JPH11110781A - Semiconductor laser device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor laser device for optical pickup with a satisfactory S/N. SOLUTION: This device has a semiconductor laser element 1 for irradiating a recording medium 14 with a laser beam, beam splitter 11 arranged in an optical path between this semiconductor laser element 1 and the recording medium 14, hologram element 28 constituted by forming a diffraction grating 9 on a light transmission substrate 8 arranged in an optical path between this beam splitter 11 and the semiconductor laser element 1, photodetectors 2 and 3 for servo signal, arranged in the optical path of diffracted light for photodetecting the diffracted light transmitted through this diffraction grating 9, and photodetector 4 for information signal light for photodetecting light different from the light made incident to the diffraction grating 9 among the beams split by the beam splitter 11. In this case, the semiconductor laser element 1, the photodetectors 2 and 3 for servo signal and the photodetector 4 for information signal are arranged in one package, and the photodetector 4 for information signal is arranged outside the optical path of diffracted light with all the order transmitted through the diffraction grating 9.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser device suitable as a light source of an optical pickup device for recording or reproducing information on an information recording medium.

[0002]

2. Description of the Related Art A conventional semiconductor laser device will be described below.

FIG. 16 shows a conventional semiconductor laser device and a recording medium. In FIG. 16, a semiconductor laser element 1, a servo signal light receiving element 2, and a servo signal light receiving element 3 are provided in a package 5, and the package 5 is sealed by a transparent sealing substrate 6. The above configuration is referred to as a semiconductor laser unit 7. In the optical path between the semiconductor laser element 1 and the information recording medium 14, a light transmitting substrate 8, a collimating lens 12, and an objective lens 13 are arranged in this order from the semiconductor laser element 1 side. A diffraction grating 9 is formed on the surface of the light transmitting substrate 8 on the side of the collimator lens 12, and a diffraction grating 10 for generating three beams is formed on the surface of the light transmitting substrate 8 on the side of the sealing substrate 6.

The light emitted from the semiconductor laser device 1 is
In the three-beam generation diffraction grating 10, the light beam is divided into three light beams in a direction perpendicular to the plane of FIG.
8 is transmitted. The three beams transmitted through the hologram optical element 28 are collimated lens 12 and objective lens 13
Is condensed on the information recording medium 14 via. The light beam reflected by the information recording medium 14, that is, the return light, returns to the hologram optical element 28 following the same optical path again, is diffracted by the diffraction grating 9 on the hologram optical element 28, and receives the servo signal light receiving elements 2, 3 A focus error signal light receiving area (not shown) divided into a plurality of elements above, and
Light is condensed on a radial error signal light receiving area (not shown) divided into a plurality of elements. The focus error signal is detected by subjecting the current output from each element in the focus error light receiving area to current-voltage conversion and then performing a differential operation. The radial error signal is also detected by differential detection using the three-beam method. On the other hand, the information signal is obtained by current-to-voltage conversion of the current output from each element in the focus error signal light receiving area, and then calculating the sum of these.

[0005]

However, in the above-described conventional semiconductor laser device, since the information signal is obtained by summing the signals from the respective elements obtained by dividing the information signal into a plurality of signals, the noise of the signal from the respective elements is obtained. Since the components are added, there is a problem that the noise component increases according to the number of elements and the S / N ratio is remarkably reduced.

[0006] The present invention solves the above-mentioned conventional problems, and provides an S / S
It is an object to provide a semiconductor laser device having a good N ratio.

[0007]

A semiconductor laser device according to the present invention comprises a semiconductor laser device for irradiating a recording medium with laser light, and an optical path between the semiconductor laser device and the recording medium. Beam splitting means, a hologram element formed by forming a diffraction grating on a light transmitting substrate disposed in an optical path between the beam splitting means and the semiconductor laser element, and diffracted light transmitted through the diffraction grating. A light receiving element for a servo signal arranged in the optical path of the diffracted light to receive the light,
A light receiving element for receiving an information signal for receiving a light different from the light incident on the diffraction grating, among the light split by the beam splitting means; the semiconductor laser element and the light receiving element for the servo signal; And the information signal light-receiving element is arranged in one package, and the information signal light-receiving element is arranged outside the optical path of diffracted light of all orders transmitted through the diffraction grating, Accordingly, since the diffracted light transmitted through the diffraction grating does not enter the information signal light receiving element, an information signal with less noise can be obtained.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to FIGS.

(First Embodiment) FIG. 1 is a diagram showing a semiconductor laser device according to a first embodiment of the present invention. FIG.
In the above, a semiconductor laser element 1, a servo signal light receiving element 2 for detecting a radial error signal and a focus error signal, a servo signal light receiving element 3, and an information signal light receiving element 4 are provided inside one package 5. Are located. The package 5 is sealed with a transparent sealing substrate 6 molded of glass or resin. The above configuration is referred to as a semiconductor laser unit 7.

In the optical path between the information recording medium 14 for recording or reproducing information and the semiconductor laser unit 7, the light transmitting substrate 8 is arranged in order from the semiconductor laser unit 7 side.
A hologram optical element 28 formed by forming a diffraction grating 9 on one surface and a diffraction grating 10 for generating three beams for diffracting incident light in a direction perpendicular to the plane of FIG. Beam splitter 1 as a splitting means
1, a collimating lens 12, and an objective lens 13 are provided. In the optical path between the beam splitter 11 and the information signal light receiving element 4, a reflector 15 is provided.
Are arranged.

Next, the operation of the semiconductor laser device according to the first embodiment of the present invention will be described.

In FIG. 1, first, a semiconductor laser device 1
Is transmitted from the hologram optical element 28 and the beam splitter 11, is once converted from a divergent light beam into a parallel light beam by the collimator lens 12, and is condensed on the information recording medium 14 by the objective lens 13. This light is reflected on the surface of the information recording medium 14, and then, as return light, passes through the objective lens 13 and the collimator lens 12 and enters the beam splitter 11. The return light incident on the beam splitter 11 is split into the direction of the hologram optical element 28 and the direction of the Wollaston prism 16. The return light branched in the direction of the hologram optical element 28 is diffracted by the diffraction grating 9. In FIG. 1, for simplicity,-
1st-order diffracted light 23, 0th-order diffracted light 24, + 1st-order diffracted light 25,
Diffraction lights other than the + 2nd-order diffraction light 26 and the + 3rd-order diffraction light 27 are omitted. Among these diffracted lights, SSD (Spot Siz) is used by using the -1st-order diffracted light 23 and the + 1st-order diffracted light 25.
eDetection method), a focus error signal,
Radial error signals are detected using a differential detection method based on a three-beam method. The light receiving element 4 for information signal is +2
Since it is located between the optical paths of the second-order diffracted light 26 and the + 3rd-order diffracted light 27, the diffracted light of the diffraction grating 9 is not directly received.

In the figures subsequent to FIG. 2, the diffracted lights other than the -1st-order diffracted light 23, the 0th-order diffracted light 24 and the + 1st-order diffracted light 25 are omitted for simplicity.

On the other hand, of the return light split by the beam splitter 11, another light different from the return light incident on the diffraction grating 9 is reflected by the reflector 15 and then received by the information signal light receiving element 4. Used as an information signal.

As described above, by providing the information signal light-receiving element 4 inside the package 5 and outside the optical path of the diffracted light by the diffraction grating 9, it is possible to obtain a good S laser without increasing the size of the semiconductor laser device. A semiconductor laser device having a / N ratio can be manufactured.

In this embodiment, a semiconductor device having an infinite optical system including a collimating lens 12 and an objective lens 13 has been described. However, a finite optical system using only the objective lens 13 has been described. Even if you use
It can be implemented similarly.

As shown in FIG. 2, the beam splitter 11 is integrated on the hologram optical element 28, or FIG.
As shown in FIG. 4, the beam splitter 11 and the reflector 15 are integrally formed as a composite prism 17 or FIG.
As shown in (1), the hologram optical element 28 may be integrated on the sealing substrate 6, and the composite prism 17 may be further integrated thereon. In these cases, by integrating and integrating a plurality of optical components, the semiconductor laser device can be further reduced in size and thickness.

Further, if the reflector 15 is constituted by a total reflection mirror, all the light for the information signal is received by the light receiving element 4 for the information signal.
, The light use efficiency increases, and the S / N ratio improves.

As shown in FIG. 5, if the three-beam generating diffraction grating 10 is formed on the upper or lower surface of the sealing substrate 6 and the diffraction grating 9 is formed on the lower surface of the beam splitter 11, the number of optical components can be reduced. Can be reduced and a plurality of optical components can be integrated and integrated, so that the semiconductor laser device can be further reduced in size, thickness, and cost.

As shown in FIG. 6, if the package 5 is sealed with a hologram optical element 28 instead of the light transmitting substrate 8, the sealing substrate 6 does not need to be used, so that durability and durability can be improved.
The number of optical components can be reduced while maintaining reliability.

Further, as shown in FIG. 7, a light intensity monitoring light receiving element 18 for receiving light emitted from the rear emission end face of the semiconductor laser element 1 may be newly disposed inside the package 5. In this case, a light intensity monitoring light receiving element 1
Since it is not necessary to separately provide 8, the semiconductor laser device can be further reduced in size and thickness.

Further, as shown in FIG. 8, in the hologram optical element 28, the divergent light beam from the semiconductor laser device 1 can be converted into a parallel light beam by giving a portion located in the optical path a curvature, so that the collimating lens 12 Can be eliminated, and the number of optical components can be reduced. At this time, in the polarization beam splitter 11, the light branched in the direction of the information signal light receiving element 4 becomes a parallel light flux.
By making the sealing substrate 6 have a curvature in the same manner as the hologram optical element 28, the light incident on the information signal receiving element 4 can be converged light.

Further, if an integrated circuit for performing current-voltage conversion or operation using electric signals from the light receiving elements for servo signals 2 and 3 or the light receiving element for information signals 4 is provided inside the package 5, the wiring length can be reduced. Since it can be shortened, the S / N ratio can be improved and the high frequency characteristics can be improved.

FIG. 9 is a side view of the semiconductor laser device.
As shown in FIG. 9, -1 of the diffraction grating 10 for generating three beams
The secondary light 16b and the + 1st-order light 16c may be received by the radial error signal light receiving elements 19 and 20, respectively, to detect the radial error signal. The zero-order light 16a is received by the information signal light receiving element 4. In this case, the sub-beam diffracted by the diffraction grating 9 is not used as a radial error detection signal. Furthermore, if the light receiving elements 19 and 20 for the radial error signal and the light receiving element 4 for the information signal are formed by one light receiving element divided into three elements, the number of light receiving elements is reduced, so that the cost of the semiconductor laser device can be reduced. Can be planned.

The radial error signal may be detected by a one-beam method using a push-pull method without the three-beam generating diffraction grating 10. In this case, since the outgoing light does not branch into three, the light amount of the information signal light 16 increases, and S / S
The N ratio is further improved.

As shown in FIG. 10, if the semiconductor laser element 1, the servo signal light receiving elements 2, 3 and the information signal light receiving element 4 are integrated and integrated on one substrate 21,
The assembling process becomes easier as compared with the case where individual elements are arranged inside the package 5, and the fine processing technology in the semiconductor processing technology can be used. Further, if such a semiconductor processing technique is used, an integrated circuit that converts an electric signal from the light intensity monitoring light receiving element 18, the servo signal light receiving elements 2, 3 or the information signal light receiving element 4 into a current-voltage conversion or performs an operation. The circuit can also be integrated on the substrate 21 at the same time. This integration, after forming all light receiving elements on the silicon substrate using semiconductor processing technology,
This is performed by forming the semiconductor laser device 1 in a hybrid by chip bonding. Alternatively, a compound semiconductor layer is monolithically formed on a silicon substrate by using a semiconductor heteroepitaxial technique, and the semiconductor laser element 1, the servo signal light receiving elements 2, 3 and the information signal light receiving element 4 are formed on a silicon substrate or a compound semiconductor. Formed in layers. Instead of using a silicon substrate, the semiconductor laser element 1, the light receiving elements for servo signals 2, 3 and the light receiving element for information signals 4 may be integrally integrated and formed only by the compound semiconductor layer.

When a surface-emitting type semiconductor laser is used as a light source in the case of integration in a hybrid, it is only necessary to bond the chip with the light-emitting surface facing upward, but an edge-emitting type semiconductor laser is used as a light source. At the time of adoption, for example, as shown in FIG. 11, a recess is formed in the substrate 21 by using a semiconductor processing technique, the semiconductor laser element 1 is chip-bonded therein, and a surface inclined at 45 ° is formed in the recess. If the reflection mirror 22 is formed by evaporating a metal or dielectric film on this surface, the semiconductor laser device 1
Is reflected by the reflection mirror 22, so that light can be extracted upward.

Further, as shown in FIG. 12, the sealing substrate 6 is eliminated, and the thickness of the light transmitting substrate 8 is changed to the portion through which the light entering the servo signal receiving elements 2 and 3 is transmitted and the information signal receiving portion. By individually setting the light incident on the element 4 and the light transmitting element, the focal position of the light incident on the servo signal receiving elements 2 and 3 and the focal point of the light incident on the information signal receiving element are set. If the positions are individually adjusted, the size of the light receiving area of the information signal light receiving element 4 can be reduced to about the diameter of the focused spot. Therefore, the semiconductor laser device can be reduced in size and thickness. In addition,
Needless to say, the cost of the semiconductor laser device is reduced as the sealing substrate 6 becomes unnecessary.

(Embodiment 2) Next, a semiconductor laser device according to Embodiment 2 of the present invention will be described.

FIG. 13 is a diagram showing a configuration of a semiconductor laser device according to the second embodiment. FIG. 14 is a plan view of the semiconductor laser unit. Light receiving element 2 for servo signal,
And the servo signal light receiving element 3 includes elements 2a, 2b, 2c, 2d, 2e, 2f, 3a, 3
b, 3c, 3d, 3e, and 3f. In addition,
The same components as those of the semiconductor laser device shown in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted. The semiconductor laser device shown in FIG. 13 basically has the same configuration as the semiconductor laser device shown in FIG. 1, but differs from the semiconductor laser device of FIG. 1 in that a radial error signal is detected by a one-beam method. Therefore, there is no diffraction grating 10 for generating three beams, and as shown in FIG.
That is, the left and right regions 9a and 9b of the cross section XX 'have different lens effects.

Hereinafter, the servo error signal processing will be described. Of the return light from the information recording medium 14, the diffraction grating 9
The light incident on a is diffracted, the + 1st-order diffracted light enters the elements 2d, 2e, and 2f of the light receiving element 2, and the -1st-order diffracted light enters the elements 3a, 3b, and 3c of the light receiving element 3. Similarly, the + 1st order diffracted light and the -1st order diffracted light by the diffraction grating 9b enter the elements 2a, 2b, 2c and the elements 3d, 3e, 3f, respectively. At this time, the focus error signal FoE is obtained by the SSD method as follows: FoE = ｛(2b + 2e) + (3a + 3c + 3d + 3)
f)｝ − ｛(3b + 3e) + (2a + 2c + 2d + 2)
f) 演算 can be detected. On the other hand, the radial error signal TE is obtained by calculating the difference between the amounts of light incident on the diffraction gratings 9a and 9b as follows: TE = ２ (2d + 2e + 2f) + (3a + 3b + 3)
c)｝-｛(2a + 2b + 2c) + (3d + 3e + 3
f) It is obtained by detecting by the operation of｝. In addition, Fo
In the equations representing E and TE, the symbols indicating the elements such as 2a and 2b indicate the intensity of light incident on the elements as they are. The information signal detection method is the same as in the first embodiment.

With the above configuration, the light receiving element 4 dedicated to information signal detection can be arranged at a position deviated from any of the diffracted lights from the plurality of divided diffraction gratings 9 having different lens effects. The semiconductor laser device for a magneto-optical pickup can be reduced in size and thickness while maintaining a good S / N ratio. Note that the configurations in FIGS. 2 to 12 in the first embodiment can be similarly applied to the present embodiment.

[0033]

As described above, the present invention increases the size of a semiconductor laser device by disposing an information signal light receiving element in a package having a semiconductor laser element and a servo signal light receiving element. S / S of the information signal without
The N ratio can be improved.

[Brief description of the drawings]

FIG. 1 is a diagram showing a semiconductor laser device according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a semiconductor laser device according to the first embodiment of the present invention.

FIG. 3 is a diagram showing a semiconductor laser device according to the first embodiment of the present invention;

FIG. 4 is a diagram showing a semiconductor laser device according to the first embodiment of the present invention;

FIG. 5 is a diagram showing a semiconductor laser device according to the first embodiment of the present invention.

FIG. 6 is a diagram showing a semiconductor laser device according to the first embodiment of the present invention.

FIG. 7 is a diagram showing a semiconductor laser device according to the first embodiment of the present invention;

FIG. 8 shows a semiconductor laser device according to the first embodiment of the present invention.

FIG. 9 is a diagram showing a light receiving element for a radial error signal of the semiconductor laser device according to the first embodiment of the present invention;

FIG. 10 is a diagram showing a semiconductor laser device according to the first embodiment of the present invention.

FIG. 11 is a diagram showing a semiconductor laser element of the semiconductor laser device according to the first embodiment of the present invention.

FIG. 12 is a diagram showing a semiconductor laser device according to the first embodiment of the present invention;

FIG. 13 is a diagram showing a semiconductor laser device according to a second embodiment of the present invention.

FIG. 14 is a plan view of a semiconductor laser unit of the semiconductor laser device according to the second embodiment of the present invention.

FIG. 15 is a plan view of a diffraction grating of the semiconductor laser device according to the second embodiment of the present invention.

FIG. 16 shows a conventional semiconductor laser device.

[Explanation of symbols]

 Reference Signs List 1 semiconductor laser element 2 light receiving element for servo signal 2a, 2b, 2c, 2d, 2e, 2f element 3 light receiving element for servo signal 3a, 3b, 3c, 3d, 3e, 3f element 4 light receiving element for information signal detection 5 package 6 Sealing substrate 7 Semiconductor laser unit 8 Light transmitting substrate 9 Diffraction grating 10 3 Beam generation diffraction grating 11 Beam splitter 12 Collimating lens 13 Objective lens 14 Information recording medium 15 Reflector 16 Information signal light 16a 0th-order information signal light 16b -1 Order information signal light 16c +1 Order information signal light 17 Composite prism 18 Light intensity monitoring light receiving element 19 Radial error signal light receiving element 20 Radial error signal light receiving element 21 Substrate 22 Reflecting mirror 23-1st order diffracted light 24 0th order diffracted light 25 +1 26th order diffracted light + 2nd order diffracted light 27 + 3rd order Diffracted light 28 holographic optical element

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Akio Yoshikawa 1-1, Komachi, Takatsuki-shi, Osaka Matsushita Electronics Corporation

Claims (7)

[Claims] A semiconductor laser device for irradiating a recording medium with a laser beam; a beam splitter disposed in an optical path between the semiconductor laser device and the recording medium; A hologram element formed by forming a diffraction grating on a light transmitting substrate disposed in an optical path between the laser element and a hologram element disposed in an optical path of the diffracted light to receive the diffracted light transmitted through the diffraction grating; A servo signal light receiving element, and an information signal light receiving element for receiving light different from the light incident on the diffraction grating, of the light split by the beam splitting means; The laser element, the servo signal light-receiving element, and the information signal light-receiving element are arranged in one package, and the information signal light-receiving element is located outside the optical path of diffracted light of all orders transmitted through the diffraction grating. Dealt A semiconductor laser device characterized in that: 2. The semiconductor laser device according to claim 1, wherein a reflecting means is provided in an optical path between said beam splitting means and said information signal light receiving element. 3. The semiconductor laser device according to claim 1, wherein the diffraction grating is divided into two or more regions. 4. The semiconductor laser device according to claim 1, wherein said regions have different lens effects. 5. The semiconductor laser device according to claim 1, wherein the hologram element has a lens effect for collimating a laser beam emitted from the semiconductor laser element. . 6. The thickness of the light transmitting substrate may be individually set for a portion through which light incident on the servo signal receiving element and a portion through which light incident on the information signal receiving element are transmitted. 2. The method according to claim 1, wherein the setting is such that a focal position of light incident on the servo signal receiving element and a focal position of light incident on the information signal receiving element are individually adjusted. Item 6. A semiconductor laser device according to any one of Items 5. 7. The hologram optical element according to claim 1, wherein the package is sealed with the hologram optical element.
The semiconductor laser device according to any one of the above.