JP4027162B2 - Semiconductor laser device and optical pickup device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor laser device and an optical pickup device having a hologram element, for example, a semiconductor laser device and an optical pickup device used in an optical disc system such as a compact disc and a video disc.
[0002]
[Prior art]
FIG. 3 shows an optical system of a conventional three-beam method hologram optical pickup apparatus. In this optical pickup device, light emitted from the semiconductor laser 106 is divided into three tracking sub-beams and an information signal readout main beam by a tracking beam generating diffraction grating 105 formed on the back surface S1 of the hologram element 111. Divided into two light beams. These three light beams are included in a conical beam 112 in FIG.
[0003]
The beam 112 composed of these three light beams passes through the hologram 104 on the upper surface S2 of the hologram element 111 as zero-order light 113, is converted into parallel light 114 by the collimator lens 103, and is then condensed by the objective lens 102. The condensed laser beam 115 is irradiated onto the optical disc 101.
[0004]
The reflected light modulated by the pits on the optical disk 101 is transmitted through the objective lens 102 and the collimating lens 103 in order, and is diffracted by the hologram 104 of the hologram element 111 to be received as a first-order diffracted light 118. The light is guided onto the light receiving surface 107.
[0005]
The hologram element 111 is disposed on the cap 109, and the semiconductor laser 106 and the light receiving element 107 are disposed in the cap 109. The cap 109 is disposed on the stem 110.
[0006]
Further, the signal detecting light receiving element 107 may be constituted by a PDIC (signal processing integrated circuit with a light receiving element) incorporating an amplifier circuit. The first-order diffracted light 118 is divided into a plurality of lights by the hologram 104 on the surface of the hologram element 111 according to the use of the optical pickup device and the signal processing method. Each of the light is condensed on a light receiving portion including a predetermined light receiving element.
[0007]
The optical pickup device divides the light of the semiconductor laser 106 reflected and returned from the optical disk 101 by the hologram element 111, and generates a tracking information signal and a recording signal for accurately reading a signal recorded on the optical disk 101. These are separated and guided to a light receiving element 107 or a signal processing integrated circuit with a light receiving element, respectively, and used in an apparatus for obtaining an output signal.
[0008]
[Problems to be solved by the invention]
By the way, in the optical pickup device, in general, light emitted from the semiconductor laser 106 has a small light intensity on the side having a larger radiation angle. Therefore, the optical design is such that the diameter of the hologram element 111, the lens system, and the like are adjusted so that the light having the larger radiation angle is not used for actual signal processing.
[0009]
However, the unnecessary light portion that is not used for the actual signal processing is reflected on the back surface S 1 and the front surface S 2 of the hologram element 111 and the inner surface of the cap 109, and becomes stray light 108. Then, the stray light 108 unnecessary for such signal processing is incident on the light receiving surface of the signal detecting light receiving element 107, causing an increase in signal offset, which causes the reproduction or writing failure of the disk 101.
[0010]
SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a highly reliable semiconductor laser device and optical pickup device that can prevent unwanted light out of light emitted from a semiconductor laser from becoming stray light and entering the light receiving surface of a signal detecting light receiving element. Is to provide.
[0011]
[Means for Solving the Problems]
In order to achieve the above object, a semiconductor laser device according to the present invention includes a semiconductor laser, a hologram element having at least one of a signal hologram or a signal diffraction grating, and a light receiving element, and a laser beam emitted from the semiconductor laser. Is applied to a predetermined laser light irradiation target via at least one of the signal hologram or the signal diffraction grating of the hologram element, and the reflected light reflected by the laser light irradiation target is reflected on the hologram. A semiconductor laser device that receives the diffracted light diffracted by the element by the light receiving element,
Of the laser beam emitted from the semiconductor laser, the laser beam is disposed at a location where light other than light passing through at least one of the signal hologram and the signal diffraction grating of the hologram element is incident, and other than the emission end face of the semiconductor laser And a stray light preventing hologram pattern portion that focuses on a region other than the light receiving surface of the light receiving element, and
A light absorbing member disposed at the focal point,
The stray light preventing hologram pattern portion has two focal points, and the two focal points are opposed to each other with an extended surface of the bonding surface of the semiconductor laser interposed therebetween .
[0012]
In the semiconductor laser device of the present invention, light other than light that passes through at least one of the hologram surface and the diffraction grating surface of the hologram element among the laser light emitted from the semiconductor laser (that is, unnecessary light) is emitted to the stray light preventing hologram. ) Is incident. Unnecessary light incident on the stray light preventing hologram is collected at a focal point in a region other than the emission end face of the semiconductor laser and other than the light receiving surface of the light receiving element, and the light intensity is arranged by the light absorbing member disposed at the focal point. Is weakened. Thereby, it is possible to prevent unnecessary light collected at the focal point from being reflected again and become stray light, and stray light can be prevented from entering the light receiving surface of the light receiving element.
[0013]
Therefore, according to the present invention, it is possible to prevent deterioration of characteristics due to stray light caused by unnecessary light portions not used in actual signal processing, and to realize a highly reliable semiconductor laser device.
[0014]
In one embodiment, the distance between the focus of the stray light preventing hologram pattern portion and the semiconductor laser is smaller than the distance between the light receiving surface of the light receiving element and the semiconductor laser.
[0015]
In the semiconductor laser device of this embodiment, the distance between the focal point of the stray light preventing hologram pattern portion and the semiconductor laser is smaller than the distance between the light receiving surface of the light receiving element and the semiconductor laser. According to this configuration, unnecessary light reflected by the stray light preventing hologram pattern portion can be efficiently collected at the focal point with a compact structure in which the size in the direction orthogonal to the laser light emission direction is suppressed.
[0016]
In the semiconductor laser device of the present invention, the stray light preventing hologram has two focal points, and the two focal points are opposed to each other with an extended surface of the junction surface of the semiconductor laser interposed therebetween. According to this configuration, unnecessary light out of laser light emitted from the semiconductor laser can be efficiently focused on the two focal points.
[0017]
An optical pickup device according to an embodiment includes the semiconductor laser device and a lens having a focal point that substantially coincides with a light emitting point of the semiconductor laser included in the semiconductor laser device.
[0018]
According to the optical pickup device of this embodiment, it is possible to realize a highly reliable optical pickup device that has less stray light due to the unnecessary light and suppresses the incidence of unnecessary light to the light receiving element.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail with reference to the illustrated embodiments.
[0020]
FIG. 1 shows an embodiment of an optical pickup device of the present invention. This optical pickup device has a semiconductor laser 6 and a light receiving element 7 attached to a base portion 15 placed on a stem 10. The semiconductor laser 6 emits laser light upward from the joint surface 6A. The light receiving element 7 is fixed to the base portion 15 with the light receiving surface 7A facing upward.
[0021]
In the light receiving element 7, a film 31 made of a material having a low light reflectance, which serves as a light absorbing member, is bonded to the end 7B closer to the semiconductor laser 6 than the light receiving surface 7A. In addition, a film 33 made of a material having a low light reflectance, which serves as the light absorbing member, is bonded to the upper surface of the convex portion 32 on the side opposite to the light receiving element 7 with respect to the semiconductor laser 6 in the base portion 15.
[0022]
The base 15 to which the semiconductor laser 6 and the light receiving element 7 are fixed is covered with a cap 9 fixed to the stem 10. The semiconductor laser 6 is disposed substantially at the center of the cap 9, and the light receiving element 7 is disposed beside the semiconductor laser 6.
[0023]
A hologram element 13 made of a translucent medium is disposed on the opening 9A formed on the upper surface of the cap 9. The hologram element 13 has a signal hologram pattern portion 4 formed on the upper surface and a signal signal on the lower surface. A diffraction grating 5 is formed.
[0024]
Further, stray light preventing hologram pattern portions 11 and 12 are formed around the region where the hologram pattern portion 4 is formed on the upper surface of the hologram element 13. The stray light preventing hologram pattern portions 11 and 12 have curved edges 11A and 12A surrounding the signal hologram pattern portion 4 as shown in FIG. Then, the sides 11B, 11C at both ends of the edge 12A are combined with the sides 11B, 11C at both ends of the edge 11A so that the curved edges 11A, 12A are opposed to each other, and the outer periphery of the hologram pattern portions 11, 12 is generally rectangular. It has become. The hologram pattern portions 11 and 12 have hologram patterns 11D and 12D as shown in FIG.
[0025]
The optical pickup device has a collimating lens 3 and an objective lens 2 above the hologram element 13 with a predetermined interval. The stem 10, the base portion 15, the semiconductor laser 6, the light receiving element 7, the cap 9, and the hologram element 13 constitute a semiconductor laser device.
[0026]
According to the optical pickup device having the above configuration, the signal light 17 incident on the signal diffraction grating 5 of the hologram element 13 out of the laser light emitted from the joint surface 6A by the semiconductor laser 6 is transmitted to the hologram pattern portion 4. , And converted into parallel light by the upper collimating lens 3, then condensed by the objective lens 2, and the condensed laser light 18 is irradiated onto the optical disk 1.
[0027]
Then, the reflected light modulated by the pits on the optical disc 1 is transmitted through the objective lens 2 and the collimating lens 3 in order, and then diffracted by the hologram pattern portion 4 of the hologram element 13 to be used as a first-order diffracted light 20 for signal detection. The light is guided onto the light receiving surface 7A of the light receiving element 7.
[0028]
Further, according to this embodiment, unnecessary light 8 incident on the stray light preventing hologram pattern portion 11 out of the laser light emitted from the joint surface 6A by the semiconductor laser 6 is received by the hologram pattern portion 11 by the light receiving element. 7 is focused on a focal point P1 on the film 31 on the end 7B. Further, the unnecessary light 8 incident on the stray light preventing hologram pattern portion 12 is condensed by the hologram pattern portion 12 at a focal point P2 on the film 33 disposed on the convex portion 32 of the base portion 15.
[0029]
Thus, according to the optical pickup device of this embodiment, the semiconductor laser 6 emits more than the signal light 17 incident on the signal diffraction grating 5 of the hologram element 13 out of the laser light emitted from the joint surface 6A. The unnecessary light 8 having a large angle and a small light intensity is condensed on the two focal points P1 and P2 by the hologram pattern portions 11 and 12 for preventing stray light. At the focal points P1 and P2, films 31 and 32 are disposed as light absorbing members made of a material having a low light reflectance that prevents light reflection. Thereby, the unnecessary light 8 can be prevented from becoming stray light as in the prior art. Therefore, it is possible to prevent the unnecessary light 8 from entering the light receiving surface 7A of the light receiving element 7, and it is possible to prevent deterioration of characteristics due to stray light caused by unnecessary light 8 that is not used for actual signal processing, and performance as an optical pickup device. Improvements can be made.
[0030]
According to this embodiment, the distance between the focal points P1 and P2 of the stray light preventing hologram pattern portions 11 and 12 and the semiconductor laser 6 is between the light receiving surface 7A of the light receiving element 7 and the semiconductor laser 6. Less than the distance. According to this configuration, with the compact structure in which the size in the direction orthogonal to the laser beam emission direction is suppressed, unnecessary light reflected by the hologram pattern portions 11 and 12 for preventing stray light can be efficiently used for the focal points P1 and P2. Can be collected.
[0031]
Further, since the focal points P1 and P2 of the stray light preventing hologram pattern portions 11 and 12 are opposed to each other with the extended surface of the joining surface 6A of the semiconductor laser 6 interposed therebetween, out of the laser light emitted from the semiconductor laser 6 Unnecessary light 8 can be efficiently focused on the two focal points P1 and P2.
[0032]
In the above-described embodiment, the films 31 and 33 are disposed as light absorbing members serving as light reflection preventing films at the focal points P1 and P2 of the stray light preventing hologram pattern portions 11 and 12, and the light intensity of the unnecessary light 8 is absorbed. However, instead of the films 31 and 33, a coating serving as a light reflection preventing film may be provided as a light absorbing member. A light receiving element for absorbing the unnecessary light 8 may be disposed at the focal points P1 and P2. Thereby, it is possible to prevent unnecessary light 8 from being reflected at the focal points P1 and P2 and becoming weak stray light again.
[0033]
【The invention's effect】
As is clear from the above, in the semiconductor laser device of the present invention, the light other than the light that passes through at least one of the hologram surface or the diffraction grating surface of the hologram element among the laser light emitted from the semiconductor laser is applied to the stray light preventing hologram. (In other words, unnecessary light) enters. Unwanted light incident on the stray light preventing hologram is collected at a focal point in a region other than the emission end face of the semiconductor laser and other than the light receiving surface of the light receiving element, and the light intensity is increased by the light absorbing member disposed at the focal point. Weakened. Thereby, it is possible to prevent unnecessary light collected at the focal point from being reflected again and become stray light, and stray light can be prevented from entering the light receiving surface of the light receiving element.
[0034]
Therefore, according to the present invention, it is possible to prevent deterioration of characteristics due to stray light caused by unnecessary light portions not used in actual signal processing, and to realize a highly reliable semiconductor laser device.
[0035]
In one embodiment, the distance between the focus of the stray light preventing hologram pattern portion and the semiconductor laser is smaller than the distance between the light receiving surface of the light receiving element and the semiconductor laser. According to this configuration, unnecessary light reflected by the stray light preventing hologram pattern portion can be efficiently collected at the focal point with a compact structure in which the size in the direction orthogonal to the laser light emission direction is suppressed.
[0036]
In the semiconductor laser device of the present invention, the stray light preventing hologram has two focal points, and the two focal points are opposed to each other with an extended surface of the junction surface of the semiconductor laser interposed therebetween. According to this configuration, unnecessary light out of laser light emitted from the semiconductor laser can be efficiently focused on the two focal points.
[0037]
Further, the optical pickup device of one embodiment, Ru and a lens having the above-described semiconductor laser device, the focus substantially coincides with the emission point of the semiconductor laser in which the semiconductor laser apparatus. According to the optical pickup device of the invention of this embodiment, it is possible to realize a highly reliable optical pickup device that has less stray light due to the unnecessary light and suppresses noise to the light receiving element.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing the structure of an embodiment of an optical pickup device of the present invention.
FIG. 2 is a plan view showing a stray light preventing hologram pattern portion provided in the optical pickup device of the embodiment.
FIG. 3 is a schematic diagram showing the structure of a conventional optical pickup device.
[Explanation of symbols]
1 ... optical disc, 2 ... objective lens, 3 ... collimating lens,
4 ... Signal hologram pattern, 5 ... Signal diffraction grating,
6 ... Semiconductor laser, 6A ... Bonding surface, 6B ... Emission end face,
7: Light receiving element for signal detection, 7A: Light receiving surface,
8 ... unwanted light, 9 ... cap, 10 ... stem,
11, 12 ... Hologram pattern portion for preventing stray light,
11D, 12D ... Hologram pattern, 17 ... Signal light,
20: First-order diffracted light, P1, P2: Focus.

Claims (3)

A semiconductor laser, a hologram element having at least one of a signal hologram or a signal diffraction grating, and a light receiving element, and a laser beam emitted from the semiconductor laser is transmitted to the signal hologram or the signal diffraction grating of the hologram element Irradiates a predetermined laser light irradiation target via at least one, and receives the diffracted light obtained by diffracting the reflected light reflected by the laser light irradiation target with the hologram element with the light receiving element. A semiconductor laser device,
Of the laser beam emitted from the semiconductor laser, the laser beam is disposed at a location where light other than light passing through at least one of the signal hologram and the signal diffraction grating of the hologram element is incident, and other than the emission end face of the semiconductor laser And a stray light preventing hologram pattern portion that focuses on a region other than the light receiving surface of the light receiving element, and
A light absorbing member disposed at the focal point,
2. The semiconductor laser device according to claim 1, wherein the stray light preventing hologram pattern portion has two focal points, and the two focal points are opposed to each other with an extended surface of the bonding surface of the semiconductor laser interposed therebetween . The semiconductor laser device according to claim 1,
A semiconductor laser device, wherein a distance between the focal point of the stray light preventing hologram pattern portion and the semiconductor laser is smaller than a distance between a light receiving surface of the light receiving element and the semiconductor laser. A semiconductor laser device according to claim 1 or 2 ,
An optical pickup device comprising: a lens having a focal point that substantially coincides with a light emitting point of the semiconductor laser included in the semiconductor laser device.

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