JPH03269835A - Optical pickup device - Google Patents

Abstract

PURPOSE:To miniaturize an optical pickup device by controlling the light output of a semiconductor laser by diffracting and detecting partial light in an optical path with an optical grating coupler arranged in the optical path. CONSTITUTION:The light emitted from the semiconductor laser 1 that is a light source transmits the optical grating coupler 4 and is emitted from a unit 6. The light made incident on the optical grating coupler 4 is diffracted by a hologramic area, and 0th-order light out of it is reflected on a mirror 7, and is made incident on a focusing lens 8, and is focused on a storage medium 9. Also, the light diffracted in the hologramic area 4e out of the light made incident on the optical grating coupler 4 is made incident on an optical detector 10 for monitor, and a signal can be obtained, and it is used to control the light output of the semiconductor laser 1. Meanwhile, reflected light from the storage medium 9 is diffracted when passing the hologramic areas 4a-4d again on the optical grating coupler 4, and a beam spot is formed on an optical detector 5 for error signal detection, thereby, an error signal can be obtained as the result of computation.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an optical pickup device that can be used in an optical disc device or the like.

Conventional technology Figure 8 shows an optical beam using a conventional diffractive optical element.

A side cross-sectional view of the Quatsub device, FIG.
Figure 10 shows the relationship between the hologram area and the photodetector, which uses the push-pull method to detect tracking errors, and the image when correctly focused on the recording medium. It is a layout diagram inside the unit which integrated the container.

In FIG. 8, 1 is a semiconductor laser as a light source, 2 is a photodetector for monitoring the optical output of the semiconductor laser 1, and 3 is a photodetector for monitoring the optical output of the semiconductor laser 1.
4 is a stem for fixing and cooling the semiconductor laser 1;
is reflected by the recording medium 8 and separates the modulated light from the optical axis to produce a focus error signal.

A hologram is formed on the surface using a diffractive optical element that generates a tracking error signal. The photodetector 5 is for detecting the light separated by the diffractive optical element 4, and a photodetector for detecting focus and tracking error signals is constructed on the photodetector 5. Unit 6 includes semiconductor laser 1. Monitor photodetector 2. A stem 32, a diffraction optical element 4°, and a photodetector 5 are integrally constituted, and nitrogen gas or the like is sealed inside to prevent deterioration of the semiconductor laser.

6a is a metal base that fixes the stem 3; 7 is a mirror that reflects the light emitted from the unit 6 and makes it enter the focus lens; 8 is a finite focus focus lens for focusing on the recording medium; 9 is a mirror that reflects the light emitted from the unit 6 and makes it enter the focus lens; The recording medium 9a is a signal pit.

Note that the actuator for driving the focus lens 8 is omitted in this figure.

In FIG. 9, 4 at 4 b is the diffractive optical element 4
4c and 4d are hologram areas that generate focus error signals, 4he and 41 are far-field patterns of reflected light from the recording medium on the hologram areas, and ea and 5b are hologram areas that generate tracking error signals formed on the surface of Photodetectors for tracking error signal detection, 5 C15d+ 5 et5f, 5g, and 5h, are photodetectors for detecting focus error signals, respectively. The hologram area 4at4b includes a spherical wave diverging from the position of the semiconductor laser 1 and a photodetector 5 for detecting tracking error.
a.

A hologram corresponding to interference fringes with the spherical wave diverging from the detection point 5b is formed. In addition, the hologram area 4
A hologram corresponding to interference fringes between a spherical wave emitted from the position of the semiconductor laser 1 and a spherical wave emitted before and after the detection points of the photodetectors 5d and 5g for focus error detection is formed on C14d.

In FIG. 10, 8b and 6d are connection terminals for focus error detection, and photodetectors 5d, 5f, 5h and 5 are connected, respectively.
g, 5 ct 5 connected to e.

8c*8i is a connection terminal for tracking error detection and is connected to the photodetectors 6a and 5b. 6h is the ground connection terminal of the photodetector 5, 6g is the anode terminal of the semiconductor laser 1, 6f is the cathode terminal of the photodetector 2, and 6e is the common terminal of the semiconductor laser 1 and the photodetector 2, which is connected to the stem 3. It is electrically connected to the photodetector 2 through the base 6a.

The operation of the conventional optical pickup device configured as described above will be explained with reference to FIGS. 8, 9, and 10.

The light emitted from the semiconductor laser 1 is divided by a hologram area formed on the diffractive optical element 4 into zero-order light and diffracted light of ±1st-order or higher orders. The light enters the orcus lens 8 and focuses on the recording medium 9. The beam spot focused on the recording medium 9 is modulated and reflected by the pin 9a. Thereafter, the light follows the opposite path to the diffractive optical element 4.

Next, a process of generating an error signal using a diffractive optical element using light reflected by a recording medium and returned will be described.

When the beam spot is focused on the recording medium, the reflected light from the recording medium is diffracted by the hologram areas 4c+4d and forms two focal points above and below the photodetectors 5d and 5g.
Beam spots with the same diameter are obtained on C~5e and 5f~5h.

On the other hand, when the beam spot is defocused, the beam spot moves in the defocusing direction, so a difference occurs in the size of the beam spot diameter on the photodetector 5.

The focus error signal is obtained by adding the outputs of 5f and 5g to the output of 5d, and adding the output of 5 as 5 d to the output of 5g, and then taking the differential of the outputs of the connection terminals 6b and 6d.

In addition, in the push-pull method, which is a method for detecting tracking error signals, in the far-field image of the reflected light from the recording medium, the portion where the intensity changes greatly due to the tracking error is diffracted by the hologram areas 4a and 4b. It is detected by detectors 5a and 5b. At this time, a tracking error signal is obtained by taking the difference between the outputs of 5a and 5b.

On the other hand, light emitted from the surface of the semiconductor laser 1 opposite to the diffractive optical element 4 is detected by a monitoring photodetector 2, and the light output of the semiconductor laser 1 is controlled to be constant.

Problems to be Solved by the Invention In the conventional configuration, the factors determining the size of the unit are dominated by the number of connection terminals for driving the semiconductor laser and the output of the photodetector, rather than the number of parts inside the unit.

In the conventional configuration described above, the semiconductor laser, a photodetector for monitoring the semiconductor laser, and a photodetector for error signal detection are integrated in the unit 6, and a large number of connection terminals are used to drive the semiconductor laser and perform two photodetections. Since the output of the optical pickup device is taken out, the outer diameter of the unit 6 becomes large, and there is a problem in that miniaturization of the optical pickup device is reaching its limit.

Furthermore, since the photodetector 2 must be disposed near the semiconductor laser, there is a problem in that it must be accurately attached to the beam.

The present invention solves the above conventional problems, and aims to provide a compact optical pickup device by reducing the number of parts in the unit and downsizing the unit.

Means for Solving the Problems To achieve this object, the present invention provides a semiconductor laser serving as a light source, a focus lens for focusing light emitted from the semiconductor laser onto a pit on a recording medium,
a diffractive optical element disposed between the semiconductor laser and the focus lens; a first photodetector that detects the light diffracted by the diffractive optical element in the optical path of the light emitted from the light source; An optical pickup device comprising a second photodetector that detects the light diffracted by the diffractive optical element in the optical path of the light reflected by the recording medium. a semiconductor laser; a focus lens for focusing light emitted from the semiconductor laser onto a pit on a recording medium; and a mirror disposed between the light source and the focus lens and having a diffraction grating formed on its surface. and a first photodetector for detecting light diffracted by a diffraction grating formed on the surface of the mirror in the optical path of the light emitted from the light source, and in the optical path of the light reflected by the recording medium. An optical pickup device comprising a second photodetector that detects light diffracted by a diffraction grating formed on the surface of the mirror.

According to the above-described configuration, the present invention separates a portion of the light emitted from the light source using a transmission type or reflection type diffraction optical element disposed in the optical path, and detects the light, thereby increasing the light output of the light source. can be controlled.

Furthermore, the light output of the light source can be controlled by separating the unused portion of the light emitted from the conventional light source using a diffractive optical element and detecting that light.

EXAMPLE Hereinafter, a first example of the present invention will be described with reference to the drawings.

FIG. 1 is a side cross-sectional view of an optical pickup device according to a first embodiment of the present invention, FIG. 2 is a diagram showing the relationship between a hologram area on a diffractive optical element, a semiconductor laser, and a monitoring photodetector, and FIG. 3 is a layout diagram inside a unit that integrates a semiconductor laser and a photodetector.

In FIG. 1, 1, 3 to 9a are the same as the component names of the conventional example. 10 is a photodetector that monitors the optical output of the semiconductor laser 1.

Note that the actuator for driving the focus lens 8 is omitted in this figure.

In FIG. 2, 4at 4bt 4ct 4d are the same as the component names of the conventional example. 4e is a hologram area for diffracting the light to a monitoring photodetector.

In FIG. 3, the component names are the same as in FIG. 10 of the conventional example.

The operation of the optical pickup device of this embodiment configured as described above will be explained below. Light emitted from a semiconductor laser 1 serving as a light source passes through a diffractive optical element 4 and is emitted from a unit 6. The light incident on the diffractive optical element 4 is diffracted by the hologram area, and the zero-order light of the light is reflected by the mirror 7, enters the focus lens 8, and focuses on the recording medium 9. In addition, the diffractive optical element 4
Of the incident light, the light diffracted by the hologram area 4e is incident on the monitoring photodetector 8 to obtain a signal, which is used to control the optical output of the semiconductor laser 1.

On the other hand, the beam spot focused on the recording medium 9 is modulated by the pits 9a, and the reflected light follows the original path. When the reflected light passes through the hologram areas 4a+ 4b+ 4c+ 4d on the diffractive optical element 4 again, it is diffracted, and a beam spot is focused on the photodetector 5 for error signal detection, and an error signal is obtained as a result of calculation.

As described above, according to this embodiment, by forming not only a hologram for error detection but also a hologram 4e for monitoring the semiconductor laser 1 on the diffractive optical element 4, the light emitted from the front surface of the semiconductor laser 1 is A part of the light can be diffracted and detected by a monitoring photodetector 8 disposed outside the unit 6. As a result, the number of parts inside the unit 6 can be reduced, the number of connection terminals for the output of the conventional photodetector 2 can be reduced, and the diameter of the unit 6 can be reduced.

Further, since a photodetector for monitoring is not required on the rear surface of the semiconductor laser, and there is no need to provide a gap with the base portion 6a of the unit, it is possible to shorten the length of the unit. As a result, the optical big step device can be downsized.

Furthermore, by configuring the monitoring photodetector to be larger than the beam spot of the diffracted light, position adjustment can be facilitated and costs can be reduced.

Further, the conventional semiconductor laser 1 was coated with an insulating film to have a reflectance of about 70% in order to extract monitoring light from the rear end face. In this embodiment, since the light from the rear end face is not monitored, the forward light output can be improved by coating with an insulating film having a 100% reflectance. Therefore, if the optical output on the focus lens surface is the same as that of the conventional example, the driving current of the semiconductor laser can be lowered, and the temperature rise of the semiconductor laser can be suppressed and the life of the semiconductor laser can be extended.

A second embodiment of the present invention will be described below with reference to the drawings.

FIG. 4 is a side sectional view of an optical pickup device according to a second embodiment of the present invention, and FIG. 5 is a diagram showing the relationship among a hologram area on a diffractive optical element, a semiconductor laser, and a monitoring photodetector.

In FIG. 4, 1, 3 to 9a are the same as the component names of the conventional example. 10 is a photodetector for monitoring the semiconductor laser 1.

Note that the actuator for driving the focus lens 8 is omitted in this figure.

In FIG. 5, the radiation angle θ1 of the light emitted from the semiconductor laser 1 in the direction perpendicular to the active layer of the semiconductor laser is larger than the radiation angle in the direction parallel to the active layer. Therefore, the far field pattern of the semiconductor laser 1 becomes an ellipse as shown in 1a. 4g and 4f are monitoring hologram areas formed on the diffractive optical element 4 between the far field pattern 1a of the semiconductor laser and the error detection hologram area.

The operation of the optical pickup device of this embodiment configured as described above will be explained below.

Light emitted from the semiconductor laser 1, which is a light source, is separated by a hologram area on the diffractive optical element 4 into zero-order light and diffracted light of ±1st-order or higher orders. Among them, the 0th order light is mirror 7
The light is reflected by the beam, enters the focus lens 8 , and focuses on the recording medium 9 . The reflected light is modulated by the pin 9a on the recording medium 9 and follows the original path. When the reflected light passes through the hologram area on the diffractive optical element 4, it is diffracted, and a beam spot is focused on the photodetector 5 for error signal detection.
An error signal is obtained as a result of the calculation.

On the other hand, among the light emitted from the semiconductor laser 1, the light incident on the hologram regions 4g and 4f is diffracted and enters the monitoring photodetector 10 to obtain a signal, which is used to control the optical output of the semiconductor laser 1. It will be done.

As described above, according to this embodiment, by forming the holograms 4g and 4f on the diffractive optical element 4 as in the first embodiment, a part of the light emitted from the front surface of the semiconductor laser l is transferred to the unit 6. The light can be diffracted and detected by a monitoring photodetector 8 disposed outside the camera. As a result, the number of parts inside the unit 6 can be reduced, the number of connection terminals for the output of the conventional photodetector 2 can be reduced, and the diameter of the unit 6 can be reduced.

In addition, the semiconductor laser 1 is emitted from the front surface of the semiconductor laser 1 using a portion of the light that is not used as a beam spot.
can be monitored, so there is no attenuation of the amount of light focused on the recording medium.

Further, as in the first embodiment, since no monitoring light is extracted from the rear end face of the semiconductor laser 1, the optical output from the front face can be improved.

Therefore, if the optical output on the focus lens surface is the same as that of the conventional example, the driving current of the semiconductor laser can be lowered, and the temperature rise of the semiconductor laser can be suppressed and the life of the semiconductor laser can be extended.

A third embodiment of the present invention will be described below with reference to the drawings.

FIG. 6 is a side sectional view of an optical pickup device according to a third embodiment of the present invention, and FIG. 7 is a diagram showing the relationship between a hologram area on a mirror and a photodetector for monitoring and error detection.

In FIG. 6, L:L8.9.9a is the same as the component name of the conventional example. 11 is a mirror on which a reflection hologram for tracking, focusing, and monitoring is formed. 12 is a photodetector, and 13 is a cover glass for sealing the case of the semiconductor laser 14. Note that the actuator for driving the focus lens 8 is omitted in this figure.

In FIG. 7, 11a+llb is a hologram area formed on the surface of the mirror 11 that generates a tracking error signal, 11ct Lid is a hologram area that generates a focus error signal, 11e is a hologram area that separates monitoring light, and 12a.

12b is a photodetector for detecting a tracking error signal;
c, 12d, 12e, 12f, 12g, 1
2h is a photodetector for detecting a focus error signal,
121 is a photodetector for monitoring.

The operation of the optical pickup device of this embodiment configured as described above will be explained below. Light emitted from a semiconductor laser 1 serving as a light source is reflected by a mirror 11, enters a focus lens 8, and is focused on a recording medium 9. The reflected light is modulated by the pits 9a on the recording medium 9 and follows the original path. The reflected light is separated by the hologram areas 11a to 11ie on the mirror 11 into 0th-order light and diffracted light of ±1st-order or higher order light.

The first-order light diffracted by the hologram areas 11a and llb is transmitted to the photodetector 1 for detecting a tracking error signal on the photodetector 12.
A tracking error signal is obtained by connecting beam spots to 2a and 12b, respectively, and calculating the detection signals.

The primary light diffracted by the hologram area 11c and the lid connects beam spots to the focus error signal detection photodetectors 12c to 12h, respectively, and a focus error signal is obtained by calculating the detection signals. hologram area l
The first-order light diffracted by the ie enters the monitoring photodetector 12i to obtain a signal, which is used to control the optical output of the semiconductor laser 1.

As described above, according to this embodiment, by forming a hologram for error detection and a hologram for monitoring the semiconductor laser 1 on the mirror 11, the photodetector for error detection and the photodetector for monitoring are integrated. The number of parts can be reduced.

In addition, there are only two parts inside the semiconductor laser case 14, the semiconductor laser chip and the stem, and the number of connection terminals is also two.Also, there is no need for a photodetector for monitoring on the back of the semiconductor laser, and the base of the unit Since there is no need to provide a gap between the case 14a and the case 14a, the case 14 can be made smaller. As a result, the optical pickup device can be downsized.

Note that in the three embodiments described above, diffracted light from a hologram for monitoring was used, but it goes without saying that higher-order diffracted light from a hologram for error detection may also be used. Note that reflection is performed using a cylindrical lens or parallel flat glass instead of using a diffractive optical element for error detection.

It can also be applied to an optical pickup using a refractive optical system.

Effects of the Invention As described above, according to the present invention, the optical output of a semiconductor laser can be controlled by diffracting and detecting a part of the light in the optical path using an optical diffraction element disposed in the optical path. . This allows the number of internal parts of the unit to be reduced, and the size of the unit to be reduced.

Furthermore, positioning of the monitoring photodetector becomes easy, and costs can be reduced.

Furthermore, since it is not necessary to take out the monitoring light from the rear end facet of the semiconductor laser, the forward light output can be improved. Therefore, if the optical output is kept constant, the drive current of the semiconductor laser can be lowered, the temperature rise of the semiconductor laser can be suppressed, and the life of the semiconductor laser can be extended, which has a great practical effect.

[Brief explanation of drawings]

FIG. 1 is a side sectional view of an optical pickup device according to a first embodiment of the present invention, and FIG. 2 is a sectional view of a semiconductor laser having a hologram on a diffractive optical element and a photodetector integrated in the first embodiment of the present invention. FIG. 4 is a side sectional view of an optical pickup device according to a second embodiment of the present invention, and FIG. 5 is an example of an embodiment on a diffractive optical element according to a second embodiment of the present invention. A side sectional view of the optical pickup device in
9 is a side sectional view of a conventional optical pickup device, and FIG. 9 is a layout diagram inside a unit in which a semiconductor laser for diffracted light and a photodetector are integrated in the conventional optical pickup device. 1... Semiconductor laser, 3... Stem, 4...
...Diffractive optical element, 2.5.10.12...Photodetector, 6...Unit, 6b-61...Connection terminal, 7°! 1... Mirror 8... Focus lens, 9... Recording medium, 9a... Pit.

Claims (7)

[Claims] (1) A semiconductor laser serving as a light source, a focus lens for focusing the light emitted from the semiconductor laser onto a pit on a recording medium, and a diffraction optic disposed between the semiconductor laser and the focus lens. a first photodetector for detecting light diffracted by the diffractive optical element in the optical path of light emitted from the light source; and a first photodetector configured to detect light diffracted by the diffractive optical element in the optical path of light reflected by the recording medium. 1. An optical pickup device comprising a second photodetector that detects the emitted light. (2) The optical pickup device according to claim 1, further comprising a mirror disposed between the light source and the focus lens. (3) In the optical pickup device according to claim 2, in which a diffraction grating is formed on the surface of the mirror of the optical pickup device, the light emitted from the light source is diffracted by the diffraction grating formed on the surface of the mirror in the optical path. 1st to detect light
An optical pickup device comprising: a photodetector; and a second photodetector that detects light diffracted by a diffractive optical element in an optical path of light reflected by a recording medium. (4) In an optical pickup device in which a diffraction grating is formed on the surface of a mirror instead of the diffraction optical element of the optical pickup device according to claim 2, the diffraction grating is formed on the surface of the mirror in the optical path of the light emitted from the light source. a first photodetector that detects the light diffracted by the diffraction grating formed on the surface of the mirror; and a second photodetector that detects the light diffracted by the diffraction grating formed on the surface of the mirror in the optical path of the light reflected by the recording medium. An optical pickup device comprising a photodetector. (5) The optical pickup device according to claim 3 or 4, wherein the first photodetector and the second photodetector are constructed from the same substrate. (6) The optical pickup device according to claim 1 or 3, wherein the light source, the diffractive optical element, and the second photodetector are configured as a unit. (7) The optical pickup device according to claim 4, wherein the light source and the second photodetector are configured as a unit.