JPH0319143A - Optical pickup - Google Patents

Abstract

PURPOSE:To miniaturize and lighten a whole device and improve the positioning precision of a knife and light-shielding precision by joining a half coated plano- convex lens where a translucent film is coated on a curved surface to a lambda/4 plate and providing a second light-receiving element receiving a light flux transmitting the half coated plano-convex lens. CONSTITUTION:The light flux which is reflected from a disk recording medium 55 and which penetrates a first polarized beam splitter 53A and the second polarized beam splitter 53B is made incident on the half coated plano-convex lens 1 where the curved surface fitted to the lambda/4 plate 54B jointed to the second polarized beam splitter 53B is coated and the second light-receiving element receives it. The light flux is projected in a direction parallel to the optical axis of a colimate lens 51 and the knife 59 light-shields a part of it, whereby the first light-receiving element 60 receives the remaining flight flux. Thus, the beam splitter becomes unnecessary and the whole device can be miniaturized. Then, the precision of the positioning of the knife can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical pickup for optically recording or reproducing information on or from a disc-shaped recording medium. [Prior art] Figures 3 and 4 show conventional examples. In the conventional example shown in FIG. 3, a semiconductor laser 50
A collimating lens 51 that converts the luminous flux emitted from the
, a beam shaping prism 52 that expands parallel light, and two polarizing beam splitters 53A . 53B, and λ/4 plates 54A. 54
B, and an objective lens 56 that focuses the light emitted from the polarizing beam splitter 53A in a direction perpendicular to the optical axis of the collimating lens 51 onto the disc-shaped recording medium 55. Then, the λ/4 plate 54B is connected to the polarizing beam splitter 53B. It is equipped with a concave mirror 57, a beam splitter 58 is arranged adjacent to the polarizing beam splitter 53B, and a knife 59 that blocks the light emitted from the beam splitter 58 in the optical axis direction of the collimating lens 5l at an arbitrary ratio. are doing. It also includes a first light receiving element 60 that receives the remaining light blocked by the knife 59 and a second light receiving element 61 that receives the light emitted from the beam splinter 58. Next, the operation of the conventional example shown in FIGS. 3 and 4 will be explained. A beam of light emitted from a semiconductor laser 50 serving as a light source becomes parallel light by passing through a collimating lens 51. This parallel light is expanded by about 2.5 times by the beam shaping prism 52 in a direction parallel to the PN junction surface of the semiconductor laser 50, and becomes a circular light beam. The expanded circular beam enters the polarizing beam splitter 53A. At this time, since the polarizing beam splitter 53A is arranged so that the light beam emitted from the collimating lens 5l is incident as S-polarized light, the light beam incident on the polarizing beam splitter 53A is directed to the junction surface coated with the dielectric multilayer film. 100% reflected. The reflected light flux passes through the λ/4 plate 54A, becomes circularly polarized light, and is focused onto the disc-shaped recording medium 55 by the objective lens 56.

The light beam reflected by the recording medium 55 is transmitted through the objective lens 56 again and the λ/4 plate 54A, and becomes linearly polarized light whose azimuth is shifted by 90' with respect to the light beam originally emitted from the semiconductor laser 50. As a result, the polarizing beam splitter 5
Injects into 3A. At this time, the luminous flux is polarized beam splitter 5
3A as P-polarized light, it passes 100% through the polarizing beam splitter 53B, becomes circularly polarized light after passing through the λ/4 plate 54B, and is condensed by the concave mirror 57.
It is reflected and transmitted through the λ/4 plate 54B again to become S-polarized light, which is 100% reflected by the dielectric multilayer coated joint surface of the polarizing beam splitter 53B and enters the beam splitter 58. 50% of the light beam incident on the beam splitter 58 is transmitted in a direction parallel to the optical axis of the collimating lens 5l, and the remaining 50% is reflected in a direction perpendicular to it. Among these, 50% of the light beam transmitted in a direction parallel to the optical axis of the collimating lens 51 is blocked by the knife 59 and received by the first light receiving element 60, and focusing control is performed by the differential output thereof.

On the other hand, the light beam emitted in the direction perpendicular to the optical axis of the remaining collimating lens 5l is received by the light receiving element 6l of 'fJ,2, and is subjected to tracking control and RF signal detection. [Problems to be Solved by the Invention] However, in the above conventional example, since the beam splitter is joined adjacent to the polarizing beam splitter, a considerable amount of space is required from the beam shaping prism to the knife that constitutes the focus detection system. In short, the disadvantage was that the entire device became larger. In addition, since the focus detection system is located in the longitudinal direction of the prism group, it is easy to cause misalignment of the optical axis between the collimating lens and the prism group, and the positioning accuracy of the knife is poor due to large variations in knife positioning. This caused an inconvenience.

[Object of the Invention] An object of the present invention is to provide an optical pickup that improves the disadvantages seen in the conventional example, reduces the size and weight of the entire device, and improves the precision of knife positioning and light shielding. There is a particular thing.

[Means to solve the problem]

The present invention includes a collimating lens that converts the light beam emitted from a semiconductor laser into parallel light, a beam shaping prism that expands the parallel light, and a beam shaping prism disposed adjacent to the beam shaping prism. a first polarizing beam splitter with a right triangular cross section that reflects in a direction perpendicular to the optical axis; a second polarizing beam splitter having the same shape as the first polarizing beam splitter and joined to the object with respect to its long side; A λ/4 plate is joined to the two exit surfaces parallel to the optical axis of the collimating lenses of the two polarizing beam splitters, and the phase is equal to one-fourth of the wavelength, and the light emitted from the first polarizing beam splitter. An objective lens that condenses the light part perpendicular to the optical axis of the collimating lens onto a disc-shaped recording medium, and an arbitrary ratio of the light in the optical axis direction of the collimating lens emitted from the second polarizing beam splitter. It has a knife that blocks light, and a first light-receiving element that receives the remaining light flux that is blocked by the knife. and,
to the λ/4 plate joined to the second polarizing beam splitter. A method is adopted in which a half-coated plano-convex lens whose curved surface is coated with a semi-transparent film is bonded, and a second light-receiving element is installed to receive the light beam that passes through this half-coated plano-convex lens. This aims to achieve the purpose mentioned above. [Operation] The light beam emitted from the semiconductor laser, which is the light source, becomes parallel light by passing through the collimating lens. This parallel light is expanded by a beam shaping prism and becomes a circular beam. The expanded circular beam enters the first polarizing beam splitter. The incident light beam is reflected by the coated junction surface of the first polarizing beam splitter. The reflected light flux passes through the λ/4 plate and becomes circularly polarized light.
The light is focused onto a disc-shaped recording medium by an objective lens.

The light beam reflected by this disc-shaped recording medium passes through the objective lens and the λ/4 plate again, and enters the second polarizing beam splitter. The incident light beam passes through the second polarizing beam splitter, passes through the λ/4 plate on the opposite side, and enters the half-coated plano-convex lens. In the half-coated plano-convex lens, half of the incident light beam is transmitted, and the second light receiving element receives this transmitted light beam. On the other hand, the remaining light beam incident on the half-coated plano-convex lens is reflected by the coated curved surface, passes through the λ/4 plate again, enters the second polarizing beam splitter, is reflected by the coated cemented surface, and is collimated. Emit light in a direction parallel to the optical axis of the lens. This light beam is further blocked by the knife, and the remaining light beam is received by the first light receiving element. [Embodiment of the Invention] An embodiment of the present invention will be described below with reference to FIGS. 1 and 2. Here, the same reference numerals are used for the same structures or members as in the conventional example described above. In the embodiment shown in FIG.
Collimating lens 5l that converts the luminous flux emitted from the
and a beam shaping prism 5 that expands this parallel light in a direction parallel to the PN junction surface of the semiconductor laser 50 to form a circular light beam.
2, a first polarizing beam splitter 53A having a right triangular cross section that reflects the light beam from the beam shaping prism 52 disposed adjacent to the beam shaping prism 52 toward the disc-shaped recording medium 55; A second polarizing beam splitter 53B having the same shape as the first polarizing beam splitter 53A and joined symmetrically with respect to its long side, and collimating lenses 5l of these two polarizing beam splitters 53A and 53B.
The light from the collimating lens 5l emitted from the λ/4 plates 54A and 54B, which shift the phase by a quarter of the wavelength, and the first polarizing beam splitter 53A, which are joined to two emission surfaces parallel to the optical axis of the The light in the direction perpendicular to the axis is transmitted to the disc-shaped recording medium 55.
An objective lens 56 that focuses light upward, a knife 59 that blocks the light in the optical axis direction of the collimating lens 5l emitted from the second polarizing beam splitter 53B at an arbitrary ratio, and the remaining light that is blocked by the knife 59. It has a first light receiving element 60 that receives the luminous flux. Then, the λ/4 plate 54B is connected to the second polarizing beam splitter 53B.
A half-coated plano-convex lens l whose curved surface is coated with a semi-transparent film is joined, and a second light-receiving element 2 for receiving the light beam transmitted through this half-coated plano-convex lens 1 is provided.

Next, the operation will be explained.

The light beam emitted from the semiconductor laser 50, which is a light source, becomes parallel light by passing through the collimating lens 51. This parallel light is expanded by the beam shaping prism 52 in a direction parallel to the PN junction surface of the semiconductor laser 50, and becomes a circular light beam. The expanded circular beam enters the first polarizing beam splitter 53A. At this time, the first polarizing beam splitter 53A is arranged so that the light beam after exiting from the collimating lens 5l enters as S-polarized light. It is 100% reflected by the junction surface of the first polarizing beam splitter 53A coated with. The reflected light flux passes through the λ/4 plate 54A, becomes circularly polarized light, and is focused onto the disc-shaped recording medium 55 by the objective lens 56.
This condensed light beam is reflected by this disc-shaped recording medium 55, passes through the objective lens 56 again, and passes through the λ/4 plate 55.
4A, it becomes a linearly polarized light having an azimuth angle of 90° with the light beam emitted from the semiconductor laser 50, and enters the first polarizing beam splitter 53A again. The incident light flux then passes through the junction surface coated with a dielectric multilayer film, so it passes straight through the second polarizing beam splitter 53B, passes through the λ/4 plate 54B on the opposite side, and is then split into a half-coated flat panel. The light enters the convex lens 1. At this time, 50% of the luminous flux
The amount of light is transmitted while being condensed, and the second light receiving element 2 receives this transmitted light flux, and its differential output performs tracking control and RF signal detection. On the other hand, the remaining amount of light incident on the half-coated plano-convex lens 1 is reflected while being focused by the coated curved surface, passes through the λ/4 plate 54B again, and becomes S-polarized light again, so it is sent to the second polarizing beam splitter 53B. The light is reflected by the junction surface coated with a dielectric multilayer film and exits in a direction parallel to the optical axis of the collimator lens 5l. This light beam is further blocked by the knife 59, and the remaining light beam is received by the first light receiving element 60, and focus control is performed by its differential output.

〔Effect of the invention〕

As explained above, according to the present invention, the light beam reflected from the disc-shaped recording medium and transmitted through the first polarizing beam splitter and the second polarizing beam splitter is spliced into the second polarizing beam splitter. The light enters a half-coated convex lens with a curved surface coating attached to the /4 plate, a part of which is transmitted through this half-coated plano-convex lens and received by the second light receiving element, and the remaining part is The polarized beam is reflected and incident on the second polarized beam splitter, and is emitted in a direction parallel to the optical axis of the collimating lens. Part of the beam is blocked by the knife, and the remaining beam is received by the first light receiving element. This eliminates the need for a beam splitter, which was previously required, making the entire device more compact.Furthermore, by making the prism group more compact, the optical axis between the collimating lens and the prism group can be reduced. It is possible to provide an unprecedented optical pickup that can reduce the deviation of the knife and improve the accuracy of knife positioning.

[Brief explanation of the drawing]

Figure 1 is a composition diagram showing one embodiment of the present invention, and Figure 2 is a diagram showing the first embodiment of the present invention.
FIG. 3 is a block diagram showing a conventional example, and FIG. 4 is a block diagram of FIG. 3 seen from above. 1...half coat to convex lens, 2...
・Second light receiving element, 50... Semiconductor laser, 5
l... Collimating lens, 52... Beam organizing prism, 53A, 53B... First,
second polarizing beam splitter, 54A. 54B...
...First and second λ/4 plates, 55...Disc-shaped recording medium, 56...Objective lens, 59...
- Knife, 60...first light receiving element.

Claims (1)

[Claims] (1) A collimating lens that converts the light beam emitted from the semiconductor laser into parallel light, a beam shaping prism that expands the parallel light, and a collimating lens that converts the light beam from the beam shaping prism arranged adjacent to the beam shaping prism. a first polarizing beam splitter with a right triangular cross section that reflects light in a direction perpendicular to the optical axis; a second polarizing beam splitter that has the same shape as the first polarizing beam splitter and is symmetrically joined with respect to its long side; A λ/4 plate is joined to each of the two exit surfaces parallel to the optical axis of the collimating lens of the two polarizing beam splitters and shifts the phase by a quarter of the wavelength, and the light emitted from the first polarizing beam splitter is an objective lens that focuses a portion of the light in a direction perpendicular to the optical axis of the collimating lens onto a disc-shaped recording medium; It has a knife that blocks light at an arbitrary ratio, and a first light receiving element that receives the remaining light flux blocked by the knife, and is connected to the second polarizing beam splitter.
This optical pickup is characterized in that a half-coated plano-convex lens whose curved surface is coated with a semi-transparent film is bonded to four plates, and a second light-receiving element is provided to receive the light beam transmitted through the half-coated plano-convex lens.