JPH075316A - Diffraction grating type polarizer and its production - Google Patents

Abstract

PURPOSE:To constitute the prescribed diffraction grating type polarizer without executing etching, etc., by forming grid-shaped dielectric films at prescribed intervals on a substrate and vapor depositing a double refractive film by a diagonal vapor deposition over the entire part of the substrate and the dielectric films. CONSTITUTION:The grid-shaped dielectric films 3 are formed at the specified intervals by a lift-off method, etc., on the substrate 1 and the double refractive film 4 is formed by the diagonal vapor deposition over the entire surface of the substrate 1 and the dielectric films 3. The double refractive film 4 has the double refractiveness dependent upon the material of the dielectric films 3 in a first block a where the isotropic or double refractive dielectric substance exists between the film and the substrate 1. The double refractive film 4 has the double refractiveness dependent upon the material of the substrate 1 in the second block b where the double refractive film 4 comes into direct contact with the substrate 1. The diffraction grating type polarizer having the prescribed characteristics is constituted by selecting the materials and thicknesses of the double refractive film 4 and the dielectric films 3 in such a manner that the phase of the one polarized light respectively transmitting the first block a and the second block b nearly coincide with each other and the phases of the other polarized light shift nearly by the half wavelength phase each.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a diffraction grating type polarizer by oblique vapor deposition and a method for manufacturing the same.

[0002]

2. Description of the Related Art In recent years, a diffraction grating type polarizer manufactured by proton exchange with LiNbO ₃ is known as a polarizing element utilizing the diffraction phenomenon (Japanese Patent Laid-Open No. 63-55501). This polarizer is thin and has mass productivity. However, it is necessary to use an expensive single crystal substrate of LiNbO _{3, and} a polarizer must be manufactured separately from other optical elements as in the conventional case, and it is not possible to downsize the entire optical device. was there. Further, there is known an optical isolator in which a Faraday rotator is provided with a function of a polarizer by forming a phase grating having a pitch smaller than ½ of the wavelength of light on the surface of the Faraday rotator (Japanese Patent Laid-Open No. Hei 2 (1998) -222). 10311). This optical isolator does not require a polarizing prism, which is advantageous for downsizing. However, there is a drawback that it is necessary to form very fine grooves on the surface of the Faraday rotator with high accuracy, which is difficult to manufacture and is not suitable for practical use.

In order to solve this problem, the present inventors have proposed in Japanese Patent Application No. 4-148951 a birefringent film formed by oblique vapor deposition and a dielectric film (isotropic or birefringent film different from the birefringent film). A diffraction grating is formed by using a glass material), and a refractive index and a thickness are defined so as to have a predetermined value and a mutual relationship, thereby forming a polarizer. More specifically, it has a diffraction grating alternately provided on the same surface with a first section formed by laminating one or more films and a second section formed by laminating one or more films,
A polarizer in which at least one layer film in at least one section has birefringence and the film having the birefringence is formed by an oblique vapor deposition method. For example, in the simplest case, a birefringent film with a certain thickness is formed on a substrate by oblique vapor deposition of a metal oxide or the like, and then a number of grooves reaching the substrate at regular intervals are formed in the birefringent film by etching. Then, these grooves are filled with an isotropic dielectric. Same width of the first and second compartments, the thickness d and the same, the refractive index of the birefringent film n _o, n _e
And the refractive index of the isotropic dielectric is n, a polarizer is obtained if the following relation is satisfied.

[Equation 1] (However, N ₁ and N ₂ are arbitrary integers, λ is the wavelength of light. 2
According to this, unlike the conventional polarizer, it is excellent in mass production workability and space saving, and can directly and easily input light and output surface of various optical elements. There are advantages such as being able to adhere.

[0004]

However, the technique for processing the above-described birefringent oblique vapor deposition film into a diffraction grating by etching has the following problems. (1) Undercutting of the birefringent film during etching is severe when the film thickness is required to act as a diffraction grating type polarizer. (2) When a photoresist is applied onto the obliquely vapor-deposited film, the resist component enters and remains in the film, and the selectivity ratio during etching is significantly reduced. (3) Since the difference in etching rate between the film and the residual resist is large, it is difficult to form a groove having a predetermined depth. (4) Anisotropy exists in etching. Due to these factors, it is quite difficult to process the obliquely vapor-deposited film into a lattice by chemical etching. Therefore, the present invention is to provide a diffraction grating type polarizer using an obliquely vapor-deposited film that does not require etching for the birefringent obliquely vapor-deposited film and is easy to manufacture.

[0005]

According to the present invention, in addition to vapor deposition conditions such as vapor deposition angle and substrate temperature,
By controlling the refractive index and birefringence of the birefringent film by utilizing factors such as the stress of the film and the state of the interface between the film and the substrate, that is, depending on the material of the underlying layer A predetermined diffraction grating type polarizer can be formed without processing.

More specifically, according to the present invention, a substrate, a lattice-shaped dielectric film formed on the substrate at regular intervals, and the entire substrate and the dielectric film are formed by oblique vapor deposition. A diffraction grating type polarizer including a birefringent film. According to the present invention, in the first section in which the isotropic or birefringent dielectric material is interposed between the substrate and the second section in which the birefringent film is in direct contact with the substrate, the double section for at least one of ordinary light and extraordinary light is provided. The refractive index of the refraction film is different. The phases of one polarized light transmitted through the first section and the second section are substantially the same,
The diffraction grating having predetermined characteristics is selected by selecting the material and thickness of the birefringent film and the dielectric film so that the phase of the other polarized light transmitted through each of the first section and the second section is shifted by half a wavelength. Type polarizer is constructed.

Further, according to the present invention, a birefringent film is formed by forming a lattice-shaped dielectric film on a substrate at regular intervals and depositing a birefringent material on the entire surface of the substrate and the dielectric film by an oblique evaporation method. Is a method of manufacturing a diffraction grating type polarizer. Any method can be used to form the dielectric layer in a lattice shape. For example, a dielectric film is formed in a lattice shape by a lift-off method, and the birefringence is formed on the entire surface of the substrate and the dielectric film by an oblique vapor deposition method. A birefringent film can be formed by depositing a material. At that time, the phase of one polarization transmitted through each of the first section and the second section of the diffraction grating type polarizer of the finished product is substantially the same, and the phase of the other polarization transmitted through each of the first section and the second section. The materials and thicknesses of the birefringent film and the dielectric film are selected so that the phase shifts by approximately a half wavelength.

The substrate may be an optical element such as a lens, prism, glass plate, magneto-optical element (Faraday rotator or the like), electro-optical element, beam splitter, beam expander, optical fiber or the like. As a result, an integrated optical isolator, optical circulator, optical switch, optical magnetic field sensor, optical modulator, etc. can be configured.

Examples of the birefringent material used as the birefringent film include materials that can be formed by oblique vapor deposition, such as Ta ₂ O ₅ , WO ₃ , Bi ₂ O ₃ and ZnS. However, the material is not particularly limited to these, and various materials can be used as long as they can provide birefringence by the oblique vapor deposition method. The oblique evaporation method is an evaporation method in which an inorganic material such as a metal oxide is evaporated on a substrate in an oblique direction. The vapor-deposited film formed by this method has a fibrous columnar structure tilted with respect to the substrate, that is, an anisotropic structure, and has a refractive index for linearly polarized light in a direction orthogonal to that for linearly polarized light in an inclined direction. There is a difference between. The vapor deposition film thus formed has birefringence. As an apparatus used in this method, a usual vacuum apparatus such as a vacuum evaporation apparatus using electron beam heating can be used, and a substrate is tilted and installed in the apparatus to perform an evaporation operation. Such a vapor deposition method is
For example, T. MOTOHIRO and Y. By TAGA
APPLIED OPTICS, Vol.28, NO.13, 2466-2482 page (1989
Since it is discussed in detail in (1), the details are omitted.

The material for forming the dielectric film must be such that it changes the birefringence of the birefringent film formed by oblique vapor deposition on the substrate and the dielectric film.
The refractive index closer to that of the birefringent film formed by oblique vapor deposition is advantageous for suppressing reflection. In addition, the film thickness of the dielectric is deteriorated if a large step is formed between the dielectric and the substrate surface. The material used as the dielectric film is, for example, SiO ₂ , TiO ₂ .
Materials such as ₂ , Y ₂ O ₃ , MgF ₂ , ZrO ₂ and ZnS can be cited. Usual vapor deposition method, sputtering method and the like can be considered, but not limited to these, various materials and manufacturing methods can be used as long as the above effects can be obtained.

Furthermore, if necessary, functions such as antireflection and phase adjustment can be added to the polarizer or various optical elements. These are selected from the materials described above for the dielectric film, and can be formed by a usual vapor deposition method, sputtering method, or the like.

FIG. 1 shows an example of a method of manufacturing the diffraction grating type polarizer of the present invention. First, a substrate 1 is prepared as shown in (A), and a grating pattern is formed thereon by using, for example, a lift-off method. The dielectric film 3 is formed, and the birefringent film 4 is formed thereon by oblique vapor deposition as in (B) to (E).

In the first section a of FIG. 1F, the birefringent film 4 has a birefringent property depending on the material of the dielectric film 2.
In the section b, the birefringent film 4 has birefringence depending on the material of the substrate 1. Therefore, the difference △ n = n _e -n _o of the first compartment and the birefringence of the second compartment does not become the same △ n ₁ ≠ △ n ₂
Becomes The widths of the first section and the second section are the same, the thickness of the birefringent film is constant d, the refractive indexes of the birefringent film of the first section are n _1e and n _1o , and those of the second section are n _2e. , N _2o , the thickness of the dielectric film is d _{d, the} refractive index is n _d, and the refractive index of air is n _o , the conditions for acting as a diffraction grating are as follows.

[Equation 2] (However, λ is the wavelength of light, N is an arbitrary integer, and the right side of these equations may be interchanged.) If the refractive index is determined by the above equation, the film thickness can be calculated by the following equation.

[Equation 3] (However, Δn ₂ = | n _2e −n _2o |, Δn ₁ = | n _1e −
n _1o |)

FIG. 2 shows a more practical constitutional example of the polarizer of the present invention, in which an antireflection laminate 5 is formed on a substrate 1, and a thickness d _d dielectric film 3 is formed on the lattice 5. The birefringent film 4 having a thickness d is formed by oblique vapor deposition, and the laminated body 6 for antireflection is further formed thereon. In this case, the uppermost part of the laminated body 5 is made of a material in consideration of the formation of the birefringent film 4.

[0015]

EXAMPLE A glass substrate was used as a substrate, and SiO ₂ (n _d = 1.45) was formed as a dielectric in a lattice shape by vapor deposition and a lift-off method. Then, by the oblique deposition method, Ta
₂ O ₅ was vapor deposited to form a birefringent film. The refractive index of the birefringent film formed on the dielectric film in the first section is n _1o =
1.85, n _1e = 1.77, and the refractive index of the birefringent film formed on the substrate in the second section is n _2o = 1.81 and n _2e =
It was 1.78. Therefore, the thickness of the birefringent film is set to d = 13.
A polarizer could be constructed by setting the thickness of the μm dielectric film to d _d = 290 nm.

[0016]

[Effects] According to the present invention, the birefringence of an obliquely vapor-deposited film depends on factors such as stress and the state of the interface, that is, the material of the underlying layer. By controlling, without etching the birefringent film,
It is possible to configure a predetermined diffraction grating type polarizer.

[Brief description of drawings]

FIG. 1 shows a manufacturing process of a diffraction grating type polarizer of the present invention.

FIG. 2 is a sectional view showing a structure of a diffraction grating type polarizer of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 3 Dielectric film 4 Oblique vapor deposition birefringent film 5 and 6 Anti-reflection laminate

Claims (6)

[Claims] 1. A diffraction grating type comprising a substrate, a lattice-shaped dielectric film formed on the substrate at regular intervals, and a birefringent film formed on the entire substrate and the dielectric film by an oblique deposition method. Polarizer. 2. The diffraction grating according to claim 1, wherein the birefringent film has different birefringence between a first section formed on the dielectric film and a second section formed on the substrate. Type polarizer. 3. The phase of one polarized light transmitted through each of the first section and the second section substantially coincides with each other, and the phase of the other polarized light transmitted through each of the first section and the second section is shifted by about a half wavelength. The diffraction grating type polarizer according to claim 1 or 2, wherein the materials and thicknesses of the birefringent film and the dielectric film are selected. 4. A birefringent film is formed by vapor-depositing a lattice-shaped dielectric film on a substrate at regular intervals, and vapor-depositing the film on the entire surface of the substrate and the dielectric film by an oblique vapor deposition method. Method of manufacturing diffraction grating type polarizer. 5. A method of manufacturing a diffraction grating type polarizer, comprising forming a dielectric film in a lattice shape on a substrate and forming a birefringent film on the substrate and the dielectric film by an oblique vapor deposition method. . 6. The phase of one polarized light transmitted through each of the first section and the second section is substantially the same, and the phase of the other polarized light transmitted through each of the first section and the second section is shifted by approximately a half wavelength. The method for manufacturing a diffraction grating type polarizer according to claim 4, wherein the birefringent film and the dielectric film are made of materials and thicknesses selected.