JPH11344616A - Polarizer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polarizer which is reduced in optical anisotropy by double refraction, high in extinction ratio, is low in insertion loss, and excellent in reliability. SOLUTION: Dielectric layers 5, in which metallic particles 4a having optical absorption anisotropy are dispersed are disposed in >=1 layers on at least one main surface of a dielectric substrate 2 having translucency. The dielectric substrate 2 and the dielectric layers 5 are formed of material of <=3.1×10<-8> cm<2> /N in optical elasticity constant to the light wavelength to be transmitted. According to such polarizer, the setting of the material having an optimum modules of elasticity according to the magnitude of stresses is made possible, thereby, the optical anisotropy by the double refraction of the dielectric layers 5 is reduced and, therefore, the polarization characteristic of the element may be made better than heretofore even under severe environment conditions.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarizer in which at least one dielectric layer in which metal particles having light absorption anisotropy are dispersed is provided on a light-transmitting dielectric substrate. The present invention relates to a polarizer suitable for an optical isolator.

[0002]

BACKGROUND OF THE INVENTION Polarizers are used to extract light polarized in a particular direction, and various configurations of polarizers have been studied. For example, a Glan-Thompson prism combining birefringent crystals, a rutile crystal having a large birefringence, a polarizing film made by stretching a dichroic polymer material in the direction of polarization, a dielectric layer and a metal thin film layer Layered polarizer (Ramipole) formed by alternately laminating the metal, a metal-dispersed polarizer (polar core) in which silver colloid is precipitated in borosilicate glass and stretched in the polarization direction, and island-shaped metal particles are insulated. And an island-shaped metal thin-film polarizer which is alternately laminated with a body film, dispersed in a dielectric film, and stretched in the polarization direction.

These polarizers include sunglasses, liquid crystal display filters, photographic filters, ski goggles,
It is widely used in optical pickups, optical sensors, and optical isolators, in addition to automotive headlights and anti-glare filters for displays, etc. In recent years, it has been small, high-performance and inexpensive in various fields such as optical recording and optical communication. The need for polarizers is growing.

However, under external stress or thermal stress, optical anisotropy is induced by birefringence due to the photoelastic effect. As a result, there is a problem that the optical anisotropy due to the birefringence changes the polarization characteristics of light, making it difficult for the polarizer to obtain desired performance.

It is considered that these mechanical external stresses and thermal stresses are mainly generated under the following conditions. Mechanical external stress is mainly caused by the glass processing process (cutting, bonding with other materials, film formation on the surface, etc.) and the operation of incorporating glass into the optical system (holding with a jig, bonding, etc.) Occurs later. Also,
Thermal stress is generated by heat generated inside the glass (such as absorption of light energy) or heat generated outside (such as heat generated by peripheral devices). Further, when heat is generated, stress is also generated when glass and a material having different coefficients of thermal expansion are contact-joined.

Therefore, when a polarizing optical system is constituted by optical components, mechanical external stress or thermal stress acts substantially.
Inducing optical anisotropy due to birefringence was inevitable.

In order to obtain a desired polarization characteristic, a phase difference caused by optical anisotropy due to birefringence is reduced to 9.5 × 10 ⁻⁵ r.
It must be less than or equal to ad. When a light beam having a polarization component parallel to the stretching direction of the polarizer and a light beam having a polarization component orthogonal thereto are transmitted through a material exhibiting birefringence, each light beam becomes an ordinary ray and an anomaly orthogonal to the ordinary ray. Divided into rays.

The polarization direction of the ordinary ray does not always coincide with the stretching direction of the polarizer, and the polarization direction of the ray incident on the material is fixed to the polarization direction of the ordinary ray.
Insertion loss will increase. Similarly, the polarization direction of the extraordinary ray does not necessarily coincide with the direction orthogonal to the stretching direction of the polarizer, and the polarization direction of the ray incident on the material is fixed to the polarization direction of the extraordinary ray, so the extinction ratio deteriorates, Insertion loss will increase. When a stress of ² N / cm ² is applied to the polarizer, the photoelastic constant is 3.1 × 10 ⁻⁸ cm ² / N or less in order to reduce the phase difference to 9.5 × 10 ⁻⁵ rad or less.

Here, the photoelastic constant is 3.1 × 10 ⁻⁸ cm.
If it is larger than ² / N, optical anisotropy occurs due to birefringence, and desired characteristics cannot be obtained. Therefore, in the polarizer obtained by such a manufacturing method, more satisfactory quality and reliability have not been obtained even as a polarizer for an optical communication device.

Accordingly, an object of the present invention is to provide a highly reliable polarizer which reduces optical anisotropy due to birefringence, has a high extinction ratio, and has a low insertion loss.

[0011]

In order to solve such problems, the polarizer of the present invention has a light-absorbing anisotropy on at least one principal surface of a light-transmitting dielectric substrate. At least one dielectric layer in which metal particles are dispersed is provided, and the dielectric substrate and the dielectric layer are made of a material having a photoelastic constant of 3.1 × 10 ⁻⁸ cm ² / N or less with respect to a light wavelength to be transmitted. It is characterized by being formed.

Specifically, an island-like metal thin film layer is provided on a dielectric substrate such as glass by vacuum evaporation, and a dielectric layer such as glass is laminated thereon by a sputtering method or the like. Then, several island-like metal thin film layers and dielectric layers are alternately formed, and then the substrate is stretched under heating, so that the metal particles of the island-like metal thin film layer have anisotropy. Each metal particle in the island-shaped metal thin film layer is stretched in the stretching direction, becomes a spheroid, and has polarization performance. At this time, a dielectric having a photoelastic constant of 3.1 × 10 ⁻⁸ cm ² / N or less is used for the dielectric substrate and the dielectric layer. Preferably, 1.0 × 10 ⁻⁸ cm ² / N
The dielectric is in the range of up to 3.0 × 10 ⁻⁸ cm ² / N.

FIG. 2 is a graph showing the relationship between 1 and 1 at a light wavelength of 1.3 μm.
0N / cm^TwoOf photoelastic constant and extinction ratio for each stress of
It shows the relationship. Photoelastic constant is 3 × 10^-8cm
^Two/ N, the stress is 7 N / cm^TwoExtinction ratio 35 below
dB or more, stress is 2N / cm ^TwoBelow, the extinction ratio is 40 dB
As described above, the photoelastic constant is 1 × 10^-8cm^Two/ N
Has a stress of 6 N / cm^TwoWith an extinction ratio of 40 dB or more below
Become.

Therefore, at least a stress of 2 N / cm ²
It is preferable that the extinction ratio is 40 dB or more, the stress is 6 N / cm ² or less, and the extinction ratio is 35 dB or more. The smaller the difference in the photoelastic constant between the layers, the better. The above relationship seems to be the same when the wavelength of the transmitted light is 0.9 to 1.6 μm.

Here, a glass substrate is most suitable as the dielectric substrate having a light transmitting property, and the photoelastic constant is 3.1 × 10 ^-8.
When the density is not more than cm ² / N, the degree of optical anisotropy due to birefringence can be reduced, and the extinction ratio can be improved.

Further, the dielectric substrate and the dielectric layer are preferably made of, for example, borosilicate glass, quartz glass or the like. The metal particles are preferably made of a noble metal element such as Au, Ag, or Pt, or at least one of Cu, Fe, Ni, Cr, Al, and W.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. As shown in FIG.
Is provided with a polarizing layer 3 on at least one main surface of a dielectric substrate 2 having a light-transmitting property. Dispersed island-shaped metal thin film layer 4 and dielectric layer 5 having translucency
Are alternately laminated. 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 at least one of the metal particles 4a.
Is a density measured when cut along a plane including the major axis and parallel to the substrate surface S.

The substrate 2 has, for example, a photoelastic constant of 2.78 × 10
^Borosilicate glass such as ^-8 cm ² / N BK glass (BK is a trademark of Hoya-Shot Co., Ltd.) and Pyrex glass (Pyrex is a trademark of Corning Glass Industry) are used. May be used. Further, other transparent materials may be used in place of such a glass material, but a glass material is preferably 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, BK glass is also used for the dielectric layer 5, and characteristics such as thermal expansion coefficient and photoelastic constant are used. Are preferably matched.

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 thus easily aggregates and 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 spheroidal and anisotropic. In FIG. 1 (however, the traveling direction of light is defined as the Z direction, and a plane orthogonal to the Z direction is defined as the XY plane), the metal particles 4a are formed.
The major axis direction is the Y direction, and the minor axis direction is the X direction.

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. 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, and the rate of increase of 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 the polarizing layer 3 is suitably from 3 to 30, and particularly preferably from 15 to 2.
5

The extinction ratio is defined as the energy ratio between the transmitted light in the X direction and the transmitted light in the Y direction in decibels when unpolarized incident light at a predetermined wavelength is used. Is 10 dB when is 10. On the other hand, the insertion loss is defined as the ratio of the total energy of incident light to the energy of transmitted light in the Y direction in decibels when incident light that is not polarized at a predetermined wavelength is used. 0.1 at 0.1 dB.

The metal particles 4a in the island-shaped metal thin film layer 4
Is ² to 37 / μm ^{2 in the} substrate surface direction.
The reason for this is that if the number density is less than ² / μm ² , it becomes difficult to obtain the characteristics as a polarizer.
This is because it is lower than B, and when it exceeds 37 / μm ² , the absorption by the metal particles is large and the insertion loss increases more than 1 dB.

Further, the insertion loss is increased due to the metal particles getting too close to each other, or the extinction ratio is not obtained because the metal particles are too far from each other. For each layer, the metal particles after stretching a certain layer have the same anisotropy, and when the spacing between the metal particles is short, the absorption peak wavelength caused by the interaction between the particles is on the shorter wavelength side than when the spacing is long. Occurs. When the length of the metal particles 4a in the minor axis direction increases, the insertion loss with respect to the polarized light in the X direction to be transmitted increases.
As described above, more preferably 15 or more, the length in the short axis direction is short and the insertion loss is preferably reduced.

As the average length of the metal particles 4a in the major axis direction increases, the absorption peak wavelength in the Y direction increases, approaching the wavelength (about 1.3 μm) used in optical communication. However, there is a limitation in manufacturing the aspect ratio of the metal particles 4a, and taking into account that an increase in the length in the short axis direction causes insertion loss, the length in the long axis direction is also limited. Therefore, preferable conditions for the metal particles 4a are that the aspect ratio is 3 to 30, and the average value of the length in the long axis direction is 100 to 3
00 nm, the average value of the length in the minor axis direction is 10 to 50 nm, more preferably the aspect ratio is 10 to 30, and most preferably the aspect ratio is 15 to 25. In the case of FIG. 1, in the incident light L1 incident in the Z direction, the polarized component in the Y direction is absorbed by resonance with the free electrons of the metal particles 4a, the polarized component in the X direction has a high transmittance, and the polarized outgoing light L2 Becomes Further, there is a difference in absorption peak wavelength between the X direction and the Y direction, and there is an absorption peak on the longer wavelength side than the X direction in the Y direction. Unless otherwise specified, the extinction ratio is determined by the wavelength at which the absorption peak in the X direction occurs.

[0029]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the present invention will be described in detail below.

[0030] Example 1 a BK7 glass substrate of the optical elastic constant 2.78 × 10 ^-8 cm ² / N used as a support, the photoelastic constant as a dielectric layer on a substrate 2.78 × 10 ^-8 cm ² / A laminate of Cu-BK7 glass was formed by alternately laminating copper (Cu) thin film layers as metal layers with N BK7 glass thin film layers.

First, a degree of vacuum of 2.0 × 10 ⁻³ Torr was formed on a BK7 glass substrate by magnetron sputtering.
r, a Cu thin film layer as a first metal thin film layer having a thickness of 30 nm is formed at a film forming rate of 10.6 nm / sec, and a vacuum degree of 2.0 × 10 ⁻³ Torr is formed on the Cu layer. A BK7 glass thin film layer as a first dielectric thin film layer having a thickness of 150 nm was formed at a film forming rate of 0.2 nm / sec.

Thereafter, the second metal thin film layer Cu
A thin film layer is formed, and a second layer BK7 is formed on the Cu layer.
A glass thin film layer was formed. Repeat this series of steps,
A laminate composed of alternate layers of a Cu layer and a BK7 glass layer was produced.

The BK7 glass substrate was heated at a temperature of 630 ° C. in the vicinity of the softening point and stretched to impart anisotropy to the shape of the island-shaped metal particles, and at the same time, to orient the particles.
As a result, each Cu layer had anisotropic island particles, and polarization characteristics were obtained in a wavelength region near 1.3 μm. When the polarization characteristics were examined, the extinction ratio was 40 dB and the insertion loss was 0.1 dB.
Had sufficient properties.

Example 2 A fluorine-containing glass substrate having a photoelastic constant of 1.0 × 10 ⁻⁸ cm ² / N was used as a support, and a photoelastic constant of 1.0 × 10 ⁻ was formed as a dielectric layer on this substrate. ^{An 8} cm ² / N fluorine-added (0.001 to 0.005% by weight) glass thin film layer is used, a copper (Cu) thin film layer is used as a metal layer, and these layers are alternately laminated to add Cu-fluorine. A glass laminate was constructed.

First, a degree of vacuum of 2.0 × 10 ⁻³ Torr was formed on a fluorine-added glass substrate by magnetron sputtering.
r, forming a Cu thin film layer as a first metal thin film layer having a film thickness of 30 nm at a film forming rate of 7.6 nm / sec.
At the top of the layer, a fluorine-added glass thin film layer as a first dielectric thin film layer having a thickness of 100 nm was formed at a degree of vacuum of 2.0 × 10 ⁻³ Torr and a film formation rate of 0.2 nm / sec. This series of steps was repeated 10 times to produce a laminate composed of alternating layers of a Cu layer and a glass thin film layer.

The temperature is set at a temperature 80 near the softening point of the glass substrate.
The film was heated at 0 ° C. and stretched to give the anisotropic metal particles anisotropy and, at the same time, to orient the particles. As a result, the shape of the island particles in each layer became the same, polarization characteristics were obtained at a specific wavelength in the infrared region, and a polarizer having a high extinction ratio having an extinction ratio of 40 dB or more was obtained.

[0037]

According to the polarizer of the present invention, it is possible to set a material having an optimum photoelastic modulus according to the magnitude of the stress, and thereby, the optical anisotropy due to the birefringence of the dielectric layer can be obtained. , The polarization characteristics of the element can be improved even under severe environmental conditions.

Also, since this polarizer uses a thin film forming method, it is easy to miniaturize, has a high degree of freedom in design, and has excellent polarization which can design an optical system with higher accuracy and a wide range of application. Can provide children.

[Brief description of the drawings]

FIG. 1 is a schematic perspective view of a polarizer according to the present invention.

FIG. 2 is a graph illustrating a relationship between a stress and an extinction ratio.

[Explanation of symbols]

 1: Polarizer 2: Dielectric substrate 3: Polarizing layer 4: Island-like metal thin film layer 4a: Metal particle 5: Dielectric layer L1: Incident light L2: Outgoing light

Claims (1)

[Claims] A polarizer comprising at least one dielectric layer in which metal particles having light absorption anisotropy are disposed on at least one principal surface of a light-transmitting dielectric substrate, A polarizer, wherein the dielectric substrate and the dielectric layer are formed of a material having a photoelastic constant of 3.1 × 10 ⁻⁸ cm ² / N or less with respect to a wavelength of light to be transmitted.