JPH09167375A - Beam shaping prism and optical head having the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a small-sized and high performance optical heat of which working, assembling and adjustment are easy and the number of components is small. SOLUTION: The optical head 20 is constituted by using the beam shaping prism 30 having two planar elements provided with the function of shaping a laser beam 6 and the function of raising the laser beam toward an optical disk 1. In the beam shaping prism 30, the laser beam 6 made incident from a first plane 31 is reflected on a second plane 32 to be emitted from the first plane 31 being the same plane as the plane on which the beam is made incident. Consequently, the beam shaping prism 30 is made thin and to be small in size and moreover since planes to be adjusted in order to obtain a prescribed optical performance become small, the beam shaping prism having a satisfactory performance is provided at a low cost. Further, the small-sized and high performance optical head using this beam shaping prism can be provided at a low cost.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical head device for irradiating an optical recording medium such as an optical disk with a laser beam to perform recording or reproduction, and a beam shaping prism used in the optical head device.

[0002]

8 and 9 show an optical system of a conventional optical head, particularly an optical system for irradiating a laser beam on an optical disk. Optical head 1 shown in FIG.
0 is equipped with a laser unit 5 which irradiates a laser beam of a predetermined wavelength forward, and the laser beam emitted forward is arranged into a parallel light flux by a collimator lens 12. The laser beam emitted from the light source unit 11 including the laser unit 5 and the collimator lens 12 is further changed in angle in a direction substantially perpendicular to the optical disc 1 by the beam shaping prism 2 and the reflection mirror 3, and the optical disc is obtained by the objective lens 13. It is focused on one recording layer.

A laser diode is mounted as a light emitting source in the laser unit 5, and the laser diode emits a laser beam having a different divergence angle depending on an axis parallel to the active layer and an axis perpendicular to the active layer. Therefore, the cross section of the light beam 6 made parallel by the collimator lens 12 has an elliptical shape, and the ratio is about 1: 2 in the laser beams emitted from many laser diodes. The beam shaping prism 2 is for shaping the elliptical light flux 6 into a circular shape. Therefore, the elliptical beam 6 having a short tangential direction is made incident on the surface 2a inclined in the tangential direction parallel to the paper surface of the prism 2,
By refracting at this surface 2a, the tangential direction is widened. The refraction on the surface 2a does not change the width of the beam 6 in the sagittal direction perpendicular to the paper surface,
The elliptical beam 6 is shaped so that a circular beam 7 can be obtained. The beam 7 having a circular cross section is vertically raised toward the optical disc 1 by the reflection mirror 3 and is focused on the optical disc by the objective lens 13.
In FIG. 8, the reflecting lens 3 is arranged so as to reflect the laser beam in a direction parallel to the paper surface in order to simply show the optical path. However, in many optical heads, the reflection mirror 3 is arranged so that the laser beam can be reflected in the direction perpendicular to the paper surface to make the optical head thin. further,
The laser beam emitted from the laser diode is linearly polarized, but the λ / 4 plate 14 is placed in front of the objective lens 13.
The optical disc 1 may be irradiated with light after being provided with a circularly polarized light.

The optical head 10 shown in FIG. 9 has almost the same structure as that described above. Instead of installing the prism 2 and the reflecting mirror 3, one prism 4 is installed in front of the light source unit 11, and the prism 4 is used. The laser beam 6 is shaped, and the direction of the laser beam is changed so as to be perpendicular to the optical disc 1. That is, the prism 4
The laser beam incident on the surface 4a is shaped by this surface 4a, and is reflected at a right angle by the surface 4b. The reflected laser beam is emitted from the surface 4c toward the objective lens 13.

The optical head 10 shown in FIGS. 8 and 9 realizes a thin and compact optical head in which the laser unit 5 and the like can be arranged in parallel with the optical disk 1 by changing the direction of the laser beam. ing. Also,
Since the laser beam shaped into a circular shape can be applied to the optical disk, the spot diameter can be reduced, and the optical head is suitable for recording and reproducing on an optical disk having a high recording density.

[0006]

In recent years, devices using an optical head such as an optical disk device have been made smaller and lighter, and accordingly, the optical head itself has been desired to be small and light. There is. Further, as the recording density of the optical disc is increased, it is necessary to perform position control such as tracking and focusing of the optical head with high accuracy and at high speed, and in this respect, it is necessary to reduce the size and weight of the optical head. For example, the optical head shown in FIG. 8 uses two optical elements, a prism and a mirror, to shape and change the direction of the laser beam emitted from the laser diode, and a space for accommodating these is required. .
Furthermore, in the manufacturing process, two optical elements are manufactured,
It is difficult to reduce the manufacturing cost because it needs to be assembled and further adjusted. In addition, it is difficult to maintain good optical performance because of the large number of parts forming the optical path.

On the other hand, the optical head shown in FIG.
The beam can be shaped by three prisms and the direction of the laser beam can be changed, so the number of parts can be reduced and the laser beam can be provided at low cost. However, the prism 4 requires at least three optical surfaces including the entrance surface 4a, the reflection surface 4b, and the exit surface 4c, and it is difficult to miniaturize the prism. In addition, in order to ensure optical performance, it is necessary to perform polishing processing and surface treatment on the three surfaces independently of each other. Therefore, the work takes time and the manufacturing cost increases. Further, it is difficult to maintain good optical performance.

Therefore, it is an object of the present invention to provide a small-sized and inexpensive optical element which has a function of shaping a laser beam and a function of changing the irradiation direction. It is also an object of the present invention to provide an inexpensive and high-performance optical element in which it is easy to secure optical performance.
Furthermore, using this optical element, excellent optical performance,
An object is to provide a small-sized optical head device at low cost.

[0009]

In the present invention, both the function of shaping a beam and the function of changing the direction of the beam are realized by using an optical element having a two-sided element. That is,
The optical element of the present invention is a prism having a first surface on which a laser beam is incident and a second surface inclined with respect to the first surface, and the laser beam incident from the first surface is a second surface.
It is characterized in that it is reflected by the surface and the reflected beam is emitted from the first surface. Since the laser beam is reflected by the second surface in the beam shaping prism of the present invention as described above, the irradiation direction of the laser beam can be changed to a predetermined direction. Further, since the first surface is inclined with respect to the second surface, the incident angle and the refraction angle when the laser beam is incident on the first surface and the incident angle and the refraction angle when the reflected beam is emitted from the first surface. Is different. Therefore, in the beam shaping prism of the present invention, it is possible to obtain a beam shaping effect by refracting the beam when entering or exiting the first surface.

As described above, the beam shaping prism of the present invention is an optical element having a two-sided element of the first and second surfaces, and in order to maintain a predetermined optical performance, the two surfaces should be precisely adjusted. Good. Therefore, the labor and cost required for manufacturing can be reduced, and a prism having excellent optical characteristics can be provided at low cost. Further, the beam shaping prism of the present invention needs only to secure a surface having two optical effects, so that it can be made small and thin. Further, since the size and weight are reduced, it becomes easy to perform fine position control of the optical head device.

Further, the beam shaping prism of the present invention, a light source section for emitting a laser beam to the first surface of the beam shaping prism, and a reflected beam emitted from the first surface of the beam shaping prism to an optical recording medium. In the optical head device provided with the objective lens for condensing the light, the laser beam emitted from the light source unit can be shaped and the direction of the laser beam can be changed by one miniaturized beam shaping prism.

Therefore, the optical head device can be downsized and its weight can be reduced. Also, since the number of parts is small, the work of adjusting the optical path is easy, and an optical head having excellent optical characteristics can be provided at low cost.

Further, in the optical head device employing the beam shaping prism of the present invention, the incident laser beam can be shaped by the beam shaping prism and can be raised as a reflected beam at a predetermined angle. Therefore, compared with the conventional optical head device that launches a laser beam shaped using a reflection mirror or prism,
Since the elliptical laser beam before shaping can be guided to the beam shaping prism of the present invention, a thin and compact optical head device can be provided.

Further, as can be seen from FIGS. 3 and 4 described later, the angle formed by the first surface and the second surface is approximately 5 degrees to 15 degrees.
The beam shaping prism in the range of degrees can provide a beam shaping prism with a shaping ratio of approximately 1.5 to 2.5, which is suitable for shaping the laser beam emitted from the laser diode, and shapes it into a substantially circular shape. It is possible to provide an optical head device capable of forming the formed spot on the optical disc.

Further, in the beam shaping prism of the present invention, the laser beam is incident on the first surface, and at the same time, the first surface
Since the reflected beam is emitted from the surface, it is desirable to form an antireflection film having a high transmittance at least in both the incident direction of the laser beam and the reflecting direction of the reflected beam on the first surface. Further, in order to increase the reflectance on the second surface, it is effective to form a reflection increasing film for the laser beam on the second surface. By providing the antireflection film and the increased reflection film, it is possible to provide a beam shaping prism in which the laser beam is less attenuated and whose beam shaping and direction can be changed.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in more detail below with reference to Examples. FIG. 1 shows a schematic configuration of an optical head according to an embodiment of the present invention. The optical head 20 of this example is provided with an irradiation unit 23 in which a laser diode 21 for emitting a laser beam 6 is installed in the center and a photodetector 22 for detecting the return beam 9 returned from the optical disk 1 is installed in the periphery. . A collimator lens 12 for converting the laser beam emitted from the laser diode 21 into a parallel light flux is installed in front of the irradiation unit 23, and the light source section 24 of the optical head 20 of this example is provided by the collimator lens 12 and the irradiation unit 23. It is configured. A polarizing grading 25 and a beam shaping prism 30 are installed in front of the light source section 24, and a λ / 4 plate 14 and an objective lens 13 are installed in a direction raised by 90 degrees by the beam shaping prism 30. ing.

In the optical head 20 of this example, the light source unit 2
The parallel light flux emitted from the beam No. 4 passes through the polarizing grating 25 installed in front of the parallel light flux and enters the beam shaping prism 30. In this beam shaping prism 30, the elliptical laser beam 6 is shaped so as to approximate a circular shape, and further, the direction is changed by approximately 90 degrees and the reflected laser beam 6 is emitted toward the objective lens 13. The reflected beam 7 emitted is circularly polarized by the λ / 4 plate 14 installed on the side of the optical disc 1 of the beam shaping prism 30, and is further spotted on the recording layer of the optical disc 1 by the objective lens 13 of the optical head 20. Are focused to form

The laser beam applied to the optical disk 1 in the form of a minute spot is reflected from the optical disk 1 and again enters the optical head 20 via the objective lens 13. The return beam returned from the optical disc 1 is modulated by the data stored in the optical disc 1 and the focusing or tracking data. The return beam becomes a parallel light beam by the objective lens 13,
It becomes a linearly polarized beam deflected in a direction different from that of the reflected beam 7 by the / 4 plate 14. Further, the return beam is transmitted by the beam shaping prism 30 to the polarizing grating 2
The polarized beam 25 is emitted in the direction 5 and diffracts the return beam 9 in a direction having a predetermined angle of view with respect to the optical axis. As a result, the return beam 9 is focused on the photodetector 22 of the irradiation unit 23.

The return beam 9 from the optical disc 1 is detected by the photodetector 22 and provided to an external information processing device or the like to reproduce the data stored in the optical disc 1. Along with this, information regarding focusing and tracking is analyzed, and the optical head 20
Based on this information, an optical disk device or the like having a built-in lens moves the optical head 20 or the objective lens 13 to perform fine position control.

FIG. 2 is an enlarged view of the beam shaping prism of this example. The beam shaping prism 30 of this example includes a first surface 31 on which the laser beam 6 is incident and a second surface 32 that reflects the incident laser beam.
The reflected beam 7 reflected by the surface is emitted from the first surface 31. The prism 30 of this example is a prism in which a prism apex angle θ ₀ is formed by the first surface 31 and the second surface 32, and is a prism having a trapezoidal cross section as a whole whose top portion is cut. The laser beam 6 is emitted from the light source unit 24 shown in FIG.
When the laser beam is incident on the first prism at the first incident angle θ ₁ , the laser beam is refracted in the prism at the first refraction angle θ ₂ . This refracted laser beam forms a second beam on the second surface 32.
Is reflected at an incident angle θ ₃ and a reflection angle θ ₃ . further,
The reflected beam again has a third incident angle θ on the first surface 31.
The light enters at ₄ , is refracted at the third refraction angle θ ₅ , and is emitted toward the objective lens 13. The return beam reflected by the optical disc 1 and made incident from the objective lens 13 follows each optical path in the reverse order to the above and is emitted in the direction of the polarizing grating 25.

The relationship between the incident angle and the refraction angle at the incident point A and the outgoing point C in the beam shaping prism 30 of this example is as follows.

Sin θ ₁ = n · sin θ ₂ (1) sin θ ₅ = n · sin θ ₄ (2) where n is the refractive index of the prism 30.

The relationship between the apex angle θ ₀ and the incident and refraction angles is as follows.

Θ ₀ = θ ₂ −θ ₃ = θ ₃ −θ ₄ (3) From the above equations (1), (2) and (3), the apex angle θ
₀ can be obtained from the refractive index n, the first incident angle θ ₁ and the third refractive angle θ ₅ .

Further, the beam shaping ratio of the beam shaping prism 30 of this example is the ratio of the direction cosine of the incident angle and the direction cosine of the refraction angle, and is the first incident on the incident point A of the first surface 31.
A larger shaping rate can be obtained by increasing the incident angle θ ₁ of. On the other hand, at the exit point C of the first surface 31, the refraction angle θ ₅ is larger than the third incident angle θ _4, so that the reverse shaping ratio is obtained. Therefore, the beam shaping rate m of the beam shaping prism 30 of this example is represented by the product of the shaping rate m1 at the incident point A and the shaping rate m2 at the outgoing point B, and is as follows.

M1 = cos θ ₂ / cos θ ₁ ... (4) m2 = cos θ ₅ / cos θ ₄ ... (5) m = m1 × m2 ... (6) The beam shaping prism 30 of this example is a beam. The first surface 31 on which the light is incident and the second light on the second surface 32 that reflects the beam
Therefore, the shaping rate m2 at the exit point B is not the reciprocal of the shaping rate m1 at the entrance point A. Therefore, in the beam organizing prism 30 of this example, the shaping ratio m does not become 1, and an appropriate beam shaping ratio m can be obtained. Therefore, the beam shaping prism 30 of the present example makes it possible to emit the elliptical laser beam 6 as a substantially circular reflected beam 7 toward the objective lens 13.

FIG. 3 shows the beam shaping ratio m of the beam shaping prism 30 of this example with respect to the _first incident angle θ ₁ . Further, FIG. 4 shows the apex angle θ ₀ of the beam shaping prism 30 of this example with respect to the _first incident angle θ ₁ . In addition,
In FIGS. 3 and 4, the rising angle θ ₆ (θ ₁ + which shows the emission direction of the reflected beam 7 at the emission point C with respect to the incidence direction of the laser beam 6 at the incidence point A.
The case where θ ₅ ) is set to 90 degrees is mainly shown, and examples in which the rising angle θ ₆ is 70 degrees and 110 degrees are also shown.

As can be seen from FIGS. 3 and 4, the apex angle is 0.
With the beam shaping prism 30 of the present invention having a degree of about 20 to 20 degrees, a wide range of beam shaping ratios of about 1 to 3 can be obtained. Most of the laser diodes emit an elliptical laser beam 6 having a ratio of the tangential direction to the sagittal direction of about 1: 2. In order to shape the laser beam 6 into a substantially circular shape, and further to make the rising angle θ ₆ at a right angle, the shaping ratio is approximately 2, and the shaping prism 30 and the laser which raise the rising angle θ ₆ to 90 degrees. The incident angle θ ₁ of the beam 6 may be selected. For example, in the case where the beam shaping prism 30 having the refractive index n of 1.5 is adopted like the optical head 20 of this example, the apex angle θ ₀ is about 12.
It is understood that the laser beam 6 may be incident on the first surface 31 of the beam shaping prism so that the first incident angle θ ₁ is about 67 degrees. Therefore, in the optical head 20 shown in FIG.
A beam shaping prism 30 having an apex angle θ ₀ of about 12 degrees and a refractive index n of 1.5 is formed.
When the laser beam 6 is installed at an angle of 90 degrees, the laser beam 6 rises substantially perpendicularly to the direction of the objective lens 13, that is, the rising angle θ _{6 is about} 90 degrees (the refraction angle θ _{5 is about} 20 degrees). The reflected beam 7 is obtained, and the cross section of the reflected beam 7 emitted from the shaping prism 30 is shaped into a substantially circular shape.

As can be seen from FIGS. 3 and 4, the present invention provides a beam shaping prism 30 having an appropriate beam shaping ratio m depending on the refractive index n, the incident angle θ ₁ and the rising angle θ ₆ . You can The rising angle θ ₆ is not limited to 90 degrees as described above, but in the thin optical head 20 that can be arranged along the optical disc 1, it is desirable to set the rising angle θ ₆ to about 90 degrees. Further, it is desirable that the spot focused on the optical disc 1 by the objective lens 13 is as circular as possible, and for that purpose, a beam shaping prism having a beam shaping ratio m of approximately 1.5 to 2.5 is effective. is there. Therefore, as can be seen from FIGS. 3 and 4, if the refractive index n is 1.5 to 1.8, it is desirable to use a beam shaping prism having an apex angle θ _{0 of} approximately 5 to 15 degrees. Such an apex angle θ
By adopting the beam shaping prism of ₀ , it is possible to irradiate the optical disk 1 with a spot having a substantially circular shape, and it is possible to provide a thin and small optical head compatible with an optical disk of high recording density.

Further, the beam shaping prism 30 of the present example.
Is provided with the antireflection film 35 on the first surface 31 on which the laser beam 6 is incident and on which the reflected beam is emitted, while providing the increased reflection film 36 on the second surface 32 on which the incident laser beam 6 is reflected. These prevent the laser beam 6 from being attenuated in the prism. The increased reflection screen 36 of the beam shaping prism 30 of this example is formed by vapor-depositing a metal such as aluminum on the second surface 32, and enhances the reflectance on the second surface 32.

The enhanced reflection film 36 is not limited to this, but may be formed by laminating dielectric films having different refractive indexes.

On the other hand, the antireflection film 35 formed on the first surface 31 of the beam shaping prism of this example is formed by a laminated dielectric vapor deposition film in which dielectric films having a high refractive index and a low refractive index are laminated. In this example, on the first surface 31, λ / 4,
An antireflection film having a modified thickness of a so-called QHQ type in which three dielectric films of λ / 2 and λ / 4 are laminated is adopted. In the light source section 24 of the optical head 20 of this example, ZnM
A gSSe-based green laser diode 21 is adopted, and a laser beam 6 having a wavelength of about 520 nm is emitted from this laser diode 21. Therefore, the antireflection film 35 of this example is set so that the transmittance of the wavelength is high at the angle of incidence of the laser beam and the angle of emission of the reflected beam. FIG. 5 shows transmission characteristics when the first incident angle θ ₁ is about 70 degrees when the laser beam 6 is incident on the first surface 31. Further, FIG. 6 shows the transmission characteristics when the third refraction angle θ ₅ is about 20 degrees when the reflected beam 7 is emitted from the first surface 31. As can be seen from these figures, the antireflection film 35 of this example has a low reflectance and a good transmittance for the wavelength region of the laser beam, that is, the S wave and the P wave in the vicinity of 520 nm at each angle. . In particular, the reflectance is extremely low for S waves with a wavelength of 520 nm emitted from the laser diode. As described above, the beam shaping prism 30 of this example includes the antireflection film 35 provided on the first surface 31 on which the laser beam enters and exits,
The attenuation of the laser beam in the beam shaping prism can be reduced by the increased reflection film 36 provided on the second surface 32 that reflects the laser beam. Therefore, the optical head 20 of this example can irradiate the laser beam with high intensity from the objective lens 13. Furthermore, the optical head 20 can provide a high-performance optical head with less reading error because the beam-shaping prism attenuates less the return beam reflected from the optical disk.

FIG. 7 shows how the laser beam incident on the beam shaping prism 30 is shaped and reflected in the optical head using the beam shaping prism 30 of this example.
It is shown in comparison with the case where the conventional reflection mirror 3 is used. In the optical head of this example, the beam shaping prism 3
The unshaped elliptical laser beam incident from the first surface 31 of 0 is shaped, is reflected by the second surface 32, rises at a predetermined angle, and is emitted from the first surface 31. on the other hand,
In the conventional optical head using the reflection mirror 3, the shaped laser beam is launched by the reflection mirror 3 at a predetermined angle. Therefore, in the optical head of this example, the laser beam 7a before shaping which is elliptical flat as an optical path for guiding the laser beam to the beam shaping prism 30.
It is enough to secure a space corresponding to. On the other hand, in the conventional optical head using the reflection mirror 3, it is necessary to secure a space corresponding to the shaped circular laser beam 7b as an optical path, and it is impossible to make the height direction thin. is there. The same applies to an optical head that raises a laser beam by using a prism or the like instead of a reflection mirror. By using the beam shaping prism 30 of this example as compared with these conventional optical heads, a thin optical head is provided. it can.

As described above, the optical head of this example uses the beam shaping prism of the two-sided element. This beam shaping prism reflects the laser beam incident from the first surface on the second surface, and further, Since it is emitted from the same first surface as the incident surface, it has both the function of shaping the beam and the function of changing the direction of the laser beam. Therefore, the reflection mirror for changing the direction of the laser beam can be omitted, and the number of parts constituting the optical head can be reduced. Further, it is possible to save the labor for assembling the optical system. Furthermore, since the number of parts can be reduced, the optical head can be miniaturized and can be provided at low cost. Further, since the beam shaping prism of this example is a prism having two-sided elements, it can be made thinner and smaller than a conventional prism having three-sided elements, and the beam shaping prism can be installed in a small space. Therefore, 3
It is possible to provide an optical head that is smaller and lighter than the prism of the surface element. Further, by adopting the beam shaping prism of the present example, the space secured as an optical path in the optical head can be reduced, so that a thinner optical head can be realized. Further, since the beam shaping prism of this example is a two-sided element, it is possible to reduce the number of surfaces that require preparation such as processing and surface treatment when manufacturing the prism. Therefore, preparation work in processing and assembling the prism is facilitated, and a high-performance beam shaping prism can be provided at low cost. Further, since the optical head can be made small and lightweight, it becomes easy to perform minute position control of the optical head in tracking and focusing, and it is possible to provide an optical head having more excellent recording / reproducing characteristics. As described above, according to the present invention, it is possible to realize an optical head which is small and lightweight, has high optical performance, is stable, and is low in cost.

The antireflection film provided on the first surface is
The antireflection film is not limited to the QHQ type described above, and may be an antireflection film having a multilayer film structure of two layers or less or four layers or more. Further, the wavelength of the antireflection film is adjusted to the wavelength of the laser beam emitted from the laser diode.
Of course, the wavelength is not limited to 0 nm. Further, the beam shaping prism of this example can be used in any type of optical head such as a read / write optical head or a read-only optical head. Furthermore, the beam shaping prism of this example can be adopted in an optical head for any type of optical disk such as a magneto-optical type or a phase change type. Further, in this example, an optical head in which a laser diode that is a light source and a photodiode that is a light receiving unit are unitized is described as an example, but the configuration of the optical head is not limited to this, and the light receiving unit is not limited to this. May be an optical head installed separately from the light source, or may be a self-coupling type optical head using a laser diode as a detector.

[0036]

As described above, in the present invention, the laser beam is incident from the first surface by the prism having the first surface on which the laser beam is incident and the second surface inclined with respect to the first surface. The beam shaping prism has the function of shaping the laser beam and the function of changing the direction of the laser beam. Therefore, the beam shaping prism of the present invention is an optical element having two-sided elements of the first and second surfaces, and in order to maintain a predetermined optical performance, the two surfaces of the first and second surfaces are optically formed. It should be processed accurately. Therefore, the labor and cost required for manufacturing the beam shaping prism can be reduced, and a prism having excellent optical characteristics can be provided at low cost.

Further, by adopting the beam shaping prism of the present invention, it is possible to construct a thin and compact optical head device with a small number of parts, which is suitable for a compact optical disc device corresponding to a high density optical disc. A high performance optical head device can be provided at low cost.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of an optical head according to an exemplary embodiment of the present invention.

FIG. 2 is an enlarged view showing a beam shaping prism of the optical head shown in FIG.

FIG. 3 is a graph showing a relationship between an incident angle and a shaping rate in the beam shaping prism shown in FIG.

4 is a graph showing a relationship between an incident angle and an apex angle in the beam shaping prism shown in FIG.

5 is a graph showing the transmission performance in the incident direction of the antireflection film provided on the first surface of the beam shaping prism shown in FIG.

FIG. 6 is a graph showing the transmission performance of the antireflection film provided on the first surface of the beam shaping prism shown in FIG. 2 in the emission direction.

FIG. 7 is a diagram showing how a laser beam is shaped and reflected by the beam shaping prism shown in FIG. 2 in comparison with the case where a conventional reflection mirror is used.

FIG. 8 is a diagram showing an example of a conventional optical head.

FIG. 9 is a diagram showing an example of a conventional optical head different from that of FIG.

[Explanation of symbols]

 1 ... Optical disk 5 ... Laser unit 10, 20 ... Optical head 11, 24 ... Light source 12 ... Collimator lens 13 ... Objective lens 14 ... λ / 4 plate 21 ... Laser diode 22 ... Photodiode 23 .. Irradiation unit 25 .. Polarizing grating 30 .. Beam shaping prism 31 .. First surface 32 .. Second surface 35 .. Antireflection film 36.

Claims (6)

[Claims] 1. A laser beam having a first surface on which a laser beam is incident and a second surface inclined with respect to the first surface, wherein the laser beam incident from the first surface is reflected by the second surface. A beam shaping prism, wherein the reflected beam is emitted from the first surface. 2. The beam shaping prism according to claim 1, wherein the angle formed by the first surface and the second surface is in the range of approximately 5 degrees to 15 degrees. 3. The beam shaping prism according to claim 1, wherein an antireflection film having a high transmittance in the incident direction of the laser beam and the emitting direction of the reflected beam is formed on the first surface. . 4. The beam shaping prism according to claim 1, wherein an increased reflection film for increasing the reflectance of the laser beam is formed on the second surface. 5. The beam shaping prism according to claim 1, a light source unit that emits the laser beam to the first surface of the beam shaping prism, and a light source that emits from the first surface of the beam shaping prism. An optical head device comprising: an objective lens that focuses the reflected beam on an optical recording medium. 6. The optical head device according to claim 5, wherein the direction of the laser beam incident on the first surface and the direction of the reflected beam emitted from the first surface are substantially perpendicular to each other. .