JPH11344617A - Polarizer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an excellent polarizer in which metallic particles are liminated without diffusing them into glass films and which is consequently capable of stably embodying a polarization characteristic (more particularly extinction ratio). SOLUTION: This polarizer is constituted by providing at least one main surface of a dielectric substrate 2 having light-transmissibility with one layer or more of polarization layers 5 formed by dispersing the metallic particles having optical absorption anisotropy in glass contg. 3 to 20 atm.% alkaline metal elements in such a manner that the number density thereof attains 3 to 37 pieces/μm<2> . The unnecessary diffusion of the metallic particles into the glass layers may be prevented as far as possible by finding out the correlation between the alkaline metal in the glass layers and the diffusion of the metallic particles and a method for controlling the alkali metal quantity in the glass layers.

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 in particular, metal particles having light absorption anisotropy in a glass film laminated on a dielectric substrate. Is related to a large number of dispersed polarizers,
It is preferably used for an optical isolator.

[0002]

2. Description of the Related Art Hitherto, as a polarizer, an element utilizing colored ions, such as a cell containing a certain kind of solution in a cell or a plastic containing a coloring agent, and a large number of dielectric thin films laminated on a substrate A device 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 a polarization component using Brewster conditions, Alternatively, a polarizing film that orients a polymer material in a certain direction and absorbs a polarized component in one direction has been dominant.

However, a conventional polarizer using colored ions has a large wavelength dependence, and it is necessary to select a polarizer having an optimum wavelength characteristic for each wavelength. A polarizer having a large refractive index has a small wavelength dependence, but there is no compact polarizer with excellent wavelength characteristics.

For such various polarizers, polarizing glass has recently been used as an optical communication device. For example, transparent glass is used as a transparent solid medium, and elliptical silver particles are aligned in a certain direction and dispersed in the medium to give anisotropy (for example, Japanese Patent Publication No. 2-40619). reference).

[0005] This 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 having a required shape. Mold on the base. Next, the glass substrate is subjected to a heat treatment under predetermined conditions to precipitate silver halide grains in the glass.

Further, the glass base is stretched by applying a tension in a predetermined temperature range, so that the silver halide grains are elongated and aligned in the tension direction. Finally, the polarizer can be obtained by exposing the stretched glass substrate to a reducing atmosphere within a predetermined temperature range to reduce a part of the silver halide to metal silver particles.

[0007]

However, in these production methods, the former method involves heat treatment in a reducing atmosphere in order to precipitate metallic silver from silver halide.
As a result, it is difficult to control the amount of metallic silver precipitated in the glass substrate, and stable optical characteristics cannot be obtained. Therefore, even if the glass substrate is heated and stretched, it is difficult to stably obtain reproducible polarization characteristics.

In addition, there is a problem that the presence of a temperature distribution in the thickness direction in the glass substrate causes silver halide not reduced to metallic silver to remain in the center, 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, and there is a problem in long-term reliability. there were. Therefore, a discontinuous island-like metal particle layer and a dielectric layer such as glass are alternately formed on a dielectric substrate such as glass by using a thin film manufacturing process such as vacuum evaporation, and the anisotropy is formed by heating and stretching. A proposal has been made to make it available (for example, see the Proceedings of the IEICE Autumn National Convention 1990, 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.

However, in this method, it is difficult to stably obtain a polarization characteristic, and particularly, it is difficult to obtain an extinction ratio at a desired wavelength.

As a result of extensive studies by the present inventors on this process, it was confirmed that copper particles diffused into the glass film during the lamination, which affected the inability to stably obtain polarization characteristics. Was. Specifically, the island-shaped metal particles refer to an aggregate of metal atoms of about 10 nm to about 80 nm in which metal atoms are aggregated. When diffusion occurs, the size of the island-shaped metal particles is reduced, and as a result, A phenomenon occurs in which copper particles large enough to be stretched cannot be obtained, and an extinction ratio cannot be obtained with desired characteristics. Even if diffusion occurs by enlarging the copper particles immediately after film formation,
Although it is possible to obtain an extinction ratio of a desired size, it is not possible to produce a product in an industrially stable manner due to the unstable state. Furthermore, the diffusion of copper particles in the glass film is caused by the refraction of the glass film. Since the rate is also changed, problems such as changing the specification of the antireflection film each time occur.

Accordingly, an object of the present invention is to provide an excellent polarizer that can stack metal particles without diffusing into a glass film and, as a result, stably realize polarization characteristics (in particular, extinction ratio). I do.

[0013]

In order to solve the above-mentioned problems, a polarizer of the present invention contains an alkali metal element in an amount of 3 to 20 atomic% on at least one principal surface of a light-transmitting dielectric substrate. And at least one polarizing layer in which metal particles having light absorption anisotropy are dispersed in a glass to have a number density of 3 to 37 particles / μm ² .

The present inventors first analyzed the compositions of the glass layers of the sample in which the diffusion of the metal particles occurred and the sample in which the diffusion did not occur by XPS (X-ray photoelectron spectroscopy).
As a result, it was confirmed that there was a difference in the alkali metal content between the two. In particular, the content of Na was greatly different, and the sample in which diffusion occurred had a very low Na content of 1% or less.

The correlation between the content of alkali metals such as Na and the diffusion will be described below.

As shown in FIG. 3 which shows the structure of quartz,
O atoms are correctly aligned at the positions corresponding to the vertices of the tetrahedron, centering on the Si atoms. For example, when an alkali metal such as Na is added to the portion, as shown in FIG. 4, modified ions or the like of the alkali metal enter the network structure to form an alkali borosilicate glass or the like. In this case, the alkali metal such as Na cuts the oxygen bridge (oxygen when the tetrahedron of SiO ₄ is connected by sharing one oxygen) and is electrostatically bonded to one oxygen bridge. Here, oxygen that is electrostatically bonded to the modifying ion is referred to as non-bridging oxygen. That is,
When other metals enter the network structure, it is considered that the site is open.

Therefore, a glass layer having a low content of an alkali metal such as Na has a high probability of diffusing Cu. Since the metal particles are supplied from the island-shaped metal particle layer, the size of the metal particles gradually decreases as the diffusion proceeds. Although Cu is divalent, it is considered that Cu enters in the form of ions such as CuO.

The result of further study on the above phenomenon will be described.

The change in the amount of light absorbed by the metal particle layer after the formation of the metal layer and the formation of the glass layer (polarizing layer),
It measured about alkali metal content, such as a. As a result, when the alkali metal such as Na in the glass layer is less than 3%,
The amount of light absorbed by the metal particle layer after the formation of the metal particle layer and after the formation of the glass layer sharply decreased.

Table 1 shows the results obtained by examining the particle size of the particles using a TEM (transmission electron microscope).

[0021]

[Table 1]

As is evident from Table 1, it is confirmed that the particle size decreases as the absorption amount decreases. In the case of diffusion, the absolute amount of copper particles does not change. However, when the order is such that the metal particles are diffused, there is no light absorbing property, so the above phenomenon is explained. In addition,
FIG. 5 shows the results of graphing Table 1.

According to the present invention, it has become possible to prevent metal particles from diffusing into the glass layer during the formation of the glass layer. As a result, it was possible to keep the size of the particles before stretching constant, and to stably obtain an extinction ratio at a desired wavelength. Further, since the refractive index itself of the glass layer changes due to diffusion, even if an extinction ratio can be obtained, it is necessary to change the specification of the antireflection film.

However, in the present invention, since the refractive index of the glass layer is stabilized, the specifications of the antireflection film can be kept constant. As a result, it has become possible to supply an industrially stable polarizer.

Here, the method of intentionally controlling the amount of an alkali metal such as Na is controlled by film forming conditions such as a temperature at the time of forming a glass layer, and the alkali metal such as Na is intentionally used as a target material. For example, there is a method of selecting a target material and a substrate material, a simultaneous sputtering for forming a film while doping with Na or the like, and a method of controlling by a film forming method such as a simultaneous vapor deposition.

[0026]

Embodiments of the present invention will be described below in detail with reference to the drawings. As shown in FIG. 1, a polarizer 1 is provided with a polarizer 3 on at least one main surface of a dielectric substrate 2 such as glass which is a light-transmitting substrate. A metal particle layer 4 which is to be an island-shaped metal thin film layer in which a large number of metal particles 4a having shape anisotropy are dispersed on a dielectric substrate 2 and a glass layer (polarizing layer) 5 having translucency are alternately formed. Are laminated.

The metal particles 4a are spheroidal and anisotropic. In FIG. 1 (however, the light traveling direction is the Z-axis direction, and the plane perpendicular to this is the XY plane) 4a
Is the X direction, and the short axis direction is the Y direction. In addition, the ratio of the length in the major axis direction to the length in the minor axis direction of the metal particles 4a is defined as an aspect ratio.
Is simply referred to as the aspect ratio.

When the incident light L1 is incident on this element,
When the size of the metal particles 4a is sufficiently smaller than the wavelength of light, light of a certain wavelength is absorbed. As shown in FIG. 1, when the metal particles 4a have a shape anisotropy, the amount of absorption and the wavelength of absorption differ between the polarized light in the X direction and the polarized light in the Y direction. With a large absorption in the obi,
When viewed at a certain wavelength (polarized light in the Y direction has a small absorption in a short wavelength band), the outgoing light L2 has a difference in transmittance depending on the polarization direction, and acts as the polarizer 1.

Here, the difference between the transmittances is represented by the extinction ratio,
The transmittance of polarized light in the Y direction is called insertion loss.

In such a polarizer 1, the number density (distribution density) of metal particles existing in the same glass layer 4 is 3 to 37 / particle.
μm ² is preferred. This was determined from the point where the insertion loss per extinction ratio was lowest. Note that the glass layer 5 may be a single layer or more layers as long as good polarization characteristics can be obtained. Here, the number density (distribution density) of the metal particles is the density of each layer in the direction of the substrate surface S,
This is the density measured when cutting along a plane including the major axis of at least one metal particle 4a and parallel to the substrate surface S.

The reason why the metal particles 4a become spheroidal is that after the polarizing layer 3 is formed on the substrate 2, the metal particles 4a are stretched or extruded in the extrusion direction together with the substrate 2 by a method such as stretching or extrusion. Because it is The aspect ratio greatly contributes to the wavelength characteristic of the extinction ratio, and 3 to 30 is appropriate for operating at 1310 nm used in optical communication.

The manufacture of the polarizer 1 was performed as follows. First, the substrate 2 has an alkali metal content of 3 atomic% or more and less than 20 atomic%,
One having an internal transmittance of 0.975 or more at m is used. Here, the internal transmittance is a transmittance when a glass having a thickness of 25 mm is used. Also, the upper limit of the alkali content is, when it exceeds 20%, the optical transmittance becomes lower (less than 0.975), the insertion loss increases, and the glass transition temperature decreases, Particle 4a
Is determined from the fact that no stress can be applied to the metal particles 4a at the temperature for stretching.

As an example of the above glass, BK7 (SiO
_{2: 68.9%, B 2 O} 3: 10.1%, Na 2 O:
_{8.8%, K 2 O: 8.4} %, BaO: 2.8%, As
₂ O ₃ : 1.0%), BK1 (SiO ₂ : 71.4%,
B ₂ O ₃ : 6.5%, Na ₂ O: 5.2%, K ₂ O: 1
3.9%, CaO: 2.0%, As 2 O 3: 1.0
%), Pyrex glass (SiO ₂ : 80.8%, A
l ₂ O ₃ : 2.3%, Fe ₂ O ₃ : 0.03% B ₂ O
₃ : 12.5, Na ₂ O: 4.0%, K ₂ O: 0.4
%) Is preferred. Note that the above composition is% by weight.

Next, the metal particle layer 4a is formed using a sputtering device (preferably a multi-source sputtering device). Next, heat treatment is performed at a temperature equal to or lower than the transition point of the glass substrate so that the formed metal particles 4a have a desired size. Examples of the metal include Ag, Cu, and Fe.
Use seeds. Next, a glass layer 4 is formed using a multi-source sputtering apparatus. The material of the glass layer 5 is BK7, BK1 (trade name of Hoya Corporation), Pyrex glass (trade name of Corning), etc. Borosilicate glass is preferred. This is because if the material of the substrate 2 and the material of the glass layer 4 are different, a film stress occurs due to a difference in thermal expansion coefficient,
As a result, separation occurs between the glass layers, and the metal particles cannot be given anisotropy. In addition, the glass layer 5
Is a method of controlling the alkali metal content of the glass layer 5 at the time of forming the glass layer 5 (preferably 150 to 20).
0 ° C., more preferably 150 to 180 ° C., too high temperature will decrease the content of alkali metal element), control of film formation conditions, selection of target material, simultaneous sputtering for film formation while doping with Na or the like And control by a film forming method such as simultaneous vapor deposition. Further, the optimum thickness of the glass layer 5 is about 150 nm for each layer, preferably 50 to 300 nm for each layer, and 3 μm in total.
m or less. If the total exceeds 3 μm, problems such as peeling occur, which is not preferable. After that, the metal particle layer 4 and the glass layer 5 are repeatedly laminated by a predetermined number so as to obtain a desired extinction ratio. Further, in order to drive out a sputtering gas (eg, Ar) trapped during film formation, the temperature is set to 300 ° C. or more. And below the glass transition point (eg, 58
(0 ° C. or less). Accordingly, the amount of Ar is preferably 1.0 × 10 ¹⁹ molecules / cm ³ or less.

Further, the vicinity of the softening point of the substrate (for example, 620
C.), the metal particles are made anisotropic by stretching while heating at a desired temperature, and desired polarization characteristics are obtained.

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.

[0037]

EXPERIMENTAL EXAMPLE In order to investigate a method for controlling the amount of alkali metal in a glass layer, 150 ° C., 200 ° C.
A glass layer was formed at each temperature of 50 ° C., and it was examined whether the amount of an alkali metal such as Na can be controlled by the temperature at the time of film formation. As a method for analyzing the alkali metal content, XPS (X-ray photoelectron spectroscopy) is used.
Was used. The substrate used was 10 mm square. A multi-source magnetron sputtering apparatus was used as a film forming apparatus, and BK7 glass (O: 5) was used as a target.
9.8%, Si: 22.0%, B: 6.4%, Na:
5.6%, K: 5.2%, Ba <1%). Further, Ar was used as a sputtering gas. Glass sputtering conditions were as follows: RF power 200 W, sputtering pressure 2.0 × 10 ⁻³ Torr, Ar gas flow rate 10 ccm,
The film thickness was set to 150 nm.

As the analyzer, Quantum 2000 manufactured by ULVAC-PHP was used. The X-ray source is mono-chro-Ar-Kα ray (100
μm, 20 W, 15 KV). The measurement range is 500 μm □.

[0039]

[Table 2]

As a result, as shown in Table 2, the amount of Na was 4% at 150 ° C., 1% at 200 ° C., and 1% at 250 ° C. (At
om%), the amount of K is 2% at 150 ° C, 1% at 200 ° C,
At 250 ° C, 1% (Atom%)
A downward trend was observed. Depending on the substrate temperature during glass deposition,
It has been discovered that it is possible to control the amount of an alkali metal such as Na in the glass layer.

Example 7 A polarizer was manufactured using BK7 glass of 76 mm × 10 mm × 1 mm as a substrate and a target. As a device for forming the metal particle layer 4 and the glass layer 5, a multi-source magnetron sputtering device was used, and as a target, copper forming the metal particle layer 4 and BK7 glass forming the glass layer 5 in FIG. Further, the sputtering gas includes Ar
Was used. Copper sputtering conditions were RF power 20W,
Sputtering pressure 2.0 × 10 ^-3 Torr, Ar gas flow rate 10c
Immediately after the film formation, a heat treatment was performed at 500 ° C. for 60 minutes in order to grow copper particles.

Here, the copper film thickness is obtained by measuring the film thickness of a film formed for 20 minutes under the above-mentioned sputtering conditions, calculating the film forming speed, and deriving from this value.

Next, in order to embed the copper particles in the glass,
BK7 glass, the same as the substrate material, was placed on the copper particles produced under the above conditions, and the alkali metal content in the glass layer was 3%.
%, The substrate temperature at the time of forming the glass was 150 ° C., and 150 nm was formed. Further, the above process was repeated 10 times, and after laminating 10 glass layers 4, a heat treatment was performed at 580 ° C. for 50 hours in order to remove Ar gas trapped during sputtering.

Thereafter, the sample was weighed at 625 ° C. for 45 kg.
The film was stretched 50 mm with a stress of / mm ² . As a result, it was possible to realize an extinction ratio of 40 dB as a polarization characteristic at a wavelength of 1310 nm. At this time, the number density of the copper particles was 23 / μm ² , the aspect ratio was 1:10, and the total thickness of the glass layer was 500 nm.

[0045]

According to the present invention, the correlation between the alkali metal in the glass layer and the diffusion of the metal particles, and a method for controlling the amount of the alkali metal in the glass layer have been found. Unnecessary diffusion can be prevented as much as possible.

As a result, it is possible to keep the size of the particles before stretching constant, and to stably maintain the desired wavelength at a desired wavelength.
A polarizer with an excellent extinction ratio can be obtained.In addition, the change in the refractive index of the glass layer due to the diffusion of metal particles can be suppressed, and the specifications of the antireflection film formed in a later process can be kept constant. Therefore, it is possible to always supply an industrially extremely stable polarizer.

[Brief description of the drawings]

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

FIG. 2 is a cross-sectional view of the polarizer of FIG. 1 taken along line AA.

FIG. 3 is a structural diagram showing an atomic arrangement of quartz in a plan view.

FIG. 4 is a structural diagram showing an atomic arrangement of general glass in a plan view.

FIG. 5 is a graph illustrating characteristics after forming a metal particle layer and after forming a glass layer.

[Explanation of symbols]

 1: Polarizer 2: Dielectric substrate 3: Polarizing layer 4: Metal particle layer 4a: Metal particle 5: Dielectric layer (polarizing layer) L1: Incident light L2: Outgoing light

Claims (1)

[Claims] 1. A glass substrate containing 3 to 20 atomic% of an alkali metal element having metal particles having a light absorption anisotropy having a number density of at least 3 on at least one principal surface of a light-transmitting dielectric substrate. A polarizer comprising one or more polarizing layers dispersed so as to have a thickness of 37 / μm ² .