JPH1123841A - Polarizer and optical isolator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polarizer small in wavelength dependency, suitable for miniaturization and excellent in optical characteristics such as insertion loss by specifying the interval between layers of a metallic particle and the distribution density of the metallic particles existing on the same layer. SOLUTION: This polarizer is provided with a transparent substrate 2 consisting of transparent material such as glass, etc., a transparent dielectric layer (polarization layer) 3 consisting of the transparent material such as glass diffusing the metallic particles 4a onto plural layers, a layer of transparent dielectric layer 3a and a diffused metallic particle part 4 diffusing a piece of metallic particle 4a of a rotary elliptic body shape. Then, the gap of the metallic particle 4a, that is, the thickness of a layer of transparent dielectric layer 3a is made 50 nm or above, preferably 100 nm or above, and the distribution density of the metallic particles 4a existing on the same layer in the diffused metallic particle part 4 is made 3-37 pieces/μm<2> . This distribution density is measured so that the diffused metallic particle part 4 is cut off by a plane containing the major axis of at least a piece of metallic particle 4a and parallel to the diffused metallic particle part 4, and the number of pieces of the metallic particles 4a in its surface are counted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to an optical communication system,
The present invention relates to a polarizer and an optical isolator used for an optical recording / reproducing device, an optical sensor application device, and the like.

[0002]

2. Description of the Related Art Conventional polarizers include the following (1) to (5).
There was something like (5).

(1) A cell in which a solution in which a coloring agent is dissolved is placed in a cell, or a coloring agent is mixed in a transparent plastic, and has anisotropy in light absorption.

(2) A large number of dielectric thin films are laminated on a substrate made of a transparent crystal having a large birefringence, and either an ordinary ray or an extraordinary ray having a different polarization direction is generated by the multilayer interference effect of the dielectric thin film. Absorb or transmit efficiently,
Polarizing prism such as Glan-Thompson prism.

(3) By utilizing the Brewster angle condition on the surface of a substrate made of a transparent crystal having a large birefringence,
A polarization beam splitter that separates polarization components having polarization directions different by 90 °.

(4) A polymer material is oriented in a certain direction in a transparent film, and a polarization component in a specific direction is absorbed or absorbed by utilizing anisotropy of light absorptivity and anisotropy of refractive index of the polymer. A polarizing film that transmits light.

(5) By dispersing metal particles such as spheroidal silver particles in a transparent solid medium made of transparent glass with their major axis or minor axis aligned in a specific direction, light absorption is improved. One having anisotropy (see Japanese Patent Publication No. 2-40619).

[0008]

However, (1)
Those using colored ions such as described above have a large wavelength dependence, and it is necessary to select a colored ion exhibiting optimal light absorption for each wavelength. In the case of using a crystal having a large birefringence as in (2) and (3), although the wavelength dependence is small, it is difficult to process the crystal, so that the size of the polarizer is limited and it is difficult to reduce the size. There was a problem. It is difficult for a film utilizing the orientation of a polymer in a film as in (4) to achieve uniform orientation in a specific direction, and it is difficult to obtain a large extinction ratio when compared with a birefringent crystal even if the orientation is good. There's a problem.

The type (5) in which spheroidal metal particles are dispersed in a transparent solid medium has a small wavelength dependence and is suitable for miniaturization, but the dispersion state of the metal particles is as follows. Therefore, it was difficult to realize an insertion loss of 0.3 dB or less required for a polarizer and a sufficient insertion loss of 0.1 dB or less for communication.

The polarizer (5) is manufactured by the following steps (a) to (d).

(A) A glass batch composed of silver and a halide (chloride, bromide, iodide, etc.) is melted and formed into a shape such as a glass substrate.

(B) Heat treatment is performed at a predetermined temperature or the like to precipitate silver halide grains in the glass.

(C) The glass substrate is stretched by applying tension while being heated to a predetermined temperature, thereby extending the silver halide grains and aligning them in the direction of the tension.

(D) The glass substrate is exposed to a reducing atmosphere while being heated to a predetermined temperature, and a part of the silver halide is reduced to metallic silver.

However, in the above-described production method, heat treatment is performed in a reducing atmosphere in order to reduce silver halide to metallic silver, but it is difficult to accurately control the amount of metallic silver in the glass by this method. Therefore, desired optical characteristics such as stable insertion loss could not be obtained.
In addition, temperature distribution tends to occur in the thickness direction of the glass during the heat treatment, and silver halide that has not been metallized remains at the center in the thickness direction, which reduces the light transmittance. Furthermore,
When reduced, silver halide grains undergo volume shrinkage of about 1/3, so that the glass surface after reduction becomes porous and causes problems such as reduced light transmittance and cracks in terms of reliability. was there.

Therefore, a discontinuous island-shaped metal layer and a dielectric layer made of glass or the like are alternately laminated on a substrate made of glass or the like by a vacuum evaporation method or the like. The one with the property added has been proposed (see the IEICE Fall 1990 National Convention C-212). In this polarizer, each island of the metal layer acts as a metal particle,
The configuration is the same as that in which the metal particles are dispersed. However, the above-described manufacturing method has a problem that it is difficult to control the dispersion state of each island of the metal layer.

It is considered that the distribution density of the metal particles in the plane of the dispersed metal particles, and particularly the spacing in the thickness direction of the dispersed metal particles, greatly affects the insertion loss. No examples were mentioned.

Accordingly, the present invention has been completed in view of the above circumstances, and an object of the present invention is to provide a polarizer which has a small wavelength dependence and is suitable for miniaturization, and has excellent optical characteristics such as insertion loss. It is in.

[0019]

The polarizer of the present invention has a transparent dielectric layer in which metal particles having light absorption anisotropy are dispersed in a plurality of layers on at least one principal surface of a transparent substrate. A polarizer, wherein the distance between the layers of the metal particles is 50.
nm or more, and the distribution density of the metal particles present in the same layer is 3 to 37 particles / μm ² ,
By specifying the thickness of the transparent dielectric layer, that is, the interval in the thickness direction of the dispersed metal particles, and the distribution density of the metal particles, optical characteristics such as insertion loss can be improved.

Preferably, the thickness of the transparent dielectric layer is 1
00 nm or more, and the distribution density is 5 to 33 / μm.
²

Further, the optical isolator of the present invention is characterized in that the polarizer of the present invention is disposed on the light incident side and / or the light output side of the Faraday rotator, and is excellent in insertion loss, extinction ratio and the like. It will be.

[0022]

FIG. 1 is a perspective view of a polarizer 1 of the present invention.
Shown in In the figure, reference numeral 2 denotes a transparent substrate made of a transparent material such as glass, and 3 denotes a transparent dielectric layer (polarizing layer) made of a transparent material such as glass in which metal particles 4a are dispersed in a plurality of layers. The transparent dielectric layer 4 is a dispersed metal particle portion in which one spheroidal metal particle 4a is dispersed, in other words, one layered portion in which the metal particles 4a are formed intermittently in the in-plane direction. It is.

The metal particles 4a are made of Cu, Au, Ag,
Pt, Rh, Ir, Fe, Ni, Cr and the like are preferable, and these have good light absorption. Then, the dispersed metal particle portions 4 and the transparent dielectric layer 3a are formed by a thin film forming method such as a sputtering method. Further, the transparent dielectric layer 3
An antireflection film or the like made of a dielectric multilayer interference film may be further formed thereon, and the transparent dielectric layer 3 may be provided on both surfaces of the transparent substrate 2.

In the present invention, the transparent substrate 2 is specifically made of SiO ₂ , B ₂ O ₃ , Na ₂ O, K ₂ O, BaO,
BK7 glass (trade name, manufactured by Hoya Glass Co., Ltd.), Pyrex glass (trade name, manufactured by Corning Glass Works Co., Ltd.), quartz glass, and the like containing As ₂ O ₃ or the like as a main component are preferable. The transparent dielectric layer 3a is preferably made of the same material as the transparent substrate 2. If the material is different, a film stress occurs due to a difference in thermal expansion coefficient. As a result, the transparent substrate 2 and the transparent dielectric layer 3 The metal particles 4a cannot be provided with light absorption anisotropy.

The distance between the metal particles 4a, that is, the thickness of one transparent dielectric layer 3a is 50 nm or more, preferably 100 nm or more, for the following reasons. In addition, the above-mentioned thickness is after the stretching, and is about three times the thickness before the stretching.

In order to control the distribution of the metal particles 4a in the same layered portion of the dispersed metal particle portion 4, it is necessary to increase the thickness of the transparent dielectric layer 3a. Then, the sputter gas such as Ar contained in the transparent dielectric layer 3a expands, and bubbles are generated at the lamination interface. When the stretching is further performed, the bubbles are torn, and cracks are generated on the surface of the outermost transparent dielectric layer 3a. Conventionally, in order to cope with such a phenomenon, degassing is performed by performing a heat treatment in a temperature range of 300 ° C. or more and a glass transition point (about 580 ° C.) or less,
Although the generation of cracks was suppressed, degassing was impossible if the thickness of the transparent dielectric layer 3a was 150 nm or more before stretching.

Therefore, by performing a heat treatment every time the transparent dielectric layer 3a is formed in the sputtering apparatus, it is possible to increase the thickness of the transparent dielectric layer 3a to 150 nm or more before stretching. When it is 150 nm or more, it becomes about 50 nm after stretching, and it is found that degassing is possible and the insertion loss becomes 0.3 dB or less, and when the film is further thickened, it becomes 0.1 dB or less. In addition, as described above, the polarizer 1 of the present invention has a glass transition point (about 5
Degassing is better in the temperature range below 80 ° C).
This is because the sputter gas starts to be emitted at around 300 ° C., is emitted more at 400 ° C. or higher, and near the glass transition point, the viscosity of the glass increases and the air permeability deteriorates.

The upper limit of the thickness of the transparent dielectric layer 3a is not particularly limited. However, if the thickness is too large, the time required for degassing by heating will be long, and the effect of improving the insertion loss will level off. , Preferably 200 nm or less.

Further, according to the present invention, the distribution density of the metal particles 4a existing in the same
Is intended to -37 pieces / [mu] m ^2, the extinction ratio is less than 3 / [mu] m ² degrades less than 20 dB, the insertion loss exceeds 0.3dB at 37 / [mu] m ² greater. More preferably,
5 to 33 pieces / μm ² . Here, the distribution density is
By cutting the dispersed metal particle portion 4 along a plane including the major axis of at least one metal particle 4a and parallel to the dispersed metal particle portion 4, counting the number of metal particles 4a in the plane , Can be measured.

Furthermore, the aspect ratio (major axis / minor axis ratio) of the spheroidal metal particles 4a is preferably 3 to 30, and in this case, the desired extinction ratio (2 at light wavelengths of 1310 nm and 1550 nm) is preferable.
0 dB or more), more preferably 15 to 20.

Further, in the transparent dielectric layer 3 of the present invention,
5 sets of the dispersed metal particle portion 4 and the transparent dielectric layer 3a
It is preferable to stack 0 sets, and if less than 5 sets, the extinction ratio is 20 dB.
When the number exceeds 20, the insertion loss tends to increase.
When used for an optical isolator, the extinction ratio is preferably 40 dB or more, and in that case, 10 to 20 sets are preferable.

The polarizer 1 of the present invention functions as shown in FIG. The major axis direction of the spheroidal metal particles 4a is assumed to be an x direction, the minor axis direction of the metal particles 4a is assumed to be a y direction, and the light incident direction is assumed to be a z direction. When the light L1 is incident on the polarizer 1, a large amount of polarized light parallel to the long axis direction (x direction) of the metal particles 4a is absorbed in the long wavelength band, so that the outgoing light L2 is parallel to the y direction in a certain wavelength band. It becomes only polarized light and acts as a polarizer.

The polarizer 1 of the present invention can be applied to an optical isolator when used with a Faraday rotator. In this case, Y is placed in a cylindrical holder made of a Ni—Fe alloy or the like.
IG (yttrium iron garnet: 3Y ₂ O ₃ .5Fe
_A disk-shaped Faraday rotator made of ₂ O ₃ ) or the like is provided, and the polarizer 1 of the present invention is arranged on the light incident side and / or the light emission side of the Faraday rotator. Around the Faraday rotator in the holder, a permanent magnet, an electromagnet, and the like for rotating the polarization direction by a magnetic field are provided.

The function of the case where the polarizer 1 of the present invention is arranged on, for example, the light incident side and the light output side of the Faraday rotator will be described. The polarizer A on the light incident side and the polarizer B on the light output side are set so that the polarization directions are different by 45 °, and the direction of change of the polarization direction by the Faraday rotator is changed from the polarization direction A of the polarizer A to the polarizer B. The optical isolator is configured to change by 45 ° toward the polarization direction B.

The light of random polarization incident on the optical isolator is converted into light in one direction of polarization A by the polarizer A, the direction of polarization is changed by 45 ° by the Faraday rotator, and becomes light in the direction of polarization B. The light passes through the child B as it is and is emitted. The light of random polarization returned from the emission side is polarized by the polarizer B so that the polarization direction A and the polarization direction are 45 degrees.
The light becomes a light having a polarization direction B different from that of the light, and further, the polarization direction is changed by 45 ° by the Faraday rotator, and the light becomes a light having a polarization direction different from the polarization direction A by 90 °, and cannot pass through the polarizer A. Therefore, it functions as an optical isolator.

Since such an optical isolator incorporates the polarizer 1 of the present invention, it has excellent optical characteristics such as insertion loss and extinction ratio.

Thus, the present invention has the effect of having a small wavelength dependence, that is, it can be used as a polarizer in a relatively wide band, is suitable for miniaturization, and has excellent optical characteristics such as insertion loss and extinction ratio. Have.

Further, a method for producing the polarizer 1 of the present invention by the following steps (1) to (6) will be described below.

(1) A transparent substrate 2 such as BK7 glass is prepared, and a dispersed metal particle portion 4 in which metal particles 4a are distributed in an island shape on one main surface thereof is formed by a sputtering method or a multi-source sputtering method. At this time, the film formation time is set to a short time of about 5 minutes to stop film formation before a complete film is formed, and when the film is formed while the transparent substrate 2 is heated to about 500 ° C., the metal particles 4a Are distributed in an island shape, and the planar shape of the island-shaped metal particles 4a is substantially circular.

(2) In order to grow the metal particles 4a to a desired size in the dispersed metal particle part 4, the transparent substrate 2 is subjected to a heat treatment at a temperature lower than the glass transition point.

(3) A transparent dielectric layer 3a of the same material as the transparent substrate 2 is formed by a multi-source sputtering method.

(4) Heating to a temperature of 300 ° C. to the glass transition point or lower, a degassing process of a sputtering gas such as Ar mixed in the transparent dielectric layer 3a is performed.

(5) The formation of the dispersed metal particles 4 and the transparent dielectric layer 3a and the heat treatment of (2) and (4) are repeated a plurality of times until the desired extinction ratio and insertion loss are obtained. The layer 3 is formed.

(6) The entire transparent substrate 2 is stretched in a specific direction while being heated, and the island-shaped metal particles 4a are formed into a spheroidal shape, thereby completing the polarizer 1.

It should be noted that the present invention is not limited to the above embodiment, and various changes may be made without departing from the scope of the present invention.

[0046]

Embodiments of the present invention will be described below.

(Example) The polarizer 1 of FIG. 1 was manufactured by the following steps (1) to (6).

(1) 76 mm × 10 mm on the transparent substrate 2
BK7 glass of × 1 mm, a multi-source magnetron sputtering device as a film forming device, Ar as a sputtering gas, and copper and transparent dielectric layer 3 forming dispersed metal particle portions 4 as targets.
The BK7 glass constituting a was used. The sputtering conditions were RF power of 20 W and sputtering pressure of 2.0 × 10 ⁻³ to.
The flow rate of rr and Ar gas was 10 ccm, the film formation time was about 5 minutes, and the transparent substrate 2 was heated to about 500 ° C., and the dispersion metal particles 4 were set to have a thickness of 24 nm and sputtering was performed.

Here, the thickness of the dispersed metal particle portion 4 was derived by measuring the film thickness of a film formed separately for 20 minutes under the above sputtering conditions, calculating the film forming speed, and using the calculated value as a reference.

(2) In order to grow the metal particles 4 a made of copper, immediately after forming the dispersed metal particle portions 4,
A heat treatment for 0 minutes was performed.

(3) In order to embed the metal particles 4a in the transparent dielectric layer 3a, the same BK7 glass as the material of the transparent substrate 2 is sputtered on the dispersed metal particle portions 4 by 90 nm, 120 nm, 150 nm, 300 nm and 300 nm, respectively. 45
Seven samples with 0 nm, 600 nm, and 750 nm were formed.

(4) Heat treatment at 580 ° C. for 1 hour
r was degassed.

(5) The steps (1) to (4) were repeated five times to form a transparent dielectric layer 3 in which five sets of the dispersed metal particle portion 4 and the transparent dielectric layer 3a were laminated.

(6) Each sample was stretched 50 mm in one direction at 625 ° C. with a stress of 45 kg / mm ² , and the metal particles 4a were formed into a spheroidal shape having an aspect ratio of about 20, and The thickness of the transparent dielectric layer 3a is 30n
m, 40 nm, 50 nm, 100 nm, 150 nm, 2
Seven polarizers 1 of 00 nm and 250 nm were produced. In each of these polarizers 1, the distribution density of the metal particles 4a was 20 particles / μm ² .

No crack was generated on the surface of the seven polarizers 1 produced, and the optical characteristics were all about 22 dB in extinction ratio.
The insertion loss is, as shown in FIG. 2, one transparent dielectric layer 3a.
Above 50 nm, the insertion loss was significantly improved.

Further, in order to evaluate the difference due to the manufacturing process, a polarizer was manufactured by the following manufacturing method. Step (1),
(2) is the same as in this embodiment, and the following steps (3a) to (6)
Prepared according to a).

(3a) Transparent dielectric layer 3a
The transparent substrate 2 is placed on the dispersed metal particles 4
The same BK7 glass as the material is sputtered to 3
A film was formed to a thickness of 00 nm.

(4a) A sample having a transparent dielectric layer 3 in which the steps of (1), (2), and (3a) are repeated five times and five sets of the dispersed metal particle portion 4 and the transparent dielectric layer 3a are laminated. 3
This was produced.

(5a) The three samples were subjected to three types of heat treatment at 580 ° C. for 12 hours, 18 hours, and 24 hours, respectively, and degassing of Ar was performed.

(6a) Each sample was stretched 50 mm in one direction at 625 ° C. with a stress of 45 kg / mm ² , and the metal particles 4a were formed into a spheroidal shape having an aspect ratio of about 20. The thickness of the transparent dielectric layer 3a is 100 n
The polarizer 1 of m was produced.

As a result, the three polarizers 1 produced cracks on the surfaces of all the samples irrespective of the heat treatment time, and the optical characteristics deteriorated to an extinction ratio of about 22 dB and an insertion loss of 1.0 dB.

Further, Au, A is used as the metal of the metal particles 4a.
Polarizer 1 was produced in the same manner as described above using g, Pt, Fe, Ni, Cr, Rh, and Ir, but the same effect as in the present example was obtained.

[0063]

According to the polarizer of the present invention, the thickness of one transparent dielectric layer is 50 nm or more, and the distribution density of metal particles present in the same layer of the dispersed metal particle portion is 3 to 37 particles / μm.
^{By being 2,} it is suitable for miniaturization, has excellent optical characteristics such as insertion loss, and has the effect of preventing cracks and the like from occurring on the surface of the polarizer.

[Brief description of the drawings]

FIG. 1 is a perspective view of a basic configuration of a polarizer of the present invention.

FIG. 2 is a graph showing the relationship between the thickness of one transparent dielectric layer of the polarizer of the present invention and the insertion loss.

[Explanation of symbols]

 1: polarizer 2: transparent substrate 3: transparent dielectric layer 3a: one transparent dielectric layer 4: dispersed metal particle part 4a: metal particle

Claims (2)

[Claims] 1. A polarizer comprising: a transparent dielectric layer in which metal particles having light absorption anisotropy are dispersed in a plurality of layers on at least one principal surface of a transparent substrate; A polarizer, wherein the distance between the layers is 50 nm or more, and the distribution density of metal particles present in the same layer is 3 to 37 particles / μm ² . 2. The optical isolator according to claim 1, wherein the polarizer according to claim 1 is disposed on a light incident side and / or a light output side of the Faraday rotator.