JP2000047031A - Polarizer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polarizer having excellent homogeneity and stable performance without performing a conventional procedure for dispersing metallic particles in a parent phase. SOLUTION: This polarizer 1 is formed by arranging granules 5 having optical absorption anisotropy in plural recessed part 4 formed on at least one principal surface 2a of a substrate 2 consisting of a transparent single crystal. Accordingly, the arrangement of the granules 5 in a polarization section can easily be made to have a desired form. In particular, by integrating the granules 5 with the crystal lattice of the transparent single crystal that is a parent phase material, in a specific crystallographic direction to closely combine them, a polarizer having uniform high homogeneity can be formed. Further, the post- processing stages affecting polarization characteristics, such as conventional stretching stage and lamination stage, can be eliminated. Thus, the objective epochal polarizer which has very stable quality and further, excellent characteristics, can be manufactured in high yield.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarizer which can be used for optical communication equipment, optical recording equipment, optical sensors, etc., and more particularly to a polarizer which can be suitably used for an optical isolator used for optical communication equipment. About the child.

[0002]

2. Description of the Related Art Conventional polarizers include elements using colored ions, such as a cell in which a certain kind of solution is put in a cell, a cell in which a colorant is put in a plastic, and a large number of dielectric thin films on a substrate. An element that uses stacked multilayer thin film interference,
A polarizing prism typified by a Glan-Thompson prism composed of a crystal having a large birefringence, a PBS (polarizing beam splitter) that separates polarized light components using Brewster conditions, or a polymer material is oriented in a certain direction.
A polarizing film or the like that absorbs a polarized light component in one direction has been mainly used.

[0003] Among the above polarizers, those using colored ions have a large wavelength dependence, and it is necessary to select a polarizer having an optimum wavelength characteristic for each wavelength. In addition, a crystal composed of a crystal having a large refractive index has a small wavelength dependency,
Until now, there has been no compact polarizer with excellent wavelength characteristics, for example, it is difficult to process, the element size is limited, and it is difficult to reduce the size.

For the above-mentioned polarizer, a polarizing glass has recently been used as an optical communication device. For example, a transparent glass is used as a transparent solid medium, and elliptical silver particles are aligned in a certain direction in this medium. A structure having a dispersed and anisotropic structure is known (see Japanese Patent Publication No. 2-40619).

[0005] This polarizing glass is manufactured as follows. First, a glass batch consisting of at least one halide selected from the group consisting of silver and chloride, bromide and iodide is melted and formed into a glass body of the required shape. Next, a heat treatment is performed on the above-mentioned glass base 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 above polarizer can be obtained by exposing the stretched glass substrate to a reducing atmosphere in a predetermined temperature range to reduce a part of the silver halide to metallic silver particles.

However, in this method for producing a polarizer, heat treatment is performed in a reducing atmosphere in order to precipitate metallic silver from silver halide. Therefore, the amount of metallic silver precipitated in the glass substrate is reduced. It is difficult to control, and stable optical characteristics cannot be obtained. For this reason, it has been difficult to stably obtain polarization characteristics with good reproducibility even when the glass substrate is stretched by heating.

In addition, there is a problem that silver halide not reduced to metallic silver remains in the center due to the temperature distribution in the thickness direction in the glass base, which adversely affects the transmittance. .

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

Therefore, a discontinuous island-like 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 deposition and the like. A proposal has been made to have the property (see, for example, Proceedings of the Institute of Electronics, Information and Communication Engineers Autumn National Convention 1990, C-212).

In this polarizer, each island in the island-shaped metal particle layer functions as a metal particle and has the same structure as that in which the metal particles are dispersed, but the metal particles are deposited in the glass film during lamination. However, it is difficult to obtain stable polarization characteristics, and it is particularly difficult to obtain an extinction ratio at a desired wavelength. As described above, conventional glass polarizers based on metal particle dispersion have inhomogeneous dispersion of metal particles in glass, inhomogeneous mechanical elongation of dispersed metal particles, diffusion of metal particles into glass. There is a problem in homogeneity such as local inhomogeneity due to solid solution, and in the case of a laminated type polarizer, the production process is complicated and there is a problem in yield.

Accordingly, an object of the present invention is to provide a polarizer having excellent homogeneity and stable performance without dispersing metal particles in a matrix as in the prior art.

[0012]

In order to achieve the above object, the polarizer of the present invention has a plurality of concave portions formed on at least one main surface of a substrate made of a transparent single crystal, and has a light absorption anisotropy. Having a granular material having the same.

The polarizer of the present invention is characterized in that the granular material is, for example, a single crystal having a columnar shape (including a needle shape).

In the polarizer of the present invention, the substrate is made of Si.
O ₂ , LiNbO ₃ , LiTaO ₃ , Gd ₃ Ga
_{It is} composed of at least one of ₅ O ₁₂ and Al ₂ O ₃ , and the granular material is Al, Cu, Fe, Sn, Ti, Zn, Cd, Ag, N
It is characterized by comprising at least one of i, Mn, and Co. Here, the substrate is a colorless and transparent optical crystal, which is preferable in that a large single crystal can be easily grown. Further, the above metal elements are suitable as those from which needle-like single crystals can be easily obtained.

Further, the polarizer of the present invention is characterized in that the granular material having anisotropic light absorption has an average minor axis length of 10 nm to 100 nm. If this is less than 10 nm, the desired wavelength range (from 1.3 μm to
(1.55 μm band), no absorption occurs, and good polarization characteristics cannot be obtained. If it exceeds 100 nm, diffraction, reflection, scattering, etc. occur in the above-mentioned wavelength region, and good polarization characteristics cannot be obtained. is there.

In the recess, for example, a submicron-order buried groove may be formed in a transparent single crystal. Then, the buried groove is filled with metal microcrystals, and a desired polarizer is manufactured in a post-processing step for making the length of the metal crystal filled thereafter uniform.

For the production of metal microcrystals, a reduction method, condensation from a gas phase, growth from a solid phase, and the like can be applied. A low melting point metal or halide is used as a metal element source. Various submicron processing techniques can be used to form the buried trench on the order of submicron, and the method of filling metal microcrystals can be a method of directly growing metal crystals in the recesses or a metal microcrystal formed by another process. A method of filling the concave portion of the crystal by a physical method or a mechanical method can be used. In the post-treatment process, the length of the metal microcrystals is kept constant, surface treatment for removing the metal microcrystals other than the recesses is ensured, and subsequent fixation to the substrate, and heat treatment and pressure treatment for integration. And the like are appropriately used.

[0018]

Embodiments of the present invention will be described below in detail with reference to the drawings.

As shown in FIG. 1, the polarizer 1 is made of Si.
O ₂ , LiNbO ₃ , LiTaO ₃ , Gd ₃ Ga
_A polarizing part 3 is provided on at least one main surface 2a of a substrate 2 made of a transparent single crystal made of at least one of ₅ O ₁₂ and Al ₂ O ₃ . A large number of the polarizing parts 3 are formed under the surface of the substrate 2 at intervals of several tens nm, and have a diameter of 10 n.
An arrangement hole 4 which is a concave portion having a depth of submicron order of m to 100 nm is formed of a granular material 5 such as a columnar (including needle-like) metal single crystal filled therein. Here, the granular material 5 is made of Al, Cu, Fe, Sn, Ti, Zn, Cd, Ag, N
It shall be composed of one or more of i, Mn, and Co. Further, in order to shield light incident on the surface of the substrate 2 other than the above-mentioned polarizing portion, a shielding film 6 made of Cr, Au, or an alloy thereof is formed. Note that the transparency of the transparent single crystal means that the transparent single crystal is transparent to light having the wavelength used by the polarizer 1.

The polarizer 1 configured as described above includes a substrate 2
Since the light L1 incident from the side surface 2b of the granular material 5 is absorbed in the long axis direction of the granular material 5, the light L1 is emitted as the polarized light L2 from which the long axis direction component is removed. The polarizer 1 having such polarization characteristics can be suitably used particularly as an optical isolator.

Next, an example of a method for manufacturing the polarizer 1 will be described with reference to FIGS. 2 (a) and 2 (b). For example, FIG.
As shown in (a), a 1-inch quartz substrate 2 having a thickness of about 500 μm having a C surface as a main surface 2a is prepared, and the surface 2a of the substrate 2 is subjected to photolithography and reactive ion etching or the like. Approximately 30n in diameter perpendicular to the C plane
An arrangement hole 4 having a depth of about 300 nm is formed. Note that the shape of the arrangement hole, which is the concave portion, is mainly determined by the shape of the mask that forms the concave portion, and can be formed into various shapes.

Next, a boat containing a high-purity Sn raw material is placed at the bottom of the quartz tube, and the surface 2a of the quartz substrate 2 is placed at the top of the boat. The quartz tube is sealed, and heat treatment is performed in a two-stage furnace. . At this time, the temperature of the upper furnace is set to about 160 ° C., and the temperature of the lower furnace is set to about 240 ° C. As a result, the surface 2a of the substrate 2
In the arrangement hole 4, needle-like crystals having a diameter of 20 nm to 500 nm and a maximum length of about 0.1 mm and having a [100] orientation are generated. Next, excess Sn microcrystals grown and adhered to the surface other than those grown in the arrangement holes 4 using hydrofluoric acid were removed.
Clean the surface of. Then, the cleaned substrate 2 is finally subjected to a heat treatment at about 180 ° C. in a vacuum furnace, thereby obtaining the heat treatment shown in FIG.
A desired polarizer 1 as shown in (b) can be obtained.

In addition to the above-described direct method of filling the metal microcrystals, the following indirect method is also applicable. That is, Sn particles are deposited and filled in the arrangement holes 4 of the substrate 2 using a thin film forming apparatus such as a sputtering apparatus, and after the surface 2a is cleaned by ion sputtering, crystal growth from a melt of Sn is performed. , [100] A method of obtaining columnar crystals is also applicable.

According to this, since the disposing holes 4 can be formed in a specific crystallographic orientation, the lattice matching between the base material and the buried metal microcrystals can be controlled. In particular, the columnar (including needle-like) crystals can be formed. This is preferable because the growth of GaAs becomes easy, and the crystal boundary surface is integrated with good consistency to form a dense structure.

Further, since the shape and density distribution of the metal microcrystals are uniquely determined by the arrangement holes to be formed, very high homogeneity with little variation can be obtained, and as a result, there is no prior art. A polarizer having excellent polarization characteristics is obtained.

The mode of the polarizing section 3 is not limited as described above. For example, as shown in a polarizer 31 shown in FIG.
Instead of being perpendicular to 2a, it may be formed obliquely to the light incident direction, and the arrangement holes 34 may be filled (formed) with the granular material 35. The polarizer 31 does not require the formation of the shielding film 6 on the substrate 32 like the polarizer 1. In the case of the polarizer 31, the light L1 made incident from the main surface 32a side has the long-axis direction component of the granular material 35 removed, and becomes the emitted light L2.

As shown in FIG. 4, a concave portion may be formed in the substrate 41 in a rectangular parallelepiped arrangement groove 44, and the arrangement groove 44 may be filled (formed) with a granular material 45. Good. This polarizer 31 also does not require the formation of the shielding film 6 on the substrate 32 like the polarizer 1. As in the case of the polarizer 31, the light L1 incident from the main surface 42a side has the long-axis direction component of the granular material 45 removed, and becomes the emitted light L2.

[0028]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, specific embodiments of the present invention will be described.

(Example 1) A 1-inch-size, 500-μm-thick quartz substrate having a C-plane as a main surface is prepared, and the surface of the substrate is vertically perpendicular to the C-plane by an average distance of about 300 nm by photolithography and reactive ion etching. Thus, an arrangement hole having a diameter of about 30 nm and a depth of about 500 nm was formed.

Next, a boat containing high-purity Al raw material is placed at the bottom of the quartz tube, and the surface of the quartz substrate is placed at the top. The quartz tube is sealed under reduced pressure, and heat-treated in a two-stage furnace for about 30 minutes. Was done. At this time, the temperature of the upper furnace was set to 550 ° C, and the temperature of the lower furnace was set to 630 ° C.

As a result, a diameter of 20 nm to 200 nm and a maximum length of about 0.5 mm <10 mm
0> Needle-like crystals were formed.

Next, the substrate was washed in a 20% aqueous solution of caustic soda (60 ° C. to 90 ° C.) to clean the surface of the substrate, and then heat-treated for about 500 hours in a vacuum furnace for about 3 hours.

Further, a Cr film as a shielding film was formed to a thickness of several μm by a vapor deposition method so that light did not enter from a surface other than the polarizing portion.

The substrate thus obtained is 3 mm ×
When a polarizer having a size of 3 mm was manufactured and its polarization characteristics were measured, it showed excellent characteristics such as an extinction ratio of 50 dB and an insertion loss of 0.06 dB.

Example 2 A 2-inch LiNbO ₃ single crystal having a thickness of 500 μm and having a C-plane as a main surface was prepared.
In the same manner as described above, the average diameter is about
An arrangement hole having a thickness of about 300 nm and a depth of about 300 nm was formed.

Next, using high-purity zinc as a metal raw material,
Helium of about 300 mmHg was sealed in a glass tube, and the substrate was subjected to heat treatment for about 30 minutes in a temperature gradient furnace set so that the temperature of the evaporating section was about 375 ° C and the temperature of the condensing section was about 350 ° C.

As a result, a diameter of 10 mm is applied to the substrate surface and the arrangement holes.
Needle-like crystals having a maximum length of about 1 mm were formed.

Next, the substrate was subjected to a surface cleaning treatment in an approximately 10% nitric acid solution, followed by a heat treatment at approximately 330 ° C. for approximately 2 hours in a vacuum furnace. A polarizer of the same size as in Example 1 was produced from the substrate thus obtained, and its polarization characteristics were measured. The extinction ratio was 55 dB and the insertion loss was 0.05 d.
B and excellent characteristic values were exhibited.

(Example 3) A LiTaO ₃ single crystal having a thickness of about 350 μm and a size of about 350 μm and having a C-plane as a main surface was prepared.
A groove having a thickness of 0 nm and a depth of about 600 nm was formed. Next, using high-purity cadmium as a metal raw material, about 50
0 mmHg of hydrogen is sealed, and the temperature of the evaporating section is about 330 ° C.
The substrate was subjected to a heat treatment for about 15 minutes in a temperature gradient furnace set to a temperature of about 250 ° C. in the condenser section.

As a result, a diameter of 30 mm is applied to the substrate surface and the arrangement holes.
Needle-like crystals having a maximum length of about 2 mm were formed. Next, the substrate was subjected to a surface cleaning treatment with a concentrated hydrochloric acid solution, and then subjected to a heat treatment in a vacuum furnace at about 230 ° C. for about 2 hours.

A polarizer having the same size as in Example 1 was manufactured from the polarizer substrate thus obtained, and its polarization characteristics were measured. The extinction ratio was 50 dB and the insertion loss was 0.07 d.
B and excellent characteristic values were exhibited.

Example 4 A 2 inch-sized Ga ₃ Gd ₅ O ₁₂ single crystal having a (110) plane as a main surface and a thickness of about 400 μm was prepared, and was prepared in the same manner as in Example 1 at an average interval of about 600 nm. An arrangement hole having a diameter of about 350 nm and a depth of about 700 nm was formed. Next, using high-purity silver as a metal source, a heat treatment was performed for about 15 minutes by the same heating method as in Example 1. In this example, the temperature of the upper furnace was about 850 ° C., and the temperature of the lower furnace was about 940 ° C.

As a result, <11
0> azimuth diameter 20nm-150nm, maximum length about 0.1m
m of acicular crystals were formed. Then, about 55%
After performing a surface cleaning treatment with a ferric nitrate solution, heat treatment was performed in a vacuum furnace at about 800 ° C. for about 3 hours.

A polarizer having the same size as in Example 1 was produced from the polarizer substrate thus obtained, and its polarization characteristics were measured. The extinction ratio was 55 dB and the insertion loss was 0.05 d.
B and excellent characteristic values were exhibited.

(Example 5) On the same substrate as in Example 4, CuI was used as a metal source, and needle-like crystals of Cu were produced by a hydrogen reduction method. In this example, the raw material powder was put in a Pt boat using a horizontal furnace, heated in a hydrogen stream (3 cc / sec) at about 630 ° C. for about 10 minutes, and then moved to a cooling section to be replaced with helium gas.

As a result, <11
Needle-like crystals having a diameter of 30 nm to 500 nm and a maximum length of about 2 mm were generated in the 0> direction. Then, the substrate was concentrated
After the surface cleaning treatment was performed in milliliter + 700 ml of water, heat treatment was performed in a vacuum furnace at about 600 ° C for 2 hours.

From the polarizer substrate thus obtained, a polarizer having the same size as in Example 1 was produced, and its polarization characteristics were measured. The extinction ratio was 58 dB and the insertion loss was 0.03 d.
B and excellent characteristic values were exhibited.

[0048] (Example 6) with the same substrate as in Example 4, using FeBr ₂ as a metal source, a nitrogen and hydrogen mixed gas stream (flow rate ratio N ₂
/ H ₂ = 5/1) to produce needle-like crystals. The generation temperature in this example was about 700 ° C., and the processing time was about 15 minutes.

As a result, <10
Needle-like crystals having a diameter of 25 nm to 350 nm and a maximum length of about 1 mm in the 0> direction were formed. Next, the surface of the substrate was cleaned in concentrated nitric acid, and then heat-treated at about 800 ° C. for about 3 hours in a vacuum furnace.

From the polarizer substrate thus obtained, a polarizer having the same size as that of Example 1 was produced, and its characteristics were measured. As a result, it was found that the extinction ratio was 56 dB, the insertion loss was 0.04 dB, and excellent characteristics were obtained. Indicated.

(Example 7) Sapphire having a size of about 350 μm and a thickness of about 350 μm having a C-plane as a main surface was prepared, and in the same manner as in Example 1, an average spacing of about 180 nm, a diameter of about 15 nm, and a depth of about 250 nm. Arranged holes were formed.

Next, NiBr was used as a metal source.
Ni needle crystals were produced by the same hydrogen reduction method as in Example 1.
In this example, the hydrogen was made wet through water, and the generation conditions were a temperature of 700 ° C. to 900 ° C. and a heating time of several minutes.

As a result, <10
0> azimuth diameter about 10nm ~ 100nm, maximum length 0.1m
About m needle-like crystals were formed. Next, the substrate was subjected to a surface cleaning treatment with a saturated aqueous solution of ferric chloride, and then a heat treatment was performed in a vacuum furnace at about 900 ° C. for about 3 hours.

From the polarizer substrate thus obtained, a polarizer having the same size as in Example 1 was produced, and its polarization characteristics were measured. As a result, it was shown that the extinction ratio was 57 dB and the insertion loss was 0.04 dB. Was.

(Example 8) On the same substrate as in Example 7, MnCl ₂ was used as a metal source, and a Mn needle-like crystal was produced by the same hydrogen reduction method as in Example 5. Generation conditions are temperature 850 ° C to 95
The heating time at 0 ° C. was about 5 minutes.

As a result, <10
0> azimuth diameter 10nm ~ 200nm, maximum length 0.2mm
Some degree of acicular crystals formed. Next, after the surface of the substrate was cleaned with hydrofluoric acid, heat treatment was performed in a vacuum furnace for about 1000 hours and about 2 hours.

A polarizer having the same size as in Example 1 was prepared from the polarizer substrate thus obtained, and its polarization characteristics were measured. The extinction ratio was 56 dB and the insertion loss was 0.05 d.
B exhibited excellent properties.

Example 9 On the same substrate as in Example 7, CoBr ₂ was used as a metal source, and in a nitrogen-hydrogen mixed gas stream (85% N _2).
+ 15% H ₂ ) to form Co needle crystals. The generation conditions were a temperature of 650 ° C. to 735 ° C. and a heating time of about 15 minutes.

As a result, <10
0> azimuth diameter 10nm ~ 150nm, maximum length 0.1mm
Some degree of acicular crystals formed. Next, the surface of the substrate was cleaned in boiling water of a saturated aqueous solution of ferric chloride, and then heat-treated in a vacuum furnace at about 1100 ° C. for about 1 hour.

A polarizer having the same size as in Example 1 was prepared from the polarizer substrate thus obtained, and its polarization characteristics were measured. The extinction ratio was 57 dB and the insertion loss was 0.05 d.
B exhibited excellent properties.

(Example 10) The same substrate as in Example 7 was prepared, TiCl ₄ was used as a metal source, H ₂ was used as a carrier gas, and a thermal CVD apparatus was used under normal pressure at a reaction temperature of 800 to 1200.
The deposition was performed at a reaction temperature of about 10 minutes.

As a result, the substrate surface and the arrangement holes were completely covered with the Ti polycrystalline film. Next, the substrate is subjected to a surface cleaning treatment with 1 volume of 40% hydrofluoric acid and 9 volumes of water (30 ° C. to 32 ° C.) to dissolve and remove the Ti thin layer other than the disposition holes. Heat treatment was performed for about 5 hours.

As a result, the Ti thin layer in the arrangement hole was <101
It was clarified by observation with a transmission electron microscope that selective growth was performed in the 0> direction and single crystallization was performed. A polarizer having the same size as that of Example 1 was produced from the polarizer substrate thus obtained, and its polarization characteristics were measured. As a result, it was found that the extinction ratio was 58 dB and the insertion loss was 0.03 dB.

[0064]

As described above in detail, according to the polarizer of the present invention, a granular material having light absorption anisotropy is disposed in a concave portion formed on at least one principal surface of a substrate made of a transparent single crystal. Therefore, it is easy to make the arrangement of the granular bodies of the polarizing section into a desired shape.

In particular, when the granular material is integrated with a crystal lattice of a single crystal as a matrix in a specific crystallographic orientation and tightly bonded, a polarizer having high uniformity without variation can be obtained. This eliminates the steps that greatly affect the polarization characteristics in the post-process, such as the conventional stretching and laminating processes, which not only results in extremely stable quality and high yield, but also provides a breakthrough with excellent characteristics. Polarizer can be provided.

[Brief description of the drawings]

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

FIGS. 2 (a) and 2 (b) are cross-sectional views showing steps of manufacturing a polarizer according to the present invention.

FIG. 3 is a schematic perspective view of another polarizer according to the present invention.

FIG. 4 is a schematic perspective view of another polarizer according to the present invention.

[Description of Signs] 1, 31, 41: Polarizers 2, 32, 42: Substrate 3: Polarizer 4, 34: Arrangement hole (recess) 44: Arrangement groove (recess) 5, 35, 45: Granular body

Claims (4)

[Claims] 1. A polarizer comprising a plurality of concave portions formed on at least one main surface of a substrate made of a transparent single crystal, and particles having light absorption anisotropy disposed in the plurality of concave portions. 2. The polarizer according to claim 1, wherein the granular material is made of a single crystal. 3. The method according to claim 1, wherein the substrate is SiO ₂ , LiNbO ₃ , L
It is composed of at least one of iTaO ₃ , Gd ₃ Ga ₅ O ₁₂ , and Al ₂ O ₃ , wherein the granular material is Al, Cu, Fe, Sn,
The polarizer according to claim 2, comprising at least one of Ti, Zn, Cd, Ag, Ni, Mn, and Co. 4. The polarizer according to claim 2, wherein the average length of the short axis of the granular material having light absorption anisotropy is 10 nm to 100 nm.