beam and the light spot 141 by the low density light beam. Of course, the focus and tracking servo operations are performed using the light spot 140 by the high-density light beam.

  Then, the ID information is read by the light spot 140 by the high-density light beam, and when the light spot 140 matches the sector where the data is to be recorded, the data is written from the sector. In this case, the positional deviation of the light spots 140 and 141 in the track direction, that is, the time deviation Δt is measured by the method described above, and the light spot 141 by the low-density light beam is always more than the light spot 140 by the high-density light beam. The positions of the light sources 51a and 51b are determined so as to be delayed. The power of the light spot for low density is increased and data is recorded with a delay of the measured time difference Δt or the time measured and known in advance.

  In the present embodiment, since a PC medium is used for the optical disk 56, even if recording is performed with a large light spot 141 using a low-density light beam, a small recording is actually performed due to the self-sharpening effect of the PC medium. A mark is formed. This recording mark is reproduced by a light spot 140 using a high-density light beam. As described above, in this embodiment, for example, recording on a high-density disk is performed with a red beam, and reproduction is performed with a green beam. However, an OTF (light transfer function) of a light spot by a low-density light beam used during recording is used. ) There is no reduction in resolution due to degradation.

  On the other hand, recording / reproduction of the optical disk for low density can be performed as in the conventional case by switching the servo system to low density if the disk can be discriminated as the disk for low density.

  In the above embodiment, a green light source is used as the high-density light source 51a and a red light source is used as the low-density light source 51b. However, when a commercially available optical disk is used, that is, a red light source and a low-density light source are used. You may use a near-infrared light source, respectively. When further increasing the density, it is also possible to use a combination of blue for the high density light source, a green light source for the low density light source, a near ultraviolet light source for the high density light source, and a blue combination for the low density light source. It is done. In short, the difference in emission wavelength between the high-density light source and the low-density light source may be about 1.2 to 1.4 times.

  In the above embodiment, the low-density light source 51b is moved with respect to the high-density light source 51a. Conversely, the high-density light source 51a may be moved with respect to the low-density light source 51b. Furthermore, although the piezo element is used as means for moving the light source in the above embodiment, a method using electromagnetic force such as a stepping motor may be used. Instead of moving the light source, the direction of the light beam before entering the collimator lens 52 may be moved. As described above, various modifications can be considered for the method of aligning the light spot in the disk radial direction by the high density light beam and the low density light beam on the optical disk.

  (Nineteenth Embodiment) Next, another embodiment of the light source unit in which the high-density light source and the low-density light source are relatively moved in the disk radial direction (tracking direction) will be described with reference to FIG. To do. 33, the semiconductor laser 91 corresponds to the high-density light source 51a in FIG. 24, and the semiconductor laser 92 corresponds to the low-density light source 51b in FIG. In this case, the semiconductor laser 92 is supported by a movable heat radiating base 93 and is configured to be movable in the tracking direction with respect to the fixed heat radiating base 95 by a piezo element 94. A slight gap is set between the movable heat radiation base 93 and the fixed heat radiation base 95.

  According to this embodiment, there is an advantage that temperature characteristics are further stabilized. Further, when stability of temperature characteristics is required, it is also effective to insert a gel material such as silicone grease having good heat dissipation characteristics into the gap between the heat dissipation base 93 and the heat dissipation base 95.

(20th Embodiment) Next , another embodiment of the optical head will be described with reference to FIG. 34, the SHG light source 100 corresponds to the high density light source 51a in FIG. 24, and the semiconductor laser 110 corresponds to the low density light source 51b in FIG. In the SHG light source 100, the output light from the excitation semiconductor laser 101 is condensed on the solid-state laser 103 by the condenser lens 102. As the solid-state laser 103, for example, a YVO4 crystal is used. The wavelength of the solid-state laser 103 is 1064 nm, and the resonator is formed by the end face of the YVO 4 crystal and the output mirror 105. The nonlinear optical crystal 104 is disposed in the resonator, and thereby, light having a wavelength of 532 nm, which is half the emission wavelength of 1064 nm of the solid-state laser 103, is obtained through the output mirror 105. As the nonlinear optical crystal 104, for example, KTP is used. By condensing the output light of the SHG light source 100 at a position corresponding to the light source 51a of FIG. 24 using the condensing lenses 106 and 107, two light sources arranged at arbitrary intervals can be realized.

  The semiconductor laser 110 is placed on the heat dissipation base 109. As shown in an enlarged view of the light source unit for low density including the semiconductor laser 110 in FIG. 35, the light source unit is formed between the condenser lens 107 and the collimator lens 112, and the semiconductor laser 110 on the heat dissipation base 109 is formed. A heat radiation base 109 is provided with a semi-conical relief at least larger than the divergence angle of the light beam so that the light beam from the SHG light source 100 can be collected by the condenser lens 107 at a position separated from the light source position by an arbitrary interval. It is. If the light source unit is configured in this manner, the heat radiation characteristic of the semiconductor laser 110 can be suppressed to a slight decrease.

  Further, the relative positions of the light spots 140 and 141 on the optical disk 56 are adjusted by moving the semiconductor laser 110 in the Y-axis direction in FIG. 35 corresponding to the disk radial direction. That is, the piezo element 111 is bonded to the heat radiating base 109, and the radiating position of the semiconductor laser 110 is adjusted by simultaneously moving the heat radiating base 109 and the semiconductor laser 110 by the piezo element 111. The base 112 supports the entire light source unit.

  In the above, the position of the large spot 141 on the optical disk 56 is adjusted by adjusting the position of the light source 51b in FIG. 24 or the semiconductor laser 110 in FIG. 35, but the position of the small spot 140 on the optical disk 56 is adjusted. Also good. In the case of FIG. 24, the position of the small spot 140 on the optical disk 56 is adjusted by adjusting the position of the light source 51a. In the case of FIG. 29, the position of the light beam collected by the condenser lens 107 is adjusted.

  (Twenty-first Embodiment) As described above, instead of moving the low density light source 51b with respect to the high density light source 51a, the high density light source 51a may be moved with respect to the low density light source 51b. That is, in the case of FIG. 24, the position of the light source 51a is adjusted to adjust the position of the light spot 40 on the optical disk 56, and in the case of FIG. 29, the position of the light beam condensed by the condenser lens 107 is adjusted. You may do it.

  Specifically, for example, as shown in FIG. 36, the position of the condensing lens 107 is moved in the direction perpendicular to the paper surface of FIG. Is adjusted to create a state in which the position of the high-density light source is moved. Instead of the condenser lens 107, the piezo element 113 may be bonded to the condenser lens 106 and used as the condenser lens 106. For the driving of the condenser lenses 106 and 107, basically any means may be used. For example, an electromagnetic drive mechanism using a coil and a magnet can be used. Further, instead of moving the condenser lenses 106 and 107, they may be slightly tilted.

  (Twenty-second Embodiment) FIG. 37 shows that the position of the high-density light source is moved by disposing an optical system 114 that tilts the traveling direction of the light beam in the collimated light beam from the SHG light source 100. This is an embodiment.

  FIG. 38 shows a specific example of the optical system 114. By slightly tilting the prism 121 having the deviation angle θ by the piezo element 122, the traveling direction of the light beam emitted from the prism 121 is changed by Δθ. Thus, the position where light is condensed by the condensing lens 123 is shifted by ΔZ. As a result, the position of the light spot 140 in the radial direction of the disk can be adjusted by the high-density light beam on the optical disk 56. In the case of this embodiment, the piezo element 111 as shown in FIG. 35 is not necessary.

  In the above description, the positional deviation due to temperature / humidity change or aging change in the focus direction is small, but if this is relatively large, the optical axis direction of the light source is the same as in the disk radial direction. What is necessary is just to change the position of. In this case, the shift amount in the focus direction between the light spot 140 and the light spot 141 on the optical disk 56 is obtained from a focus error signal obtained from the light spot not subjected to focus control, and the position of the light source in the optical axis direction is changed. Like that.

  For example, the focus error signal is obtained from the photodetector 59b that detects the reflected light of the light spot 141 in a state where the focus control is applied to the light spot 140, and the amount of shift in the focus direction between the light spots 140 and 141 is obtained. Get. Accordingly, the position of the light source corresponding to the one not subjected to focus control is moved in the optical axis direction.

  (23rd Embodiment) FIG. 39 is a diagram showing a configuration of a light source unit in which a semiconductor laser 110 not subjected to focus control is moved in the optical axis direction (Z-axis direction) by a piezo element 115. In FIG. 37 may be configured to be driven in the optical axis direction, and the condenser lens 107 may be moved in the optical axis direction. The same effect can be obtained by moving the condenser lens 106. The driving means may not be a piezo element, but may be any means that can move in another optical axis direction.

  (24th Embodiment) Next, an embodiment in which two light sources are not in close proximity will be described with reference to FIG. In FIG. 40, the SHG light source 100, which is a high-density light source, is the same as in FIG. 34, but the condensing lenses 106 and 107 are configured so that the light beam emitted from the condensing lens 107 is in a collimated state. Yes. On the other hand, a light beam emitted from a semiconductor laser 130 which is a light source for low density and collimated by a collimator lens 131 is reflected by a dichroic prism 132 to synthesize light beams from the two light sources. In this case, the method described above can be used to adjust the relative positions of the two light sources. The SHG light source 100 may be replaced with a semiconductor laser.

  (Twenty-fifth Embodiment) FIG. 41 is a diagram showing an optical system of an optical head device according to a twenty-fifth embodiment, which is a modification of the first embodiment. In FIG. 41, the same parts as those of the first to seventeenth embodiments shown in FIGS. 1 to 23 are denoted by the same reference numerals, and description will be made only when necessary.

  In this embodiment, a polarizing beam splitter 35 is used instead of the polarizing beam splitter 3. As shown in FIG. 43, the beam splitter 35 transmits all the p-polarized components and reflects the s-polarized components with respect to the wavelengths λ1 and λ2. Further, a mirror 42 is used instead of the deflecting beam splitter 6, and a diffractive element (HOE) 17 is disposed at the entrance of the photodetector 11 instead of the detection system lens 11. The mirror 42 changes the direction of the light beam and can be omitted without affecting the effect of the invention.

  Next, the operation of the optical head device of FIG. 41 will be described.

  First, the operation of the optical system when reproducing from, for example, a high-density optical disk using the light source 1 having the wavelength λ1 will be described. In this case, the light beam of wavelength λ1 emitted from the light source 1 reaches the photodetector 11 through substantially the same change as the optical head device of the first embodiment of FIG. 1, as shown in FIG. That is, the light beam from the light source 1 is transmitted through the beam splitter 35 and then collimated by the collimator lens 4 to become a parallel beam. Since the beam splitter 35 has a characteristic of transmitting all the p-polarized components, it transmits all the light beams from the light source 1.

  The light beam having the wavelength λ 1 collimated by the collimator lens 4 enters the beam splitter 5. As shown in FIG. 4, the beam splitter 5 reflects both the p-polarized component and the s-polarized component for the wavelength λ1, transmits the p-polarized component for the wavelength λ2, and reflects all the s-polarized component. Has characteristics. Accordingly, the light beam having the wavelength λ 1 is reflected by the beam splitter 5 and guided to the mirror 42.

  The light beam reflected by the mirror 42 is irradiated onto the optical disk 9 through the quarter-wave plate 7 and the objective lens 8 in the same manner as in the first embodiment of FIG. 1, and the reflected light is returned to the mirror 42. It is. The light beam reflected by the mirror 42 is further reflected by the beam splitter 5, passes through the collimator lens 4, and enters the beam splitter 35. Since the beam splitter 35 has a characteristic of reflecting only the s-polarized light component, a part of the reflected light beam having the wavelength λ 1 is reflected by the beam splitter 35. The light beam reflected by the beam splitter 35 enters the photodetector 11 through the diffractive element 17. Then, the reproduction of the information signal recorded on the optical disc 9, the focus error detection, and the tracking error detection are performed by the output signal from the photodetector 11.

  Next, the operation of the optical system when performing recording or erasure on the low density optical disk or the high density optical disk using the light source 2 having the wavelength λ2 will be described. In this case, the light beam having the wavelength λ2 emitted from the light source 2 reaches the photodetector 11 through the change shown in FIG. That is, the light beam from the light source 2 is collimated by the collimator lens 12 to become a parallel beam, and the beam shape prism 13 shapes the beam shape into a circle. The light beam shaped by the beam shaping prism 13 is incident on the beam splitter 5 as p-polarized light whose deflection direction is the y-axis direction, and is transmitted in accordance with the p-polarized light transmittance Tp shown in FIG. According to the example of FIG. 4, since the transmittance Tp is almost 100% at the wavelength λ2, the light beam having the wavelength λ2 is almost transmitted. The characteristic of the beam splitter 5 with respect to the wavelength λ2 may be a characteristic of transmitting a part of the p-polarized component if all the s-polarized component is reflected.

  The light beam having the wavelength λ 2 that has passed through the beam splitter 5 is incident on the mirror 42. The light beam having the wavelength λ2 reflected by the mirror 42 is converted into circularly polarized light by the quarter-wave plate 7 optimized for the wavelength λ2, and then narrowed down by the objective lens 8 to be applied to the optical disk 9 for recording. Or erase.

  Next, the reflected light having the wavelength λ 2 reflected by the optical disk 9 passes through the objective lens 8 in the direction opposite to the incident light beam, and becomes linearly polarized light in the x-axis direction by the quarter wavelength plate 7. Next, the light is reflected by the mirror 42, becomes linearly polarized light in the z-axis direction, and enters the beam splitter 5. The characteristic of the beam splitter 5 with respect to the wavelength λ 2 is that the s-polarized component is reflected. Therefore, the light beam from the mirror 42 is reflected by the beam splitter 5, passes through the collimator lens 4, and enters the beam splitter 35. Since the characteristic of the beam splitter 35 with respect to the wavelength λ 2 reflects the s-polarized component, the light beam from the collimator lens 4 is reflected by the beam splitter 35. Therefore, the reflected light of wavelength λ2 from the optical disk 9 does not return to either of the light sources 1 and 2. The light beam reflected by the beam splitter 35 passes through the diffractive element 17 and reaches the photodetector 11.

  As described above, in the present embodiment, the reflected light from the optical disk 9 of the light beam having the wavelength λ2 having a large power emitted from the light source 2 does not return to the light sources 1 and 2. 2 can be stably recorded / erased / reproduced.

  Next, the operation of the diffractive element 17 will be described with reference to FIG. In FIG. 44, the beam splitter 35 is omitted for simplification of explanation, but the obtained effect is not affected. The light beams having the wavelengths λ1 and λ2 that have passed through the collimator lens 4 are incident on the diffractive element 17 and then diffracted.

  Since the wavelengths of the incident light beams are different, the diffraction angles θλ1 and θλ2 are different. In general, the diffraction angle θ is sin θ = λ / T. Here, λ is the wavelength, and T is the grating pitch of the diffractive element. Therefore, in FIG. 44, only the + 1st order diffracted light is shown, and the light beams of the respective wavelengths are applied to the detection surfaces 11a and 11b of the detector. Therefore, the + 1st order diffracted light of the light beams having the wavelengths λ1 and λ2 can be detected independently.

  Here, for example, the grating pattern of the diffractive element 10 is changed so that the light beam shape on the photodetector 11 changes according to the relative positional deviation between the objective lens 8 and the optical disk 9. If the lattice pattern is designed, the focus error signal can be obtained by calculating each output signal of the divided light detection surface. For example, a diffractive element as in the optical head device disclosed in Japanese Patent Laid-Open No. 3-257 may be used. Of course, a reproduction signal can be obtained. Further, although + 1st order diffracted light is shown in the figure, other orders of diffracted light can also be used. In the present invention, the diffracted light of the light beams having the wavelengths λ1 and λ2 can be completely separated on the photodetector. The detection surfaces 11a and 11b corresponding to the respective wavelengths do not necessarily have to be in the same photodetector, and can be arranged in different detectors.

  The information signal can be reproduced from the output of the photodetector 11 corresponding to the light beam of each wavelength. Further, focus error detection and tracking error detection can be obtained by calculating the output of the divided detection surface. Returning to FIG. 41, the signals from the photodetector 1 are amplified by the amplification circuits 214 and 215. The amplifier circuit 214 amplifies the signal detected from the light beam having the wavelength λ1, and the amplifier circuit 215 amplifies the signal having the wavelength λ2. The next error signal calculation units 216 and 217 generate a focus error signal and a tracking error signal for each wavelength. Next, the switch circuits 218 and 219 select which wavelength of the light beam is used for control. Using the error signal selected by the switch circuits 218 and 219, the objective lens 8 is moved in the optical axis direction and the radial direction by the focus and tracking drive circuits 220 and 221 and the focus drive coil 222 and the tracking drive coil 223. As a result, the relative position of the micro beam spot converged with respect to the information recorded on the optical disk is controlled, and information is recorded, erased and reproduced stably. The reproduction signal is obtained from the amplifier circuit 214 or 215. The outputs of the light sources 1 and 2 are controlled by the drive circuits 224 and 225.

  Next, twenty-sixth to twenty-eighth embodiments, which are modifications of the twenty-fifth embodiment, will be described with reference to FIGS. In these embodiments, portions corresponding to those in the twenty-fifth embodiment are denoted by the same reference numerals in the drawing, and only differences will be described.

(26th Embodiment) FIG. 45 shows an optical head apparatus according to the 26th embodiment, in which several elements in the 25th embodiment are integrated. According to this embodiment, the optical system can be further downsized.

(27th Embodiment) FIG. 46 shows an optical head device according to a 27th embodiment. The positions of the collimator lens 4 and the beam splitter 35 in the 25th embodiment are interchanged, and a beam shaping unit 36 is added to the beam splitter 35. It has been added. For this reason, a convex lens 18 is added to the detection system. With this configuration, the light use efficiency of the light source 1 is improved. In this case, it is not always necessary to perform recording with the light source having the wavelength λ2 and to reproduce the high density optical disk using the light source 1 having the wavelength λ1. Since the light use efficiency of the light source 1 is high, recording / erasing / reproduction with respect to a high-density optical disk is sufficiently possible when the light source 1 having a high output wavelength λ1 is used. Further, in order to increase the detection efficiency of the reflected light from the optical disk 9, the quarter wavelength plate 7 may be optimized for the wavelength λ1.

  (Twenty-eighth Embodiment) FIG. 47 shows an optical head device according to a twenty-eighth embodiment. In this embodiment, the photodetector is separated into two. Here, the + 1st order diffracted light of the light beam of wavelength λ1 and the −1st order diffracted light of the light beam of wavelength λ2 or the −1st order diffracted light of the light beam of wavelength λ1 and the light beam of wavelength λ2 are used. This is a case where + 1st-order diffracted light is detected by 11f and 11s with separate detectors. In this case, the position of the photodetector can be adjusted independently, and the error signal can be detected with higher accuracy.

  In the twenty-fifth to twenty-eighth embodiments, when the first light source can emit a light beam sufficient for recording, the first light source is independently used for both recording and reproduction with respect to the high-density optical disk. In addition, the second light source can be used independently to perform both recording and reproduction on the low density optical disc. At this time, one of the first and second light sources is preferably turned off when the other is used, thereby preventing the light beam from one from affecting the beam from the other, Reliable recording / playback can be performed.

  Further, the adjusting mechanisms of the eighteenth and nineteenth embodiments having two light beam axes that are shifted from each other are also applicable to the twenty-fifth to twenty-eighth embodiments having coaxial light beam axes.

Next, with reference to FIG. 48 to FIG. 51, an embodiment for dealing with a difference in optical disc thickness by using two light sources will be described. In the following embodiments, and plays back the recorded by the first light beam of a short wavelength λ1 for high density optical disc, for the low density optical disc recording and reproduction by the second light beam having a long wavelength λ2 Assumes to do.

  (Twenty-ninth Embodiment) FIG. 48 is a diagram showing an optical head device according to a twenty-ninth embodiment.

  The optical system of the optical head device in FIG. 48 includes a first light source 301 having a wavelength λ1, a second light source 314 having a wavelength λ2, a collimator lens 302, a beam shaping prism 303, a beam splitter 304, a dichroic mirror 305, a mirror 306, and 1/4. A wave plate 307, an objective lens 308, and a mirror 310 are provided. A convex lens 311, a first diffractive element (first HOE) 312, and a photodetector 313 are disposed adjacent to the mirror 310 as a light beam detection system having a wavelength λ 1. A second diffractive element (second HOE) 315 and a photodetector 316 are disposed adjacent to the dichroic mirror 305 as a detection system for light of wavelength λ2. Amplifiers 317 and 318, error signal calculators 319 and 320, and switching circuits 321 and 322 are connected to the first and second photodetectors 313 and 316. Focus and tracking drive circuits 323 and 324, a focus drive coil 325, and a tracking drive coil 326 are connected to the switching circuits 321 and 322.

  The beam splitter 304 has a characteristic of transmitting p-polarized light and reflecting s-polarized light with respect to a light beam having a wavelength of λ1. The dichroic mirror 305 has a characteristic of transmitting a light beam having a wavelength λ1 and reflecting a light beam having a wavelength λ2. The mirrors 306 and 310 are for changing the traveling direction of the light beam, and do not affect the function of the optical head even if they are not provided.

  Next, the operation of the optical head device of FIG. 48 will be described.

  First, recording / erasing / reproduction of the normally thin high-density optical disk D1 will be described. The light beam having the wavelength λ 1 emitted from the light source 301 becomes a parallel light beam by the collimator lens 302, and is shaped from the anisotropic light beam into an isotropic shape by the beam shaping prism 303. Thereafter, it passes through the beam splitter 304 and the dichroic mirror 305. Then, after being deflected by the mirror 306 and passing through the quarter-wave plate 307, the objective lens 308 is condensed as a minute spot on the recording layer D1b through the substrate D1a of the optical disc D1. The objective lens 308 is designed so that the aberration amount of the light beam having the wavelength λ1 at the condensing position is equal to or less than the reference value in consideration of the aberration generated in the substrate D1a.

  The light beam reflected by the recording layer D 1 b of the optical disk D 1 passes through the objective lens 308 and the quarter wavelength plate 307 and is reflected by the mirror 306. The reflected light passes through the dichroic mirror 305, is reflected by the beam splitter 304, is further deflected by the mirror 310, and enters a signal detection system including the condenser lens 311, the first HOE 312, and the photodetector 313.

  The outgoing light beam of the light source 301 having the wavelength λ1 is linearly polarized light. Since the linearly polarized light becomes circularly polarized light when passing through the quarter wavelength plate 307, the light beam incident on the optical disc D1 becomes a circularly polarized beam. The circularly polarized reflected light from the optical disk D1 passes through the quarter wavelength plate 307 again. At this time, the linearly polarized light having a direction different from the polarization direction of the linearly polarized light first incident on the quarter wavelength plate 307 is 90 degrees. It becomes. Therefore, the reflected light from the optical disc D1 is reflected by the beam splitter 304.

  The first HOE 312 is configured such that the light beam shape changes on the detection surface of the photodetector 313 in accordance with the focus error of the objective lens 308. Therefore, the focus error signal is obtained by calculating the output signal of the photodetector 313 having the divided detection surface. Tracking error signal detection is a push-pull method. Further, an information reproduction signal can be obtained by calculating the sum of all the divided surfaces of the photodetector 313 by the amplifier circuit 317.

  After passing through the amplifier circuit 317, the error signal calculation unit 319 generates a focus error signal and a tracking error signal. With these signals, currents are passed through the focus drive coil 325 and the tracking drive coil 326 in the focus and tracking drive circuits 323 and 324 via the switch circuits 321 and 322, and the objective lens 308 is moved in the optical axis direction and on the optical disc D1. Move in the direction perpendicular to the track. As a result, the information recorded on the recording layer D1b of the optical disc D1 can be controlled so that the position of the minute light spot condensed by the objective lens 308 coincides, and information can be recorded / erased / reproduced stably.

  Although the first HOE 312 is used for focus error signal detection and the push-pull method is used for tracking error signal detection, the effect of the present invention is not lost even if any other error detection method using, for example, an astigmatism method is used. . Further, the division of the light detection surface can be freely changed according to other error detection methods. The information reproduction and the configuration and operation of the control system are described in detail in the optical head device disclosed in Japanese Patent Application Laid-Open No. 3-257 filed by the present applicant.

  Next, specific numerical examples of the specification of the objective lens 308 are shown. The numerical aperture NA of the objective lens is 0.6, the focal length f is 2.1 mm, the working distance WD is 0.9 mm, and the wavelength λ is 690 nm. For the optical disk D1 having a thickness of the substrate D1a of 0.6 mm, the amount of aberration at the focusing position of the objective lens 308 is 0.027λ, which is less than the reference value (0.03λ), and is determined by λ / NA. A spot is obtained.

  Next, a case where the optical head device processes the high density optical disc D1 and the low density optical disc D2 having different thicknesses will be described. As shown in FIG. 49A, when a parallel light beam is incident on the objective lens 308, for the optical disc D1 on the 0.6 mm substrate D1a, the aberration amount at the condensing position of the objective lens 308 is equal to or less than the reference value. . However, when the thickness of the substrate D2a of the disc D2 is different from that of the substrate D1a of the disc D1, the amount of aberration at the condensing position of the objective lens 308 is not less than the reference value. For this reason, the objective lens 308 cannot obtain a light spot determined by λ / NA.

  In such a case, however, as shown in FIG. 49B, there is a P point position where the amount of aberration of the light beam from the point P point light source at the focusing position of the objective lens 308 is equal to or less than a reference value. The result of calculating the aberration amount at the condensing position of the objective lens 308, where d is the distance from the objective lens at the point P, is as shown in FIG. The thickness of the substrate D2a is 1.2 mm. The position of the point light source is d = 27.8 mm, and the amount of aberration at the condensing position of the objective lens 308 is 0.02λ. Further, the range of the position of the point light source that is equal to or less than the reference value is about 2.1 mm.

  Therefore, by setting the light source to the position of the point light source according to the thickness of the substrate D2a, the objective lens 308 can focus the light beam on a minute light spot. That is, by changing the radius of curvature of the light beam incident on the objective lens 308, it is possible to correct the aberration that occurs due to the change in the thickness of the substrate. Normally, the objective lens 308 is moved in the optical axis direction (usually about ± 0.3 mm at maximum) for focus control, but even in this case, the aberration amount is suppressed to a reference value or less. By arranging the point light source near the center of the range of the position of the point light source that is equal to or less than the reference value, an allowable value for the movement of the objective lens 308 in the optical axis direction becomes a target, and the objective lens 308 focuses on a minute light spot. Is done.

  Further, in this case, the working distance WD = 0.71 mm and the focal length f = 2.4 mm, and the focused spot position on the objective lens 308 is shifted. This can be corrected by applying an offset to the objective lens drive coil 325 according to the amount of deviation by the focus drive circuit 323. The effective numerical aperture is about NAe = 0.55. For this reason, the recording density is a value determined by λ / NAe.

The wavelength of the light source placed at the position of point P is longer than the wavelength of the main light source . For example, when a light source with a wavelength of 780 nm is used, the distance from the objective lens 308 at point P is d = 28.1 mm. Here, the light source is placed at a position where the aberration amount of the light spot collected by the objective lens 308 is equal to or less than the reference value.

  Next, a light source is arranged at the point P. For example, a light source 314 having a wavelength λ2 is arranged as shown in FIG. The light beam emitted from the light source having the wavelength λ 2 passes through the second HOE 315 and is reflected by the dichroic mirror 305. Next, the light passes through the mirror 306, passes through the quarter-wave plate 307, and is focused on the optical disk D <b> 2 by the objective lens 308. The reflected light from the optical disk D2 passes through the objective lens 308 again, passes through the quarter-wave plate 307, passes through the mirror 306, and is reflected by the dichroic mirror 305. Thereafter, the light beam diffracted by the second HOE 315 is detected by the photodetector 316 to obtain a focus error signal and a tracking error signal. The second HOE 315 can be realized by the same design method as the first HOE 312.

  Next, 30th and 31st embodiments which are modifications of the 29th embodiment will be described. In these embodiments, corresponding portions are denoted by the same reference numerals in the drawings, and only differences will be described.

  30th Embodiment FIG. 50 is a diagram showing an optical head device according to a 30th embodiment. In this embodiment, a configuration of a separation optical system is adopted, and a portion surrounded by a dotted line in the figure is a movable portion, and the rest is a fixed portion. A biaxial objective lens actuator is disposed on the movable part. The movable part is moved in the radial direction of the optical discs D1 and D2 together with the biaxial objective lens actuator to perform access control on the disc. Further, focus control and tracking control are performed by a biaxial objective lens actuator.

  In this way, the light source 314, the second HOE 315, the detector 316, the dichroic mirror 305, the mirror 306, the quarter-wave plate 307, and the objective lens 308 are moved simultaneously with the biaxial actuator of the objective lens, so that the light source 314 and the objective The distance of the lens 308 can be kept constant. Therefore, the light beam of the light source 314 can be condensed as a minute light spot through the objective lens 308, and recording / erasing / reproduction can be performed even on optical disks having different substrate thicknesses.

  (Thirty-first Embodiment) FIG. 51 is a view showing an optical head device according to a thirty-first embodiment, which is a modification of the thirtieth embodiment. That is, this embodiment also adopts the configuration of the separation optical system, and the part surrounded by a dotted line in the figure is the movable part, and the rest is the fixed part. The direction of the reflecting surface of the dichroic mirror 305 is different, and a mirror 320 is disposed between the dichroic mirror 305 and the beam splitter 304. Since the mirror 320 is for changing the direction of the light beam, it can be omitted.

  In the twenty-ninth to thirty-first embodiments, the case where light sources having different wavelengths are used has been described. Usually, the reproduction signal or the like of an optical disc is optimized for a certain wavelength. For example, a compact disc is 780 nm. The signal can be reproduced even if the wavelength is slightly shifted, but the best is that the wavelength is in the recording medium. Therefore, as in the present invention, it is preferable to use a light source having a wavelength suitable for each recording medium having a different substrate thickness, that is, each optical disk.

  In the above embodiment, the case where the PC medium is used as the optical disk is shown. However, it goes without saying that the present invention can be similarly applied to the case where the MO medium or the WO medium is used. Not only a thing but a card-like thing etc. may be sufficient. The mechanism for identifying the high-density and low-density disks used in the eighteenth embodiment is applicable to all other embodiments.

1 is a configuration diagram of an optical head device according to a first embodiment. FIG. The figure which shows the deflection state in each part of the light of 1st wavelength (lambda) 1 in FIG. The figure which shows the deflection state in each part of the light of 2nd wavelength (lambda) 2 in FIG. The figure which shows the wavelength characteristic of the beam splitter 5 in FIG. The figure which shows the wavelength characteristic of the beam splitter 6 in FIG. The block diagram of the optical head apparatus which concerns on 2nd Embodiment. The figure which shows the wavelength characteristic of the beam splitter 5 in FIG. The figure which shows the wavelength characteristic of the beam splitter 6 in FIG. The block diagram of the optical head apparatus which concerns on 3rd Embodiment. The block diagram of the optical head apparatus which concerns on 4th Embodiment. The block diagram of the optical head apparatus which concerns on 5th Embodiment. The block diagram of the optical head apparatus which concerns on 6th Embodiment. The block diagram of the optical head apparatus which concerns on 7th Embodiment. The block diagram of the optical head apparatus which concerns on 8th Embodiment. The block diagram of the optical head apparatus concerning 9th Embodiment. The block diagram of the optical head apparatus which concerns on 10th Embodiment. The block diagram of the optical head apparatus concerning 11th Embodiment. The block diagram of the optical head apparatus which concerns on 12th Embodiment. The block diagram of the optical head apparatus concerning 13th Embodiment. The block diagram of the optical head apparatus concerning 14th Embodiment. The block diagram of the optical head apparatus concerning 15th Embodiment. The block diagram of the optical head apparatus concerning 16th Embodiment. The block diagram of the optical head apparatus concerning 17th Embodiment. The block diagram of the optical disk apparatus which concerns on 18th Embodiment. FIG. 6 is an explanatory diagram of arrangement of light spots on the optical disc in the embodiment. Operation | movement explanatory drawing when a light spot shifts | deviates on the optical disk in the embodiment. The figure for demonstrating the light beam position on the photodetector when the light spot shifts | deviates on the optical disk in the embodiment. FIG. 25 is a diagram showing a specific configuration of a relative displacement detection circuit in FIG. 24. Explanatory drawing of operation | movement when the light spot on the optical disk in the embodiment has shifted | deviated to the track direction. The figure which shows the reproduction signal waveform of the reference pit in the embodiment. FIG. 25 is a diagram showing a specific configuration of a positional deviation amount detection circuit in the track direction of the light spot in FIG. 24. 6 is a time chart for explaining operations during recording in the embodiment. The block diagram of the light source part of the optical head which concerns on 19th Embodiment. The block diagram of the optical head which concerns on 20th Embodiment. The block diagram of the light source part in FIG. The block diagram of the optical head which concerns on 21st Embodiment. The block diagram of the optical head which concerns on 22nd Embodiment. The figure which shows the structural example of the optical system for changing the light beam advancing direction in FIG. The block diagram of the light source part of the optical head which concerns on 23rd Embodiment. The block diagram of the light source part of the optical head which concerns on 24th Embodiment. The block diagram of the optical head apparatus based on 25th Embodiment. FIG. 42 is a diagram showing a deflection state of each part of light having the second wavelength λ2 in FIG. FIG. 42 is a diagram illustrating wavelength characteristics of the beam splitter 35 in FIG. 41. FIG. 42 is a configuration diagram of a light detection system in FIG. 41. The block diagram of the optical head apparatus concerning 26th Embodiment. The block diagram of the optical head apparatus which concerns on 27th Embodiment. The block diagram of the photon detection system of the optical head apparatus based on 28th Embodiment. The block diagram of the optical head apparatus based on 29th Embodiment corresponding to specific embodiment of this invention . The block diagram which shows the effect | action in 29th Embodiment. The block diagram of the optical head apparatus which concerns on 30th Embodiment. The block diagram of the optical head apparatus concerning 31st Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... 1st light source, 2 ... 2nd light source, 3 ... Beam splitter, 4 ... Collimator lens, 5 ... Beam splitter, 6 ... Beam splitter, 7 ... 1/4 wavelength plate, 8 ... Objective lens, 9 ... Optical disk, 10 DESCRIPTION OF SYMBOLS ... Detection system lens, 11 ... Photo detector, 12 ... Collimator lens, 13 ... Beam shaping prism, 14 ..., Beam splitter, 15 ... Beam splitter, 16 ... 1/2 wavelength plate, 17 ... Diffractive element, 21, 23 ... convex lens, 22, 24 ... photodetector, 31 ... detection system lens, 32 ... photodetector, 35 ... beam splitter, 41, 42 ... mirror, 51a ... first light source, 51b ... second light source, 52 ... collimator lens 53 ... Polarizing beam splitter, 54 ... 1/4 wavelength plate, 55 ... Objective lens, 56 ... Optical disk, 57 ... Focus error generating element, 58 ... Dichroic prism 59a, 59b ... photodetectors, 60 ... servo system switching circuit, 61 ... focus error calculation circuit, 62 ... tracking error calculation circuit, 63 ... focus drive circuit, 64 ... tracking drive circuit, 65 ... focus actuator, 66... Tracking actuator, 67... Relative displacement detection circuit, 68. Piezo element, 69. Piezo element drive circuit, 70... Switch circuit, 71, 72 ... Preamplifier, 73 ... Deviation amount detection circuit, 74. 75 ... Recording timing correction circuit, 76, 77 ... Light source drive circuit, 78 ... Optical disc cartridge, 79 ... Sensor hole, 80 ... Sensor hole detector, 81 ... Disc discrimination circuit, 82, 83 ... Binarization circuit, 84 ... Time Interval measurement circuit, 91, 92... Semiconductor laser, 93... , 94 ... piezoelectric element 95 ... fixed heat radiating base.

Claims (2)

An optical head device that selectively irradiates a high density medium or a low density medium having different information recording densities with first and second light beams,
A first light source that emits the first light beam of a first wavelength;
A second light source that emits the second light beam having a second wavelength longer than the first wavelength;
An objective lens for condensing the first light beam or the second light beam on the high density medium or the low density medium as a first light spot or a second light spot, respectively;
A first optical path for guiding the first light beam emitted from the first light source to the objective lens;
A second optical path for guiding the second light beam emitted from the second light source to the objective lens,
In the first optical path, light incident on the objective lens is parallel light, and the first light spot is set so as to be adapted to the high-density medium,
In the second optical path, the light incident on the objective lens is light diffusing from a point light source, and the second light spot is set so as to be adapted to the medium for low density,
The optical head device is characterized in that the high-density medium has a smaller thickness of the substrate located on the light beam incident surface side than the recording layer as compared with the low-density medium. A high-density medium or a low-density medium having different information recording densities is selectively irradiated with the first and second light beams, and the reflected light from the high-density medium or the low-density medium is reproduced as a reproduction signal. A device for converting to
  A first light source that emits the first light beam of a first wavelength;
  A second light source that emits the second light beam having a second wavelength longer than the first wavelength;
  An objective lens for condensing the first light beam or the second light beam on the high density medium or the low density medium as a first light spot or a second light spot, respectively;
  A first optical path for guiding the first light beam emitted from the first light source to the objective lens;
  A second optical path for guiding the second light beam emitted from the second light source to the objective lens,
  In the first optical path, light incident on the objective lens is parallel light, and the first light spot is set so as to be adapted to the high-density medium,
  In the second optical path, the light incident on the objective lens is light diffusing from a point light source, and the second light spot is set to be adapted to the low density medium,
  The high-density medium has a smaller thickness of the substrate located on the light beam incident surface side than the recording layer, compared to the low-density medium.
  Means for obtaining a reproduction signal by extracting reflected light reflected by the high-density medium and returning through the first optical path through a first diffractive element;
  Means for obtaining a reproduction signal by extracting the reflected light reflected by the low-density medium and returning through the second optical path through a second diffractive element;
  A signal reproducing apparatus comprising:

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