JP3299383B2 - Polarizing beam splitter and optical head device using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarizing beam splitter and an optical head device using the same.

[0002]

2. Description of the Related Art Conventionally, various optical devices such as a magneto-optical disk are provided with a polarizing beam splitter that varies the diffraction efficiency depending on the polarization direction. Various proposals have been made for this polarizing beam splitter, and are described in, for example, JP-A-63-314502.

The polarizing beam splitter described in Japanese Patent Application Laid-Open No. 63-314502 has an ion exchange region (proton exchange portion) having a period on the main surface of a lithium niobate crystal plate.
As a means for forming an optical diffraction grating, and as a means for canceling a phase change that an ordinary light component transmitted through the diffraction grating receives between a region subjected to ion exchange and a region not subjected to ion exchange, for example, ion exchange is used. A dielectric layer for phase compensation is provided above the region where the extraordinary light is applied, and extraordinary light is diffracted.

[0004]

However, the polarizing beam splitter has the following problems. That is, since proton exchange is a process of isotropic diffusion, there is a problem that it is difficult to precisely control the lattice pitch, and the accuracy is reduced.

[0005] In addition, since a dielectric grating for phase compensation must be further aligned with the proton exchange portion where it is difficult to obtain the positional accuracy, there is a problem that manufacturing is difficult.

[0006] The above-mentioned problem similarly occurs in, for example, an optical head device using the polarizing beam splitter.

Accordingly, an object of the present invention is to provide a polarizing beam splitter which can be easily manufactured and whose accuracy is improved, and an optical head device using the same.

[0008]

According to a first aspect of the present invention, there is provided a polarizing beam splitter having an uneven surface.
A substrate made of a birefringent material on which a periodic lattice of
At least one of the concave and convex portions of the birefringent substrate
Birefringence different from the material of the birefringent substrate formed on the part
A folding material layer, and a position of ordinary light between the concave portion and the convex portion.
One of the phase difference and the phase difference of the extraordinary light is an even multiple of π,
And diffracts one of the above ordinary light and extraordinary light.
The other is so as not to be diffracted so that the thickness d of the birefringent material layer is
2, d3 and the recess depth d1 of the substrate .

[0009]

According to a second aspect of the present invention, there is provided a polarizing beam splitter according to the first aspect , further comprising:
Isotropic material formed by filling.

[0011]

According to a third aspect of the present invention, in order to achieve the above object, in addition to the first and second aspects, an anti-reflection film is provided on at least one of the front and rear surfaces.

According to a fourth aspect of the present invention, in order to achieve the above object, a light source, an objective lens, and a light beam traveling from the light source to the information recording medium and a light beam reflected by the information recording medium are separated. in the optical head device including a light beam separating means, a photodetector for receiving the reflected light beam, and the polarization beam splitter according to claim 1 to 3, wherein arranged in the optical path between the light beam separating means and the light detector Do it.

According to a fifth aspect of the present invention, in order to achieve the above object, in addition to the fourth aspect , the optical axis of the birefringent material of the polarizing beam splitter is set to be parallel to the polarization direction of the reflected light of the information recording medium. Is set to approximately 45 °.

The optical head device according to claim 6, in order to achieve the above object, a light source, an objective lens, and lambda / 4 plate, a photodetector for receiving the light beam reflected from the information recording medium,
In the optical head device, the polarizing beam splitter according to claims 1 to 3 is disposed in the optical path from the light source to the photodetector, and the phase difference with respect to the unevenness of light incident from the light source in the polarizing beam splitter is The light beam from the light source is made incident on the polarizing beam splitter so that it becomes an even multiple of π.

[0016]

According to the polarizing beam splitter of the first to third aspects, the concave and convex grating and the groove of the substrate can be simultaneously processed by, for example, one etching, so that the positional accuracy is improved. In addition, since it is only necessary to fill the concave portion or the groove with the filler, manufacturing is facilitated. Therefore, the optical head device according to claims 4 to 6 using this can also improve the positional accuracy and can be easily manufactured.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a longitudinal sectional view of a polarizing beam splitter according to a first embodiment of the present invention.

In FIG. 1, reference numeral 1 denotes a birefringent substrate made of a birefringent material such as calcite, and a periodic lattice is formed on the surface of the birefringent substrate 1 by irregularities. For example, quartz crystal 2 is formed as a birefringent material film different from the material of the birefringent substrate 1 on the convex portion 1 a on the surface of the birefringent substrate 1. The groove formed by the film 2 is filled with a filler 30 made of an isotropic material.

Here, the thickness of the birefringent substrate 1 is t, the groove depth of the concave portion 1b of the birefringent substrate 1 is d1, the thickness of the birefringent material film 2 is d2, and the refractive index of the birefringent substrate 1 with respect to ordinary light. Is no
1. The refractive index of the birefringent substrate 1 for extraordinary light is ne1, the refractive index of the birefringent material film 2 for ordinary light is no2, the refractive index of the birefringent material film 2 for extraordinary light is ne2, and the refractive index of the filler 30 is nc. Assuming that the wavelength of light is λ and k = 2π / λ, the phase of ordinary light that passes through the polarizing beam splitter on which the birefringent material film 2 is formed (passes the region A in FIG. 1) is: t + no2 · d2｝ k (1) The phase of ordinary light that passes through the polarizing beam splitter on which the birefringent material film 2 is not formed (passes the region B in FIG. 1) is: ｛no1 (t−d1) + nc · ( d1 + d2)｝ k (2) Accordingly, the phase difference OPD (o) of ordinary light can be calculated from the following equation (1) and equation (2): OPD (o) =） (no1-nc) d1 + (no2-nc) d2｝ k ... 3

On the other hand, the phase of the extraordinary light passing through the region A is {ne1 · t + ne2 · d2}... 4 The phase of the extraordinary light passing through the region B is: {ne1 (t−d1) + nc · (d1 + d2) Therefore, the phase difference OPD (e) of the extraordinary light can be calculated from the following equation (4) −5: OPD (e) = {(ne1-nc) d1 + (ne2-nc) d2} k ... 6

Here, in order to prevent the extraordinary light from being diffracted, it suffices that 6 of the above equations 3 and 6 be an even multiple of π. That is, OPD (e) = {(ne1-nc) d1 + (ne2-nc) d2} k = 2pπ, (p = 0, ± 1, ± 2...) 7 In order to prevent ordinary light from diffracting. In this case, it suffices that three of the above equations 3 and 6 be an even multiple of π. That is, OPD (o) = {(no1-nc) d1 + (no2-nc) d2} k = 2pπ, (p = 0, ± 1, ± 2...) 8

By the way, under these two conditions, depending on the setting of d1 and d2, there is a case where the amount of light that does not diffract is also present in the diffracted light among the ordinary light and the extraordinary light. The polarizing beam splitter of the present invention can be used, for example, in a pickup of an optical disk device.In such an application, one of ordinary light and extraordinary light is diffracted, and the other is not diffracted at all. It is desirable to do. For this purpose, in addition to equation 7, OPD (o) = {(no1-nc) d1 + (no2-nc) d2} k = (2q + 1) π, (q = 0, ± 1, ± 2 ...) ... 9 or 8 plus OPD (e) = {(ne1-nc) d1 + (ne2-nc) d2} k = (2q + 1) π, (q = 0, ± 1, ± 2 ...) ... Equation 10 At this time, in order to determine the thickness d2 of the birefringent material film 2, from the equations (7-9) and (8-10), [OPD (o) -OPD (e)] = ｛(no1-ne1) ) D1 + (no2-ne2) d2｝ k = (2j + 1) π, (j = 0, ± 1, ± 2)... 11 may be determined so that d1 and d2 are satisfied.

If the thickness d2 of the birefringent material film 2 and the groove depth d1 of the birefringent substrate 1 are set so as to satisfy the expression 7 or 8, the polarization beam splitter functions as a diffraction grating, and Alternatively, only one of the extraordinary lights can be prevented from diffracting.

As described above, in the first embodiment, the substrate 1 made of calcite as a birefringent material having an uneven periodic lattice formed on the surface, and the substrate 1 formed on the convex portion 1a of the birefringent substrate 1 And a quartz crystal 2 as a birefringent material layer different from the material of the birefringent substrate 1. The phase difference OPD (o) of the ordinary light between the concave portion and the convex portion and the phase difference OPD (e) of the extraordinary light are provided. The thickness d2 of the quartz crystal 2 and the depth d1 of the concave portion of the birefringent substrate 1 are set so that one of them becomes an even multiple of π, so that it functions as a polarizing beam splitter as described above. Is available.

Here, the polarizing beam splitter does not use the proton exchange portion or the dielectric grating for phase compensation described in the prior art, and the birefringent material film 2 and the groove 1b of the substrate 1 Since they can be processed simultaneously by multiple etchings, it is possible to improve positional accuracy. In addition, since the positioning can be naturally performed only by filling the groove 1b with the filler 30, the manufacturing can be easily performed.

FIG. 2 is a longitudinal sectional view of a polarizing beam splitter according to a second embodiment of the present invention. The polarization beam splitter of the second embodiment is different from that of the first embodiment in that the birefringent substrate 1 has a concave portion 1b having a predetermined depth d1.
A birefringent material film 12 made of the same material as the birefringent material film 2
This is a point newly formed for the thickness d3.

Here, the phase of the ordinary light passing through the region A in FIG. 2 is the same as the expression {no1 · t + no2 · d2} k (1) The phase of the ordinary light passing through the region B in FIG. t−d1) + no2 · d3 + nc (d1 + d2−d3)｝ k (12) Accordingly, the phase difference OPD (o) of ordinary light can be calculated from the following equation (1) and equation (12): OPD (o) = ２− (d2−d3) no2 + no1 · d1 −nc (d1 + d2-d3)｝ k Expression 13

On the other hand, the phase of the extraordinary light passing through the region A is the same as {ne1 · t + ne2 · d2}... 4 The phase of the extraordinary light passing through the region B is {ne1 (t−d1) + ne2 · d3 + nc (d1 + d2-d3)｝ k Equation 14 Accordingly, the phase difference OPD (e) of the extraordinary light is obtained from the equation 4-14 as follows: OPD (e) = ｛(d2-d3) ne2 + ne1 · d1-nc (d1 + d2- d3)｝ k ... formula 15

Here, in order to prevent the extraordinary light from being diffracted, it suffices that Expression 15 out of Expressions 13 and 15 is an even multiple of π. That is, OPD (e) = {(d2-d3) ne2 + ne1 · d1-nc (d1 + d2-d3)} k = 2pπ, (p = 0, ± 1, ± 2...) Expression 16 Also, ordinary light is not diffracted. In order to make
It suffices that Expression 13 out of Expression 15 and Expression 15 is an even multiple of π. That is, OPD (o) = {(d2-d3) no2 + no1 · d1-nc (d1 + d2-d3)} k = 2pπ, (p = 0, ± 1, ± 2...) ... 17

Under these two conditions, depending on the setting of d1, d2, and d3, there is a case where there is an amount of light that is not diffracted among the ordinary light and the extraordinary light to be diffracted. The polarizing beam splitter of the present invention can be used, for example, in a pickup of an optical disk device.In such an application, one of ordinary light and extraordinary light is diffracted, and the other is not diffracted at all. It is desirable to do. For this purpose, in addition to equation 16, OPD (o) = {(d2-d3) no2 + no1 · d1-nc (d1 + d2-d3)} k = (2q + 1) π, (q = 0, ± 1, ± 2 ...) ... In addition to equation 18 or equation 17, OPD (e) = {(d2-d3) ne2 + ne1 * d1-nc (d1 + d2-d3)} k = (2q + 1) π, (q = 0, ± 1, ± 2 ...) Expression 19 At this time, the thickness d of the birefringent material films 2 and 12 is
In order to determine 2, d3, equations (16-18) and (1
From equation 7-19), [OPD (o) -OPD (e)] = {(no2-ne2). (D2-d3) + d1 (no1-ne1)} k = (2j + 1) π, (j = 0, ± 1, ± 2) ... d1, d2, and d3 may be determined so that Equation 20 is satisfied.

The thickness d2 of the birefringent material film 2 and the thickness d of the birefringent material film 12 are set so as to satisfy Expression 16 or Expression 17.
3. If the groove depth d1 of the substrate 1 is set, the polarization beam splitter functions as a diffraction grating, and can prevent either ordinary light or extraordinary light from diffracting.

It is needless to say that the same effect as in the first embodiment can be obtained even with this configuration.

FIG. 3 is a longitudinal sectional view of a polarizing beam splitter according to a third embodiment of the present invention. The polarization beam splitter of the third embodiment differs from those of the first and second embodiments in that irregular birefringent material films 2 and 22 are formed on a flat birefringent substrate 1.

Even in the third embodiment, when the calculation is performed in the same manner as in the first and second embodiments, OPD (o) = (d2-d3) · (no2-nc)｝ ·
k OPD (e) = (d2-d3) · (ne2-nc)｝ ·
k.

Therefore, similarly to the first and second embodiments,
In order to prevent ordinary light from diffracting, OPD (o) = (d2-d3) · (no2-nc)｝ · k = 2qπ, (q = 0, 1, 2,...) Formula 21 or diffracting extraordinary light In order not to make it occur, OPD (e) = (d2-d3) · (ne2-nc)｝ · k = 2qπ, (q = 0, 1, 2,...) 22

The thickness d2 of the birefringent material film 2 and the thickness d3 of the birefringent material film 22 are set so as to satisfy the expression 21 or 22.
Is set, it is possible to prevent only one of ordinary light and extraordinary light from diffracting as a polarizing beam splitter.

It is needless to say that the same effects as those of the first and second embodiments can be obtained with this configuration.

In the first to third embodiments, the groove is filled with the isotropic material 30 having the refractive index nc. However, the filler 30 may be air. is there. In this case, nc = 1.

When the refractive index of the filler 30 in the first and second embodiments is set so as to satisfy the following equation, d1 = 0, and the thickness of the concave portion of the birefringent substrate 1 is set to 0. can do. That is, it is possible to omit the groove processing on the substrate 1. nc = m · | no2-ne2 |
+ No2 (or ne2), (m is an integer)

When a material having a refractive index satisfying the following formula is selected as the filler in the third embodiment, OPD (o) = 2qπ and OPD (e) = (2p +
1) π or OPD (o) = (2p + 1) π and OPD
(E) = 2qπ, which allows not only ordinary light and extraordinary light to be diffracted but also diffracts all the other light, which is suitable for differential detection of an isolator or an optical head.

Further, an antireflection film may be provided on at least one of the front and back surfaces of the polarizing beam splitter described in the first to third embodiments to improve the overall light use efficiency.

The optical axis of the substrate 1 and the optical axis of the birefringent material film 2 are set so as to be substantially parallel or substantially perpendicular to each other. The direction or pattern of the groove 1b is
This can be set irrespective of the optical axis of the birefringent material film 2 or the optical axis of the birefringent material film 2, thereby improving the degree of freedom.

In the above embodiments, the example in which the birefringent film is formed directly on the substrate has been described. However, the same applies to the case where an adhesive layer is interposed between the substrate and the birefringent film. It is possible to obtain various effects.

FIG. 4 is a perspective view of an optical head device using a polarizing beam splitter according to a fourth embodiment of the present invention.
As the polarizing beam splitter of the fourth embodiment, the first
The polarization beam splitter described in the third to third embodiments is used, and this polarization beam splitter is used, for example, for differential detection of an optical pickup device.

Here, the optical head device shown in FIG. 4A includes a light source 53, an objective lens 51 for condensing a light beam from the light source 53 on an information recording medium 50, and an information recording medium from the light source 53. A light beam separating means 52 for separating the light beam traveling toward the optical recording medium 50 from the light beam reflected by the information recording medium 50; and a photodetector 54 having a large number of divided light receiving portions for receiving the reflected light beam. In the optical path between the separating means 52 and the photodetector 54, the above-mentioned polarizing beam splitter is arranged. The optical axis X of the birefringent material of the polarizing beam splitter is set to approximately 45 ° with respect to the polarization direction Y of the reflected light of the information recording medium 50. Therefore, the diffraction of the reflected light from the information recording medium 30 is performed. The light and zero-order light are received by the photodetector 54 so that differential detection is possible.

The optical head device shown in FIG. 4B includes a light source 53, an objective lens 51 for condensing a light beam from the light source 53 on an information recording medium 50, a λ / 4 plate 55, and an information recording medium. Photodetector 5 for receiving the light beam reflected from 50
And the polarization beam splitter is disposed in the optical path from the light source 53 to the photodetectors 54 and 54, and is adapted to cope with unevenness of light incident from the light source 53 in the polarization beam splitter. The light beam from the light source 53 is incident on the polarizing beam splitter so that the phase difference is an even multiple of π. That is, the outgoing path is transmitted because the phase difference is an even multiple of π, and the return path is an odd multiple of π, so that all the light beams are diffracted and can be received by the photodetectors 54 and 54.

As described above, in the optical head device of the fourth embodiment, since the above-described polarization beam splitter which is easily manufactured and whose accuracy is improved is used, this polarization beam splitter is used. Similarly, the optical head device
It can be manufactured easily and the accuracy can be improved.

Although the invention made by the inventor has been specifically described based on the embodiments, the present invention is not limited to the above-described embodiments, and can be variously modified without departing from the gist thereof. Needless to say.

[0049]

As described above, according to the polarization beam splitters of the first to third aspects, the polarization beam splitter can be used as a polarization beam splitter without using the proton exchange part or the dielectric grating for phase compensation described in the prior art. Since the function can be exhibited and the grooves of the concave and convex grating and the grooves of the substrate can be simultaneously processed by, for example, one etching, the positional accuracy can be improved.
In addition, since it is only necessary to fill the recesses and the grooves with the filler, manufacturing can be easily performed. Therefore, the optical head device according to claims 4 to 6 using this can also improve the positional accuracy and can easily manufacture the optical head device.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a polarizing beam splitter according to a first embodiment of the present invention.

FIG. 2 is a longitudinal sectional view of a polarizing beam splitter according to a second embodiment of the present invention.

FIG. 3 is a longitudinal sectional view of a polarizing beam splitter according to a third embodiment of the present invention.

FIG. 4 is a perspective view of an optical head device using a polarizing beam splitter according to a fourth embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Birefringent substrate 1a, 1b Concavo-convex part of birefringent substrate 2, 12, 22 Birefringent material layer 30 Filler 50 Information recording medium 51 Objective lens 52 Light beam separating means 53 Light source 54 Photodetector 55 λ / 4 plate d1 Substrate Depth of recesses d2, d3 Thickness of uneven portion of birefringent material layer X Optical axis of birefringent material Y Polarization direction of reflected light

Claims (6)

(57) [Claims] 1. A substrate made of a birefringent material having a concave and convex periodic grating formed on a surface thereof, and a birefringent substrate formed on at least a convex portion of the concave portion and the convex portion of the birefringent substrate. A birefringent material layer different from the material, and any one of the phase difference of the ordinary light and the phase difference of the extraordinary light between the concave portion and the convex portion is an even multiple of π, and
A polarizing beam splitter in which the thickness d2, d3 of the birefringent material layer and the depth d1 of the concave portion of the substrate are set so that one of the extraordinary lights is diffracted while the other is not diffracted. 2. The polarization beam splitter according to claim 1 , wherein the concave portion is filled with an isotropic material. 3. The polarizing beam splitter according to claim 1 or 2, wherein the at least one surface of front and back surfaces, polarizing beam splitters provided with the antireflection film. 4. A light source, an objective lens, a light beam separating means for separating a light beam from the light source toward the information recording medium and a light beam reflected by the information recording medium, and a photodetector for receiving the reflected light beam. An optical head device comprising: the polarization beam splitter according to any one of claims 1 to 3 disposed in an optical path between a light beam separating unit and a photodetector. 5. The optical head device according to claim 4 , wherein the optical axis of the birefringent material of the polarization beam splitter is set at approximately 45 ° with respect to the polarization direction of the reflected light of the information recording medium. . 6. A light source, an objective lens, a λ / 4 plate, a photodetector for receiving a light beam reflected from an information recording medium,
An optical head device comprising: the polarizing beam splitter according to any one of claims 1 to 3 , wherein the polarizing beam splitter is disposed in an optical path from a light source to a photodetector; An optical head device in which a light beam from a light source is incident on the polarizing beam splitter so as to be an even multiple of π.