JPH08190019A - Optical element, its production and optical head using this optical element - Google Patents

Abstract

PURPOSE: To realize such an optical element that is inexpensive and suitable for mass production and has both properties of a 1/4 wavelength plate and for separation of polarized light and to obtain a small-sized optical head by using this optical element. CONSTITUTION: Periodical proton-exchanged layers 2 are formed on one surface of a lithium niobate crystal substrate 1. A vapor deposition film 3 is formed by oblique vapor deposition of tantalum pentoxide (Ta2 O5 ) on the other surface of the substrate 1. Since the refractive index of the proton-exchanged layer 2 is different from that of the substrate 1, the proton-exchanged part shows properties for separation of polarized light. The film by oblique vapor deposition shows properties as a 1/4 wavelength plate. Thus, by forming the optical element (A), enough accuracy for flatness is obtd. and the element can be made thin.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical element used in an optical information processing device or an optical communication device,
In particular, the present invention relates to an optical element for polarization-separating laser light and converting it into circularly polarized light or linearly polarized light, a method for manufacturing the same, and an optical head using the optical element.

[0002]

2. Description of the Related Art In recent years, an optical head for recording / reproducing information on / from an optical recording medium has been actively reduced in size and cost.
In particular, an optical head using a polarization splitting element has been proposed as an element that realizes downsizing and cost reduction of the optical head (see, for example, Japanese Patent Application Laid-Open No. 3-29129).

FIG. 15 is a block diagram of a conventional optical head (also called an optical pickup). This optical head uses a light source 15
1, polarization separation element 152, collimator lens 153, 1
The quarter-wave plate 154, the objective lens 155, the first photodetector 157, and the second photodetector 158 are included.

The light source 151 is composed of, for example, a semiconductor laser element, and outputs coherent light for recording and reproduction to the recording layer of the optical disc 156. The polarization separation element 152 is
For example, as disclosed in JP-A-63-314502, an optical element having a substrate of lithium niobate on which a periodic proton exchange layer is formed and a dielectric film formed on the proton exchange layer. Is. The proton exchange layer is the lithium ion (Li ⁺ ) in lithium niobate.
Is a layer replaced with hydrogen ions (H ⁺ : proton).

The polarization separation element 152 performs polarization separation by utilizing the fact that the refractive index of the proton exchange layer for ordinary light and extraordinary light is different from that of the lithium niobate substrate for ordinary light and extraordinary light. That is, the transmittance of ordinary rays is 100%, and the transmittance of extraordinary rays can be made 0% by the action of the diffraction grating. As a result, an element having the property of polarization separation can be formed.

The collimator lens 153 collimates the laser light emitted from the light source 151 into parallel light. Quarter wave plate 15
Reference numeral 4 is a non-linear optical element made of, for example, crystal. That is, the linearly polarized laser light output from the light source 151 is converted into circularly polarized light by the quarter-wave plate 154. The laser light reflected by the recording layer of the optical disc 156 by the quarter-wave plate 154 is converted into linearly polarized light in a direction different from the polarization direction of the light emitted from the light source 151.

The photodetector 157 receives the + 1st-order light diffracted by the polarization separation element 152 among the laser light reflected by the optical disk 156. In addition, the photodetector 158 detects the polarization beam splitting element 1 of the laser light reflected by the optical disc 156.
The −1st order light diffracted by 52 is received.

The operation of the optical head configured as described above will be described. The linearly polarized laser light emitted from the light source 151 passes through the polarization separation element 152 with 100% transmittance. Then, this light is collimated by the collimator lens 153 and converted into circularly polarized light by the quarter-wave plate 154,
It is condensed on the optical disk 156 by the objective lens 155.

The circularly polarized light reflected from the optical disk 156 is transmitted through the objective lens 155 and then the quarter wavelength plate 1
54 converts the light emitted from the light source 151 into linearly polarized light in a direction orthogonal to the polarization direction. The linearly polarized light is transmitted through the collimator lens 153 and then diffracted by the polarization separation element 152. The diffracted + 1st order light is incident on the photodetector 157, and the diffracted −1st order light is detected by the photodetector 158.
Is incident on.

The photodetector 157 outputs a focus error signal indicating a focused state of light on the optical disk 156 and a tracking error signal indicating a light irradiation position. The focus error signal is given to a focus control device (not shown). Based on the focus error signal, the focus control device controls the position of the objective lens 155 in the optical axis direction so that the light is always focused on the optical disc 156 in a focused state.

Further, the tracking error signal is given to a tracking control device (not shown). The tracking control device controls the position of the objective lens 155 based on the tracking error signal so that the light is focused on a desired track on the optical disc 156. Further, the photodetector 158 reproduces the information recorded on the optical disc 156.

[0012]

However, in the optical head having the above-mentioned configuration, in order to obtain the function of the polarization separation element 152, the 1 / The four-wave plate 154 is essential.

In the quarter-wave plate 154, the difference Δn between the refractive index of the crystal forming the quarter-wave plate 154 with respect to ordinary light and the refractive index with respect to extraordinary light (hereinafter referred to as the difference Δn in refractive index).
Is a value indicating the characteristic of birefringence, d is the thickness of the crystal, and λ is the wavelength of the incident light, in order to have the property as a quarter-wave plate, the following formula (1) must be satisfied. I won't. Δn · d = λ / 4 (1) Here, Δn · d on the left side of the equation (1) represents the optical path difference between ordinary light and extraordinary light. From this, the thickness d of the crystal is expressed by the following equation (2). d = λ / (4 · Δn) (2)

In equation (2), the difference in refractive index of the birefringence of the crystal Δn =
Substituting 0.009, the wavelength of light λ = 780 nm, 1
The thickness d of the crystal forming the quarter wave plate is 21.7 μm.
It is practically difficult to manufacture a quarter-wave plate having this thickness. For this reason, it is one of the crystals with good plane accuracy that maintains mechanical strength.
The thickness of the quarter-wave plate has an optical path difference of Δn · d = (2N + 1)
If λ / 4 (N is a natural number), it will be about 0.5 mm. In this case, the quarter wave plate 154 itself is 0.5 m
Since the thickness is as thick as m, this thickness of the quarter-wave plate 154 hinders further downsizing of the optical head.

A quarter-wave plate 154 made of crystal is also used.
As mentioned above, the thickness is as thick as 0.5 mm, so 1/4
The action of the wave plate on the incident angle of the incident light beam becomes very sensitive. Therefore, when the quarter-wave plate is incorporated in the optical head, high precision is required for setting the quarter-wave plate. Therefore, there is a problem that it is difficult to mass-produce the optical head and reduce the cost.

In order to further reduce the size of the optical head,
It is necessary to bond the polarization separation element 152 and the quarter-wave plate 154 together to integrate them. When these elements are attached to each other, it is necessary to attach the polarization separation element 152 and the quarter-wave plate 154 with high precision while maintaining the parallelism on both sides to be attached. However, maintaining parallelism is not easy. If the parallelism is not maintained, there is a problem that aberration occurs in the wavefront of the transmitted light of the bonded elements.

Further, there is a limit to the area of the quarter-wave plate 154 made of quartz that is practically available, and the area is one λ.
/ 4 wavelength plate. Therefore, the quarter wave plate 154
And the polarization splitting element 152 are integrated into 1/4.
The wave plate and the polarization beam splitting element 152 must be manufactured after they have a size suitable for being incorporated in an optical head, and then bonded together. Such an element bonding work is complicated and is not suitable for mass production,
In addition, the manufacturing price will be high. Therefore, problems arise in terms of mass production and cost reduction of optical heads.

An object of the present invention is to solve such a conventional problem. The first purpose is to provide an optical element that combines the properties of polarized light separation and the properties of a quarter-wave plate, is suitable for mass production, is extremely thin at a low price, and does not cause aberration in the wavefront of transmitted light. It is to be realized. A second object is to provide a compact and low cost optical head by using this optical element.

[0019]

According to a first aspect of the present invention, there is provided an obliquely vapor-deposited film in which a dielectric is obliquely vapor-deposited on a hologram element having a different diffraction efficiency depending on the polarization direction.

According to a second aspect of the present invention, a first antireflection film for preventing reflection of incident light is provided on the hologram element having different diffraction efficiency depending on the polarization direction, and reflection between adjacent layers on the hologram element is prevented. A second antireflection film, an oblique vapor deposition film in which a dielectric is obliquely vapor-deposited on the second antireflection film, and a third antireflection film which is on the oblique vapor deposition film and prevents reflection of incident light. It is equipped with.

According to a seventh aspect of the present invention, a first step of forming a mask pattern for ion exchange on the surface of a LiTa _x Nb _1-x O ₃ (0 ≦ x ≦ 1) crystal substrate and LiTa _x Nb _{1- x} O ₃
In the region specified by the mask pattern of the first step on the surface of the (0 ≦ x ≦ 1) crystal substrate, lithium ions (Li
⁺ ) Is ion-exchanged with hydrogen ions (H ⁺ ), a third step is performed to selectively etch the region ion-exchanged in the second step, and LiTa _x Nb _1-x O ₃ ( 0 ≦
x ≦ 1) a fourth step of vapor-depositing dielectric molecules on the other surface of the crystal substrate obliquely with respect to the normal line of the crystal substrate surface to form an oblique vapor-deposited film.

The invention of claim 9 relates to LiTa _x Nb _1-x O ₃
(0 ≦ x ≦ 1) A first step of forming obliquely vapor-deposited films by obliquely vapor-depositing dielectric molecules on the surface of the crystal substrate with respect to the normal line of the crystal substrate surface, and LiTa _x Nb _1-x O ₃ (0 ≦ x ≦ 1) Second step of forming an ion-exchange mask pattern on the other surface of the crystal substrate, and LiTa _x Nb _{1 -x} O ₃ (0 ≦ x ≦
1) A third step of ion-exchanging lithium ions (Li ⁺ ) into hydrogen ions (H ⁺ ) in a portion of the other surface of the crystal substrate specified by the mask pattern of the second step, and a third step And a fourth step of selectively etching the ion-exchanged region.

According to the invention of claim 11, a light source that outputs coherent light, and a condensing optical system that condenses the light of the light source onto the optical recording medium and condenses the light reflected by the optical recording medium, An optical element provided between the condensing optical system and the light source,
And a photodetector which receives the diffracted light diffracted by the optical element and detects a focus error signal and a tracking error signal of the optical recording medium and an information signal recorded on the optical recording medium.

When a dielectric material is obliquely deposited on a transparent substrate, a birefringent film having different refractive indexes for ordinary light and extraordinary light is obtained. In the optical element of claims 1 and 2, the properties of the polarization separation element and the property of the quarter wavelength plate are combined,
An oblique vapor deposition film is provided on the hologram element having different diffraction efficiency depending on the polarization direction. This makes it possible to form an optical element that is extremely thin and has good plane accuracy, as compared with a conventional composite element in which a quarter-wave plate and a polarization separation element are joined together. Further, the influence of the incident angle of the light entering this optical element is reduced, and it is possible to separate the + 1st-order diffracted light and the -1st-order diffracted light without giving any aberration to the light.

In the method for manufacturing an optical element according to claims 7 and 9, the ion exchange layer is formed on one surface of the LiTa _x Nb _1-x O ₃ (0 ≦ x ≦ 1) crystal substrate by using an ion exchange mask pattern. Are formed by thermal diffusion. By doing so, the refractive index of ordinary and extraordinary light of these ion exchange layers and LiTa _x N
The optical element functions as a polarization separation element because the refractive indices of the ordinary and extraordinary rays of the crystal substrate of b _{1 -x} O ₃ (0 ≦ x ≦ 1) are different.

LiTa _x Nb _1-x O ₃ (0 ≦ x ≦ 1)
The dielectric oblique deposition film on the other surface of the crystal substrate functions as a quarter-wave plate due to the arrangement of the dielectric material having a columnar structure. The optical element having such a structure can be formed by using a thin film forming process on a crystal substrate having a relatively large area. Therefore, many optical elements can be manufactured by a single thin film forming process.

In the optical head of the eleventh aspect, the light emitted from the light source reaches the optical recording medium via the condensing optical system and the optical element. In this case, since the thickness of the optical element is thin, the dimension of the optical head including the optical element and the focusing optical system in the optical axis direction becomes small.

[0028]

BEST MODE FOR CARRYING OUT THE INVENTION

(First Embodiment) FIG. 1 is a sectional view showing the arrangement of a first optical element A according to the first embodiment of the present invention. In FIG. 1, the optical element A has a multi-layer structure of a lithium niobate substrate 1, a proton exchange layer 2, and an oblique vapor deposition film 3. The lithium niobate substrate 1 is made of LiTa _x Nb _1-x O ₃ (0 ≦
It is a substrate formed on the X-plane of a crystal having a chemical formula of x ≦ 1) and is a ferroelectric used as a nonlinear optical material. The proton exchange layer 2 is a band-shaped diffusion layer formed by periodically displacing (proton exchange) some of the lithium atoms (Li) with hydrogen ions (H ⁺ ) on the surface of the lithium niobate substrate 1. .

The element configured as described above is generally called a hologram element. The oblique vapor deposition film 3 is a vapor deposition film in which tantalum pentoxide (Ta ₂ O ₅ ) is vapor-deposited at an angle of 70 degrees with respect to the normal line of the lithium niobate substrate 1.

A method of manufacturing the above optical element A will be described later. The surface of the proton exchange layer 2 periodically formed on the lithium niobate substrate 1 is deeper than the surface of the lithium niobate substrate 1. The element having this structure has a property as a polarization separation element.

In this embodiment, as shown in FIG. 7, tantalum pentoxide is vapor-deposited from the direction of 70 degrees with respect to the normal line of the substrate. As a result, the refractive index difference Δn, which is the difference between the refractive index for ordinary light and the refractive index for extraordinary light, becomes 0.07 based on the molecular arrangement. The thickness of the film is 2.6 μm in order to act as a quarter-wave plate.

A method of forming a birefringent film acting as a quarter-wave plate by obliquely vapor-depositing a tantalum pentoxide film on a glass substrate is disclosed in JP-A-63-312970. This prior art aims at providing a birefringent film on a liquid crystal display panel.

FIG. 2 is a photograph showing the aberration of the transmitted wavefront of the optical element A of this embodiment. FIG. 3 is a photograph showing the aberration of the transmitted wavefront of the optical element in which the quarter-wave plate made of quartz and the polarization separation element used in the conventional example are bonded together. Specifically, FIG. 2 shows interference fringes obtained by making plane wave light incident on the optical element A and causing the transmitted light to interfere with the reference light that is a plane wave. Aberrations were measured by interference fringes.

FIG. 3 shows interference fringes obtained by causing the plane wave light and the reference light of the plane wave to pass through the optical element in which the quarter-wave plate made of quartz and the polarization separation element are bonded together.
As in the case of FIG. 2, the aberration was measured by the interference fringes in the rectangular frame in FIG. Generally, in the interference between plane waves, plane interference fringes are formed. Therefore, if there is no distortion in the optical element through which light is transmitted, linear interference fringes can be obtained. However, in the case of the conventional example of FIG. 3, the interference fringes are distorted. The aberration of the transmitted wavefront obtained from the distortion of the interference fringe is 38 mλ (mλ =
λ / 1000). On the other hand, in the optical element A of the present embodiment, the interference fringes are almost linear as shown in FIG. 2, and the aberration of the transmitted wavefront is as small as 8 mλ.

In the present embodiment, since the tantalum pentoxide film serving as the quarter-wave plate is formed by vapor deposition, it is possible to uniformly form a film having good plane accuracy. On the other hand, when the quarter-wave plate made of quartz is attached to the polarization separation element as described in the conventional example, it is quite difficult to secure the plane accuracy. The quarter-wave plate made of quartz needs to have a thickness of about 0.5 mm in order to maintain mechanical strength. On the other hand, in vapor deposition, the thickness can be controlled accurately, so it is very difficult to form a vapor-deposited film with a thickness of 2.6 μm, which is the minimum thickness for exhibiting the properties of a quarter-wave plate. Easy to. Therefore, there is an advantage that the optical element A itself becomes very thin.

Next, let us compare the incident angle dependence of light between the optical element A of this embodiment and a conventional quarter-wave plate made of quartz. In the conventional quarter-wave plate 154, as shown in FIG. 4, the refractive index difference, which is the difference between the two refractive indices in birefringence, is Δn.
1, the thickness is d1, the wavelength of the incident light is λ, and the incident angle of the incident light is θ1, the optical path difference x1 between ordinary light and extraordinary light when passing through this element is given by the following equation (3). Become. x1 = Δn1 · d1 / cos θ1 (3) Since this element has a property as a quarter-wave plate, Δn
1 · d1 = (2N + 1) λ / 4 (N is a natural number),
The following equation (4) is obtained. x1 = (2N + 1) λ / 4cos θ1 (4) Therefore, the deviation Δx1 from the optical path difference when the incident angle is zero (θ1 = 0) is expressed as follows: Δx1 It becomes like the formula (5). Δx1 = (2N + 1) λ (1 / cos θ1 -1) / 4 (5)

In the optical element A of the present invention, the refractive index difference of the birefringence of the obliquely evaporated film 3 of the optical element A is Δn2, the thickness is d2,
Assuming that the wavelength of the incident light is λ and the incident angle of the incident light is θ2, the optical path difference x2 when the ordinary light and the extraordinary light pass through this element is given by the following equation (6). x2 = Δn2 · d2 / cos θ2 (6) Here, since the obliquely vapor-deposited film 3 has a property as a quarter wavelength plate, Δn2 · d2 = λ / 4, and the following formula (7) is obtained. Is established. x2 = λ / 4cos θ2 (7) Therefore, the deviation Δx2 of the optical path difference from the case of θ2 = 0
Becomes like the following formula (8). Δx2 = λ (1 / cos θ2 -1) / 4 (8)

The thickness of the conventional quarter-wave plate made of crystal is 0.
It is about 5 mm. Now, assuming that value is 0.499 mm, N = 11, and the equation (5) becomes the following equation (9). Δx1 = 23λ (1 / cos θ1 -1) / 4 (9) When Δx1 and Δx2 are equal, the incident angles θ1 and θ
2 has the following equation (10) from equations (8) and (9). 23 (1 / cos θ1 −1) = (1 / cos θ2 −1) (10) From the equation (10), the deviation Δx1 and Δx2 of the optical path difference when the incident angle θ1 is shifted by 1 degree are equal. Angle of incidence θ2
Is 4.8 degrees. Therefore, the optical element A of the present embodiment has a small incident angle dependency due to the conventional quarter-wave plate.

In the formula (6), the refractive index difference Δn2 of the birefringence of the obliquely vapor-deposited film 3 is assumed to be constant regardless of the incident angle, but actually it depends on the incident angle. However, this dependency is considered to be small when the incident angle is very small, such as several degrees or less. Further, as disclosed in JP-A-63-132203, if the obliquely vapor-deposited film has a two-layer structure, the dependency of the birefringence on the incident angle is further reduced,
It is possible to prevent the deterioration of the properties as the quarter-wave plate due to the incident angle of light.

As described above, according to the first embodiment, by obliquely vapor-depositing a dielectric material such as tantalum pentoxide on the polarization beam splitting element, it is possible to form an optical element having high plane accuracy. Optical element A made by the above process
Is much thinner than an element in which a conventional polarization separation element and a quarter-wave plate made of quartz are bonded together. Further, it is possible to form an optical element having a small incident angle dependency of light.

In the first embodiment, the case where the surface of the proton exchange layer 2 is concave with respect to the surface of the lithium niobate substrate 1 has been described, but the surface of the proton exchange layer 2 is formed on the surface of the lithium niobate substrate 1. Even if the dielectric film 50, which has the same level as the surface and acts as a phase compensation film, is deposited on the proton exchange layer 2 as shown in FIG. 5, the same effect can be obtained (Japanese Patent Laid-Open No. 63-314502). (See the official gazette). Further, JP-A-61-186731 and JP-A-6-86731.
It is also possible to perform oblique vapor deposition of the dielectric material of the present invention on the element having the structure shown in Japanese Patent Laid-Open No. 3-26604.

(Second Embodiment) First of the first optical element A
The manufacturing method will be described with reference to FIG. First, FIG. 6 (a)
As shown in, a tantalum (Ta) film 60 is vapor-deposited on the surface of the lithium niobate substrate 1 on the X surface. Next, FIG. 6B
As shown in, a predetermined striped pattern of the resist film 61 is formed on the surface of the tantalum film 60 by photolithography. Then, as shown in FIG. 6C, a pattern of the tantalum film 60 is formed by etching using the resist film 61 as a mask.

The lithium niobate substrate 1 having the mask of the tantalum film 60 shown in FIG. 6C is heat-treated for about 110 minutes using a pyrophosphoric acid solution at 230 ° C. During this heat treatment, the surface of the lithium niobate substrate 1 without the tantalum film 60 is protected from the pyrophosphoric acid solution by a protective film or the like. As a result, as shown in FIG. 6D, hydrogen ions (H ⁺ ) are thermally diffused to form the proton exchange layer 2.
Next, as shown in FIG. 6E, the tantalum film 60 is removed and the proton exchange layer 2 is selectively etched in an etching solution containing hydrofluoric acid. Finally, as shown in FIG. 6 (f), tantalum pentoxide is applied to the surface where the proton exchange layer 2 does not exist, and an angle of θ = 70 degrees with respect to the normal line of the lithium niobate substrate 1 as shown in FIG. Is obliquely evaporated to form an obliquely evaporated film 3.

When forming the obliquely vapor-deposited film 3, it is desirable to vapor-deposit the element formed in the step (e) of FIG. 6 while heating it at a high temperature in order to improve the adhesion. In this case, the proton exchange depth of the proton exchange layer 2 and the depth of the surface of the proton exchange layer 2 from the surface of the lithium niobate substrate 1 may deviate from the optimum conditions. Therefore, the proton exchange layer 2
The deviations from the optimum conditions of the proton exchange depth and the depth from the surface of the lithium niobate substrate 1 to the surface of the proton exchange layer 2 are estimated in advance. By using the estimated amount, the step of proton exchange shown in FIG. 6D and the step of etching shown in FIG. 6E can be performed to manufacture the optical element A having desired properties.

The obliquely vapor-deposited film 3 formed in the step of FIG. 6 (f) may be a film which is not transparent because oxygen is partially separated and tantalum is deposited. In this case, it is necessary to oxidize the obliquely deposited film 3. Any method may be used as the oxidation method. When the method of applying heat to oxidize is used, the proton exchange depth of the proton exchange layer 2 and the
Note that the optimum condition of the depth of the surface of the proton exchange layer 2 from the surface of the lithium niobate substrate 1 may be deviated.

In the case where the conventional quarter-wave plate made of crystal and the polarization separation element are bonded together, there is a limit to the manufacturable area of the quarter-wave plate. After processing into, the process of pasting was taken. However, this method is not suitable for mass production and is a costly manufacturing method.

On the other hand, in the manufacturing method of this embodiment, there is no limit to the area of the obliquely deposited film 3. That is, a large number of optical elements A are formed on a wafer-shaped lithium niobate substrate having a large area, and a large number of optical elements A can be simultaneously manufactured by scribing and dividing them. This is suitable for mass production at a low cost, as compared with the conventional method in which a plurality of elements are bonded to each optical element. In the second embodiment, the proton exchange layer 2 is etched by wet etching using an etching solution containing hydrofluoric acid, but fluorine radical dry etching does not cause any problem.

(Third Embodiment) Next, the first optical element A
The second manufacturing method will be described with reference to FIG. First, in FIG. 8A, the lithium niobate substrate 1 on the X surface is formed.
Tantalum pentoxide is obliquely vapor-deposited on the lower surface of to form an oblique vapor deposition film 3. Next, as shown in FIG. 8B, tantalum is deposited on the upper surface without the obliquely deposited film 3 to form a tantalum film 60.

Next, as shown in FIG. 8C, the resist film 6 is formed on the surface of the tantalum film 60 by photolithography.
1 pattern is formed. Then, as shown in FIG. 8D, a pattern of the tantalum film 60 is formed by etching using the resist film 61 as a mask. Then, the lithium niobate substrate 1 having the mask of the patterned tantalum film 60 is about 1 by using pyrophosphoric acid at 230 ° C.
After heat treatment for 10 minutes, the proton exchange layer 2 as shown in FIG. 8 (e) is formed. During this heat treatment, the surface of the lithium niobate substrate 1 without the tantalum film 60 is protected from the pyrophosphoric acid solution by a protective film or the like. Finally, FIG. 8 (f)
And as shown in (g), the element of (e) of FIG. 8 is etched by dry etching using fluorine radicals.

In such a manufacturing method, since the oblique deposition film 3 is formed on the lithium niobate substrate 1 in the first process, the proton exchange depth of the proton exchange layer 2 and the niobate on the surface of the proton exchange layer 2 are increased. The optimum condition of the depth from the surface of the lithium substrate 1 does not shift. However, when the proton exchange layer 2 is etched with an etching solution containing hydrofluoric acid, the obliquely evaporated film 3 is dissolved in this etching solution. Therefore, when the obliquely vapor-deposited film 3 is formed first as in this manufacturing method, the proton exchange layer 2
At the time of etching, the dry etching must be used as described above, or an etching solution that does not dissolve the obliquely deposited film 3 must be used.

Like the first manufacturing method, this second manufacturing method can be performed using a wafer-shaped lithium niobate substrate. Therefore, it can be said that the manufacturing method is suitable for mass production. In the first and second manufacturing methods, the heat treatment is performed with pyrophosphoric acid using the tantalum film as a mask for the proton exchange method, but the method is not limited to this as long as it is a heat treatment with acid using the metal film as a mask. For example, heat treatment may be performed in benzoic acid using a conventionally used aluminum film as a mask. During this heat treatment, the surface of the lithium niobate substrate 1 that does not have the tantalum film 60 is protected from acid by a protective film or the like.

In the optical elements manufactured by the first and second manufacturing methods, the surface of the proton exchange layer 2 is recessed with respect to the surface of the lithium niobate substrate 1, but the surface shown in FIG. 5 may be used. That is, when depositing the dielectric film 50 on the proton exchange layer 2, the oblique vapor deposition film 3 may be formed before or after the step of forming the portion having the property of polarization separation. As for the effect, it can be said that it is a manufacturing method that is suitable for mass production at a low price, similar to the above.

(Fourth Embodiment) FIG. 9 is a sectional view showing the structure of the second optical element B of the present invention. In FIG. 9, an optical element B is a lithium niobate substrate 1, a proton exchange layer 2, an oblique vapor deposition film 3, a silicon dioxide (SiO ₂ ) film 90,
Mixed film 91 and magnesium fluoride (MgF ₂ ) film 92
have.

The silicon dioxide film 90 is an antireflection film for incident light on the surface of the lithium niobate substrate 1. Assuming now that the refractive index of lithium niobate (about 2.25) is n _LN and the refractive index of air (about 1) is n _AIR , the refractive index n1 of the antireflection film is n 1.
Is expressed by the following equation (11). n1 = (n _LN × n _AIR ) ^1/2 (11) Substituting n _LN = 2.25 and n _AIR = 1 into the equation (11), the refractive index n1 of the antireflection film is 1.5. Becomes Here, since the refractive index of the silicon dioxide film 90 is 1.45, the silicon dioxide film 90 satisfies the condition for preventing reflection on the surface of the lithium niobate substrate 1. If the thickness of the silicon dioxide film 90 is (2N + 1) λ / 4 (λ is the wavelength of incident light, N is a natural number), the silicon dioxide film 9
0 is an antireflection film.

Next, the mixed film 91 will be described. The mixed film 91 is a film made of silicon dioxide and tantalum pentoxide. The mixed film 91 prevents reflection of incident light at the interface between the lithium niobate substrate 1 and the obliquely evaporated film 3. _Assuming that the refractive index of lithium niobate is n _LN and the refractive index of the obliquely deposited film 3 of tantalum pentoxide (about 1.6) is nd, the refractive index n2 of the antireflection film is expressed by the following equation (12). To be done. n2 = (n _LN × nd) ^1/2 (12)

In this equation (12), n _LN = 2.25, nd =
Substituting 1.6, the refractive index n2 of the antireflection film becomes 1.9. Here, since the refractive index of silicon dioxide is 1.45, and the refractive index of the film in which tantalum pentoxide is vapor-deposited perpendicularly to the substrate is 2.0, the mixed film 91 composed of silicon dioxide and tantalum pentoxide is mixed. If the ratio is changed appropriately, the refractive index will be 1.
It can be 9. Therefore, by appropriately selecting the mixing ratio of the both, the condition for preventing reflection at the interface between the lithium niobate substrate 1 and the obliquely evaporated film 3 can be satisfied. That is, the thickness of the mixed film 91 is (2N + 1) λ /
4 (λ is the wavelength of incident light and N is a natural number), the mixed film 91 serves as an antireflection film.

Next, the magnesium fluoride film 92 will be described. This magnesium fluoride film 92 is the oblique vapor deposition film 3
This is to prevent reflection of incident light on the surface of the.
Now, the refractive index of the obliquely evaporated film 3 is nd, and the refractive index of air is n.
_{Assuming AIR} , the refractive index n3 of the antireflection film is as follows (13)
It looks like an expression. n3 = (nd × n _AIR ) ^1/2 (13) Substituting nd = 1.6 and n _AIR = 1 into the equation (13), the refractive index n3 of the antireflection film becomes 1.26. . However, there are few ideal materials that can deposit such a low refractive index and durable thin film layer. The refractive index of magnesium fluoride is 1.38, which is close to 1.26. Therefore, the magnesium fluoride film 92 can be used as the obliquely evaporated film 3
Satisfies the conditions to prevent reflection on the surface of. When the thickness of the magnesium fluoride film 92 is (2N + 1) λ / 4 (λ is the wavelength of incident light, N is a natural number), the magnesium fluoride film 92 serves as an antireflection film.

As described above, the silicon dioxide film 90 is provided on the lithium niobate substrate 1, the mixed film 91 made of silicon dioxide and tantalum pentoxide is provided between the lithium niobate substrate 1 and the obliquely evaporated film 3, and Magnesium fluoride film 9
By providing 2 on the oblique vapor deposition film 3, reflection at the optical element B can be completely prevented.

Although silicon dioxide, a mixture of silicon dioxide and tantalum pentoxide, and magnesium fluoride were used as the material of the antireflection film, other materials may be used as long as they have a desired refractive index. (Fifth Embodiment) FIG. 10 is a sectional view showing the arrangement of a third optical element C. As shown in FIG. In FIG. 10, an optical element C is a silicon dioxide film 90, 100, 1 in addition to the lithium niobate substrate 1, the proton exchange layer 2, and the obliquely evaporated film 3 of the optical element A.
03, tantalum pentoxide films 101 and 102.

First, the silicon dioxide film 90 will be described. The silicon dioxide film 90 is a film that prevents reflection of incident light on the surface of the lithium niobate substrate 1 as described in the fourth embodiment. Since the refractive index of lithium niobate and the refractive index of air are stable and do not change, and the refractive index of silicon dioxide is very close to the refractive index required for antireflection, a single layer film of silicon dioxide is an antireflection film. Work as.

Next, the silicon dioxide film 100 between the lithium niobate substrate 1 and the obliquely deposited film 3 of tantalum pentoxide.
A two-layer film composed of the tantalum pentoxide film 101 will be described. This two-layer structure film prevents reflection of incident light at the interface between the lithium niobate substrate 1 and the obliquely evaporated film 3. The mixed film made of silicon dioxide and tantalum pentoxide having the refractive index of 1.9 described in the fourth embodiment is difficult to keep the refractive index stable in the forming process. Therefore, the refractive index may deviate from 1.9. As a result, the reflection of incident light at the interface between the lithium niobate substrate 1 and the obliquely evaporated film 3 increases, and the light utilization efficiency decreases.
On the other hand, if the antireflection film can be formed by forming a two-layer film having a stable refractive index as in the fifth embodiment, the non-reflective condition is hardly deviated. Therefore, the reflectance at the interface between the lithium niobate substrate 1 and the obliquely deposited film 3 can be always 0%.

Here, the reflectance when a two-layer film is formed on the substrate 10 will be described. As shown in FIG.
The refractive index of the substrate 10 is ns. First film 1 on substrate 10
The refractive index and the thickness of 1 are n1 and d1, respectively. The refractive index and the thickness of the second film 12 thereon are n2 and d2.
The refractive index of the substrate 13 thereon is n3. Further, it is assumed that the wavelength of the incident light L is λ, and the light L is vertically incident on the interface between the second film 12 and the substrate 13. In such a case, when the complex reflection coefficient is calculated by solving the characteristic matrix of the two-layer film, the following (1
It becomes like the formula 4). {(M11 + m12 × ns) n3- (m21 + m22 × ns)} / {(m11 + m12 × ns) n3 + (m21 + m22 × ns)} (14) where, m11 = cosβ1 × cosβ2- ( n1 / n2) × sinβ1 × sinβ2 m12 = -i (1 / n1 × sinβ1 × cosβ2 + 1 / n2 × cosβ1 × sinβ2) m21 = -i (n1 × sinβ1 × cosβ2 + n2 × cosβ1 × sinβ2) m22 = cosβ1 × cos β2- (n2 / n1) × sin β1 × sin β2 β1 = (2 × π / λ) n1 × d1 β2 = (2 × π / λ) n2 × d2 i is an imaginary number

Since the reflectance is obtained by squaring the absolute value of the complex reflection coefficient, the reflectance becomes 0 when both the real part and the imaginary part of the complex reflection coefficient become zero. That is, the two-layer film serves as an antireflection film.

In FIG. 10, the lithium niobate substrate 1
Consider a two-layer film composed of a silicon dioxide film 100 and a tantalum pentoxide film 101 between the obliquely vapor-deposited film 3. In this case, in the formula (14), the refractive index (2.25) of the lithium niobate substrate 1 is substituted for ns, the refractive index (1.45) of the silicon dioxide film 100 is substituted for n1, and tantalum pentoxide is substituted for n2. The refractive index (2) of the film 101 is substituted, and the refractive index (1.6) of the obliquely evaporated film 3 is substituted for n3.
When the wavelength is 780 nm, the thicknesses of the silicon dioxide film 100 and the tantalum pentoxide film 101 are 0.021.
At 3 μm and 0.0571 μm, the reflectance is completely 0.
You can

Next, a two-layer film composed of the tantalum pentoxide film 102 and the silicon dioxide film 103 on the obliquely evaporated film 3 will be described. This two-layer structure film is an obliquely evaporated film 3
Prevents the reflection of incident light at the interface between air and air. In the fourth embodiment, a non-reflection film is formed of a single layer film of the magnesium fluoride film 92. However, since the refractive index of the obliquely deposited film 3 is as low as 1.6, the single layer magnesium fluoride film 92 has a reflectance of about 1%. In terms of light utilization efficiency, we want to suppress reflection as much as possible. Therefore, in the configuration of the fifth embodiment, for example, the tantalum pentoxide film 102 has a thickness of 0.04.
16 μm, the thickness of the silicon dioxide film 103 is 0.1688
When the thickness is set to μm, the reflectance at the interface between the obliquely vapor-deposited film 3 and the air is completely 0 for the light having the wavelength of 780 nm according to the formula (14).
Can be Thus, if the film thickness of the tantalum pentoxide film 102 and the film thickness of the silicon dioxide film 103 are designed to be non-reflective conditions with respect to the wavelength of the incident light, the reflectance of the incident light can be completely zero. can do.

Further, since the obliquely vapor-deposited film 3 is formed by obliquely vapor-depositing an oxide such as tantalum pentoxide in order to have a sub-refraction, there are many depletion layers, which lowers the adhesion. I will end up. Therefore, in the present embodiment, the adhesion degree is considerably improved by using all the materials used for the antireflection film as oxides similar to those used for the obliquely evaporated film 3.

As described above, the silicon dioxide film 90 is provided on the lithium niobate substrate 1, and the two-layer structure film composed of the silicon dioxide film 100 and the tantalum pentoxide film 101 is used as the lithium niobate substrate 1 and the obliquely deposited film 3 And a two-layer structure film composed of a tantalum pentoxide film 102 and a silicon dioxide film 103 is provided on the obliquely evaporated film 3 to completely and stably prevent reflection at the optical element C. You can Furthermore, the degree of adhesion is also improved.

Although silicon dioxide and tantalum pentoxide are used as the material of the antireflection film, other materials having a refractive index of a combination that makes the expression (14) 0 can be used.

In the fourth and fifth embodiments described above, the surface of the proton exchange layer 2 is concave with respect to the surface of the lithium niobate substrate 1. However, as shown in FIG. Alternatively, the dielectric film 50 may be deposited. It goes without saying that the same effect can be obtained by providing the above-mentioned film at the same place. Moreover, although the single-layer and two-layer antireflection films have been described, a multilayer antireflection film having three or more layers may be used.

The obliquely vapor-deposited film 3 can be obtained by applying Optics 28 (1989), pages 2466 to 24.
Page 82 (APPLIED OPTICS Vol. 28.
(1989) P. 2466-2482), the value indicating the birefringence characteristic and the refractive index change depending on the vapor deposition angle. Therefore, if a proper vapor deposition angle is selected, the refractive index becomes n2 or n3 as described above. . Further, it is possible to provide birefringence such that the thickness has a value represented by (2N + 1) λ / 4 (λ is the wavelength of incident light, N is a natural number) and has a property of a ¼ wavelength plate. By doing so, the oblique vapor deposition film 3 can prevent the reflection between the lithium niobate substrate 1 and the oblique vapor deposition film 3 or the reflection on the oblique vapor deposition film 3. Therefore, it is not necessary to provide an antireflection film in such an optical element. Therefore, the manufacturing of the optical element is facilitated, and the optical element becomes thinner.

In each of the above embodiments, each layer was formed on the substrate using the X plane of lithium niobate 1, but there is no problem even if the Y plane is used. Further, lithium tantalate or a mixed crystal of lithium niobate and lithium tantalate may be used in place of lithium niobate. Further, in each of the above embodiments, tantalum pentoxide was used as the material of the obliquely deposited film 3, but tungsten trioxide (WO ₃ ) or bismuth (III) oxide (Bi ₂ ) was used.
A dielectric material such as O ₃ ) may be used. Further, the vapor deposition angle may be any number as long as it causes birefringence (JP-A-59).
-49508 and Japanese Patent Laid-Open No. 63-129970).

(Sixth Embodiment) Next, the first optical element A,
A first optical head using one of the second optical element B and the third optical element C will be described. FIG. 12 shows the sixth
It is a block diagram of the 1st optical head of embodiment. In FIG. 12, the optical head includes a light source 120 and a collimator lens 12
1, an optical element 122 (optical element A or B or C), an objective lens 123, a first photodetector 125, and a second photodetector 126.

The optical element 122 is arranged so that the surface having the obliquely deposited film layer 127 faces the objective lens 123 and the surface having the proton exchange layer 128 for polarization separation faces the collimator lens 121. The condensing optical system includes a collimator lens 121 and an objective lens 123. The coherent light emitted from the light source 120 is condensed by the objective lens 123, and the optical recording medium 12
Information is recorded on or reproduced from the recording layer of No. 4.

The operation of the thus constructed first optical head will be described with reference to FIG. The linearly polarized light emitted from the light source 120 is collimated by the collimator lens 121 and is transmitted through the optical element 122 with a transmittance of almost 100%. The transmitted light is converted from linearly polarized light to circularly polarized light. The circularly polarized light is condensed on the optical recording medium 124 by the objective lens 123. Next, the circularly polarized light reflected from the optical recording medium 124 passes through the objective lens 123 and then enters the optical element 122.

In the optical element 122, the circularly polarized light is converted into the linearly polarized light in the direction orthogonal to the polarization direction of the light emitted from the light source 120 by the oblique vapor deposition film 127. This linearly polarized light is diffracted by the proton exchange layer 128 that performs polarization separation with a diffraction efficiency of almost 100%, and the collimator lens 12
1 is transmitted. The + 1st-order diffracted light enters the photodetector 125, and the -1st-order diffracted light enters the photodetector 126.

The photodetectors 125 and 126 detect a focus error signal indicating a focused state of light on the optical recording medium 124 and a tracking error signal indicating a light irradiation position. This detection is performed by changing the grating vector of the diffraction grating of the proton exchange layer 128 depending on the location and appropriately adjusting the wavefront of the diffracted light. In other words, a method of detecting an error signal using a conventional hologram element (for example, Japanese Patent Laid-Open No. 62-137736 and Japanese Patent Laid-Open No. 63-137736).
229640). Then, based on the focus error signal obtained by the above-described method, a focus control device (not shown) always uses the objective lens 123 so that the light is always focused on the optical recording medium 124.
Control the position of in the direction of the optical axis. A tracking control device (not shown) uses the tracking error signal obtained by the above method to focus the light on the desired track on the optical recording medium 124 to the objective lens 123.
Control the position of. Further, the photodetectors 125 and 126 detect the information signal recorded on the optical recording medium 124.

In the above-described optical head using the diffraction grating disclosed in Japanese Patent Laid-Open No. 62-137736 and Japanese Patent Laid-Open No. 63-229640, the diffracted light is transmitted through the diffraction grating even in the forward path of light. Occurs. This diffracted light becomes stray light and causes noise in the reproduction signal and the error signal. On the other hand, in the optical head of the sixth embodiment, the optical element 122 transmits the incident light depending on the polarization direction with a transmittance of 100% or diffracts it with a diffraction efficiency of 100%, so that stray light is generated in the outward path. There is no problem such as. Further, as compared with the optical head shown in FIG. 15, a very small optical head can be realized by using the optical element 122. Further, since the optical element 122 of the present embodiment has a small dependency on the incident angle of light, it becomes easy to adjust the position of the optical element 122 when assembling the optical head. Therefore, this optical head is suitable for mass production and can be reduced in price.

(Seventh Embodiment) First optical element A, second optical element
A second optical head using one of the optical element B and the third optical element C will be described. FIG. 13 is a configuration diagram of the second optical head. 13, the same parts as those in FIG. 12 are denoted by the same reference numerals and detailed description thereof will be omitted. In the optical element 122, the surface having the obliquely vapor-deposited film 127 faces the objective lens 123, and the proton exchange layer 1 that performs polarization separation is provided.
The surface having 28 is arranged so as to face the light source 120. Unlike the optical head shown in FIG. 12, the condensing optical system is composed of only the objective lens 123.

Next, the operation of the second optical head will be described with reference to FIG.
3 will be used for the explanation. The linearly polarized light emitted from the light source 120 passes through the optical element 122 with a transmittance of almost 100%, and the transmitted light is converted from the linearly polarized light to the circularly polarized light. The circularly polarized light is condensed on the optical recording medium 124 by the objective lens 123. Next, the circularly polarized light reflected from the optical recording medium 124 passes through the objective lens 123 and then enters the optical element 122.

The light is the oblique vapor deposition film 127 of the optical element 122.
Is converted from circularly polarized light into linearly polarized light in a direction orthogonal to the polarization direction of the light emitted from the light source 120. Then, this light is approximately 10
Of the diffracted light that is diffracted with a diffraction efficiency of 0%,
The + 1st-order light is incident on the first photodetector 125, and the -1st-order light is incident on the second photodetector 126. The focus error signal and the tracking error signal are detected from the + 1st order light, and the reproduction signal of the information recorded on the optical recording medium 124 is detected from the −1st order light. In the above detection method, since the reproduced signal is not extracted from the + 1st order light, the head amplifier used when converting the current into the voltage may have a low frequency band, and the cost can be reduced.

Differences between the second optical head and the conventional optical head shown in FIG. 15 will be described below. The operation of the quarter-wave plate made of quartz used in the conventional optical head largely depends on the incident angle of light as described above. Therefore, the light source 1
The divergent light emitted from 51 must be collimated by the collimator lens 153 and incident on the quarter-wave plate 154. However, in the present embodiment, the action of the optical element 122 is not significantly affected by the incident angle of light. Therefore, it is not necessary to make the divergent light from the light source 120 into parallel light using the collimator lens, and the divergent light from the light source 120 can be used.
It can be directly incident on 22. Since it is not necessary to use a collimator lens, the size of the optical head can be further reduced. Further, since the collimator lens adjustment process is unnecessary, a low-cost optical head can be realized.

(Eighth Embodiment) Next, the first optical element A,
A third optical head using one of the second optical element B and the third optical element C will be described. FIG. 14 is a configuration diagram of the third optical head. 14, the same parts as those of the optical head of FIG. 12 are denoted by the same reference numerals and detailed description thereof will be omitted. In this third optical head, the optical path of light is bent between the collimator lens 121 and the objective lens 123 by the mirror 141 at a substantially right angle. The optical element 122 is arranged between the objective lens 123 and the mirror 141.

The condensing optical system is composed of a collimator lens 121 and an objective lens 123. Also, the optical element 1
As shown in FIG. 14, 22 is arranged so that the surface having the obliquely evaporated film 127 faces the objective lens 123 and the surface having the proton exchange layer 128 for polarization separation faces the mirror 141. Here, the objective lens 12
3 and the optical element 122 are integrated. Therefore, the position control of the objective lens 123 and the optical element 122 is simultaneously performed by a focus control device and a tracking control device (not shown).

Next, the operation of the third optical head having the above structure will be described. The linearly polarized light emitted from the light source 120 is collimated by the collimator lens 121, and the direction of the light is converted by the mirror 141. This light passes through the optical element 122 with a transmittance of almost 100%,
The transmitted light is converted from linearly polarized light to circularly polarized light. This light is condensed on the optical recording medium 124 by the objective lens 123. The outgoing path of the light from the light source 120 to the optical recording medium is indicated by a solid line, and the optical element 122 to the photodetectors 125, 1
The return path to 26 is indicated by a broken line.

The circularly polarized light reflected from the optical recording medium 124 passes through the objective lens 123. Next, the light is converted by the obliquely evaporated film 127 of the optical element 122 from circularly polarized light into linearly polarized light having a polarization direction orthogonal to the polarization direction of the light from the light source 120. This light has a proton exchange layer 128 for polarization separation.
Is diffracted with a diffraction efficiency of almost 100%, and the direction of the diffracted light is changed by the mirror 141.

The + 1st-order light transmitted through the collimator lens 121 is incident on the first photodetector 125, and the -1st-order light is the second-order light.
Is incident on the photodetector 126. The focus error signal, the tracking error signal, and the reproduction signal of the information recorded on the optical recording medium 124 are detected by the same method as that of the first or second optical head, respectively.

Conventionally, in order to reduce the size of the optical head, the objective lens may be integrated with the optical element in which the quarter-wave plate made of quartz and the polarization separation element are bonded together. In that case, since the thickness of the conventional quarter-wave plate made of quartz is about 0.5 mm, the optical head will be large. On the other hand, the eighth
The optical element used in the embodiment may have a thickness of the oblique vapor deposition 127 as a quarter-wave plate of 2.6 μm. Therefore, the height of the optical head can be further reduced by about 0.5 mm.
This is important for realizing a compact and flat portable optical disk device.

Although the collimator lens is used in the eighth embodiment to collimate the light emitted from the light source, the collimator lens is eliminated as described in the seventh embodiment relating to the second optical head. But there is no problem. If there is no collimator lens, the adjustment process is not required, so the cost is low.

[0089]

As described above, according to the present invention, the oblique vapor deposition film is provided on the hologram element having the different diffraction efficiency depending on the polarization direction, so that the polarization separation property and the quarter wave plate property are combined. An optical element can be realized. Furthermore, it is possible to realize an optical element that is very thin without giving aberration to the wavefront of transmitted light and suitable for mass production. Further, by using this optical element, it is possible to realize a small-sized optical head suitable for mass production and at a low cost.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a configuration of a first optical element of the present invention.

FIG. 2 is a photograph showing interference fringes of light transmitted through the first optical element and reference light.

FIG. 3 is a photograph showing interference fringes of light transmitted through a pasted optical element of a conventional quarter-wave plate and a polarization separation element and reference light.

FIG. 4 is an explanatory view showing incident light on a conventional quarter-wave plate.

FIG. 5 is a cross-sectional view showing another configuration example of the first optical element.

FIG. 6 is a process drawing showing the first method for manufacturing an optical element of the present invention.

FIG. 7 is a diagram showing vapor deposition angles of oblique vapor deposition films in the optical element of the present invention.

FIG. 8 is a process drawing showing the second manufacturing method of the optical element of the present invention.

FIG. 9 is a sectional view showing a configuration of a second optical element of the present invention.

FIG. 10 is a sectional view showing a configuration of a third optical element of the present invention.

FIG. 11 is an explanatory diagram showing parameters used for reflectance calculation of a two-layer film.

FIG. 12 is a configuration diagram of a first optical head of the present invention.

FIG. 13 is a configuration diagram of a second optical head of the present invention.

FIG. 14 is a configuration diagram of a third optical head of the present invention.

FIG. 15 is a configuration diagram of a conventional optical head.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Lithium niobate substrate 2 Proton exchange layer 1 + 2 Hologram element 3 Oblique vapor deposition film 50 Dielectric film 60 Tantalum film 61 Resist 90 Silicon dioxide film 91 Mixed film 92 Magnesium fluoride film 100, 103 Silicon dioxide film 101, 102 Tantalum pentoxide film 120 light source 121 collimator lens 122 optical element A, B or C 123 objective lens 124 optical recording medium 125 first photodetector 126 second photodetector

[Procedure amendment]

[Submission date] November 8, 1995

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Figure 2

[Correction method] Change

[Correction content]

FIG. 2 is a halftone image displayed on a display by photographing an interference fringe of light transmitted through the first optical element of the present invention and reference light obtained by passing the light through a pinhole and displayed on a display. Photo

[Procedure Amendment 2]

[Document name to be amended] Statement

[Name of item to be corrected] Figure 3

[Correction method] Change

[Correction content]

FIG. 3 is a display in which an interference fringe of light transmitted through a pasted optical element of a quarter-wave plate and a polarization separation element and reference light obtained by passing the transmitted light through a pinhole is photographed by a video camera. Photo showing the halftone image shown above

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroshi Shiraiwa 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Seijiro Okada, 1006 Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd.

Claims (15)

[Claims] 1. An optical element comprising a hologram element having a different diffraction efficiency depending on the polarization direction, and an oblique vapor deposition film in which a dielectric is obliquely vapor-deposited on the hologram element. 2. A hologram element having a different diffraction efficiency depending on the polarization direction, a first antireflection film on the hologram element for preventing reflection of incident light, and a reflection between adjacent layers on the hologram element. A second antireflection film for preventing the reflection; an oblique evaporation film in which a dielectric is obliquely evaporated on the second antireflection film; and a third antireflection film for preventing reflection of incident light on the oblique evaporation film.
An optical element comprising the antireflection film of. 3. The hologram element is LiTa _x Nb _1-x
3. The optical element according to claim 1, which is formed by ion-exchanging a predetermined portion of the X plane or the Y plane of the O ₃ (0 ≦ x ≦ 1) crystal substrate. 4. The first antireflection film is composed of silicon dioxide (SiO ₂ ), and the second antireflection film is a mixture of silicon dioxide (SiO ₂ ) and tantalum pentoxide (Ta ₂ O ₅ ). The third antireflection film is formed of magnesium fluoride (Mg)
The optical element according to claim 2, wherein the optical element is composed of F ₂ ). 5. The material of the obliquely deposited film is an oxide,
The optical element according to claim 2, wherein the material used for the second and third antireflection films is an oxide. 6. The first antireflection film is composed of silicon dioxide (SiO ₂ ), and the second antireflection film is the LiTa _x Nb _1-x O ₃ (0
≦ x ≦ 1) of the first film formed of silicon dioxide (SiO ₂ ) on the non-ion exchanged surface of the crystal substrate and the second film formed of tantalum pentoxide (Ta ₂ O ₅ ) thereon. The third antireflection film has a two-layer structure. The third antireflection film is formed of tantalum pentoxide (Ta ₂ O ₅ ) on the obliquely evaporated film and silicon dioxide (SiO ₂ ) is formed on the third film. The optical element according to claim 2, wherein the optical element has a two-layer structure of a fourth film that is formed. 7. A mask pattern for ion exchange treatment is L
iTa _x Nb _1-x O ₃ (0 ≦ x ≦ 1) The first step of forming on the surface of the crystal substrate, and the LiTa _x Nb _1-x O ₃ (0 ≦ x ≦ 1) crystal substrate surface. A second step of exchanging lithium ions (Li ⁺ ) for hydrogen ions (H ⁺ ) in the region specified by the mask pattern formed in the first step; and ion exchange in the second step A third step of selectively etching the region, and a second surface of the LiTa _x Nb _1-x O ₃ (0 ≦ x ≦ 1) crystal substrate at a predetermined angle with respect to a normal to the crystal substrate surface. A fourth step of obliquely evaporating the molecules of the dielectric material to form an obliquely evaporated film, the optical element manufacturing method. 8. The method of manufacturing an optical element according to claim 7, wherein the dielectric in the fourth step is tantalum pentoxide (Ta ₂ O ₅ ). 9. A LiTa _x Nb _1-x O ₃ (0 ≦ x ≦ 1) crystal substrate is obliquely vapor-deposited on a crystal substrate surface at a predetermined angle with respect to a normal line to the crystal substrate surface, A first step of forming a deposited film, a second step of forming an ion-exchange mask pattern on the other surface of the LiTa _x Nb _1-x O ₃ (0 ≦ x ≦ 1) crystal substrate, and LiTa _x Nb _1-x O ₃ (0 ≦ x ≦ 1) Lithium ions (Li ⁺ ) and hydrogen ions (H ⁺ ) in the region specified by the mask pattern formed in the second step on the other surface of the crystal substrate. ⁺ ) And a third step of performing ion exchange, and a fourth step of selectively etching the region subjected to ion exchange in the third step. 10. The method of manufacturing an optical element according to claim 9, wherein the dielectric in the first step is tantalum pentoxide (Ta ₂ O ₅ ). 11. A light source that outputs coherent light, a light collecting optical system that collects the light of the light source onto an optical recording medium, and collects the light reflected by the optical recording medium, An optical element provided between an optical system and the light source, and the diffracted light diffracted by the optical element is incident to be recorded on the focus error signal and the tracking error signal of the optical recording medium and the optical recording medium. And an optical detector for detecting the information signal. 12. The optical head according to claim 11, wherein the optical element is provided integrally with the condensing optical system. 13. The first light for detecting a focus error signal and a tracking error signal of the optical recording medium by injecting + 1st order light out of the diffracted light diffracted by the optical element. The optical head according to claim 11, further comprising: a detector and a second photodetector that receives the minus first-order light and detects an information signal recorded on the optical recording medium. 14. The optical head according to claim 11, wherein the optical element comprises a hologram element having a different diffraction efficiency depending on a polarization direction and an oblique vapor deposition film in which a dielectric is obliquely vapor-deposited on the hologram element. 15. The optical element comprises a hologram element having different diffraction efficiency depending on a polarization direction, a first antireflection film on the hologram element for preventing reflection of incident light, and a hologram element on the hologram element. A second antireflection film for preventing reflection between adjacent layers;
An obliquely vapor-deposited film in which a dielectric is obliquely vapor-deposited on the anti-reflection film, and a third on the obliquely vapor-deposited film for preventing reflection of incident light.
12. The optical head according to claim 11, further comprising an antireflection film.