JPH04332185A - Forward emitted light detection mechanism and light intensity adjustment method for semiconductor laser - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to detection of forward emitted light from a semiconductor laser in an optical memory device.

0002

2. Description of the Related Art A schematic diagram of a conventional optical head is shown in FIG. 9, and will be explained based on the diagram. The diverging light emitted from the semiconductor laser 901 is converted into parallel light by a collimator lens 902, and is then converted into a parallel light by a beam splitter 903.
and an optical path that is focused onto a recording medium 904 by an objective lens 905. Further, the light reflected by the recording medium 904 is passed through the beam splitter 903 to the signal detection unit 90.
6 to obtain an error signal used for servo and a data reproduction signal.

In optical memory devices, auto power control (APC) is used to detect the amount of emitted light and apply feedback to the laser to keep the amount of emitted light constant, so that the amount of laser emitted light does not change due to changes in temperature or returned light.
It has a servo loop called. The light amount detection used in APC is performed by guiding the light emitted from the semiconductor laser to the light amount detection section by the beam splitter 903 in FIG.

Further, driving of a semiconductor laser by APC is shown in a schematic diagram in FIG. 10. The light emitted from the semiconductor laser 951 is transferred to the APC photodiode 95.
4, the output is converted into a voltage by a current-voltage converter 952, and the output is normalized by the volume so that the output adjuster 953 in the next stage has a specified value per output. APC operation is performed by applying negative feedback to this output to the semiconductor laser drive circuit 955.

[0005]

[Problems to be Solved by the Invention] However, as optical heads become smaller and optical components become simpler and more integrated, the light amount detection section for APC becomes relatively large, which becomes a major factor hindering miniaturization. There was a problem. Further, since the APC drive circuit includes an output adjustment section, variations in the band, S/N, etc. of the APC detection section occur between individual optical heads.

The present invention solves the above-mentioned problems, and its purpose is to provide an optical memory device in which the optical head is made smaller and does not require output adjustment in a circuit. be.

[0007]

[Means for Solving the Problems] The forward emitted light detection mechanism and light amount adjustment method for a semiconductor laser according to the present invention are as follows: (1)
The optical head of an optical memory drive using a semiconductor laser keeps the optical output of the semiconductor laser emitted light constant (APC
) is characterized by having a mechanism for detecting light emitted outside the effective diameter of the collimator lens or the objective lens among the forward emitted light of the semiconductor laser.

(2) The light detection mechanism is characterized in that a prism is installed outside the effective diameter of the collimator lens or the objective lens and within the range where the semiconductor laser emitted light exists. (3) The prism is made of the same member as the photodetecting element, or the prism is bonded to the photodetecting element.

(4) The semiconductor laser forward emitted light detection mechanism is attached to the collimator lens barrel, or is constructed of the same member, and moves simultaneously with the collimator lens.

(5) An optical head that uses a hologram element to obtain a servo error signal or a reproduction signal is characterized in that the light diffracted by the hologram element is used to detect the amount of light for APC.

(6) A feature is that the amount of detected light is adjusted by moving the photodetecting element used for APC.

(7) The photodetection element used for APC is
It is characterized by adjusting the amount of detected light by moving it in a direction perpendicular to the light emission direction.

(8) A feature is that the amount of detected light is adjusted by moving the prism and photodetecting element used in APC in a direction parallel to the optical axis of the lens.

[0014]

【Example】

(Embodiment 1) FIG. 1 is a schematic diagram of a photodetector for APC in a first embodiment of the present invention. Semiconductor laser 10
The light emitted from 5 has a spread as shown at 108. When the emitted light enters the collimator lens 103, only the radial light beam 106 within the entrance pupil diameter 101 of the collimator lens is collimated and contributes to recording and reproducing information. Emitted light 107 from the semiconductor laser outside the entrance pupil of the collimator lens is taken into the APC light detection sensor 102. As a result, the light picked up by the APC photodetector element is the light that would have been discarded in the conventional case, so it does not affect recording/reproduction and servo error signal detection at all, and moreover, APC light can be detected without loss of light quantity. In addition, by arranging the APC photodetector in the direction of the large radiation angle of the semiconductor laser (perpendicular to the bonding surface), more light can be incident on the APC photodetector, resulting in stable frequency characteristics. Good APC operation can be obtained.

(Embodiment 2) FIG. 2 shows the second embodiment of the present invention.
FIG. 2 is a schematic diagram showing an APC photodetection section in an embodiment of the present invention. A total reflection prism 210 is installed in an area 207 outside the entrance pupil diameter of the collimator lens 209, and the emitted light from the semiconductor laser 205 passes through the optical path 206 and enters the photodetector element 202. The prism 210 allows the photodetection element to be installed parallel to the optical axis, eliminating any restrictions on the size of the photodetection element, and allowing for a thin structure.

(Embodiment 3) FIG. 3 shows the third embodiment of the present invention.
FIG. 2 is a schematic diagram showing an APC photodetection section in an embodiment of the present invention. A total reflection prism 310 is installed in an area 307 outside the entrance pupil diameter of the collimator lens 309, and the emitted light from the semiconductor laser 305 passes through an optical path 306 and enters the photodetector element 302. Here, the prism 310 and the photodetecting element 302 are bonded together. Since the prism 310 is made of the same member as the photodetecting element, a new prism fixing member is not required, resulting in a very simple structure.

(Embodiment 4) FIG. 4 shows the fourth embodiment of the present invention.
FIG. 2 is a schematic diagram showing an APC photodetection section in an embodiment of the present invention. A total reflection prism 410 is installed in an area 407 outside the entrance pupil diameter of the collimator lens 409, and the emitted light from the semiconductor laser 405 passes through an optical path 406 and enters the photodetector element 402. Here, the prism 410, the photodetector element 402, and the collimator lens barrel 411 are made of the same member. Therefore, since the member for fixing the prism 410 and the photodetecting element 402 to the photodetecting element also serves as the lens barrel 411 of the collimating lens, the APC photodetecting unit can be made very simple and at the same time downsized. . Also, APC
Since the optical detection section is fixed in advance to the lens barrel of the collimator lens, the prism 410 does not enter the entrance pupil diameter of the collimator lens, and can be attached without adjustment.

(Embodiment 5) FIG. 5 shows the fifth embodiment of the present invention.
FIG. 2 is a schematic diagram showing an APC photodetection section in an embodiment of the present invention. Emitted light from a semiconductor laser 501 is collimated by a collimator lens 503 and enters a hologram element 504 . A light beam 509 that has not been affected by diffraction by the hologram 504 is directly focused onto the recording medium by the objective lens and used for recording/reproduction and error signal detection. On the other hand, it passes through the collimator lens and the hologram element 5
The light opened at 04 has a certain diffraction angle with respect to the optical axis and is 508
Proceed along the optical path shown in . An APC photodetector element 510 is installed within the light beam 508 and outside the area of the light beam 509.

(Embodiment 6) FIG. 6 shows the sixth embodiment of the present invention.
It is a schematic diagram showing the adjustment method of the light detection part for APC in the example. A photodetector element 605 is installed in an area 604 outside the entrance pupil diameter of the collimator lens 603 using emitted light from the semiconductor laser 601, and has a structure that can be adjusted by moving in 606 directions. By adjusting the movement of the photodetecting element 605 in the direction 606, the sensor does not enter the entrance pupil diameter 607 of the collimating lens 603, and the amount of light incident on the photodetecting element can be adjusted, so that APC operation is performed as shown in block diagram 8. An APC operation circuit without output adjustment can be built on the circuit.

(Embodiment 7) FIG. 7 shows the seventh embodiment of the present invention.
It is a schematic diagram showing the adjustment method of the light detection part for APC in the example. A prism 704 and a photodetector element 705 are installed in an area 703 outside the entrance pupil diameter of a collimator lens 702 using emitted light from a semiconductor laser 701, and are configured to be movable and adjustable in 709 directions. By moving and adjusting the prism 704 integrated with the photodetecting element 705 in the direction 709, the prism 706 and the photodetecting element 708 can be moved to the positions indicated by dotted lines, and the amount of light taken in can be adjusted. Therefore, the tip of the prism does not enter the entrance pupil diameter 710 of the collimating lens 702, and since the moving direction is parallel to the optical axis, the amount of light incident on the photodetecting element can be adjusted with a simple adjustment mechanism. As shown in the figure, an APC operation circuit without output adjustment can be built on an APC operation circuit.

[0021]

As explained above, according to the present invention, the optical head of an optical memory device can be miniaturized, and even in a structure in which a semiconductor laser and a signal detection element are integrated using a hologram element, etc., the optical head for APC can be easily detected. This method does not require a new space, and since it detects light that would otherwise have been discarded, stable light detection for APC can be achieved that does not affect the light utilization efficiency or signal detection at all. Further, by performing the adjustment using the APC photodetector according to the present invention, the light amount can be adjusted accurately with a very simple mechanism, and furthermore, the output gain adjustment of the APC drive circuit can be omitted.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing a photodetector for APC according to a first embodiment of the present invention.

FIG. 2 is a schematic diagram showing a photodetector for APC according to a second embodiment of the present invention.

FIG. 3 is a schematic diagram showing a photodetector for APC according to a third embodiment of the present invention.

FIG. 4 is a schematic diagram showing a photodetector for APC according to a fourth embodiment of the present invention.

FIG. 5 is a schematic diagram showing a photodetector for APC according to a fifth embodiment of the present invention.

FIG. 6 is a schematic diagram showing a method for adjusting an APC photodetector element according to a sixth embodiment of the present invention.

FIG. 7 is a schematic diagram showing a method for adjusting an APC photodetector element according to a seventh embodiment of the present invention.

FIG. 8 is a block diagram showing an APC drive circuit according to the present invention.

FIG. 9 is a schematic diagram showing a conventional photodetector for APC.

FIG. 10 is a block diagram showing a conventional APC drive circuit.

Claims (8)

[Claims] [Claim 1] In an optical head of an optical memory drive using a semiconductor laser, in detecting the amount of emitted light for automatic power control (hereinafter referred to as APC) to keep the optical output of the semiconductor laser emitted light constant, A forward emitted light detection mechanism for a semiconductor laser, comprising a mechanism for detecting light emitted outside the effective diameter of a collimator lens or an objective lens among the emitted light. 2. The forward emitting device for a semiconductor laser according to claim 1, wherein a prism is installed in the photodetection mechanism outside the effective diameter of the collimator lens or the objective lens and within a range where the semiconductor laser emitted light exists. Light detection mechanism. 3. The forward emitted light detection mechanism for a semiconductor laser according to claim 1, wherein the prism is made of the same member as a photodetection element, or the prism is bonded to the photodetection element. 4. A semiconductor laser forward emitted light detection mechanism,
2. The forward emitted light detection mechanism for a semiconductor laser according to claim 1, wherein the mechanism is attached to a collimator lens barrel or is constructed of the same member and moves simultaneously with the collimator lens. 5. Forward emitted light detection for a semiconductor laser, characterized in that, in an optical head that uses a hologram element to obtain a servo error signal or a reproduction signal, the light diffracted by the hologram element is used as light amount detection for APC. mechanism. 6. The light amount adjustment method according to claim 1, wherein the amount of detected light is adjusted by moving a photodetecting element used for APC. 7. The forward emitted light detection mechanism for a semiconductor laser according to claim 1, wherein the light detection element used for APC is moved in a direction perpendicular to the light emission direction to adjust the amount of detected light. 6. The light amount adjustment method described in 6. 8. The forward emitted light detection mechanism for a semiconductor laser according to claim 3, wherein the prism and the light detection element used for APC are moved in a direction parallel to the optical axis of the lens to adjust the amount of detected light. , The light amount adjustment method according to claim 6.