JPH11248935A - Polarizer and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To uniformly form a metal particle layer on a substrate surface and to obtain the polarizer superior in characteristics at a low cost by providing a heat conductive layer on the reverse surface of the dielectric substrate and providing a polarizing layer which has metal particle layers and dielectric layers laminated alternately on the top surface of the substrate. SOLUTION: On the reverse surface of the translucent glass substrate 2, a heat conductive layer 5 of silicon, etc., having higher heat conductivity than the glass substrate 2 is formed. Onto the top surface of the substrate 2, metal particulates 6 of copper, etc., are adhered and the substrate 2 is heated at temperature lower than the glass softening point to form a metal particle layer 4 consisting of metal particles 4a obtained by growing the metal fine particulates 6. On the metal particle layer 4, a dielectric layer 3a is formed. This process is repeated to form the laminated body 3 of alternate metal particle layers 4 and dielectric layers 3a on the substrate 2. The substrate 2, while heated almost at the softening point,is thermoplastically deformed by drawing, etc., to give light absorption anisotropy to the metal particles 4a dispersed in the metal particle layer 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarizer used for optical communication equipment, optical recording equipment, optical sensors and the like, and more particularly to a polarizer in which metal particles having light absorption anisotropy are dispersed in a dielectric. It can be suitably used for, for example, an optical isolator.

[0002]

2. Description of the Related Art Conventionally, for example, a polarizer constructed by putting a certain kind of solution into a cell, a polarizer using a coloring agent by mixing a coloring agent into plastic, and a dielectric thin film formed by laminating a large number of dielectric thin films on a substrate. A polarizer utilizing interference of a multilayer thin film, a polarizing prism represented by a Glan-Thompson prism composed of a crystal having a large birefringence, a PBS (polarizing beam splitter) for separating polarization components using Brewster conditions, or A polarizing film that orients a polymer material in a certain direction and absorbs a polarized component in one direction is generally known as a polarizer.

However, for example, a polarizer using the above-mentioned colored ions has a large wavelength dependency, so that it is necessary to select a polarizer having an optimum wavelength characteristic for each wavelength.
Although a polarizer made of a crystal having a large refractive index has a small wavelength dependence, it is difficult to process and has a limited element size, making it difficult to miniaturize. Did not.

Recently, a polarizing glass has been used as an optical communication device for such a polarizer. This is a structure in which, for example, a transparent glass is used as a medium, and silver particles are aligned in a certain direction and dispersed in the medium to have optical anisotropy (see Japanese Patent Publication No. 2-40619). .

The method for producing a polarizing glass comprises first melting a glass batch comprising at least one halide selected from the group consisting of silver and chloride, bromide and iodide, and forming a glass substrate having a required shape. Mold into Next, the glass substrate is subjected to a heat treatment under predetermined conditions to precipitate silver halide grains in the glass. Further, the glass substrate is stretched by applying tension in a predetermined temperature range, and the silver halide grains are elongated,
Align in the tension direction. Finally, the elongated glass base is exposed to a reducing atmosphere within a predetermined temperature range, and a part of silver halide is reduced to metallic silver particles to obtain a polarizing glass.

[0006] However, the above-mentioned method for producing a polarizing glass has the following disadvantages.
Although heat treatment is performed in a reducing atmosphere, it is difficult to control the amount of metallic silver precipitated in the glass substrate, and stable optical characteristics cannot be obtained. And even if this glass substrate was heated and stretched, it was difficult to stably obtain the polarization characteristics with good reproducibility.

[0007] Further, there is also a problem that, due to the temperature distribution in the thickness direction in the glass substrate, silver halide in which no metallic silver is deposited remains in the center portion, which adversely affects the transmittance. .

Further, when the silver halide grains are reduced to metallic silver, the volume shrinks by about 1/3, so that the surface portion of the glass substrate being reduced becomes porous, which causes a problem in long-term reliability. was there.

In order to solve such problems, a discontinuous island-like metal particle layer and a dielectric material such as glass are formed on a dielectric substrate such as glass using a thin film manufacturing process such as vacuum deposition. There is also proposed a layer in which layers are alternately formed so as to have anisotropy by heating and stretching (for example, 1).
990 IEICE Autumn National Convention, Conference proceedings C
-212). In this polarizer, each island in the island-shaped metal particle layer serves as a metal particle, and has the same structure as that in which the metal particles are dispersed.

[0010]

However, in the case of the above polarizer, it is difficult to make the size of the metal particles to be dispersed and the distribution state of the metal particles uniform in the in-plane direction of the substrate, and therefore, the polarizer is manufactured industrially stably. It was difficult to do.

As a result of intensive studies by the present inventors on this manufacturing process, it has been confirmed that the substrate temperature is an important parameter for the growth of metal particles. In addition, when the metal particles are formed by a vacuum evaporation apparatus or the like, the existence position is changed according to the energy state of the substrate surface. Therefore, if a temperature distribution exists on the substrate surface, an in-plane distribution of the metal particles occurs. .

Since the substrate temperature is usually as high as 300 ° C. or more, it is necessary to make the substrate surface uniform and to keep the same substrate surface uniform during film formation.

Conventionally, when a substrate is heated, a method of attaching the substrate to a heater via a substrate holder holding the substrate, or a method of using an incandescent lamp, requires heating a substrate which is a dielectric. Because of the difficulty, a method of heating the substrate holder once and heating the substrate by heat conduction from the substrate holder has been adopted. For this reason, at such high temperatures, it is difficult to make the temperature within the same substrate uniform because the thermal conductivity of the glass is low. Many polarizers with excellent characteristics cannot be obtained.

Accordingly, the present invention provides a polarizing plate comprising a polarizing layer in which metal particle layers in which metal particles having light absorption anisotropy are dispersed and dielectric layers are alternately laminated on one principal surface of a dielectric substrate. It is an object of the present invention to enable a metal particle layer to be uniformly formed on a substrate surface in a polarizer, and to provide a polarizer having excellent characteristics in large quantities at low cost.

[0015]

In order to solve the above problems, a polarizer of the present invention has a light-transmitting lower surface of a light-transmitting dielectric substrate, and has a higher thermal conductivity than the dielectric substrate. A high heat transfer layer is provided, and a polarizing layer in which a metal particle layer in which metal particles having light absorption anisotropy are dispersed and a dielectric layer are alternately stacked on the upper surface of the dielectric substrate is provided. Do it.

In particular, a light-transmitting silicon oxide layer is formed on the lower surface of a light-transmitting glass substrate, and metal particles having light absorption anisotropy are dispersed on the upper surface of the glass substrate. A polarizer comprising a polarizing layer in which metal particle layers and dielectric layers are alternately stacked in multiple layers is provided. Here, in particular, the thickness of the silicon oxide layer is 1 to 4000 °, more preferably 500 to 2000 °.

A polarizing layer formed by alternately laminating metal particle layers in which metal particles having light absorption anisotropy are dispersed and dielectric layers made of glass are formed on the upper surface of a glass substrate having translucency. In the method for producing a polarizer, the polarizing layer is formed by repeating the steps A to B in the following step A a plurality of times, and then stretching the glass substrate while heating, and dispersing the glass substrate in the metal particle layer. Characterized in that the metal particles provided have light absorption anisotropy. A: A step of forming a silicon layer on the lower surface of a glass substrate by a thin film forming method.
B: Step of depositing and forming metal fine particles on the upper surface of a glass substrate by a thin film forming method. C: a step of heating the glass substrate at a temperature lower than the softening point to grow the metal fine particles and form a metal particle layer. D: forming a dielectric layer on the metal particle layer by a thin film forming method.

Further, the above-mentioned manufacturing method is characterized in that the method includes a step of heating the silicon layer to generate a silicon oxide layer having a light-transmitting property.

[0019]

Embodiments of the present invention will be described below in detail with reference to the drawings. 1 and AA of FIG.
As shown in FIG. 2 (g), which is a line cross-sectional view, the polarizer 1 of the present invention has a heat-transfer material having a higher thermal conductivity than the glass substrate 2 on the lower surface of the glass substrate 2 which is a transparent dielectric substrate. The transmission layer, for example, silicon (Si) is oxidized by a thermal oxidation process to be described later, and has a light-transmitting silicon oxide (Si).
An O ₂ ) layer 7 is provided, and on the upper surface of the glass substrate 2, a large number of metal particles 3 a having optical anisotropy are dispersed (number density: ^{2 to} 37 particles / μm ² ). Layer 3a
Are arranged alternately in a multilayer structure. In the metal particle layer 4, a portion between the metal particles 4a and the metal particles 4a is a part of the dielectric layer 3a.

When the silicon layer is provided on the lower surface of the dielectric substrate as described above, the insertion loss increases if the silicon layer remains. Therefore, it is preferable that the silicon layer be thermally oxidized by a heat treatment step described later to obtain transparent silicon oxide. When the heat transfer layer is opaque and cannot be made transparent even in a step such as heat treatment, such a heat transfer layer may be removed by polishing or the like. When the heat transfer layer is formed of a thin film of a metal such as gold or platinum that transmits light, the heat transfer layer having such a light-transmitting property may be left as it is. . In addition, having translucency means being transparent with respect to the used wavelength. The number density of the metal particles is a density in the direction of the substrate surface S, and is a density including a major axis of at least one metal particle 4a and measured when cut along a plane parallel to the substrate surface S.

The substrate 2 is made of, for example, borosilicate glass such as Pyrex glass (Pyrex is a trade name of Corning Glass Industry) or BK glass (BK is a trade name of Hoya Glass Co., Ltd.). Low melting point glass such as high melting point silicate glass or soda glass such as glass may be used. Further, other transparent dielectric materials may be used in place of such a glass material, but a glass material can be suitably used because it is inexpensive and easy to stretch. The dielectric layer 5 is preferably made of the same material as the substrate 2. For example, when BK glass is used for the substrate 2, it is preferable that BK glass is also used for the dielectric layer 5 so that properties such as the coefficient of thermal expansion match.

Au, Ag, Pt, R
h, Ir and other noble metal elements, Cu, Fe, Ni, Cr, A
It is preferably at least one metal selected from transition metals such as l and W, and is a metal that has poor wettability with the substrate 2 and the dielectric layer 5 and is easy to aggregate, and is hardly oxidized. What can exist as metal particles 4a is preferred.
Among them, particularly preferred are Au, which has a low melting point and is easy to aggregate, has poor wettability with glass, and is hardly oxidized, and Cu is inexpensive and has poor wettability with glass. The metal particles 4a are not limited to a single metal, but may be an alloy.

The metal particles 4a are substantially spheroidal and have shape anisotropy. In FIG. 1 (however, the traveling direction of light is defined as the Z direction, and a plane orthogonal to this is defined as the XY plane). ,
The major axis direction of the metal particles 4a is the X direction, and the minor axis direction is the Y direction.

The ratio between the length of the metal particles 4a in the major axis direction and the length in the minor axis direction is defined as the aspect ratio. Here, the average value of the aspect ratios of a large number of metal particles 4a is simply referred to as the aspect ratio. .

The reason why the metal particles 4a have a spheroidal shape is as follows.
This is because the metal particles 4a are stretched in the stretching direction together with the substrate 2 during stretching after the polarizing layer 3 is formed on the substrate 2. The extinction ratio increases as the aspect ratio increases, but at the same time, the stretching rate of the substrate 2 increases, making stretching difficult. In addition, the rate of increase in the extinction ratio decreases in a region having a large aspect ratio. The aspect ratio (length in the major axis direction / length in the minor axis direction) of the metal particles 4a in 3 is 3 to 3.
30 is suitable, and particularly preferably 15 to 25.
Incidentally, the extinction ratio, when using unpolarized incident light at a predetermined wavelength, it is assumed that the energy ratio of the polarization component in the Y direction and the polarization component in the X direction is shown in decibel units,
It is 10 dB when the energy ratio is 10. Insertion loss described later, when using incident light that is not polarized at a predetermined wavelength, the ratio of the total energy of the incident light and the energy of the polarization component in the X direction is expressed in decibels,
0.1 dB when the energy ratio is 0.1.

The number density of the metal particles 4a in the metal particle layer 4 is ² to 37 / μm ^{2 in the} direction of the substrate surface. This is because the number density is less likely to appear the characteristics of the polarizer and falls below two / [mu] m ^2, for example, because the extinction ratio is lower than 20 dB, also, in the metal particles exceeds than 37 / [mu] m ² Is large, and the insertion loss increases more than 1 dB. That is, if the ratio is out of the above range, the metal particles are too close to each other to increase the insertion loss, or are too far from each other to obtain an extinction ratio.

Next, a method for manufacturing the polarizer 1 according to the present invention will be described. First, as shown in FIG. 2A, a heat transfer layer 5 having a higher heat conductivity than a glass substrate 2 made of silicon or the like is provided on a lower surface of a glass substrate 2 made of borosilicate glass or the like having translucency.
Is formed by a thin film forming method such as sputtering (step a).

Next, as shown in FIG. 2 (b), metal fine particles 6 such as copper are formed on the upper surface of the glass substrate 2 by sputtering by a thin film forming method (step b). afterwards,
The glass substrate 2 is heated at a temperature lower than the glass softening point to form the metal particle layer 4 composed of the metal particles 4a on which the metal fine particles 6 are grown (step c).

Then, a dielectric layer 3a is formed on the metal particle layer 4 by a thin film forming method such as sputtering (step d).

By repeating the above steps b to d a plurality of times in this manner, a laminate 3 in which the metal particle layers 4 and the dielectric layers 3a are alternately laminated is formed on the glass substrate 2. (Steps e and f).

Then, in order to remove the argon gas used in the thin film forming method such as the above-mentioned sputtering, a heat treatment is performed at a temperature lower than the glass softening point to reduce the amount of argon in the dielectric layer 3a to 1.0 × 10 ^19. Degas to make molecules / cm ³ or less. Thereafter, while the glass substrate 7 is heated near the softening point, a stress is applied in the XX ′ direction to cause thermoplastic deformation such as stretching, and the metal particles 4 a dispersed in the metal particle layer 4 are subjected to light absorption anisotropy. (Steps f and e).

Note that, except for the step a, the glass substrate 2
Is attached in close contact with a substrate holder made of, for example, SUS, and the substrate holder is brought into contact with a heating source such as a heater so that the entire glass substrate has a uniform temperature, and the metal fine particles 6 and the dielectric layer 4a are attached. Each film is formed.

Now, the incident light L having polarization components in the X and Y directions
1 is incident on the polarizer 1, the short axis direction (Y
Direction), more polarized light parallel to the major axis direction (X direction) is absorbed in a longer wavelength band than the polarized light parallel to the longer axis direction. Therefore, the outgoing light L2 becomes only polarized light parallel to the Y direction in a certain wavelength band. Acts as a child. The polarizer obtained by such a manufacturing method can be used for various optical components such as an optical isolator and an interferometer, and can be widely used in the field of optical communication.

As described above, by forming the heat transfer layer of silicon (Si) or the like on the lower surface of the glass substrate before forming the metal particle layer, the heat conductivity of silicon can be reduced during the formation of the metal particle layer. The heat of the glass substrate is homogenized, and a remarkable temperature distribution on the surface of the glass substrate is prevented as much as possible, so that the dispersion of the metal particles in the surface of the glass substrate can be made uniform, and the size of the metal particles can be made uniform. can do. In this method, it is possible to heat the glass substrate by radiation of an incandescent light bulb or the like, which was impossible in the past.However, in order to make the temperature more uniform, radiant heat is received by the substrate holder and the substrate is heated. Is preferred.

In addition, it is considered that the formed silicon may cause a loss due to a difference in refractive index from the glass substrate as it is, which may cause a problem in functioning as a polarizer. In a polarizer having a polarizing layer in which a metal particle layer in which metal particles having anisotropy are dispersed and a dielectric layer are alternately laminated on one surface side of a glass substrate having optical properties, for example, sputtering or the like is used. In the heat treatment process for removing the argon (Ar) gas trapped during the film formation by the thin film formation method of the above, it is oxidized and becomes transparent, for example, silicon oxide (SiO ₂ ).
There is no problem as a polarizer. However, the heat treatment temperature performed to desorb the Ar is 600
° C, which allows thermal oxidation and has a limit on the thickness of Si that contributes to heat transfer. As a result of intensive studies, the inventors have found that this optimum film thickness is 1 to 4000 mm (however,
When BK7 glass described later is used as the substrate, 200
0 ° was the upper limit), and it was found that the film thickness without impairing the polarization characteristics was 500-2000 °.

[0036]

EXAMPLE First, as a dielectric substrate, 76 mm × 10 m was used.
BK7 glass (SiO ₂ : 69) having a size of mx 1 mm
%, B ₂ O ₃ : 10%, Na ₂ O: 8%, K ₂ O: 8
%, BaO: 3% (however, composition is% by weight), softening point is 7%
24 ° C.).

On the lower surface (back surface) of these glass substrates, Si (thermal conductivity: 168 W / mK) is 500 °, 10 ° C.
Ten sheets each of five kinds were formed so as to have a film thickness of 00, 1500, 2000 and 2500 degrees. Next, a plurality of metal particle layers and dielectric layers were alternately laminated on the upper surfaces of these glass substrates. That is, FIG.
Steps (d) to (d) were repeated five times, and a metal particle layer made of Cu and a dielectric layer made of BK7 glass were alternately formed into five layers.

Ar is used as a sputtering gas.
The sputtering conditions for the metal particles were as follows: RF power 20 W, sputtering pressure 2.0 × 10 ⁻³ Torr, Ar gas flow rate 10 ccm,
To set the copper film thickness to 24 nm and grow copper particles,
Immediately after the film formation, heat treatment was performed at 500 ° C. for 60 minutes. Here, the copper film thickness is obtained by measuring the film thickness of a film formed for 20 minutes under the above sputtering conditions, calculating the film formation rate, and deriving the value from this value. Next, in order to embed the metal particles in the dielectric layer, the dielectric layer was formed with a thickness of 150 nm.

After the formation of the metal particle layer, the metal particle layer was annealed in a vacuum at about 500 ° C. by a heater heating method to cause aggregation, and the shape of the island-shaped metal particles was adjusted to a substantially spherical shape.
At this time, the number density of the metal particles was 5 to 10 particles / μm ² . The heating of the dielectric layer was not performed.

Thereafter, in order to desorb Ar gas trapped in the dielectric layer during sputtering, a heat treatment was performed at 600 ° C. for 50 hours. At this time, all of the Si film formed on the lower surface of the glass substrate was thermally oxidized into light-transmitting SiO _{2 in} the sample having a thickness of 2000 ° or less. However,
In the 2500 ° sample, Si remained at the interface between the BK7 substrate and SiO ₂ .

The above sample having a Si content of 2000 ° or less
The film was stretched at 25 ° C. with a stress of 45 kg / mm ² . The yield with an extinction ratio of 20 dB and an insertion loss of 0.05 dB is 20% at 500 °, 30% at 1000 °,
The result is 60% in the case of 1500 ° and 90% in the case of 2000 °. As the thickness of Si increases, the yield is improved.

However, in the sample in which Si was formed at 2500 °, reflection occurred at the interface between SiO ₂ and Si and the interface between BK7 and Si, and the extinction ratio was 20 dB and the insertion loss was 10 dB.
It became B.

[0043]

As described above in detail, according to the polarizer and the method of manufacturing the same of the present invention, the metal particle layer is formed on the upper surface of the glass substrate by forming the heat transfer layer on the lower surface of the glass substrate. The surface temperature of the glass substrate
This makes it possible to eliminate the distribution of metal particles in the surface of the glass substrate, and to provide a polarizing element having excellent characteristics with a high yield.

In particular, when a heat transfer layer made of silicon is provided on the lower surface of the glass substrate, it can be easily oxidized by a heat treatment step of the glass substrate, and can be made of a silicon oxide having a light transmitting property. An excellent polarizer that does not lose its characteristics without removing the silicon oxide can be provided very easily.

[Brief description of the drawings]

FIG. 1 is a perspective view illustrating an embodiment of a polarizer according to the present invention.

FIGS. 2A to 2G are schematic cross-sectional views illustrating steps of manufacturing a polarizer according to the present invention.

[Explanation of symbols]

 1: Polarizer 2: Glass substrate (dielectric substrate) 3: Polarizing layer 3a: Dielectric layer 4: Metal particle layer 4a: Metal particle 5: Heat transfer layer 6: Metal fine particle 7: Silicon oxide layer

Claims (4)

[Claims] 1. A light transmitting layer having a light transmitting property and a higher thermal conductivity than the dielectric substrate is provided on a lower surface of a dielectric substrate having a light transmitting property, and a light absorbing layer is provided on an upper surface of the dielectric substrate. A polarizer comprising a polarizing layer in which metal particle layers in which isotropic metal particles are dispersed and dielectric layers are alternately laminated in a multilayer. 2. A metal particle layer comprising a transparent silicon oxide layer formed on a lower surface of a glass substrate and metal particles having light absorption anisotropy dispersed on an upper surface of the glass substrate, and a dielectric layer. And a polarizer in which polarizing layers are alternately laminated. 3. Polarized light having a polarizing layer in which metal particle layers in which metal particles having light absorption anisotropy are dispersed and dielectric layers made of glass are alternately laminated on the upper surface of a glass substrate. In the method for manufacturing a polarizer, the polarizing layer repeats the steps A to B a plurality of times in the following step A, and then plastically deforms the glass substrate while heating the glass substrate. A method for producing a polarizer, comprising: A: A step of forming a silicon layer on the lower surface of a glass substrate by a thin film forming method. B: Step of depositing and forming metal fine particles on the upper surface of a glass substrate by a thin film forming method. C: a step of heating the glass substrate at a temperature lower than the softening point to grow the metal fine particles and form a metal particle layer. D: forming a dielectric layer on the metal particle layer by a thin film forming method. 4. The method according to claim 3, further comprising the step of heating the silicon layer to form a silicon oxide layer having a light-transmitting property.