JPH03134835A - Optical head - Google Patents

Abstract

PURPOSE:To correct anisotropy of laser light emitting from a semiconductor laser without increasing number of parts in an optical head by using two prisms of different refractive indices for a beam splitter for beam shaping. CONSTITUTION:An isotropic light beam 2 emitted from a semiconductor laser 1 which is the light source of linearly polarized light is changed into parallel incident light 4 by a collimator lens 3, enters a beam splitter 5 through the incident surface 5a with an oblique angle where the beam is shaped. Since two prisms 5b, 5d which constitute the beam splitter 5 have different refractive indices from each other, the incident surfaces 5a and the beam splitting surface 5c have an effect of beam shaping, and thus, the beam 2 is changed into isotropic for any direction and exits from the exit surface 5e. The beam 2 is now a first irradiating light 10, reflected by a mirror 6, focused by an objective lens 7, and made to irradiate the recording surface 8 of a disk 8. By this constitution, anisotropy of semiconductor laser light can be corrected without using more parts in the optical head.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to an optical disk device that records or reproduces information on an information recording medium using a light beam from a semiconductor laser, and the present invention relates to an optical disk device that records or reproduces information on an information recording medium using a light beam from a semiconductor laser. The present invention also relates to an optical head using a beam splitter.

[Conventional technology]

・　4 FIG. 16 is a configuration diagram showing a conventional optical head.

The anisotropic light beam 2 emitted from the semiconductor laser 1 is
A light beam 61 is converted into parallel incident light 4 by the collimator 1-lens 3, and isotropic in the vertical and horizontal directions by being obliquely incident on the incident surface 60a of the beam shaping prism 60.
It passes through the beam splitter 62, becomes the first emitted light 10, is focused by the objective lens 7, and is irradiated onto the disk (information recording medium) 8. The reflected light passes through the objective lens 7 again, is reflected by the beam splitter 62, and is vertically emitted as second emitted light 11, which is irradiated onto the detector 16 by the detection lens 12. The beam shaping prism 60 has the effect of changing the shape of the passing beam from an ellipse to a circle, thereby improving the light collection efficiency of the objective lens 7.

However, in this conventional technique, it is necessary to add a prism 60 for beam shaping, which increases the number of parts constituting the optical head.

On the other hand, as described in Japanese Unexamined Patent Publication No. 58-1214.8, a configuration has been proposed in which the entrance surface of a prism for beam shaping is a Be-11 splinter surface. According to this configuration, beam shaping is possible without increasing the number of parts included in the optical head 1.

[Problem to be solved by the invention]

However, in the above-described conventional technology, no consideration is given to the fact that the optical axes of the incident light and the outgoing light with respect to the beam splitter or the beam shaping prism are bent, resulting in a problem that the structure of the optical head becomes complicated. On the other hand, by adding 11 beam shaping prisms and appropriately arranging two beam shaping prisms, it is possible to make the optical axes of the incident light and the outgoing light parallel. However, in this case, there is a problem that the number of parts of the optical head increases.

An object of the present invention is to provide an optical head 1 capable of correcting anisotropy of a semiconductor laser without increasing the number of parts of the optical head.

Another object of the present invention is to correct the anisotropy of the semiconductor laser 6 while keeping the optical axes of the incident light and the emitted light parallel to the beam splitter or beam shaping prism. The purpose is to provide a splitter or prism.

[Means to solve the problem]

In order to achieve the second object, the present invention employs the following technical means.

(1) In the optical parts 1 to 1, the two prisms constituting the beam splitter have different refractive indexes to perform beam shaping.

(2) In the optical head, a beam shaping prism composed of two prisms with different refractive indexes is provided between the collisso 1 lens and the objective lens, and the refraction of the two prisms constituting this prism is provided. 4< NHI N
The relative angles α and β between the incident surface and the boundary surface with respect to the L exit surface are N H > N L .

was set to satisfy.

[Effect]

By making the two prisms constituting the beam splitter different in refractive index, the transmitted light is refracted at the beam splitter surface, which is the boundary surface. Since the light beam is obliquely incident on the beam splitter surface and refracted, the light beam is also obliquely incident on the beam splitter entrance surface and is refracted. Therefore, the beam is shaped at both the beam splitter surface and the entrance surface. According to this configuration, beam shaping is possible without increasing the number of parts of the optical head 1-, and anisotropy of the semiconductor laser beam can be corrected.

Further, the refractive index N1□ of the two brises 11 constituting the prism for shaping the beam 11, Hz, and the relative angles α and β between the incident surface and the boundary surface with respect to the exit surface are N H>N L .

By setting the conditions such that the refraction at the incident surface and the refraction at the boundary surface cancel out the bending of the optical axis, it becomes possible to shape the beam while keeping the optical axes of the incident light and the output light parallel. The anisotropy of laser light can be corrected.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram showing a first embodiment of an optical switch 1- of the present invention.

In FIG. 1, an anisotropic light beam 2 emitted from an l'-conductor laser 1, which is a linearly polarized light source, is emitted from a collisor 1-
The lens 3 converts the incident light into parallel incident light 4. The light beam 2 is beam-shaped by obliquely entering the incident surface 5a of the beam splitter 5. Since the two prisms 5b and 5d constituting the beam splitter 5 have different refractive indexes, the transmitted light is refracted even at the beam stripe 1-plane 5G, which is the boundary surface, and is shaped into a beam. Due to the beam shaping action of the incident surface 5a and the beam splinter I/surface 5G, the light beam is shaped into a vertically and horizontally isotropic light beam and passes through the exit surface 5e. Then, it becomes the first emitted light 10, and after being further reflected by the mirror 6, it is reflected by the objective lens 7.
The light is narrowed down and irradiated onto the information recording surface 8a'2 of the disk 8, which is a magneto-optical information recording medium.

The reflected light beam 9 from the disk 8 is again converted into a parallel light beam 10 by the objective lens 7, and is reflected by the mirror 6 and beam splitter 5. The reflected parallel light beam 11 enters a convex lens 12, which is a detection lens, and becomes a convergent light beam 14. The convergent beam 14 enters a polarizing beam splitter 15, which is an analyzer. Here, the convergent light beam 14 is polarized into P-polarized light 14a and S-polarized light 14b, and then enters the photodetector 1G.

According to this embodiment, beam shaping is possible without increasing the number of parts in the optical head, anisotropy of semiconductor laser light can be corrected, and the number of components from the polarizing beam splitter to the photodetector can be adjusted. By shortening the distance, the optical head can be made smaller.

Next, the shape and beam shaping effect of the beam splitter 5 will be explained.

FIG. 2 is a configuration diagram showing a first example of the beam splitter 5 of the present invention.

In FIG. 2, the beam splitter 5 has an incident surface 5a, unlike a general cubic shape.

0 The beam splitter surface 5c has an inclined shape.

The relative angle of the entrance surface 5a to the exit surface 50 is α, and the exit surface 5
Let β be the relative angle of the beam splitter surface 50 with respect to e,
It is assumed that the incident light 4 and the output light 10 are parallel, and the output light 10 and the output surface 5e are perpendicular. In this case, the angle of incidence of the incident light 4 on the incident surface 5a is α, and the angle of exit of the output light 10 from the splitter surface 5c of the beam 11 is β. The refractive index of the prism 5b is NL, and the refractive index of the prism 5d is N.

, the output angle from the incident surface 5a is α', and the incident angle to the beam splitter surface 5c is β', the following relationship holds true.

In addition, the diameter of the light flux of the incident light 4 is d, the diameter of the light flux after passing through the incident surface 58 is 1), and the diameter of the light flux after passing through the beam splitter surface 5c is C.
Then, the Be 11 shaping ratio m is expressed as follows.

For example, calculations for the case where the glasses of the prisms 5b and 5d are BK-7 and SF-ml, respectively, and the beam shaping ratio rn is 2, are as follows.

Therefore, the following formula (4) holds true.

However, the magnitude relationship of the refractive index shall be expressed by the following equation (5).

N4, <N,.

(5) On the other hand, the relative angle of the output surface 5f to the output surface 5e is (π/2
-γ) It is assumed that the emitted light 10 and the emitted light 11 are directly connected to the refrigerator 2. In this case, the output surface 5 of the output light 11
The exit angle from f is γ. The angle of incidence on the exit surface 5f is γ
′, the following relationship holds.

Therefore, the following equation (14) holds true.

When the above-mentioned BK-7 and 5F-11 are used, the numerical value H1 is calculated as follows.

γ=34−. 377 (degrees) - (15) According to this example, beam shaping is possible while keeping the optical axes of the incident light 4 and the output light 10 parallel, and the anisotropy of the semiconductor laser light can be corrected. Can be done.

Further, according to the present example, since the output surface 5f is also inclined, the optical axis of the output light [O] and the optical axis of the output light 11 can be kept perpendicular.

In this example, a case has been described in which the exit surface 5f is not perpendicular to the exit surface 5e, but the invention is not limited to this, and the exit surface 5f may be perpendicular.

Next, FIG. 3 is a configuration diagram showing a second example of the beam splitter 5 of the present invention.

In FIG. 3, the cross-sectional shape of the prism 5d is a right isosceles triangle like a general cubic shape.

In this case, γ=O...(16) Therefore, from equation (14), β=π/4=45[degrees]...(17). (
α is found from equation (4), and 1 is found from equation (6).

For example, if the glass materials of the prisms 5b and 5d are BK-7 and 5F-11, respectively, and the beam shaping ratio rn is calculated as follows.

α=30.028 C degree] Medium・(18)m=
'J, , 367... (19)
According to this example, beam shaping is possible while keeping the optical axis of the incident light 4 and the optical axis of the output light 10 parallel, and anisotropy of the laser light of the semiconductor laser can be corrected.

Furthermore, according to this example, the cross-sectional shape 1 of the bridge b 5 d:
Since the 3 4 shape is a right-angled isosceles triangle, the optical axis of the emitted light 11 and the optical axis of the emitted light 10 can be kept perpendicular.

In addition, in FIGS. 2 and 3, the beam splitter S
Since the same applies to the case where the present invention is used in a beam shaping prism, the explanation has been omitted.

Further, in this example, only a configuration in which the optical axis of the incident light 4 and the optical axis of the output light 10 are made parallel has been described, but the present invention is not limited to this. By appropriately setting the shapes and refractive indices of the two prisms, the optical axis of the incident light 4 and the optical axis of the output light 10 can be set at any angle.

Further, chromatic aberration can be corrected by setting the refractive index of the glass material of the beam splitter 5 or the two prisms constituting the beam shaping prism and the wavelength dispersion in a predetermined relationship. Wavelength dispersion ΔN41 of the two prisms. Δ
NL or Al1. “”tan (・i・−′(”−r・β))+
tan (...-'(, Fi, s3...)) is set to satisfy as much as possible. Thereby, even if the wavelength of the light beam changes, the optical axis of the incident light 4 and the optical axis of the output light 10 can always be kept parallel.

Moreover, the beam 11 splitter 5 described in this example is not only used for correcting anisotropy of laser light from a semiconductor laser.
Generally, it is effective for beam shaping.

It is also effective when the beam splitter 5 or the Bea-24 prism is placed in the convergent light to generate astigmatism.

Next, the polarization separation effect of the polarization beam splitter 15 will be explained using FIG. 4.

As shown in FIG. 4, the polarizing beam splitter 15 has a parallelogram prism 151) at one end (on the right side of the figure) that transmits P-polarized light (polarized light in the vibration direction parallel to the paper surface) and S-polarized light (perpendicular to the paper surface). A polarizing film 15a that reflects polarized light (in the vibration direction) is sandwiched between a parallelogram prism 15a and a transparent parallel plate 15 having the same refractive index as the parallelogram prism 5b.

At one end (on the left side of the figure), an antireflection film 15e is sandwiched between transparent parallel flat plates having a refractive index different from that of the 5-by-16-row quadrilateral prism I51 and having a total reflection film 15g. The convergent light beam 14 enters the polarizing film 1.5a from above the parallelogram prism 151). P transmitted through the polarizing film 15a
The polarized light 14a is directed to the back plane 1.5 of the transparent parallel plate 1.5c.
After being reflected by cl and passing through the polarizing film 15a again, it travels to the left through the parallelogram prism 1.5b, and then passes through the anti-reflection film 11-film 1.
5e, the light passes through the transparent parallel plate +5f, is totally reflected by the total reflection film 15g, travels toward the F side of the transparent parallel plate +5f, passes through the antireflection film 15e again, and travels through the parallelogram prism +5b. At this time, astigmatism is given to the P-polarized light 14a.

On the other hand, the S-polarized light 14b reflected by the polarizing film 15a degrees Celsius also travels in the same direction as the P-polarized light 14a, and is given the same astigmatism as the P-polarized light 14a by passing through the transparent parallel plate 15f. The light enters the photodetector section.

Here, astigmatism imparted to the P-polarized light 14a, the S-polarized film 4b will be explained using FIG.

In FIG. 5, 100 is a transparent parallel flat plate having a refractive index nz+plate thickness t, which is aligned with the optical axis 1.01 and inclined by an inclination angle O. Further, 102a and 102b are prisms having a refractive index T)1 different from that of the transparent parallel plate 100, and the transparent parallel plate 100 is sandwiched from both sides, and the surface 103a of the prism 102a and the surface 103 of the prism 102b
1) is perpendicular to the optical axis 101. This optical component 1
When 00' is placed in the focused light, astigmatism occurs in the transmitted and refracted light. Astigmatism difference Δ occurring under the conditions shown in Figure 5
Z is given by equation (20).

Here, N=n2/n□.

Therefore, the optical component 100' is placed in an optical path in which the reflected light reflected by the optical information recording medium is a convergent light, so that astigmatism is produced in the reflected light, and the reflected light is focused by a photodetector. A focus error signal can be obtained by detecting the shape.

Here, when the detection range of the focus error signal (the amount of variation of the optical recording medium when the focus error signal changes from the minimum value to the maximum value) is Δ■], the astigmatism difference that should be generated by the parallel plate 100 Δ2 is 7 8 ΔZ=-2・ΔDK2 ・ ・ (21)
It is expressed as Here, K is the lateral magnification of the optical system. Further, the reason why it is 2.DELTA.D is that the light spot (virtual image) on the medium fluctuates twice as much as the optical recording medium fluctuates.

In the present invention, each variable is set so as to satisfy the relational expressions obtained from equations (20) and (21). For example, ΔD=1
1μm K=6.25 n□=1.765 n2=1. ．． 5] If O-45°, t=1. ．． 26 mm, and a glass parallel flat plate with a thickness of about 1 mm, which is available from a radiographic source, can be used.

In addition, as shown in FIG. 6, in an optical component 104 in which a parallel plate 100 is bonded to a prism 104 having a different refractive index to generate astigmatism in catadioptric light, convergent light passes through the parallel plate 100 twice. Because of the transmission, an astigmatism difference that is twice as large as that in the transmission case shown in FIG. 2 occurs.

For example, the astigmatic difference ΔZ obtained with the configuration shown in FIG. 5 above can be obtained with a parallel flat plate of 1/2t (=0.53 mm) in the configuration shown in FIG.

From the above, the astigmatism given to the P polarized light 1.4a and the S polarized light 14b can be arbitrarily set according to equations (20) to (22).

For example, parallelogram prism], 5b is 5FII (refractive index n, = 1..765), transparent parallel plate 15f
is BK7 (refractive index n2 = 1.5]), plate thickness t2 is 0
．． 63 mm, the focal length f DE of the detection lens (focal length of the convex lens 12) is 25 mm, and the focal length fobj of the objective lens is 4 + nm, then the astigmatism difference ΔZ#860 μm that makes the debris detection range ΔD 11 μm is P Polarization],
4a and S polarized light 1/lb]90 respectively.

In this example, the parallelogram prism 15b is SF4.1°, and the transparent parallel plate 15f is BK7, but the parallelogram prism 15b is BK7. Transparent parallel plate 1.5f 5F11
It may be reversed or other materials may be used. In short, any combination of materials that transmit light and have different refractive indexes may be used.

Furthermore, since the angle of incidence on the back surface of the transparent parallel plate 5c can be made larger than the critical angle for total reflection, no coating for total reflection is required. If the refraction of the transparent parallel plate 15c is "$n," then the critical angle Da is as follows.When the incident angle of the optical axis of the convergent light is 45 degrees, the range of the incident angle α of the convergent light that does not require total internal reflection coating is as follows. , α1≦45 degrees −〇〇 (24).For example, when optical glass BK7 is used as the transparent parallel flat plate 15c, the following formula is obtained.When optical glass 5FII is used, the following formula is obtained. The relationship is the same for transparent parallel plates] and 5f.

Next, FIG. 7 is a diagram showing the photodetector 16 as seen from the direction of arrow A in FIG.

As shown in FIG. 7, the photodetector 16 has a light-receiving surface 6g inside a rectangular transparent plastic package 6f. The light receiving surface 16g is S as shown in FIG.
16+1 which receives the polarized light 14b and a square-shaped four-part light receiving area which receives the P polarized light 14a], 6b, 16c,
16d and 16e, and each light receiving area 168~
16e is a 5-divided light receiving element integrally formed on the same plane.

Here, if the thickness of the transparent parallel plate 15c is L□, then the distance d between the P polarized light 14a and the S polarized light 14b to be separated is
becomes d=4-tl (27).

For example, the distance d between the P-polarized light 14a and the S-polarized light 14a and 4b is d'=0, 36mm - (28
), from equation (8), the thickness t of transparent parallel plate], 5c
.

, LlL: 0.25mm --(29)
You can set it to .

Output signals 17 of light receiving areas 16b and 1.6d and light receiving area 1
The output signals 18 of 6c and +6e are added together by an adder 19 to become a signal 20. The output signal 21 and signal 20 of the light receiving area 16a are subtracted by a subtracter 22, and a reproduced signal 23 by the differential reproduction method is detected. On the other hand, the output signal 17 and the output signal 18 are subtracted by a subtracter 24, and a focus error signal 25 is detected. Further, the signal 20 and the output signal 21 are added by an adder 26, and a sum signal 27 is detected. From the sum signal 27, the amount of 1 to racking error, etc. is detected, but since it is not directly related to the gist of the present invention, the explanation will be omitted.

Here, the polarizing beam splitter is arranged to be rotated by 45 degrees around the optical axis of the convergent beam 14. In addition, 4 divided light receiving areas], 6b, 1.6c, 16d, 16
e is equally divided by a boundary line 16i parallel to one side 16h of the package 16f and a boundary line 16j perpendicular to it. Further, the light receiving area 16a is divided into four parts, such as the light receiving area 16b.
, 16c.

16 d and 1.6 e are oriented at 45 degrees.

With the above configuration, the direction of polarization incident on the analyzer can be rotated by 45 degrees while keeping the optical system small, so an optical rotator such as a 1/2 wavelength plate is not required.

Furthermore, since a convergent beam enters the photodetector and the diameter of the beam just before the photodetector is minute, a small polarizing beam splitter can be placed just before the photodetector.

Furthermore, the polarizing beam splitter and the photodetector can be configured to be able to be integrally adjusted in translation and rotation.

3 4 , the spot shape of the S-polarized light 14b becomes slightly elliptical. This is ■] polarized light, 4alJ'XS polarized light 14b
This is because the length of the optical path traveling through the transparent parallel plate 15c is longer than that of the transparent parallel plate 15c. Therefore, considering the influence of the defocus caused by this, that is, the leakage of the S-polarized light 14b into the four-division light-receiving area, as shown in FIG. The arrangement direction 151 of the two spots of P polarized light 1.4a and S polarized light 14b is arranged in a perpendicular relationship.

As explained in detail above, according to the first embodiment,
Beam shaping is possible without increasing the number of parts for the optical head, and compared to the conventional method of tilting a parallel plate with respect to the optical axis in air to generate astigmatism, polarization On the inclined surface of the beam splitter 15 -
By physically providing it (actually, by adhering it), it is possible to achieve a structure that is easy to attach.

Here, the thickness of the adhesive layer is sufficiently thinner than that of a parallel flat plate, and the influence can be ignored by making the refractive index of the adhesive layer approximately equal to that of a transparent parallel flat plate. Alternatively, the thickness itself may be used.

Next, an optical head according to a second embodiment of the present invention will be explained using FIG. 9. In this embodiment, instead of the polarizing beam splitter U-- as an analyzer, a Walrus 1-hem prism consisting of two crystals exhibiting birefringence is arranged and rotated by 45 degrees around the convergent optical axis.

In FIG. 9, the same symbols as in FIG. 1 indicate the same parts.

An anisotropic light beam 112 emitted from the semiconductor laser device 1, which is a linearly polarized light source, is converted into parallel incident light 4 by the collimating lens 3.

The light beam A2 is the incident surface 5a of the beam splitter 5.
The beam is shaped by making it obliquely incident on the beam. Since the two prisms 5b and 5d constituting the beam splitter 5 have different refractive indexes, the transmitted light is refracted and beam-shaped even at the beam splitting surface 5C, which is the boundary surface. Due to the beam shaping action of the incident surface 5a and the beam springs 1 to 5C, the light beam is shaped into a vertically and horizontally isotropic light beam and passes through the exit surface 5e. The light then becomes the first output light 106, which is further reflected by the mirror 6, focused by the objective lens 7, and irradiated onto the information recording surface 8a of the disk 8, which is a magneto-optical information recording medium.

The reflected light beam 9 from the disk 8 is again converted into a parallel light beam 10 by the objective lens 7, and is reflected by the mirror 6 and beam splitter 5. The reflected parallel light beam 11 enters a convex lens 12, which is a detection lens, and becomes a convergent light beam 14. The convergent light beam 14 passes through the cylindrical lens 13, is given astigmatism, and enters the Wollaston prism 29. In the Wollaston prism 29, the optical axis 30b of the crystal body 29b is parallel to the plane of the paper and perpendicular to the optical axis of the convergent light beam 14, and the optical axis 30a of the crystal body 29a is perpendicular to the plane of the paper, and the two are perpendicular to each other. Convergent light beam 1 incident on this Wollaston prism 29
4 is polarized and separated into P-polarized light 14a and S-polarized light 14b, whose traveling direction is symmetrical with respect to the optical axis of the convergent light beam 14, and each enters the photodetector 16.

Note that items such as the signal detection method and focus error signal in this embodiment are based on the photodetector J shown in FIGS. 7 and 8.
Since this is the same as the first embodiment using 6, the explanation will be omitted.

Here, Wallas 1 Hembris 1329 is the convergent luminous flux 1
4 and rotated by 45 degrees around the optical axis.

With this configuration, the direction of polarization incident on the analyzer can be rotated by 45 degrees while keeping the optical system small, so an optical rotator such as a 1/2 wavelength plate is not required.

Furthermore, instead of the analyzer in this embodiment, an analyzer (described in Japanese Patent Application No. 621/1986) having a configuration in which the transparent parallel plate +5f of the polarizing beam splitter 15 shown in FIG. 4 is removed may be used.

Next, an optical head according to a third embodiment of the present invention will be explained using FIG. 10. This embodiment is based on the Wollaston prism 29 in the optical head of the second embodiment shown in FIG.
It has a tea garden configuration with astigmatism function.

In FIG. 10, the same symbols as in FIG. 9 indicate the same parts. The process until the parallel light beam 11 enters the convex lens 12 which is a detection lens and becomes the convergent light beam 14 is the same as in the first and second embodiments. The convergent light beam 14 enters a Wollaston prism 31, which is an analyzer. In the Wollaston prism 31, the optical axis 30b of the crystal body 3+,b is perpendicular to the paper surface, the optical axis 30a of the crystal body 3]a is perpendicular to the paper surface, and the optical axis 30b and the optical axis 30a are perpendicular to each other. . The entrance surface 31c is perpendicular to the optical axis of the convergent beam 14, whereas the exit surface 31d is inclined. The convergent light beam 14 incident on this Wallas 1hen 31 is P polarized light +4a
and S-polarized light 14b, each of which is given an arbitrary astigmatism, and then enters the photodetector 16.

Note that the signal detection method and the focus error signal, etc. in this embodiment are described in Section 1] using the photodetector 16 shown in FIGS. 7 and 8. Since this is the same as the second embodiment, the explanation will be omitted.

Here, the Wollaston prism 31 is arranged to be rotated by 45 degrees around the optical axis of the convergent light beam 14.

With this configuration, the direction of polarization incident on the analyzer can be rotated by 45 degrees while keeping the optical system small, so an optical rotator such as a 1/2 wavelength plate is not required.

Furthermore, in this embodiment, astigmatism is obtained by having only the exit surface 3 and d of the Wollaston prism 31 tilted with respect to the optical axis of the convergent beam 14, but the entrance surface 3 and c are also tilted. However, it is of course possible to obtain astigmatism.

Next, an optical head according to a fourth embodiment of the present invention will be explained using FIG. 11. In this embodiment, the third
Instead of the Wollaston prism 31 having an astigmatism function in the optical head of the embodiment, an analyzer is used in which an astigmatism function is added to a Savard plate made of two crystals exhibiting birefringence. .

In FIG. 11, the same reference numerals as in FIG. 10 indicate the same parts. The process until the parallel light beam 11 enters the concave lens 12, which is a detection lens, and becomes the convergent light beam 14 is the same as in the first to third embodiments. The convergent light beam 14 enters a Savard plate 32, which is an analyzer. As shown in FIG. 12, the Savart plate 32 is composed of two viscous bodies 32a and 32b having optical axes 30a and 30b which are inclined with respect to the optical axis of the incident light beam 14 and are orthogonal to each other. The entrance surface 32c is perpendicular to the optical axis of the incident light beam 14, and the exit surface 32d has a non-perpendicular shape. The convergent light beam 14 that has entered the Savart plate 32 is polarized into r) polarized light 14a and S-polarized light 14b, each of which is given astigmatism.
The light beams are emitted from each other at a distance of 1.5 mm, and each enters a photodetector 16.

Here, the distance d between the P-polarized light 14a and the S-polarized light +4b emitted from the Savart plate 32 is made to match the distance between the two regions of the photodetector that receives the P-polarized light 14a and the S-polarized light 14b.

Note that items such as the signal detection method and focus error signal of this embodiment are based on the photodetector 1 shown in FIGS. 7 and 8.
Since this is the same as the first to third embodiments using 6, the explanation will be omitted.

Here, the Savart plate 32 is arranged to be rotated by 45 degrees around the optical axis of the convergent light beam 14. With this configuration, the direction of polarization incident on the analyzer can be rotated by 45 degrees while keeping the optical system small, so an optical rotator such as a 1/2 wavelength plate is not required.

Further, in this embodiment, only the exit surface 32d of the Savard board is tilted with respect to the optical axis of the convergent light beam 14 to obtain astigmatism, but the entrance surface 32c is tilted or the entrance surface 32
Naturally, it is possible to obtain astigmatism even if the exit surface 32d and the exit surface 32d are respectively inclined.

In the first to fourth embodiments, in order to detect a focus error signal in addition to the reproduced signal, the astigmatism generating means and the
Although the divided light receiving areas are provided, the present invention is not limited to this.

FIG. 13 shows an optical head according to a fifth embodiment of the present invention. This embodiment is a modification of the optical head of the second embodiment shown in FIG.

In FIG. 13, the same symbols as in FIG. 9 indicate the same parts. The process is the same as in the first to fourth embodiments until the parallel light beam 11 enters the convex lens 12, which is a detection lens, and becomes a convergent light beam 14. The convergent light flux 14 is the left half of the light flux 5 of the light flux 14.
0 (not shown) A light beam 50' is formed by the Foucault prism 33 inserted halfway into the converging light beam 14.

5Ql+ (not shown) is deflected and enters the 2-I prism 29, which is an analyzer. On the other hand, the right half of the convergent light beam 5] (not shown) in which the Eucobism 33 is not inserted continues straight and enters the Wollaston prism 29. The luminous flux JO' + 50" g 51 incident on Wollaston Priz 1329 is P polarized light 50
'a.

50''a, 51th and S polarized light 50'b,
After the light is polarized and separated into 50'''b and 51b, it enters the photodetector, respectively.

Next, FIG. 14 is a diagram showing the current state of the photodetector.

The light receiving surface 341 of the photodetector 34 receives S polarized light 50' b ,
34a and 34b that receive 50”b and S polarized light 511
), 34e, 34f that receive P polarized light 50'a, 50''a, and 2 divided light receiving regions 34g, 3 that receive P polarized light 51.a.
4h, and each light receiving area 34a to 34h is an eight-divided light receiving element integrally formed on the same plane.

The output signal 35 of the light receiving area 34g and the output signal 36 of the light receiving area 34h are subtracted by a subtracter 37, and a focus error signal 25 is detected. Output signal 38 of light receiving area 34a
．． Output signal 39 of light receiving area 34e. Output signal 40 of light receiving area 34b. The output signal 41 of the light receiving area 34f is subtracted by a subtracter (output signals 40 and 4 are obtained from the sum of output signals 38 and 39).
1) and a tracking error signal 43 is detected. On the other hand, the output signal 38. Output signal 44 of light receiving area 34c. Output signal 45 of light receiving area 34d. The four output signals 40 and the four output signals 39, 35, 36° 41 are subtracted by a subtracter 46, and a reproduced signal 23 is detected by the differential reproduction method. Furthermore, output signal 3
5.36.38.39.40.41.44.45 are added by an adder 47, and a sum signal 27 is detected.

Here, the Wollaston 29 is arranged rotated by 45 degrees around the optical axis of the convergent light beam 14, similarly to the first to fourth embodiments. Moreover, the light receiving areas 34e, 34f, 34
g, 3/lh are light receiving areas 34a, 34b, 3
4c and 34d.

With the above configuration, the direction of polarization incident on the analyzer can be rotated by 45 degrees while keeping the optical system small, so an optical rotator such as a 1/2 wavelength plate is not required.

FIG. 15 shows a modification of the photodetector 34 shown in FIG. 14. As shown in FIG. 15, the main optical detection 3 and 34 [light receiving surface 35 of the on base 35] are S-polarized light 50'b, 50''.
34a, 34b that receives the light beam b, two divided light receiving areas 34c, 34d that receive the S polarized light 51b, and the P polarized light 50'a,
50''a, 35a for receiving light 51a, and each light receiving area 34a to 34d and 35a are integrally formed on the same plane.

The output signal 44 of the light receiving area 34c and the output signal 45 of the light receiving area 34d are subtracted by a subtracter 37, and a focus error signal 25 is detected. Output signal 38 of light receiving area 34a
The output signal 40 of the light receiving area 34b is subtracted by a subtracter 49, and a tracking error signal 43 is detected.

On the other hand, the four output signals 40, 44, 45, 38 and the output signal 48 of the light receiving area 35a are subtracted by a subtracter 50, and a reproduced signal 23 by the differential reproduction method is detected. Furthermore, the output signals 40.44.45.38.48 are added by an adder 51, and a sum signal 27 is detected.

As explained above, according to the present invention, beam shaping is possible without increasing the number of parts of the optical head, and anisotropy of semiconductor laser light can be corrected, which is not necessary in the past. The optical head can be made smaller by shortening the distance from the analyzer to the photodetector without using an optical rotator such as a /2-wavelength plate.

〔Effect of the invention〕

As explained above, according to the present invention, the two prisms constituting the beam splitter have different refractive indexes to perform beam shaping, without increasing the number of parts in the optical head. , it is possible to correct anisotropy of laser light from a semiconductor laser.

In addition, the refractive index of the two prisms N, , N, , the relative angle α between the entrance surface and the exit surface, and the relative angle β between the boundary surface and the exit surface are set to satisfy the following, so that the incident light and The anisotropy of the laser beam of the semiconductor laser can be corrected while keeping the emitted light parallel to the output beam.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a first embodiment of an optical spatula 1- according to the present invention, and FIG. 2 is a block diagram showing a first embodiment of a 5 rad beam splitter according to the embodiment of the present invention.
FIG. 3 is a block diagram showing a second example of the beam splitter of the optical head of the first embodiment, FIG. 4 is a block diagram showing the polarizing beam splitter shown in FIG. 1, and FIGS. FIG. 4 is a schematic diagram for explaining the action of the polarizing beam splitter, FIGS. 7 and 8 are schematic diagrams for explaining the photodetector shown in FIG. 1, and FIG. 9 is a diagram according to the present invention. FIG. 10 is a block diagram showing a second embodiment of the optical head, FIG. 10 is a block diagram showing a third embodiment of the optical head according to the present invention, and FIG. 11 is a block diagram showing a fourth embodiment of the optical head according to the present invention. Configuration diagram, 12th
11 is a schematic diagram for explaining the Sahar plate shown in FIG. 11, FIG. 13 is a configuration diagram showing a fifth embodiment of the optical head according to the present invention, and FIG. 14 is a schematic diagram for explaining the optical head shown in FIG. FIG. 15 is a schematic diagram for explaining the detector, FIG. 15 is a diagram showing a modification of the photodetector shown in FIG. 14, and FIG. 16 is a configuration diagram showing a conventional optical head. 1 Semiconductor laser, 2. Light beam, 3. Coritsu 1-lens, 4 Incident light, 5. Beam splitter,
6.-Mirror 36. 7.Objective lens, 8 Disk, 10.1.
1...Emission light, 15.Polarizing beam splitter, +6.34.35...Photodetector, NL, NH...Refractive index, α, β...Relative angle. 7 38. 3-～-]Remating Shinmata Patsu 1 object δ---Bay Sufu 10---Prism O2---Pi'-4 Otsu, splitter

Claims (1)

[Claims] 1. A semiconductor laser device, a collimating lens that converts a first light beam, which is a diverging light emitted from the semiconductor laser device, into a parallel second light beam, and the second light beam. an objective lens that condenses the beam and guides it to the information recording surface of the magneto-optical information recording medium; and an objective lens that guides the second light beam to the objective lens, and at the same time directs the reflected light beam from the information recording surface from the semiconductor laser element. a beam splitter for separating the beam from an optical path; a detection lens for condensing the separated beam; a first analyzer for detecting the separated beam; and a beam detected by the first analyzer. In an optical head having a photodetector for detecting, the beam splitter has a first prism arranged on a side where the second light beam is incident, and a refractive index different from that of the first prism, and a second prism disposed on the output side of the first prism, and the first analyzer is configured to detect P-polarized light (or S-polarized light) for detecting the reflected light flux or the transmitted light flux from the information recording surface. ) through S
A polarizing film that reflects polarized light (or P-polarized light), a parallelogram prism having a total reflection surface parallel to the polarizing film provided in contact with the polarizing film, and the same refractive index as the parallelogram prism. a first transparent parallel plate having a total reflection surface and having a total reflection surface, and a second transparent parallel plate provided in contact with the second inclined surface of the parallelogram prism and having a refractive index different from that of the parallelogram prism and having a total reflection surface. 2 transparent parallel flat plates are integrally provided, and are rotated by an angle of 45 degrees around the incident optical axis into the convergent light between the detection lens and the photodetector. Features an optical head. 2. The beam splitter has refractive indexes N_H and N_L of the two prisms constituting the beam splitter, and relative angles α and β between the incident surface and the boundary surface with respect to the exit surface are N_H.
>N_L, α+β=sin^-^1[(1/N_L)sinα]+
The optical head according to claim 1, wherein the optical head is set to satisfy sin^-^1 [(N_H/N_L) sin β]. 3. The optical head according to claim 1, wherein in the beam splitter, the second prism constituting the side from which the light beam exits has an isosceles triangle shape. 4. The optical head according to claim 1, further comprising, in place of the first analyzer, a second analyzer composed of two crystals exhibiting birefringence. 5. The optical system according to claim 4, wherein in the second analyzer, at least one of an incident surface and an exit surface of the second analyzer is inclined with respect to the incident optical axis. head. 6. The optical head according to claim 4, wherein a Foucault prism is newly provided in the optical path between the beam splitter and the second analyzer. 7. The photodetector has two light-receiving areas for focus error signals and two groups of light-receiving areas for tracking error signals located on both sides of the two-part light-receiving area in the direction of the dividing line of the two-part light-receiving area. 7. The optical head according to claim 6, wherein the optical heads are arranged on the same plane in directions at 45 degrees from each other. 8. The photodetector includes a two-part light-receiving area for a focus error signal, a light-receiving area for a tracking error signal, which is positioned to sandwich the two-part light-receiving area in the direction of the dividing line of the two-part light-receiving area; 7. The optical head according to claim 6, further comprising another light receiving area on the same plane next to the group of light receiving areas.