JP2001134972A - Semiconductor laser module and optical information reproducing apparatus using the same - Google Patents

Abstract

(57) [Summary] In an optical pickup device equipped with a laser module, the light intensity distribution of a light beam incident on an objective lens is made flatter without increasing the number of components constituting an optical system. The light spot diameter on the optical disk is made smaller to improve the resolution of the reproduction signal and to significantly reduce the crosstalk. In order to solve the above problem, the width or depth of a grating groove of the linear diffraction grating or the holographic diffraction grating provided in a window of a module is set to the center of a laser beam emitted from a semiconductor laser light source. By controlling the light intensity distribution of the 0th-order diffracted light of the laser light emitted from the semiconductor laser light source by making the region where the light flux near the portion passes and the region where the light flux near the outer edge portion passes different from each other, the objective lens To improve the RIM intensity and optimize the light spot intensity distribution on the optical disk.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical pickup for converging a light spot on an optical information recording medium (hereinafter, referred to as an optical disk) and optically reading an information signal, and more particularly to an optical pickup on an optical disk. It relates to optimization of intensity distribution.

[0002]

2. Description of the Related Art In an optical pickup device, the intensity distribution of a laser beam emitted from a semiconductor laser light source is generally a Gaussian distribution. The light intensity decreases toward the outside with respect to the light intensity of the portion. For this reason, a minute spot on the optical disk is not narrowed down, the resolution of the reproduction signal in the time axis direction is reduced, or a signal recorded on an adjacent track is leaked into the reproduction signal as a crosstalk component, and the S / S of the reproduction signal is reduced. This causes a problem of deteriorating the N ratio.

As means for solving such a problem, for example, in Japanese Patent Application Laid-Open Nos. 63-222340 and 63-222341, a diffraction grating for three spots whose grating groove width and depth are continuously changed is introduced. A technique is disclosed in which the diffraction efficiency of incident light is controlled depending on the location, thereby shaping the intensity distribution of a laser beam for signal reproduction incident on the objective lens so as to obtain desired reproduction characteristics. This method is an effective method that can improve the signal reproduction characteristics without increasing the number of optical parts.

On the other hand, recently, the miniaturization of the optical pickup device,
For the purpose of simplification, a semiconductor laser module (hereinafter simply referred to as a module for simplicity) has been rapidly becoming popular in an optical pickup device. FIG. 1 is a diagram showing a general optical pickup device using a module. The module 50 includes a semiconductor laser chip 1 attached to each predetermined position of the stem 2, a multi-segmented photodetector 5, a cover 6 for enclosing them, and a cover 6
A transparent member 3 provided with a linear diffraction grating or a holographic diffraction grating 4 in an upper window portion.

FIG. 2 shows a general optical pickup device using the above module. In FIG. 2, the light beam emitted from the laser light source 1 in the module 50 is
The diffracted light is diffracted by the diffraction grating 4 provided above, and the 0th-order diffracted light is incident on the collimator lens 7 to become parallel light, and is condensed on the optical disk 9 by the objective lens 8.
The light beam reflected by the optical disc 9 follows the original optical path in reverse and reenters the linear diffraction grating or the holographic diffraction grating 4, and the returning diffraction light generated by the diffraction grating 4 is located at a predetermined position of the photodetector 5. Incident and detected. This photo detector 5
, An information signal is obtained.

[0006] As shown in FIG. 2, these modules basically comprise an optical pickup device including only an objective lens for condensing a laser beam on an optical disk and an actuator for controlling the position of the objective lens. Since it can be configured, it is very advantageous for miniaturization and simplification of the device.

[0007]

However, in an optical pickup using a conventional module, a linear diffraction grating or a holographic diffraction grating 4 comprising a land portion and a groove portion provided in a window of the module reflects an optical disk. It only plays a role of guiding the laser light to the multi-segmented photodetector, and there is no disclosure of a technique for shaping the intensity distribution of the laser beam for signal reproduction incident on the objective lens using the diffraction grating 4.

Therefore, in the present invention, in the optical pickup using the module, the intensity of the light beam incident on the objective lens is applied to the diffraction grating 4 which originally only plays a role of guiding the laser beam reflected from the optical disk to the multi-segmented photodetector. A device that improves the resolution of reproduced signals and significantly reduces crosstalk by reducing the light spot diameter on an optical disk without increasing the number of components that make up the optical system by having a function to shape the distribution. Is to provide.

[0009]

In order to achieve the above object, the present invention provides a semiconductor laser light source and a laser beam emitted from the semiconductor laser light source and reflected by an optical information recording medium to generate a predetermined information signal. A linear diffraction grating or a holographic diffraction grating having the function of guiding the laser beam reflected from the optical information recording medium to the multi-segment photodetector, which houses the multi-segment photodetector to be detected in the same housing. In a module formed on a transparent member and provided with the transparent member in a window of the housing, a laser beam emitted from a semiconductor laser light source is obtained by adjusting a grating groove width or a grating groove depth of the linear diffraction grating or the holographic diffraction grating. The semiconductor laser light source is emitted by making the region near the center portion of the light beam through which the light beam passes and the region near the outer edge portion through which the light beam passes different from each other. By controlling the light intensity distribution of the zero-order diffracted light of the laser light, the RIM intensity of the objective lens (the ratio of the light intensity at the outer edge of the lens to the light intensity at the center of the lens) is improved, and the light spot intensity distribution on the optical disk is improved. The optimization improves the resolution of the reproduced signal and significantly reduces crosstalk.

More specifically, when the linear diffraction grating or the holographic diffraction grating portion through which the vicinity of the center of the laser beam emitted from the semiconductor laser light source passes is defined as the first region, Average lattice period
p ₁ , the average grating groove width is w ₁ , and when the linear diffraction grating or the holographic diffraction grating portion through which the vicinity of the outer edge of the laser beam emitted from the semiconductor laser light source passes is defined as the second region, the second region Assuming that the average lattice period of the region is p ₂ and the average lattice groove width is w ₂ , <Equation 1> is satisfied, and the first region and the second region
In the region between the first region and the second region, as the width of the grating groove of the linear diffraction grating or the holographic diffraction grating changes in one or more stages or continuously, and approaches the second region from the first region. A semiconductor laser module characterized by monotonically increasing or decreasing is used.

Alternatively, in the semiconductor laser module, the refractive index of a transparent member provided with the linear diffraction grating or the holographic diffraction grating is set to n, and the vicinity of the center of a laser beam having a wavelength λ emitted from the semiconductor laser light source. When the linear diffraction grating or the holographic diffraction grating portion through which the laser beam passes is the first region, the average grating groove depth of the first region is h ₁ , and the vicinity of the outer edge of the laser beam emitted from the semiconductor laser light source When the linear diffraction grating or holographic diffraction grating portion through which the light passes passes is defined as a second region, assuming that the average grating groove depth of the second region is h ₂ , positive integers m ₁ and m ₂ including zero. When Expression 2 is satisfied using Expression 2, Expression 3 is satisfied, and in the region between the first region and the second region, the grating groove depth of the linear diffraction grating or the holographic diffraction grating is satisfied. The semiconductor laser module is characterized in that the semiconductor laser module changes in one or more steps or continuously, and monotonically increases or decreases from the first area to the second area.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to the drawings. Normally, in an optical pickup device using a module as shown in FIG. 2, a light beam which enters an objective lens and forms a light spot on an optical disk is a zero-order diffracted light beam among light beams diffracted and separated by the diffraction grating 4.

On the other hand, since the intensity distribution of the laser beam emitted from the semiconductor laser light source 1 is Gaussian, the zero-order diffracted light incident on the objective lens has a Gaussian distribution conventionally, and the light at the center of the objective lens The light intensity of the light beam passing through the outer edge of the lens is lower than the intensity. On the other hand, the grating groove width, grating period, and grating groove depth of the diffraction grating 4 are set such that the light intensity of the 0th-order diffraction light is weak at the center of the diffraction grating 4 and the light intensity of the 0th-order diffraction light is strong at the outer edge. Set diffraction grating 4
If the light intensity distribution of the zero-order diffracted light is made closer to a flat state by changing the diffraction efficiency of
A fine spot can be narrowed down on the optical disk.

Generally, a light beam incident on a linear diffraction grating is separated into a zero-order light 101a and ± first-order lights 101b and 101c as shown in FIG. If the grating groove width of the grating is defined as w, the grating period is defined as p, and the grating groove depth is defined as h, the light intensity I ₀ of the zero-order light 101a and the + 1st-order light 101b
The light intensity I ₁ of the (-1 order light 101c) is w, p, highly dependent on h, or to the light intensity of the incident light and the 1 "Number 4" can be expressed as.

[0015]

(Equation 4)

Here, n is the refractive index of the transparent member 3 on which the linear diffraction grating is cut, and λ is the wavelength of the light beam emitted from the semiconductor laser. Considering that the range of the value of β is 0 <β <1, ± 1 is obtained as the value of β is closer to 0.5 from Equation 4, that is, as the width of the lattice groove approaches half the length of the lattice period.
It can be seen that the light intensity of the 0th-order diffracted light increases, and conversely, the light intensity of the 0th-order diffracted light decreases.

Now, the diffraction grating 4 must play the role of guiding the light beam reflected from the disk to the multi-segmented photodetector. However, since the light diffraction direction depends only on the grating period p, the grating groove width w and the grating groove width w The groove depth h can be changed freely. Therefore, by changing the grating groove width w and the grating groove depth h according to the location, it is possible to control the intensity of the zero-order diffracted light incident on the objective lens according to the location. Specifically, as shown in FIG. 1, in the diffraction grating 4, a region through which a light beam near the center of the light beam 100 emitted from the semiconductor laser passes is defined as a first region.
The width of the grating groove is made closer to half the length of the grating period, and the area through which the light flux near the outer edge passes is designated as a second area.
If the grating groove width is far from half the length of the grating period in the region, the 0th-order diffracted light 101a has a lower light intensity in the first region near the center than in the second region at the outer edge. The rate increases. As a result, the light intensity distribution of the laser beam incident on the objective lens becomes closer to flat, for example, from 21 to 22, so that a minute spot can be narrowed down on the optical disk. Hereinafter, the embodiments of the present invention will be described assuming that the center of the light beam emitted from the semiconductor laser light source 1 passes through the center of the diffraction grating 4.

FIGS. 4 to 7 are a plan view and a front sectional view showing an embodiment of the diffraction grating 4 provided on the transparent member 3. FIG. In FIGS. 4 and 5, in the direction perpendicular to the direction in which the grating is cut, the width of the grating groove in the central portion approaches half the length of the grating period, and the width of the grating groove in the peripheral portion is half the grating period. Try to stay away from the length. 6 and 7, in the direction in which the grid is cut,
The width of the lattice groove in the central portion is set to approach half the length of the lattice period, and the width of the lattice groove in the peripheral portion is set apart from the length of half the lattice period. In any of the cases shown in FIGS. 4 to 7, in the direction in which the grating groove width is changed, the intensity distribution of the light incident on the objective lens is made flatter. Can be done.

FIG. 8 shows a second embodiment, which is an embodiment in which FIGS. 4 to 7 are combined. In FIG. 8, in both the direction in which the grating is cut and the direction perpendicular thereto, the grating groove width in the central portion approaches the length of half the grating period, and the grating groove width in the peripheral portion moves away from half the grating period. Like that. Therefore, in both of the above directions,
A small spot can be narrowed down on the optical disk.

Next, a third embodiment of the present invention will be described with reference to the drawings. In the above-described first and second embodiments, attention has been paid to the value of β appearing in <Equation 4>, but here, attention is paid to the value of α. From the above <Equation 4>, it can be seen that the light intensity of the 0th-order diffracted light diffracted by the diffraction grating 4 can be weakened when the value of α approaches an odd multiple of π. This is because the value of α is π
In the case of an odd multiple of, since the optical path length difference between the light traveling straight between the grooves of the lattice and the light traveling straight through the lattice grooves is an odd multiple of exactly half a wavelength, the phase difference between the two lights is Just 18
This is because they become 0 ° and cancel each other. In other words, in the first region, which is a region where the light beam near the center of the laser light beam emitted from the semiconductor laser light source 1 in the diffraction grating 4 passes, the value of α indicated by << Equation 4 >> approaches an odd multiple of π. By setting the grating groove depth such that the value of α goes away from an odd multiple of π in the second region where the light beam near the outer edge passes, if the laser beam is incident on the objective lens, The light intensity distribution becomes more flat, and a minute spot can be narrowed down on the optical disk.

FIGS. 9 to 12 are a plan view and a front sectional view showing an embodiment of the diffraction grating 4 provided on the transparent member 3. FIG. In FIGS. 9 and 10, in the direction perpendicular to the direction in which the lattice is cut, the depth of the lattice groove in the central portion is set such that the value of α shown in Equation 4 approaches an odd multiple of π, and The lattice groove depth is set so that the value of α shown in << Equation 4 >> goes away from odd multiples of π. FIG.
In FIGS. 1 and 12, in the direction in which the lattice is cut, the depth of the lattice groove in the central portion is set so that the value of α shown in Equation 4 approaches an odd multiple of π, and the depth of the lattice groove in the peripheral portion is
4> is kept away from odd multiples of π. In any of FIGS. 9 to 12, in the direction in which the grating groove depth is changed, the intensity distribution of light incident on the objective lens acts to be flatter, so that in this direction, a minute spot on the optical disk is narrowed down. I can do things.

FIG. 13 shows a fourth embodiment, which is an embodiment in which FIGS. 9 to 12 are combined. FIG. 13 shows that the lattice groove depth at the central part in both the direction in which the lattice is cut and the direction perpendicular thereto is such that the value of α shown in Equation 4 approaches an odd multiple of π, and the depth of the lattice groove in the peripheral part. Is set so that the value of α shown in Equation 4 goes away from odd multiples of π. Therefore, as in the embodiment shown in FIG. 8, a minute spot can be narrowed down on the optical disc in both of the above directions.

In this embodiment, the land portion is flat and the depth of the groove portion changes stepwise or continuously. However, the present invention is not limited to this configuration. May be included in a predetermined plane, and the height of the land portion may be changed stepwise or continuously so as to form a groove having the above-described depth.

In the above embodiment, in the diffraction grating 4,
A grating groove in a region between a first region, which is a region through which a light beam near the center of the laser beam emitted from the semiconductor laser light source passes, and a second region, which is a region through which a light beam near the outer edge passes. Although the width or the depth of the grating groove is not particularly mentioned, the grating groove width or the grating groove depth of the diffraction grating in this region varies, for example, in one or more steps in multiple stages or continuously, and is different from the first region. The groove width or groove depth may be set so as to monotonically increase or decrease as approaching the second region.

In general, the diffraction grating 4 is multi-divided, and a grating having a different pattern may be carved for each of the multi-divided regions. However, even in this case, it does not matter. For example, when the diffraction grating 4 as in FIG. 14 is divided into two parts with the S _1, S _2, in the region of S _1, the S ₂ to the light flux of the central portion near the laser beam emitted from the semiconductor laser light source 1 passes through the The grating groove width of the diffraction grating should be close to half the length of the grating period, or the grating groove depth should be such that the value of α shown in Equation 4 approaches an odd multiple of π. pass
In the region within S ₁ and S ₂ , the grating groove width of the diffraction grating should be kept away from half the length of the grating period, or the value of α shown in (Equation 4) should be kept away from odd multiples of π. If the light intensity distribution of the zero-order diffracted light is controlled by setting the grating groove depth, the light intensity distribution of the light incident on the objective lens can be made flatter.
FIG. 15 shows a fifth embodiment as an embodiment in this case. In each of the regions S ₁ and S ₂ in FIG. 15, as in the embodiment shown in FIG. 8, in the region through which the light beam near the center of the laser beam passes in both the direction in which the grating is cut and the direction perpendicular thereto. The width of the grating groove of the diffraction grating is made closer to half the length of the grating period, and the width of the grating groove of the diffraction grating is set away from half the length of the grating period in the region near the outer edge where the light beam passes. As a result, the light intensity distribution of the 0th-order diffracted light generated in each of the regions S ₁ and S ₂ becomes flatter in the direction in which the grating is cut and in the direction perpendicular thereto, and it is possible to narrow a minute spot on the optical disc in this direction. I can do it.

Here, an embodiment in which the diffraction grating 4 is divided into two parts has been described. However, the same applies to a case where the diffraction grating 4 is divided into more parts. In the portion where the light beam near the center of the emitted laser beam passes, make the grating groove width of the diffraction grating closer to half the length of the grating period, or << Equation 4 >>
The depth of the grating groove is set so that the value of α shown in the figure approaches an odd multiple of π, and the width of the grating groove of the diffraction grating is kept away from half the length of the grating period in the portion where the light flux near the outer edge passes. Alternatively, the depth of the lattice groove may be set so that the value of α shown in << Equation 4 >> goes away from odd multiples of π.

All the embodiments described above can also be applied to a module as shown in FIG. 16 in which the diffraction grating 10 for three spots is formed on the transparent member 3 on the semiconductor laser light source 1 side.

[0028]

As described above, in an optical pickup device using a semiconductor laser module, an optical disk can be formed by shaping the intensity distribution of a light beam incident on an objective lens without increasing the number of components constituting an optical system. By making the diameter of the light spot smaller, the resolution of the reproduced signal is improved and the crosstalk is greatly reduced.

[0029]

[Explanation of symbols]

1 ····· Semiconductor laser light source, 4 ···· Linear or holographic diffraction grating, 20 ···· Light intensity distribution of light beam emitted from semiconductor laser, 22 ··· 0th-order diffracted light Intensity distribution,
100 ······ Semiconductor laser emitting light beam, 101a ···· Zero-order diffracted light.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a semiconductor laser module.

FIG. 2 is a component layout diagram of a general optical pickup device using a semiconductor laser module.

FIG. 3 is a schematic diagram showing diffracted light that has been diffracted and separated by a linear diffraction grating.

FIG. 4 is a schematic diagram showing an embodiment in which a grating groove width is monotonously increased from a peripheral portion to an outer edge in a direction perpendicular to a direction in which the grating is cut.

FIG. 5 is a schematic view showing an embodiment in which a grating groove width is monotonously reduced from a peripheral portion toward an outer edge portion in a direction perpendicular to a direction in which the grating is cut.

FIG. 6 is a schematic view showing an embodiment in which the width of the grating groove is monotonously reduced from the peripheral portion toward the outer edge in the direction in which the grating is cut.

FIG. 7 is a schematic diagram showing an embodiment in which the width of the grating groove is monotonously increased from the peripheral portion toward the outer edge in the direction in which the grating is cut.

FIG. 8 is a plan view and a front sectional view of a diffraction grating showing a second embodiment.

FIG. 9 is a schematic diagram showing an embodiment in which the depth of the grating groove is monotonously decreased from the peripheral portion toward the outer edge in a direction perpendicular to the direction in which the grating is cut.

FIG. 10 is a schematic diagram showing an embodiment in which the depth of the grating groove is monotonously increased from the peripheral portion toward the outer edge in a direction perpendicular to the direction in which the grating is cut.

FIG. 11 is a schematic diagram showing an embodiment in which the depth of the grating groove is monotonously reduced from the peripheral portion toward the outer edge in the direction in which the grating is cut.

FIG. 12 is a schematic view showing an embodiment in which the depth of the grating groove is monotonously increased from the peripheral portion toward the outer edge in the direction in which the grating is cut.

FIG. 13 is a plan view and a front sectional view of a diffraction grating showing a fourth embodiment.

FIG. 14 is a schematic diagram of a diffraction grating divided into two.

FIG. 15 is a plan view and a front sectional view of a diffraction grating showing a fifth embodiment.

FIG. 16 is a schematic view of a semiconductor laser module provided with a diffraction grating for three spots.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Kuniichi Onishi, 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Prefecture Inside Digital Media Development Division, Hitachi, Ltd. 292 Digital Media Development Division, Hitachi, Ltd. (72) Inventor Hideo Suenaga 1 Kitano, Majo, Mizusawa-shi, Iwate F-term in Hitachi Media Electronics Co., Ltd. 2H049 AA03 AA25 AA57 AA66 5D119 AA11 AA14 BA01 EB10 FA05 FA30 JA03 JA04 5F073 AB25 BA04 EA18 EA27 FA02 FA06 FA23

Claims (10)

[Claims] 1. A semiconductor laser light source and a multi-split photodetector for receiving a laser beam emitted from the semiconductor laser light source and reflected by an optical information recording medium and detecting a predetermined information signal are housed in the same housing. And forming a linear diffraction grating or a holographic diffraction grating having a function of guiding the laser light reflected by the optical information recording medium to the multi-segmented photodetector on a transparent member, and forming the transparent member on the housing. In the semiconductor laser module provided in the window part, the linear diffraction grating or the holographic diffraction grating has at least a central portion thereof in a laser beam emitted from the semiconductor laser light source and passing through the linear diffraction grating or the holographic diffraction grating. A grating groove width or a grating groove depth in a region where a nearby light beam passes, and a vicinity of an outer edge portion of a laser light beam emitted from the semiconductor laser light source. The semiconductor laser module in which the grating groove width or the grating groove depth in the region where beams pass and wherein mutually different. 2. In the semiconductor laser module, the average grating period of the linear diffraction grating or the holographic diffraction grating portion passing near the center of the laser beam emitted from the semiconductor laser light source is p ₁ , and the average grating groove is Width
w ₁ , assuming that the average grating period of the linear diffraction grating or the holographic diffraction grating portion through which the vicinity of the outer edge of the laser beam emitted from the semiconductor laser light source passes is p ₂ , and the average grating groove width is w ₂ 1) 2. The semiconductor laser module according to claim 1, wherein the following conditions are satisfied. 3. In the semiconductor laser module, a refractive index of a transparent member provided with the linear diffraction grating or the holographic diffraction grating is defined as n, and a central portion of a laser beam having a wavelength λ emitted from the semiconductor laser light source. The average grating groove depth of the linear diffraction grating or holographic diffraction grating portion passing through the vicinity is h ₁ , and the linear diffraction grating or holographic grating passing near the outer edge of the laser beam of wavelength λ emitted from the semiconductor laser light source passes Assuming that the average grating groove depth of the diffraction grating portion is h ₂ , a positive integer m ₁ including zero,
Using m ₂ When expressed by 2. The semiconductor laser module according to claim 1, wherein the following conditions are satisfied. 4. The semiconductor laser module according to claim 1, wherein the linear diffraction grating or the holographic diffraction grating has a portion near the center of a laser beam emitted from the semiconductor laser and passing through the linear diffraction grating or the holographic diffraction grating. The first area that passes and the second area that passes near the outer edge
In the region between the first region and the second region, as the width of the grating groove of the linear diffraction grating or the holographic diffraction grating changes in one or more stages or continuously, and approaches the second region from the first region. 3. The semiconductor laser module according to claim 2, wherein the increase or decrease monotonically occurs. 5. The semiconductor laser module according to claim 1, wherein the linear diffraction grating or the holographic diffraction grating has a portion near a center portion of a laser beam emitted from the semiconductor laser and passing through the linear diffraction grating or the holographic diffraction grating. The first area that passes and the second area that passes near the outer edge
In the region between the first region and the second region, the depth of the grating groove of the linear diffraction grating or the holographic diffraction grating changes in one or more steps in multiple stages or continuously, and approaches the second region from the first region. 4. The semiconductor laser module according to claim 3, wherein the value increases or decreases monotonically as the value increases. 6. A semiconductor laser module according to claim 1, further comprising a function of reproducing a predetermined information signal from an optical information recording medium or recording an information signal on said optical information recording medium. Optical pickup device. 7. An optical information reproducing apparatus or an optical information recording apparatus equipped with the optical pickup device according to claim 6. 8. A laser light source for irradiating a laser beam for irradiating an optical disk, a multi-segment photodetector for receiving an optical signal and detecting an information signal, and a laser beam reflected on a recording surface of the optical disk. Said diffraction grating leading to a split photodetector,
The depth of each groove | channel of the said diffraction grating changes stepwise or continuously, The semiconductor laser module characterized by the above-mentioned. 9. A laser light source for irradiating a laser beam for irradiating an optical disk, a multi-segment photodetector for receiving an optical signal and detecting an information signal, and a laser beam reflected by a recording surface of the optical disk. Said diffraction grating leading to a split photodetector,
Wherein the diffraction grating comprises: a land portion of the diffraction grating included in a first curved surface; and a groove portion of the diffraction grating included in a second curved surface. A semiconductor laser module, wherein a relative positional relationship between a curved surface and the second curved surface changes stepwise or continuously. 10. A laser light source for irradiating a laser beam for irradiating an optical disk, a multi-segment photodetector for receiving an optical signal and detecting an information signal, and a laser beam reflected by a recording surface of the optical disk. The diffraction grating leading to the split photodetector, wherein the groove provided in the diffraction grating is a parallel groove, and the distance between a predetermined groove and an adjacent groove of the diffraction grating is A semiconductor laser module characterized in that it changes dynamically or continuously.