JP2571037B2 - Optical head - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head for irradiating a beam and detecting an incident beam for recording and reproducing information on and from an optical recording medium.

[0002]

2. Description of the Related Art An optical head used in an optical recording / reproducing apparatus or the like records or reproduces information by irradiating an optical recording medium with a beam and detecting a modulated beam from the optical recording medium. I do. The optical head is
Since the optical recording medium is used in a non-contact manner, a focus servo is required. As the focus error detection method, there are various methods, and the astigmatism method is frequently used.

FIG. 11 shows a conventional example of an optical head. In the optical head 1, the beam 4 emitted from the semiconductor laser 2 and reflected by the beam splitter 3 passes through the objective lens 5 and enters the optical recording medium 6. The objective lens 5 and the beam splitter 3 reflected by the optical recording medium 6
Is transmitted through the cylindrical lens 7 of a tumbling type, and enters the photodetector 8 in a state where astigmatism is generated.

That is, in the optical head 1, the semiconductor laser device 9, the beam splitter 3, the cylindrical lens 7, and the optical detector 8 constitute a semiconductor laser device 9, and the semiconductor laser device 9 and the objective The lens 5 constitutes the optical head 1.

[0005]

However, in such an optical head 1, since the four optical components constituting the semiconductor laser device 9 are separated from each other, these four optical components are assembled when the optical head 1 is assembled. Adjustment work such as positional adjustment between optical parts and optical axis alignment is required. Therefore, the cost of the optical head 1 is high. Also, this optical head 1
Since many optical components are required as described above, the size is large and the cost is high.

[0006]

An optical head according to the present invention comprises a photodetector formed on a semiconductor substrate, a semiconductor laser fixed to the semiconductor substrate, and the photodetector of the semiconductor substrate. At least one prism fixed to the upper position and having a slope facing the semiconductor laser and inclined with respect to the optical axis of a beam emitted from the semiconductor laser; The optical axis of the reflected beam is deflected by the inclined surface to reflect the beam, and the beam incident on the prism via the inclined surface is detected by the photodetector.

In the optical head according to the present invention, the irradiation of the beam and the detection of the incident beam are performed by an integrated optical component.
Also, if the beam incident on the prism is in a convergent state,
Astigmatism is generated in the incident beam by passing through the prism, and this prism has a function of generating astigmatism in addition to the function of the beam splitter. In addition, since the prism is directly fixed at a position on the light detection unit in the semiconductor substrate, the light detection unit and the prism are not spatially separated.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First to fifth embodiments of the present invention will be described below with reference to FIGS. Figures 1 and 2
7 shows a semiconductor laser device 21 in the first specific example. In this semiconductor laser device 21, a silicon substrate 24 is fixed on a stem 23 having a lead 22, and a PIN, which is a photodetector for signal detection, is provided on the silicon substrate 24.
A diode 25 and a PIN diode 26 as a photodetector for monitoring a laser output are formed.

A triangular prism 27 is fixed by an adhesive on the silicon substrate 24 at the position where these PIN diodes 25 and 26 are formed. Another silicon substrate 28 is fixed. In addition, this silicon substrate 2
A laser diode chip 31 which is a semiconductor laser is mounted on the end of the triangular prism 27 on the side of 8.

The slope 27a of the triangular prism 27 facing the laser diode chip 31 has a reflectance of about 50%, and the other slope 27b is coated with a total reflection to have a reflectance of 100%. Have.

A cap 33 having a window glass 32 is mounted on the stem 23, and the above-mentioned optical system is hermetically sealed. The PIN diodes 25 and 26 and the laser diode chip 31 and the leads 22 are connected by wires (not shown).

FIG. 3 shows a semiconductor laser device 21 as described above.
1 shows an optical head 34 of a first specific example using the optical head. In the optical head 34, the beam 4 emitted from the laser diode chip 31 and reflected on the inclined surface 27 a of the triangular prism 27 passes through the window glass 32 and the objective lens 5 and enters the optical recording medium 6.

The objective lens 5 reflected by the optical recording medium 6
The beam 4 transmitted through the window glass 32 and the slope 27a is P
The light enters the IN diode 25. Incidentally, the beam 4 reflected by the optical recording medium 6 is incident on the inclined surface 27a in a converged state, and there is a refractive index difference between the triangular prism 27 and air. Therefore, the beam 4 enters the PIN diode 25 in a state where astigmatism has occurred.

As a result, the PIN diode 2
The beam spot 35 of the beam 4 incident on the beam 5 shown in FIG.
The laser diode chip 31 has a shape as shown in FIG.
If the positional relationship between the and the PIN diode 25 is determined,
A beam spot 35 having a shape as shown in FIGS. 4A and 4C is formed on the PIN diode 25 in accordance with the shift from the focused state.

Accordingly, if a circuit as shown in FIG. 5 is used,
Four photodetectors A constituting the PIN diode 25
To D via a subtractor 36 to obtain a focus error signal (A
+ C)-(B + D), and a tracking error signal and a reproduction signal A + B + C + D can be obtained via the phase comparator 37 and the adder 38, respectively.

If a sufficient astigmatism cannot be obtained only by the difference in the refractive index between the triangular prism 27 and air, a part of the triangular prism 27 is cut off as shown by a virtual line in FIGS. Thereby, the cylindrical lens portions 41 and 42
May be formed.

In the semiconductor laser device 21 of the first embodiment, as shown in FIG. 1, the beam 4 emitted from the laser diode chip 31 passes through the slope 27a of the triangular prism 27 and directly Then, the light is reflected by the slope 27b and also enters the PIN diode 26. Therefore, the output of the laser diode chip 31 can be adjusted based on the output from the PIN diode 26.

In the semiconductor laser device 21 in the first embodiment described above, the beam 4 emitted from the laser diode chip 31 and reflected by the inclined surface 27a of the triangular prism 27 is used.
However, it does not return directly to the laser diode chip 31.
Therefore, generation of noise in the laser diode chip 31 is small.

Since the single triangular prism 27 functions as a beam splitter, the cost of the semiconductor laser device 21 is low. Further, since the PIN diodes 25 and 26 are formed on the same surface of the same silicon substrate 24, these PIN diodes 25 and 26 can be formed simultaneously by lithography.

FIG. 6 shows a semiconductor laser device 43 in a second embodiment of the present invention. This semiconductor laser device 43
Are two right angle prisms 44, 4 having different refractive indexes from each other.
Except that a beam splitter is constituted by 5, the configuration may be substantially the same as that of the semiconductor laser device 21 in the above-described first specific example shown in FIG. 1.

FIG. 7 shows the relationship between the distance that the optical recording medium 6 moves in the optical axis direction of the beam 4 in the optical head of the second specific example using such a semiconductor laser device 43.
The amount of the signal obtained from the IN diode 25 is shown.

The signal amount is obtained by using optical glasses BK7 and SF11 as the right-angle prisms 44 and 45, setting the height of this beam splitter to 1 mm, and using a finite magnification lens having an NA of 0.47 as the objective lens 5. Although not shown in FIG. 3, the results are obtained when a collimator lens having an NA of 0.14 is used.

FIG. 8 shows a semiconductor laser device 46 according to a third embodiment of the present invention. This semiconductor laser device 46
Is formed of two right-angle prisms 48 and 49 having different refractive indexes from each other in which the formation of the PIN diodes 25 and 26 and the mounting of the laser diode chip 31 are performed on the integrated silicon substrate 47. 1 except that the beam splitter is fixed only on the PIN diode 25 to the silicon substrate 47.
The configuration may be substantially the same as that of the semiconductor laser device 21 in the first specific example described above.

FIG. 9 shows a semiconductor laser device 51 according to a fourth embodiment of the present invention. This semiconductor laser device 51
Is a silicon substrate 28 fixed on the silicon substrate 24 and on which the laser diode chip 31 is mounted.
The semiconductor laser device 46 of the third specific example shown in FIG. 8 may be substantially the same as the semiconductor laser device 46 shown in FIG. Therefore, in this semiconductor laser device 51, PI
The N diode 26 is used as a back monitor of the laser diode chip 31.

FIG. 10 shows a semiconductor laser device 52 according to a fifth embodiment of the present invention. This semiconductor laser device 5
2 is substantially the same as the semiconductor laser device 51 in the fourth specific example shown in FIG. 9 except that the PIN diode 26 is also formed on the silicon substrate 24 on which the PIN diode 25 is formed. A similar configuration may be used.

[0026]

In the optical head according to the present invention, since the irradiation of the beam and the detection of the incident beam are performed by an integrated optical component, there is little adjustment work such as positional adjustment between components and optical axis alignment during assembly. Cost can be reduced. Further, since the prism has both the function of the beam splitter and the function of generating astigmatism, it is possible to reduce the size and cost. In addition, since the photodetector and the prism are not spatially separated from each other, it is also possible to reduce the size.

[Brief description of the drawings]

FIG. 1 is a side sectional view of a semiconductor laser device in a first specific example of the present invention.

FIG. 2 is a plan view of a main part of the semiconductor laser device in the first specific example.

FIG. 3 is a side view of the first specific example.

FIG. 4 is a plan view of a photodetector for showing a beam spot.

FIG. 5 is a block diagram showing a circuit system of a first specific example.

FIG. 6 is a side sectional view of a semiconductor laser device in a second specific example of the present invention.

FIG. 7 is a waveform diagram of a signal obtained by the optical head of the second specific example.

FIG. 8 is a side sectional view of a semiconductor laser device in a third specific example of the present invention.

FIG. 9 is a side sectional view of a semiconductor laser device in a fourth specific example of the present invention.

FIG. 10 is a side sectional view of a semiconductor laser device in a fifth specific example of the present invention.

FIG. 11 is a side view of a conventional example of the present invention.

[Explanation of symbols]

 Reference Signs List 4 beam 21 semiconductor laser device 24 silicon substrate 25 PIN diode 27 triangular prism 31 laser diode chip 34 optical head 43 semiconductor laser device 45 right angle prism 46 semiconductor laser device 47 silicon substrate 49 right angle prism 51 semiconductor laser device 52 semiconductor laser device

Claims (1)

(57) [Claims] A light detection unit formed on a semiconductor substrate; a semiconductor laser fixed to the semiconductor substrate; and a semiconductor laser fixed to a position on the light detection unit of the semiconductor substrate. At least one prism having an inclined surface facing the optical axis of a beam emitted from the semiconductor laser and facing the optical axis, wherein the optical axis of the beam emitted from the semiconductor laser is deflected by the inclined surface. An optical head that reflects a lever beam and detects a beam incident on the prism through the inclined surface with the photodetector.