HK1077394B - Semiconductor laser unit and optical head device - Google Patents

Description

Semiconductor laser unit and optical head device

Technical Field

This invention relates to a semiconductor laser unit capable of emitting a plurality of laser beams and an optical head device equipped with the semiconductor laser unit, and more particularly, to a semiconductor laser unit and an optical head device improved in focusing characteristics of a plurality of laser beams.

Background

Optical pickup apparatuses have been widely used for recording to and reproducing from optical discs such as DVDs (digital versatile discs), CDs (compact discs), and the like. The optical head device 100 shown in fig. 10 as a conventional example is equipped with one conventional semiconductor laser unit 101 called a multibeam semiconductor laser unit capable of emitting a plurality of laser beams. A half mirror 102 is provided on the light emitting side of the semiconductor laser unit 101. A collimator lens 103 and an objective lens 104 are arranged in this order on the light reflection side of the half mirror 102. At or near the focus of the objective lens 104, an optical disc 105 or 106 is set to record thereto or reproduce therefrom. Here, the optical disk 105 is, for example, a DVD whose protective layer has a small thickness, and the optical disk 106 is, for example, a CD whose protective layer has a larger thickness than the DVD. The light detector 107 is disposed on the light transmitting side of the half mirror 102 as viewed from the collimator lens 103.

The semiconductor laser unit 101 used in the optical head device 100 includes one shown in JP- ｃA-2001-298238 (hereinafter referred to as ｃA first background art). A semiconductor laser unit 101 shown in fig. 11 as a first background art includes a case 108, a heat-resistant block 109 attached to the case 108, an auxiliary fixture 110 provided on the heat-resistant block 109, and a multibeam semiconductor laser unit 111 provided on the auxiliary fixture 110. The multibeam semiconductor laser unit 111 has light emission points 112 and 113 spaced apart by about 100 microns. The first light emission point 112, which emits a laser beam of a shorter wavelength than the second light emission point 113, is located at the center of the outer shape of the housing 108. The semiconductor laser unit 101 is disposed on the optical head device 100 so that the optical axis of the laser beam emitted from the first light emission point 112 coincides with the optical axis 114 of the collimator lens 103 and the objective lens 104 as shown in fig. 10. For example, the light emitting points 112 and 113 emit laser beams having a wavelength of 650nm for recording into or reproducing from a DVD and 780nm for recording into or reproducing from a CD, respectively.

The laser beam emitted from the first light emitting point 112 of the semiconductor laser unit 101 shown in fig. 11 is reflected onto the half mirror 102 shown in fig. 10, and then enters the collimator lens 103 where it is converted into a collimated laser beam. Thereafter, it enters the objective lens 104 and is focused onto the optical disc 105. The laser beam reflected onto the optical disc 105 travels through a reverse optical path to pass through the half mirror 102, and is then irradiated onto the photodetector 107. In the optical detector 107, a reproduction signal from the optical disc 105 and signals required for focusing and tracking are detected. Similarly, the laser beam emitted from the second light emitting point 113 of the semiconductor laser unit 101 is focused on another optical disc 106. In the photodetector 107, a reproduction signal from the optical disc 106 and signals required for focusing and tracking are detected.

For the first light emission point 112, a high performance focusing characteristic can be obtained without being affected by aberrations of the collimator lens 103 and the objective lens 104 because the axis of the laser beam emitted from the first light emission point 112 is on the optical axis 114. On the other hand, with the second light emission point 113, since the axis of the laser beam emitted therefrom is not on the optical axis 114, the incidence on the collimator lens 103 and the objective lens 104 is oblique, and thus is inevitably affected by aberrations. However, the CD irradiated with the laser beam of a longer wavelength emitted from the second light emitting point 113 has a larger margin in terms of wavelength and lens focusing performance than the DVD, and thus has no significant trouble in actual operation.

JP- ｃA-2002-25103 as ｃA second background art discloses an optical head device similar to the first background art. This technique shows: when a semiconductor laser unit having two light emission points for emitting laser beams of different wavelengths is mounted on the optical head device 100, the light emission point (first light emission point 112) that emits a laser beam of a shorter wavelength coincides with the optical axis 114 or the distance between the light emission point (first light emission point 112) that is set to emit a laser beam of a shorter wavelength and the optical axis 114 may be shorter than the distance between the light emission point (second light emission point 113) that emits a laser beam of a longer wavelength and the optical axis 114. In this case, similarly to the first background art, the light emission point (first light emission point 112) that emits the laser beam of shorter wavelength is set to a position close to the optical axis 114 with priority over the light emission point (second light emission point 113) that emits the laser beam of longer wavelength because it is easily affected by the aberrations of the collimator lens 103 and the objective lens 104.

Meanwhile, in the optical head device 100, astigmatism generally exists in the multibeam semiconductor laser unit in addition to aberration caused by a positional relationship between the lens system (here, the collimator lens 103 and the objective lens 104) and the light emission point. Preferably, the astigmatism is suppressed to a possible small extent, since it also has an influence on the focusing characteristics.

JP- ｃA-2002-251314 as ｃA third background art discloses ｃA conventional optical head device as shown in fig. 12, in which reference numerals 100 to 107 and reference numeral 114 are the same as those shown in fig. 10. The astigmatism compensation plate 115 is disposed on the optical path between the semiconductor laser unit 101 and the half mirror 102. The astigmatism compensation plate 115 takes the form of a parallel plate made of a transparent optical member such as glass or resin. As shown in fig. 13, a plane constituted by axes 116 and 117 of laser beams emitted from the two light emission points 112 and 113, respectively, is in the same plane (X-Z plane in fig. 13) as a normal line of an incident surface of the astigmatism compensation plate 115. Also, the astigmatism compensation plate 115 is disposed to be inclined to the plane formed by the axes 116 and 117 of the laser beams.

It is apparent that: in the case where the divergently emitted laser beam is transmitted through the parallel plate astigmatism compensation plate 115 disposed obliquely with respect to the axes 116, 117, astigmatism occurs in the laser beam. The amount of astigmatism that occurs is affected by the refractive index of the optical members that constitute the astigmatism compensation plate 115, the thickness of the parallel plates, the tilt angle at the time of disposing the astigmatism compensation plate 115, and the like. In the case where astigmatism already exists in the laser beam entering the astigmatism compensation plate 115, where the added is astigmatism due to transmission through the astigmatism compensation plate 115. Accordingly, the refractive index, thickness and inclination angle of the astigmatism compensation plate 115 are set so as to give an astigmatism having an opposite direction and equal magnitude to that of the astigmatism existing in the laser beam entering the astigmatism compensation plate 115, so that the astigmatism thereof after the laser beam is transmitted through the astigmatism compensation plate 115 can be suppressed. As explained above, since astigmatism is generally present in the multibeam semiconductor laser unit 111 itself, it is very effective to adopt such an astigmatism compensation plate 115.

Further, the astigmatism compensation plate 115 applied to the multi-beam semiconductor laser unit 111 also has the effect as shown in the fourth background art JP- ｃA-2001-237501. That is, for laser beams of different wavelengths emitted by the light emission points 112 and 113, the axes 116 and 117 thereof are refracted on both the incident and exit surfaces of the astigmatism compensation plate 115. In general, the refractive index of the optical member depends on the wavelength, i.e., increases with decreasing wavelength. Thus, the shorter wavelength laser beam 116 undergoes a longer refractive action to achieve a greater amount of parallel shift in the laser beam axis 116 than in the longer wavelength laser beam axis 117 before entering the astigmatism compensation plate 115 and after exiting the astigmatism compensation plate 115. As shown in fig. 13, in the case where the astigmatism compensation plate 115 is disposed to be inclined to some extent near the light emission point 113 for emitting the laser beam of the longer wavelength, the distance B between the axes 116 and 117 of the two laser beams after exiting from the astigmatism compensation plate 115 is smaller than the distance a between the axes 116 and 117 of the two laser beams before entering the astigmatism compensation plate 115. In contrast, in the case where the astigmatism compensation plate 115 is disposed to be inclined to some extent near the light emission point 112 for emitting the laser beam of the shorter wavelength, the distance B between the axes 116 and 117 of the two laser beams after exiting from the astigmatism compensation plate 115 is larger than the distance a between the axes 116 and 117 of the two laser beams before entering the astigmatism compensation plate 115. In this manner, by changing the tilt angle of the astigmatism compensation plate 115, the distance between the axes 116 and 117 of the two laser beams can be changed after entering and exiting the astigmatism compensation plate 115. It is thus possible to freely adjust the positional relationship between the two light emission points 112, 113 and the optical axis 114.

However, the conventional semiconductor laser unit 101 and the optical head device 100 equipped with the semiconductor laser unit 101 have involved the following problems.

In the first and second background arts, the light emitting point 112 for emitting a laser beam of a shorter wavelength is disposed on the optical axis 114 or close to the optical axis 114 in order to preferentially ensure focusing performance, for example, strict aberration conditions for a DVD as compared with a CD. However, there is a problem in sacrificing the focusing performance of the laser beam emitted from the light emitting point 113 for a long time.

Meanwhile, the third background art is configured so that astigmatism existing at the two light emission points 112, 113 of the multi-beam semiconductor laser unit 111 is compensated by using the astigmatism compensation plate 115. Thus, in the case where the two light emission points 112, 113 emit laser beams of the same wavelength and have the same astigmatism as each other, the two light emission points 112, 113 can be easily compensated for. However, when the two light emitting points 112, 113 emit laser beams of different wavelengths, they do not necessarily have the same astigmatism because the materials constituting the light emitting points 112, 113 of the multibeam semiconductor laser unit 111 are different. Thus, it is difficult to simultaneously compensate for the astigmatism of the two light emission points 112, 113 having different astigmatism. Thus, what is further needed is a means for ensuring that the focusing performance of the light emission points is compensated for more inadequately between the two light emission points.

Meanwhile, in the fourth background art, the astigmatism compensation plate 115 is arbitrarily tilted to adjust the distance between the axes 116 and 117 of the two laser beams after passing through the astigmatism compensation plate 115 to a desired value. However, due to the inclination angle of the astigmatism compensation plate 115, the amount of astigmatism of the laser beam after passing through the astigmatism compensation plate 115 varies. Thus, there arises a problem that it takes a long time to measure the distance B or in a process of adjusting the astigmatism compensation plate 115.

Further, any of the first to fourth background arts is explained only for obtaining the optimum focusing characteristics of the optical axes 114 of the collimator lens 103 and the objective lens 104 of the optical head device 100, but is not explained in relation to the focusing characteristics (including astigmatism occurring in the above-described lens system). Thus, from a strict optical design point of view, there is a problem that the structure is not optimized for the focusing characteristics of both laser beams at the same time.

Summary of The Invention

The present invention has been made in order to eliminate the above-mentioned problems, and it is an object of the invention to provide a semiconductor laser unit and an optical head device for simultaneously optimizing focusing characteristics of a plurality of laser beams.

The semiconductor laser unit according to the present invention includes: the laser device includes a plurality of semiconductor laser elements arranged parallel to each other in a laser beam emission direction, and a base for positioning and fixing the plurality of semiconductor laser elements. The plurality of semiconductor laser elements are arranged such that an axis of a laser beam emitted by a semiconductor laser element having the largest astigmatism among the plurality of semiconductor laser elements coincides with a reference axis of the base.

In another aspect of the present invention, a semiconductor laser unit includes: a plurality of semiconductor laser elements arranged in parallel with each other in a laser beam emission direction, wherein at least two of the plurality of semiconductor laser elements have astigmatism substantially the same as each other; and a base for positioning and fixing the plurality of semiconductor laser elements. The plurality of semiconductor laser elements are arranged such that the axes of the laser beams emitted by the at least two semiconductor laser elements sandwich the reference axis of the mount and are maintained at a substantially equal distance from the reference axis.

In the case where the semiconductor laser unit is provided on an optical head device, it is possible to equalize astigmatism for each focal point formed on an optical disc regardless of the magnitude of astigmatism inherently present in each semiconductor laser element.

In another aspect of the present invention, a semiconductor laser unit includes: a plurality of semiconductor laser elements arranged in parallel with each other in a laser beam emission direction, at least two of the plurality of semiconductor laser elements having astigmatism substantially the same as each other; a base for positioning and fixing the plurality of semiconductor laser elements; and an astigmatism compensator provided on the base opposite to the laser beam emitting surfaces of the plurality of semiconductor laser elements for compensating astigmatism of the at least two semiconductor laser elements. The plurality of semiconductor laser elements are arranged so that the axes of the laser beams emitted from the at least two semiconductor laser elements sandwich the reference axis of the mount after passing through the image dispersion compensator and are maintained at a substantially equal distance from the reference axis.

In another aspect of the present invention, a semiconductor laser unit includes: a plurality of semiconductor laser elements arranged in parallel with each other in a laser beam emission direction, the plurality of semiconductor laser elements including a first semiconductor laser element having a maximum astigmatism and a second semiconductor laser element having a smaller astigmatism than the first semiconductor laser element; a base for positioning and fixing the plurality of semiconductor laser elements; and an astigmatism compensator provided on the base opposite to the laser beam emitting surfaces of the plurality of semiconductor laser elements for compensating astigmatism of the second semiconductor laser element. The plurality of semiconductor laser elements are arranged so that the laser beam emitted from the first semiconductor laser element has an axis coincident with the reference axis of the base after passing through the image dispersion compensator.

In another aspect of the present invention, a semiconductor laser unit includes: a plurality of semiconductor laser elements arranged in parallel with each other in a laser beam emission direction, the plurality of semiconductor laser elements including a first semiconductor laser element having a maximum astigmatism and a second semiconductor laser element having a smaller astigmatism than the first semiconductor laser element; a base for positioning and fixing the plurality of semiconductor laser elements; and an astigmatism compensator provided on the base opposite to the laser beam emitting surfaces of the plurality of semiconductor laser elements for compensating astigmatism of the first semiconductor laser element. The plurality of semiconductor laser elements are arranged so that the laser beam emitted from the first semiconductor laser element has an axis coincident with the reference axis of the base after passing through the image dispersion compensator.

In the case where the semiconductor laser unit is provided on the optical head device, astigmatism of each focal point formed on the optical disc can be easily equalized. In addition, the plurality of semiconductor laser elements can be protected from dust or dirt or oxygen in the air.

An optical head device according to the present invention for recording to and/or reproducing from an optical medium includes: a plurality of semiconductor laser elements arranged parallel to each other in a laser beam emission direction, an optical lens for irradiating the optical medium with laser beams emitted by the plurality of semiconductor laser elements, and a photodetector for detecting the laser beams irradiated onto the optical medium. The plurality of semiconductor laser elements are arranged such that an axis of a laser beam emitted from a semiconductor laser element having the largest astigmatism among the plurality of semiconductor laser elements coincides with an optical axis of the optical lens.

In another aspect of the present invention, an optical head device for recording to and/or reproducing from an optical medium includes: a plurality of semiconductor laser elements arranged in parallel with each other in a laser beam emission direction, at least two of the plurality of semiconductor laser elements having astigmatism substantially the same as each other; an optical lens for irradiating the optical medium with laser beams emitted from the plurality of semiconductor laser elements; and a photodetector for detecting the laser beam irradiated onto the optical medium. The plurality of semiconductor laser elements are arranged such that the axes of the at least two semiconductor laser elements emitting laser beams sandwich the optical axis of the optical lens and are maintained at a substantially equal distance from the optical axis.

It is possible to make the astigmatism of each focal point formed on the optical disc equal regardless of the magnitude of the astigmatism inherently present in each semiconductor laser element.

In another aspect of the present invention, an optical head device for recording to and/or reproducing from an optical medium includes: a plurality of semiconductor laser elements arranged in parallel with each other in a laser beam emission direction, at least two of the plurality of semiconductor laser elements having astigmatism substantially the same as each other; and a dispersion compensator disposed opposite to a laser beam emitting surface of the plurality of semiconductor laser elements for compensating astigmatism of the at least two semiconductor laser elements. The optical head device further includes an optical lens for irradiating the laser beam transmitted through the aberration compensator to the optical medium, and a photodetector for detecting the laser beam irradiated to the optical medium. The plurality of semiconductor laser elements are arranged so that the axes of the laser beams emitted from the at least two semiconductor laser elements sandwich the optical axis of the optical lens after passing through the astigmatism compensator and are maintained at a substantially equal distance from the optical axis.

In another aspect of the present invention, an optical head device for recording to and/or reproducing from an optical medium includes: a plurality of semiconductor laser elements arranged in parallel with each other in a laser beam emission direction, the plurality of semiconductor laser elements including a first semiconductor laser element whose astigmatism is largest and a second semiconductor laser element whose astigmatism is smaller than the first semiconductor laser element; and a dispersion compensator disposed opposite to a laser beam emitting surface of the plurality of semiconductor laser elements for compensating astigmatism of the second semiconductor laser element. The optical head device further includes an optical lens for irradiating the laser beam transmitted through the aberration compensator to the optical medium, and a photodetector for detecting the laser beam irradiated to the optical medium. The plurality of semiconductor laser elements are arranged so that the axis of the laser beam emitted by the first semiconductor laser element will coincide with the optical axis of the optical lens after passing through the astigmatism compensator.

In another aspect of the present invention, an optical head device for recording to and/or reproducing from an optical medium includes: a plurality of semiconductor laser elements arranged in parallel with each other in a laser beam emission direction, wherein the plurality of semiconductor laser elements include a first semiconductor laser element whose astigmatism is largest and a second semiconductor laser element whose astigmatism is smaller than the first semiconductor laser element; and a dispersion compensator disposed opposite to a laser beam emitting surface of the plurality of semiconductor laser elements for compensating astigmatism of the first semiconductor laser element. The optical head device further includes an optical lens for irradiating the laser beam transmitted through the aberration compensator to the optical medium, and a photodetector for detecting the laser beam irradiated to the optical medium. The plurality of semiconductor laser elements are arranged so that the axis of the laser beam emitted by the first semiconductor laser element will coincide with the optical axis of the optical lens after passing through the astigmatism compensator.

The astigmatism of each focal point formed on the optical disc can be easily made equal. In addition, the plurality of semiconductor laser elements can be protected from dust or dirt or oxygen in the air.

Brief description of the drawings

Fig. 1 is a structural view of a semiconductor laser unit and an optical head device of embodiment 1;

fig. 2 is a cross-sectional view of a multibeam semiconductor laser unit of embodiment 1;

FIG. 3 is an image height profile of an objective lens;

fig. 4 is a cross-sectional view of a multibeam semiconductor laser unit of embodiment 2;

fig. 5 is a sectional view of a semiconductor laser unit of embodiment 3;

FIG. 6 is a structural view of a semiconductor laser unit and an optical head device of embodiment 4;

fig. 7 is a sectional view of a semiconductor laser unit of embodiment 4;

FIG. 8 is a structural view of a semiconductor laser unit and an optical head device of embodiment 5;

FIG. 9 is a structural view of a semiconductor laser unit and an optical head device of example 6;

fig. 10 is a structural view of a conventional general optical head device;

fig. 11 is a sectional view of a conventional semiconductor laser unit in the first background art;

fig. 12 is a structural view of a conventional optical head device in a third background art; and

fig. 13 is a structural diagram showing a relationship between a multibeam semiconductor laser unit and an astigmatism compensation plate in a conventional optical head device.

Description of The Preferred Embodiment

The invention will now be described in detail with reference to the accompanying drawings, in which embodiments are shown.

Example 1

In fig. 1, an optical pickup apparatus 1 is used for recording to and reproducing from an optical disc. The semiconductor laser unit 2 has the capability of emitting a plurality of laser beams, and the unit shown here is mounted with an integrally integrated multibeam semiconductor laser unit 3. The multibeam semiconductor laser unit 3 includes semiconductor laser elements 4 and 5.

The semiconductor laser elements 4 and 5 emit laser beams 14 and 16, respectively. The half mirror 8 is disposed on the light emission side of the semiconductor laser unit 2. A collimator lens 9 and an objective lens 10 are arranged in this order on the light-reflecting side of the half mirror 8. The optical axis 7 of the objective lens 10 generally coincides with the optical axis of the collimator lens 9. Optical discs (optical media) 11 and 12 are arranged substantially at the focal point of the objective lens 10. The laser beams 14 and 16 are focused at focal points 15 and 17 on the optical discs 11 and 12, respectively. An optical detector 13 is disposed on the light transmitting side of the half mirror 8, as viewed from the collimator lens 9, to detect each reflected light of the laser beams 14, 16 reflected by the optical disks 11, 12.

In fig. 1 and 2, the semiconductor laser elements 4 and 5 constituting the multi-beam semiconductor laser unit 3 are arranged in parallel with each other in a direction in which laser beams 14 and 15 are emitted. The mount T1 is provided for positioning and fixing the multi-beam semiconductor laser unit 3, and S1 is a reference axis of the mount T1. The block T11 is for supporting the multi-beam semiconductor laser unit 3, and the stem T13 is for holding the block T11, which is generally a cylindrical or rectangular column. The block T11 and the socket T13 form a base T1. The reference axis S1 of the base T1 is an axis which has been previously determined so that the reference axis S1 coincides with the optical axis 7 of the objective lens 10 or an extending axis thereof (in fig. 1, the optical axis 7 is reflected by the half mirror 8) when the semiconductor laser unit 2 is set on the optical head device 1. For example, in the case where the stem T13 of the semiconductor laser unit 2 is a cylinder, the reference axis S1 is generally the axis of the cylinder. The outer shape of the semiconductor laser unit 2 is determined such that the reference axis S1 of the base T1 coincides with the optical axis 7 of the objective lens 10 or an extending axis thereof.

In fig. 2, vertical light emission points V1 and V2 (perpendicular to the width direction of the active layer) are generally present only on the light emission end faces 6 of the semiconductor laser elements 4 and 5, and horizontal light emission points H1 and H2 (width direction of the active layer) are generally present several to ten and several micrometers inward thereof. This feature is called astigmatism, i.e., each of the semiconductor laser elements 4 and 5 has vertical and horizontal light emission points that do not coincide with each other. Note that: astigmatism of each of the semiconductor laser elements 4 and 5 can be measured by near-field image observation generally known to those skilled in the art.

In example 1, the astigmatism existing in the semiconductor laser element 4 is assumed to be larger than that of the semiconductor laser element 5. As shown in fig. 1 and 2, the semiconductor laser elements 4, 5 constituting the semiconductor laser unit 3 are arranged such that the axis of the laser beam 14 emitted from the semiconductor laser element 4 having a large astigmatism coincides with the reference axis S1 of the base T1. Since the reference axis S1 of the base T1 coincides with the optical axis 7 of the objective lens 10 or its extending axis when the semiconductor laser unit 2 is disposed on the optical head device 1, the axis of the laser beam 14 emitted from the semiconductor laser element 4 having large astigmatism coincides with the optical axis 7 of the objective lens 10.

The operation of the optical head device 1 of embodiment 1 will now be explained. A laser beam 14 emitted from the semiconductor laser element 4 having a large astigmatism of the semiconductor laser unit 2 is reflected onto the half mirror 8 and enters the collimator lens 9, where the collimator lens 9 is converted into a collimated laser beam, and then enters the objective lens 10, thereby being focused onto the optical disc 11. At this time, a focal point 15 is formed on the optical axis 7 of the objective lens 10 of the optical head device 1. The laser beam 14 reflected onto the optical disc 11 travels through a reverse optical path and passes through the half mirror 8, and is then irradiated onto the photodetector 13. In the photodetector 13, a reproduction signal of the optical disc 11 and signals required for focusing and tracking are detected.

Likewise, the laser beam 16 emitted from the semiconductor laser element 5 with less astigmatism of the semiconductor laser unit 2 enters the objective lens 10 obliquely with respect to the optical axis 7 of the objective lens 10, and is then focused on the optical disc 12. At this time, the focal point 17 is formed at a point shifted from the optical axis 7 by h. Generally, this displacement h from the optical axis 7 is referred to as the image height. The laser beam 16 reflected onto the optical disc 12 likewise travels through the reverse optical path and passes through the half mirror 8 to be irradiated onto the photodetector 13. In the photodetector 13, a reproduction signal of the optical disc 12 and signals required for focusing and tracking are detected.

Of the two focal points 15 and 17, the focal point 15 is formed on the optical axis 17 of the objective lens 10, and the other focal point 17 is formed outside the optical axis 7. In this case, the two focal points 15 and 17 have different focusing states due to the so-called image height characteristic of the objective lens 10. This will be explained using fig. 3.

In fig. 3, a displacement from the focal point of the objective lens 10 is taken on the horizontal axis and the displacement of each focal point 15, 17 from the optical axis 7, i.e. the image height, is taken on the vertical axis. The focal length of the objective lens 10 depends on the direction of each laser beam 14, 16 incident on the objective lens 10 and it is optically constituted by a sagittal image plane and a meridional image. Here, in the arrangement of the multi-beam semiconductor laser unit 3 shown in fig. 2, the laser beams 14, 16 emitted from the vertical light emission points V1, V2 and the horizontal light emission points H1, H2 are each focused on the sagittal image plane and the meridional image plane, respectively. With an image height of zero, i.e. the laser beam 14 is focused on the optical axis 7, the focal length coincides between the sagittal and the meridional image planes. In the case of the other laser beam 16, the focal distances in the sagittal and meridional image planes are shifted toward the objective lens 10, and the amount of shift in the meridional image plane is greater than the amount of shift in the sagittal image plane. This means that: even if the semiconductor laser elements 4, 5 themselves do not astigmatism, the astigmatism occurs at the focal points 15, 17 where the laser beams 14, 16 are focused off the optical axis 7 of the objective lens 10.

As shown in fig. 2, the semiconductor laser elements 4, 5 have horizontal light emission points H1, H2 positioned farther than the vertical light emission points V1, V2 as viewed from the objective lens 10. The laser beam 14 propagating from the light emission points H1, V1 with its axis coincident with the optical axis 7 is not affected by the image height characteristics in the objective lens 10. However, in addition to astigmatism at the light emission points H2, V2, the laser beam 16 propagating from H2, V2 with its axis deviated from the optical axis 7 also undergoes an astigmatism effect in the same direction in conformity with the image height characteristic of the objective lens 10. Thus, in order to make the astigmatism characteristics the same at the two focal points 15, 17, it is necessary to arrange the semiconductor laser elements 4, 5 such that the axis of the laser beam 14 emitted from the semiconductor laser element 4 with large astigmatism coincides with the optical axis 7, while the axis of the laser beam 16 emitted from the semiconductor laser element 5 with small astigmatism is offset from the optical axis 7.

Incidentally, although the relationship between the image height characteristic of the objective lens 10 and the arrangement of the semiconductor laser elements 4, 5 is described above, the image height characteristic is also present in the collimator lens 9. However, in the optical system of the optical head device 1, the longitudinal magnification calculated from the focal lengths of the collimator lens 9 and the objective lens 10 is sufficiently smaller than 1. For this reason, the influence of the image height characteristic possessed by the collimator lens 9 is negligibly small and is therefore satisfactory when considering the objective lens 10.

Although embodiment 1 shows a case where the multibeam semiconductor laser unit 3 is configured by two semiconductor laser elements, the number thereof may be three or more. In such a case, the plurality of semiconductor laser elements may be arranged such that the axis of the laser beam emitted from the semiconductor laser elements with the largest astigmatism among the semiconductor laser elements coincides with the reference axis S1 of the base T1, i.e., the optical axis 7 of the objective lens 10.

Example 2

Although embodiment 1 shows a case where the semiconductor laser element 4 has a larger astigmatism than the semiconductor laser element 5, embodiment 2 shows a case where the two semiconductor laser elements have equal astigmatism.

In fig. 4, semiconductor laser elements 19 and 20 constitute a multibeam semiconductor laser unit 18. The vertical light emission points V3 and V4 are generally present at the light emission end faces 6 of the semiconductor laser elements 19 and 20, respectively. Here, the horizontal light emission points H3 and H4 are present at the same distance inward from the light emission end faces 6 of the semiconductor laser elements 19 and 20, respectively, and thus the astigmatism of the two semiconductor laser elements 19 and 20 is the same. Laser beams 21 and 22 are emitted by the two semiconductor laser elements 19 and 20, respectively.

In embodiment 2, the two semiconductor laser elements 19 and 20 having the same astigmatism are arranged such that the axes of the laser beams 21 and 22 sandwich the reference axis S2 of the submount, and they are kept at an equal distance from the reference axis S2. Similarly to embodiment 1, when the semiconductor laser unit 18 is disposed on the optical head device 1, the reference axis S2 of the base coincides with the optical axis 7 of the objective lens 10 or its extending axis. The result is: the multi-beam semiconductor device 18 is arranged such that the axes of the laser beams 21, 22 emitted from the two semiconductor laser elements 19, 20 sandwich the axis 7 of the objective lens 10 and are kept at an equal distance from the optical axis 7.

In the case where the semiconductor laser unit 2 having such a multibeam semiconductor laser unit 18 is provided on the optical head device 1 as shown in fig. 1, the image height characteristic on the objective lens 10 exhibits axial symmetry about the optical axis 7 as shown in fig. 3. Thus, when the laser beams 21, 22 emitted from the semiconductor laser elements 19, 20 are focused onto the optical discs 11, 12, the respective focal points have the same image height, thus exhibiting the same astigmatic characteristic and maintaining a uniform focusing characteristic.

Although embodiment 2 shows a case where the multibeam semiconductor laser unit 18 is constituted by two semiconductor laser elements, they may be three or more in number. In this case, the semiconductor laser elements are arranged so that the reference axis S2 of the mount is sandwiched from the axes of the laser beams emitted from at least two of the semiconductor laser elements having the same astigmatism as each other, and at an equal distance from the reference axis S2, i.e., so that the optical axis 7 of the objective lens 10 is sandwiched and at an equal distance from the optical axis 7.

Example 3

In fig. 5 showing the semiconductor laser unit 23 according to embodiment 3, reference symbols 3 to 5, 14, and 16 are the same as those of fig. 1. The mount T3 is used to position and fix the multi-beam semiconductor laser unit 3. The block T31 is for supporting the multi-beam semiconductor laser unit 3, the housing T32 is for protecting the multi-beam semiconductor laser unit 3, and the stem T33 is for fixing the block T31 and the housing T32, respectively. The block T31, housing T32 and stem T33 form a base T3. The cover glass 25 in the form of a parallel plate is fixed to the housing T32, which is opposed to and parallel to the emission surfaces of the laser beams 14, 16 emitted from the semiconductor laser elements 4, 5 constituting the multi-beam semiconductor laser unit 3. As the cover glass 25, a cover made of synthetic resin may also be used instead of the cover made of glass as long as it is a light transmitting member in the form of a parallel plate.

Next, the operation will be explained. The laser beams 14, 16 emitted by the semiconductor laser elements 4, 5, respectively, are transmitted through the cover glass 25. This cover glass 25 is disposed opposite to the laser beam emitting surfaces of the semiconductor laser elements 4, 5 and takes the form of a parallel plate. Thus, this has no influence of astigmatism on the laser beams 14, 16 emitted from the semiconductor laser elements 4, 5, and functions to protect the multi-beam semiconductor laser unit 3 from dust and dirt. Further, in the case where the semiconductor laser elements 4, 5 are likely to be damaged by oxygen in the air depending on the materials thereof, the cover glass 25 and the case T32 are provided to shield and protect the semiconductor laser elements 4, 5 from the air. After the laser beams 14, 16 have passed through the cover glass 25, they are transmitted toward the half mirror 8 similarly to the case of embodiment 1.

Although embodiment 3 shows the case of using the multibeam semiconductor laser unit 3 having the semiconductor laser elements 4, 5 as shown in embodiment 1, the cover glass 25 used in embodiment 3 may also be applied to the multibeam semiconductor laser unit 18 having the semiconductor laser elements 19, 20 as shown in embodiment 2.

Example 4

In fig. 6, reference symbols 7 to 13 are the same as those shown in fig. 1. In the optical head device 27 shown in fig. 6, a semiconductor laser unit 28 having the capability of emitting a plurality of laser beams is mounted with an integrally integrated multibeam semiconductor laser unit 29. The multibeam semiconductor laser unit 29 includes semiconductor laser elements 30 and 31. Here, the two semiconductor laser elements 30 and 31 have the same astigmatism.

Laser beams 32 and 33 are emitted from the semiconductor laser elements 30 and 31, respectively. The laser beams 32, 33 are focused onto focal points 36, 37 of the optical discs 11, 12.

In fig. 6 and 7, the semiconductor laser elements 30, 31 constituting the multibeam semiconductor laser unit 29 are arranged in parallel with each other in a direction in which laser beams 32 and 33 are emitted. The mount T4 is used to position and fix the multi-beam semiconductor laser unit 29, and S4 is a reference axis of the mount T4. The block T41 is for supporting the multi-beam semiconductor laser unit 29, the housing T42 is for protecting the multi-beam semiconductor laser unit 29, and the stem T43 is for the fixing block T41 and the housing T42. The block T41, housing T42 and stem T43 form a base T4.

A cover glass 35 in the form of a parallel plate is fixed to a housing T42 of a submount T4, which is inclined with respect to and opposed to the laser beam emission surface of the laser beam 32, 33 of the semiconductor laser element 30, 31. The material reflectance and thickness of the cover glass 35 and the inclination angle of the laser beam emitting surface with respect to the laser beams 32, 33 are determined so as to eliminate astigmatism inherently present in the two semiconductor laser elements 30, 31. The cover glass 35 may be a synthetic resin light-transmitting member other than that made of glass, as long as it can compensate for astigmatism of the two semiconductor laser elements 30, 31. It is possible to use cylindrical lenses, holograms, fresnel lenses, coupling lenses, etc.

The laser beams 32, 33 have axes 38 and 39, respectively, after being transmitted through the cover glass 35. The multi-beam semiconductor laser unit 29 is disposed so that the shafts 38, 39 sandwich the reference axis S4 of the mount T4 and maintain an equal distance from the reference axis S4. The semiconductor laser unit 28 is externally shaped so that a reference axis of the mount T4 may coincide with the optical axis 7 of the objective lens 10 or an extension axis thereof. Thus, the multi-beam semiconductor laser unit 29 is arranged such that the axes 38, 39 of the laser beams 32, 33 sandwich the optical axis 7 of the objective lens 10 and maintain equal distances from the optical axis 7 after passing through the cover glass 35.

The operation of the optical head device 27 of embodiment 4 will now be explained. Laser beams 32, 33 emitted from the semiconductor laser elements 30, 31 are transmitted through the cover glass 35. By propagating the laser beams 32, 33 whose astigmatism is to be compensated for by transmission through the cover glass 35, the same astigmatism existing on the two semiconductor laser elements 30, 31 is eliminated. Further, the cover glass 35 together with the enclosure T42 protects the multi-beam semiconductor laser units 3 from dust and dirt and oxygen in the atmosphere.

After transmission through the cover glass 35, the laser beams 32, 33 have axes 38, 39, which axes 38, 39 sandwich the reference axis S4 of the mount T4 and keep the same distance from the reference axis S4, i.e. the axes 38, 39 sandwich the optical axis 7 of the objective lens 10 and keep the same distance from the optical axis 7. They are then focused by the objective lens 10 to form focal points 36, 37. Since the two focal points 36, 37 have mutually equal image heights, they are equally subject to the image height characteristic effect of the objective lens 10 shown in fig. 3, maintaining the same focusing characteristics.

Although embodiment 4 shows a case where the multibeam semiconductor laser unit 29 is constituted by two semiconductor laser elements, they may be three or more in number. In this case, the plurality of semiconductor laser elements are arranged such that the axes of the laser beams emitted from at least two of the semiconductor laser elements having the same astigmatism as each other sandwich the reference axis S4 of the base T4 and are kept at an equal distance from the reference axis S4, i.e., sandwich the optical axis 7 of the objective lens 10 and are kept at an equal distance from the optical axis 7, after passing through the cover glass 35.

Example 5

In fig. 8, reference symbols 7 to 13 are the same as those in fig. 1. The optical head device 40 in embodiment 5 includes a semiconductor laser unit 41 capable of emitting a plurality of laser beams, and the unit shown here is mounted with an integrally-integrated multibeam semiconductor laser unit 42. The multibeam semiconductor laser unit 42 is constituted by semiconductor laser elements 43 and 44. Of the two semiconductor laser elements 43 and 44, the semiconductor laser element 43 has astigmatism larger than that of the semiconductor laser element 44.

In fig. 8, laser beams 45, 46 are emitted from semiconductor laser elements 43, 44, respectively. The semiconductor laser elements 43 and 44 constituting the multi-beam semiconductor laser unit 42 are arranged so that the laser beams 45 and 46 are parallel to each other in the laser beam emission direction. The base T5 is used for positioning and fixing the multibeam semiconductor laser unit 42, and S5 is a reference axis of the base T5. The block T51 is for supporting the multi-beam semiconductor laser unit 42, the housing T52 is for protecting the multi-beam semiconductor laser unit 42, and the stem T53 is for fixing the block T51 and the housing T52, respectively. Block T51, housing T52 and stem T53 form a base T4.

A cover glass 49 in the form of a parallel plate is fixed to a housing T52 of a submount T5, which is inclined with respect to the laser beam emitting surface of the laser beams 45, 46 emitted by the semiconductor laser elements 43, 44. The reflectivity and thickness of the cover glass 49 and the inclination of the laser beam emitting surface with respect to the laser beams 45, 46 are set to eliminate astigmatism inherently present in the semiconductor laser element 44. The cover glass 49 may be a synthetic resin light-transmitting member other than one made of glass, as long as it can compensate for the astigmatism of the semiconductor laser element 44 whose astigmatism is small. It is possible to use cylindrical lenses, holograms, fresnel lenses, coupling lenses, etc.

The multi-beam semiconductor laser unit 42 is arranged so that the axis of the laser beam 45 emitted from the semiconductor laser element 43 having a large astigmatism coincides with the reference axis S5 of the base T5 after passing through the cover glass 49. The outer shape of the semiconductor laser unit 41 is determined such that the reference axis S5 of the base T5 coincides with the optical axis 7 of the objective lens 10 or its extending axis. Thus, the multibeam semiconductor laser device 42 is disposed such that the axis of the laser beam 45 coincides with the optical axis of the objective lens 10 after passing through the cover glass 49.

The laser beams 45, 46 are focused to focal points 47, 48 on the optical discs 11, 12, respectively. In the case where the laser beam 45 emitted from the semiconductor laser element 43 having a large astigmatism is focused on the optical disc 11, the focal point 47 is formed on the optical axis of the objective lens 10. On the other hand, a laser beam 46 emitted from the semiconductor laser element 44 having a smaller astigmatism is focused on the optical disc 12, forming a focal point 48 having an image height.

The operation of the optical head device 40 of embodiment 5 will now be explained. Laser beams 45, 46 emitted from the semiconductor laser elements 43, 44, respectively, are transmitted through a cover glass 49. By propagating the laser beam 46, whose astigmatism is to be compensated, by transmission through the cover glass 49, the astigmatism existing on the semiconductor laser element 44 is eliminated. In addition, the cover glass 49 together with the enclosure T52 functions to protect the multi-beam semiconductor laser units 42 from dust and dirt and oxygen in the atmosphere. Since the laser beam 46, after passing through the cover glass 49, has its axis misaligned from the optical axis 7 and deviates from said optical axis 7, it is focused by the objective lens 10 to form a focal point 48 which has an image height. Because the focal point 48 experiences the image height characteristic effect of the objective lens 10 shown in fig. 3, it is transformed into a point that has recently been astigmatic.

On the other hand, since the astigmatism existing on the semiconductor laser element 43 is larger than that on the semiconductor laser element 44, propagating the laser beam 45 with partially-retained astigmatism through the housing 49 by means of light transmission does not completely eliminate the astigmatism. The laser beam 45 has its axis coincident with the optical axis 7 and is therefore focused without being affected by the image height characteristics of the objective lens 10.

In this manner, for the laser beam 46 emitted from the semiconductor laser element 44 having a small astigmatism, an astigmatism is newly generated due to the image height characteristic of the objective lens 10 because it propagates on an axis deviated from the optical axis 7. However, astigmatism possessed by the semiconductor laser element 43 is suppressed by the cover glass 49. Meanwhile, for the laser beam 45 emitted from the semiconductor laser element 43 having a large astigmatism, the astigmatism cannot be completely compensated by the cover glass 49. However, astigmatism due to the image height characteristics of the objective lens 10 does not newly occur since it is propagated on the axis of the optical axis. Thus, the astigmatic difference between the laser beams 45 and 46 is not increased. It is unlikely that one of the focal points 47, 48 will have its focusing characteristics severely degraded, thus maintaining the uniformity of the focusing characteristics.

Although embodiment 5 shows a case where two semiconductor laser elements constitute the multi-beam semiconductor laser unit 42, they may be three or more in number. In such a case, the semiconductor laser element is disposed so that the axis of the laser beam emitted from the semiconductor laser element with the largest astigmatism among the plurality of semiconductor laser elements coincides with the reference axis S5 of the base T5, that is, the optical axis 7 of the objective lens 10. Further, for a semiconductor laser element having smaller astigmatism than the above-described astigmatism, it is preferable to employ a cover glass 49 for compensating the astigmatism for a semiconductor laser element having the second largest astigmatism.

Example 6

In fig. 9, reference symbols 7 to 13 are the same as those in fig. 1. The optical head device 50 in embodiment 6 includes a semiconductor laser unit 51 capable of emitting a plurality of laser beams, which is shown here as being mounted with an integrally-integrated multibeam semiconductor laser unit 52. The multibeam semiconductor laser unit 52 is constituted by semiconductor laser elements 53 and 54. Of the two semiconductor laser elements 53 and 54, the semiconductor laser element 53 has astigmatism larger than that of the semiconductor laser element 54.

Laser beams 55, 56 are emitted from the semiconductor laser elements 53, 54, respectively. The semiconductor laser elements 53 and 54 constituting the multi-beam semiconductor laser unit 52 are arranged so that the laser beams 55 and 56 are parallel to each other in the laser beam emission direction. The mount T6 is used to position and fix the multi-beam semiconductor laser unit 52, and S5 is a reference axis of the mount T6. The block T61 is for supporting the multi-beam semiconductor laser unit 52, the housing T62 is for protecting the multi-beam semiconductor laser unit 52, and the stem T63 is for fixing the block T61 and the housing T62, respectively. Block T61, housing T62 and stem T63 form a base T6.

A cover glass 59 in the form of a parallel plate is fixed to a housing T62 of a submount T6, which is inclined with respect to the laser beam emitting surface of the semiconductor laser element 53, 54. The reflectivity and thickness of the cover glass 59 and the inclination angle of the laser beam emitting surface with respect to the laser beams 53, 54 are set to eliminate astigmatism inherently present in the semiconductor laser element 53. The cover glass 59 may be a synthetic resin light-transmitting member other than one made of glass, as long as it can compensate for the astigmatism of the semiconductor laser element 53 having a large astigmatism. It is possible to use cylindrical lenses, holograms, fresnel lenses, coupling lenses, etc.

The semiconductor laser elements 53, 54 are arranged such that the axis of the laser beam 55 emitted from the semiconductor laser element 53 having a large astigmatism coincides with the reference axis S6 of the mount T6 after passing through the cover glass 59. The semiconductor laser unit 51 is shaped externally so that the reference axis S6 of the base T6 coincides with the optical axis 7 of the objective lens 10 or its extending axis. Thus, the multi-beam semiconductor laser device 52 is arranged such that the axis of the laser beam 55 coincides with the optical axis 7 of the objective lens 10 after passing through the cover glass 59.

The laser beams 55, 56 are focused to focal points 57, 58 on the optical discs 11, 12. In the case where the laser beam 55 emitted from the semiconductor laser element 53 having a large astigmatism is focused on the optical disc 11, a focal point 57 is formed on the optical axis 7 of the optical head device 50. On the other hand, in the case where the laser beam 56 emitted from the semiconductor laser element 54 having a smaller astigmatism is focused on the optical disc 12, a focal point 58 having an image height is formed.

The operation of the optical head device 50 of embodiment 6 will now be explained. Laser beams 55, 56 emitted from the semiconductor laser elements 53, 54, respectively, are transmitted through the cover glass 59. By propagating the laser beam 55 whose astigmatism is to be compensated for by transmission through the cover glass 59, the astigmatism existing on the semiconductor laser element 53 whose astigmatism is large is eliminated. In addition, the cover glass 59 together with the enclosure T62 function to protect the multi-beam semiconductor laser units 52 from dust and dirt and oxygen in the atmosphere. Since the laser beam 55, after passing through the cover glass 59, has its axis coincident with the optical axis 7 of the objective lens 10, it is focused to form a focal point 57 unaffected by the image height characteristics of the objective lens 10. I.e. no astigmatism is present at the focal point 57.

On the other hand, since the astigmatism existing on the semiconductor laser element 54 is smaller than that existing on the semiconductor laser element 53, propagating the laser beam 56, which has recently had an astigmatism opposite to the original one, through the transmission of the housing 59 results in additional elimination of the astigmatism. Since this laser beam 56 has an axis that is not coincident with the optical axis 7 of the objective lens 10, it is focused by the objective lens 10 to form a focal point 58, which has image height characteristics. This focal point 58 experiences an astigmatism effect due to the image height characteristics of the objective lens 10 shown in fig. 3, and this serves to cancel out the opposite astigmatism present in the laser beam 56. The degree of cancellation depends on the amount of astigmatism inherent to the semiconductor laser element 54 and the image height characteristics of the objective lens 10. By adjusting the astigmatism, the image height characteristic, and other conditions, it is possible to make the cancellation near zero. As a result, the two focal points 57, 58 can be provided with astigmatism that does not exist at the same time. It is possible to provide an advantageous focusing feature.

In this manner, for the laser beam 55 emitted from the semiconductor laser element 53 having a large astigmatism, the astigmatism is compensated by the cover glass 59. Further, because the laser beam 55 propagates on the axis of the optical axis 7 after passing through the cover glass 59, astigmatism does not newly occur. On the other hand, for the laser beam 56 emitted from the semiconductor laser element 54 having a smaller astigmatism, additional compensation is made by the cover glass 59 to reverse the direction of the astigmatism. Furthermore, because the propagation on the laser beam axis deviates from the optical axis 7, recent astigmatism occurs due to the image height characteristics of the objective lens 10. However, it is structurally possible to eliminate this astigmatism and the opposite astigmatism by the cover glass 59. Thus, uniformity of the focusing characteristics of the laser beams 55, 56 may be obtained.

Although embodiment 6 shows a case where two semiconductor laser elements constitute the multi-beam semiconductor laser unit 52, they may be three or more in number. In such a case, a cover glass is used for astigmatism compensation of the semiconductor laser element having the largest astigmatism among the plurality of semiconductor laser elements. Further, the plurality of semiconductor laser elements are arranged so that the laser beams emitted from the semiconductor laser element having the largest astigmatism have their axes coincident with the reference axis S6 of the base T6, i.e., the optical axis 7 of the objective lens 10.

Example 7

In the multibeam semiconductor laser unit in each of embodiments 1 to 6, there is no particular limitation on the relationship with the wavelength of each semiconductor laser element constituting the multibeam semiconductor laser unit, provided that the arrangement of the plurality of semiconductor laser elements on the semiconductor laser unit or the optical head device depends on the astigmatism size as described above. It is desirable to emit laser beams of the same wavelength or different wavelengths. For example, in the case where a DVD and a CD are used while ensuring compatibility with the discs 11 and 12, the semiconductor laser element corresponding to the DVD emits a laser beam at 650nm, and the semiconductor laser element corresponding to the CD emits a laser beam at 780 nm. Also, in the case of applying the multibeam scheme or the like, a plurality of semiconductor laser elements having emission of the same wavelength are employed.

As for the semiconductor laser element, embodiments 1 to 6 show the use of a monolithically integrated semiconductor laser element, and a discrete laser element may also be provided.

In actually adopting one of the illustrated embodiments 1 to 6, it may be determined by considering the astigmatism size, required performance, and the like of the individual semiconductor laser elements.

The preferred embodiments explained above are exemplary of the invention, which is only illustrated by the following claims. It should be understood that: modifications to the preferred embodiment may be made, as will occur to those of ordinary skill in the art.

Claims (4)

1. A semiconductor laser unit, comprising:

a plurality of semiconductor laser elements arranged parallel to each other in a light beam emission direction emitted by a laser, at least two of the semiconductor laser elements having a 1 st light emission point perpendicular to a width direction of an active layer on an emission end surface of the laser beam and a 2 nd light emission point in the width direction of the active layer at a position separated from the emission end surface by a predetermined distance in an internal direction opposite to the emission direction of the laser beam; and

a base for positioning and fixing the plurality of semiconductor laser elements;

the 2 nd light emitting points of the at least two semiconductor laser elements are approximately equal to each other in the predetermined distance from the emission end surface;

wherein the plurality of semiconductor laser elements are arranged so that axes of laser beams emitted from the at least two semiconductor laser elements sandwich a reference axis of the mount and maintain an equal distance from the reference axis.

2. A semiconductor laser unit comprising:

a plurality of semiconductor laser elements arranged parallel to each other in a light beam emission direction emitted by a laser, at least two of the semiconductor laser elements having a 1 st light emission point perpendicular to a width direction of an active layer on an emission end surface of the laser beam and a 2 nd light emission point in the width direction of the active layer at a position separated from the emission end surface by a predetermined distance in an internal direction opposite to the emission direction of the laser beam; and

a base for positioning and fixing the plurality of semiconductor laser elements; and

an optical flat plate disposed on the base opposite to the laser beam emitting surfaces of the plurality of semiconductor laser elements for compensating astigmatism of the at least two semiconductor laser elements;

wherein the plurality of semiconductor laser elements are arranged such that the axes of the laser beams emitted by the at least two semiconductor laser elements sandwich the reference axis of the mount after passing through the optical flat and are at an equal distance from the reference axis.

3. An optical head device for recording to and/or reproducing from an optical medium, the optical head device comprising:

a plurality of semiconductor laser elements arranged parallel to each other in a light beam emission direction emitted by a laser, at least two of the semiconductor laser elements having a 1 st light emission point perpendicular to a width direction of an active layer on an emission end surface of the laser beam and a 2 nd light emission point in the width direction of the active layer at a position separated from the emission end surface by a predetermined distance in an internal direction opposite to the emission direction of the laser beam;

an optical lens for irradiating the laser beams emitted by the plurality of semiconductor laser elements toward the optical medium; and

a photodetector for detecting the laser beam reflected from the optical medium;

the 2 nd light emitting points of the at least two semiconductor laser elements are approximately equal to each other in the predetermined distance from the emission end surface;

wherein the plurality of semiconductor laser elements are arranged such that axes of the laser beams emitted from the at least two semiconductor laser elements sandwich an optical axis of the optical lens and are maintained at an equal distance from the optical axis.

4. An optical head device for recording to and/or reproducing from an optical medium, the optical head device comprising:

a plurality of semiconductor laser elements arranged parallel to each other in a light beam emission direction emitted by a laser, at least two of the semiconductor laser elements having a 1 st light emission point perpendicular to a width direction of an active layer on an emission end surface of the laser beam and a 2 nd light emission point in the width direction of the active layer at a position separated from the emission end surface by a predetermined distance in an internal direction opposite to the emission direction of the laser beam; and

an optical flat plate disposed opposite to one laser beam emitting surface of the plurality of semiconductor laser elements for compensating astigmatism of the at least two semiconductor laser elements;

an optical lens for irradiating the laser beam transmitted through the optical flat plate to the optical medium; and

a photodetector for detecting the laser beam reflected from the optical medium;

wherein the plurality of semiconductor laser elements are arranged such that the axes thereof sandwich the optical axis of the optical lens after the laser beams emitted from the at least two semiconductor laser elements are transmitted through the optical flat plate, and are maintained at an equal distance from the optical axis.