JPH09318813A - Polarizer - Google Patents

Abstract

(57) [Abstract] [PROBLEMS] To provide an excellent polarizing element which is excellent in long-term stability and does not deteriorate in characteristics even in severe reliability tests. SOLUTION: A polarized light is formed by disposing a polarizing layer in which metal particles 2 having anisotropy are dispersed in a dielectric material containing silicon oxide on at least one main surface of a dielectric substrate 1 having translucency. The device is characterized in that the metal particles 2 of the polarizing layer are made of a metal whose standard enthalpy of formation for forming the metal oxide is higher than that of silicon oxide.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarizing element used in optical communication equipment, optical recording equipment, optical sensors and the like, and is preferably used for optical isolators and the like used in optical communication equipment. And a highly reliable polarizing element having a high extinction ratio.

[0002]

2. Description of the Related Art Conventionally, optical isolators have been used in transmitters, repeaters, various amplifiers, etc. as important devices for optical communication. The polarizing element is one of the main components of such an optical isolator, and has a function of passing only light having a specific polarization direction and blocking light having a polarization direction orthogonal to this polarization direction. It was done.

By the way, there have been parts for utilizing optical anisotropy obtained by stretching a material for a long time, and a polarizing film using a polymer film and the like are widely known. Further, by the anisotropic fine metal particles dispersed in the glass, a polarizing element that exhibits polarization characteristics in the infrared region is also known, because loss is smaller than that of a polymer, and because of high durability, It is widely used in the field of optical communication.

Such a polarizing element is manufactured as follows. For example, by aggregating silver halide by heat treatment in a glass containing silver halide, and then by heat stretching, deformation of fine silver halide grains into a spheroid,
After simultaneously performing the major axis orientation of the spheroid,
A polarizing element is produced by reducing silver halide to metallic silver so as to generate a polarizing characteristic (for example, Japanese Patent Laid-Open No. Sho 5).
See JP-A 6-169140: hereinafter referred to as a melting method).

As shown in FIG. 4, this polarizing element absorbs the polarized component 14 in the major axis direction of the spheroidal metal particles 13 dispersed in the glass G with respect to the incident light 12 and has the minor axis. It functions to almost transmit the polarized component 15 of the direction.

However, the polarizing element produced by the melting method is
Since it is necessary to reduce silver halide to metallic silver, a reducing gas may be introduced. Since reducing gas reacts with other substances, it is not only careful to handle but also expensive.
Further, since the reduction proceeds from the surface of the silver halide and the portion related to the polarized light has a depth of several tens of μm from the surface,
Most silver remains silver halide. Therefore, silver halide, which does not contribute to the polarization characteristics, has also been a factor of increasing the insertion loss.

In order to deal with these various problems, the following has been proposed as a polarizing element in which fine metal particles are dispersed in glass. In order to disperse metal particles, this polarizing element has a layer in which a metal is formed in an island shape (hereinafter referred to as an island metal) on a dielectric substrate such as glass by using a thin film forming process such as vacuum deposition. In some cases, dielectric layers such as glass are alternately formed and anisotropy is provided by heating and stretching (hereinafter referred to as a thin film method). Compared with the melting method, such a thin film method does not require reduction,
There are merits such as easy process (for example, 1
990 IEICE Autumn National Conference, Proceedings,
See C-212).

[0008]

In the polarizing element manufactured by the above-mentioned thin film method, the metal in the glass is less affected by outside air or oxygen in the glass at room temperature in a short time after manufacturing, but after a long time, In some cases, the oxygen entering the glass reacts with the metal, or the oxygen contained in the glass reacts with the metal to form a compound, which deteriorates the polarization characteristics.

Further, in particular, when the polarizing element is used for optical communication, in the process of assembling the polarizing element with other constituent members, soldering or bonding with a low melting point glass is used.
When it is placed in a high temperature state of ~ 500 ° C or when it is completed as an optical isolator, a reliability test of 150 ° C for several thousand hours may be imposed. In such a case, the metal in the glass reacts with oxygen. As a result, the metal deteriorates and the polarization characteristics deteriorate, which is a serious problem for optical communication components that require strict environmental resistance and reliability.

Therefore, the present invention focuses on the standard enthalpies of formation of silicon and silicon oxide in the dielectric, the standard enthalpies of formation of metals and their oxides in the dielectric, and the metal particles that contribute to polarization are oxides. It is an object of the present invention to provide an excellent polarizing element which is excellent in long-term stability and does not deteriorate in characteristics even in a severe reliability test or the like by selecting it based on the standard enthalpy of formation.

[0011]

In order to solve the above-mentioned problems, the polarizing element of the present invention has a dielectric substrate containing a silicon oxide on at least one main surface of a dielectric substrate having translucency. A polarizing element comprising a polarizing layer in which a large number of metal particles having anisotropy are dispersed, wherein the metal particles of the polarizing layer have a standard enthalpy of formation for forming the metal oxide of silicon oxide. It is characterized by being composed of a metal having a larger enthalpy of formation than standard. Furthermore, it is more preferable that the metal particles do not form a silicic acid compound.

Further, the aspect ratio of the metal particles (long-axis average length / short-axis average length) is 10 to 30. The reason for setting the aspect ratio in this range is that the extinction ratio increases as the aspect ratio increases, but when stretching the substrate to impart anisotropy to the metal particles, the stretching ratio of the substrate increases and stretching This is because it becomes difficult and the rate of increase of the extinction ratio decreases in a region having a high aspect ratio. In addition, especially preferably, it is about 15 to 25.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings. As shown in FIG. 1, for example, the polarizing element of the present invention has a dielectric layer 3 containing silicon oxide on at least one main surface (or both main surfaces) of a dielectric substrate 1 having translucency. In the polarizing element P1 provided with the polarizing layer H1 in which the spheroidal metal particles 2 having anisotropy are dispersed, the standard enthalpy of formation for the metal particles 2 to generate the metal oxide is silicon. It is a metal that is larger than the standard enthalpy of formation of oxides (eg SiO ₂ ). That is, SiO as the silicon oxide
_When considering ₂ , standard enthalpy of formation ΔHf [kcal /
ge] (standard enthalpy of formation of 1 mol of metal oxide converted to 1 gram equivalent of oxygen) is -53 [kcal /
ge], the standard enthalpy of formation of CuO is -20 [kcal / ge] and that of Ni is -28 [kcal].
/ ge], Cu and Ni can be used as metal particles. In addition, on the uppermost layer 3u of the polarizing layer H1,
A single-layer or multi-layer (composite) antireflection film 4 made of a dielectric material such as TiO ₂ , SiO ₂ , or MgO is provided.

Here, the dielectric substrate 1 is made of, for example, Pyrex glass (Pyrex is a trademark of Corning Glass Industry) or BK glass (BK is HOY).
Borosilicate glass (trade name of Company A) is used, and in addition to this, high-melting glass such as silica glass and low-melting glass such as soda glass containing silicon oxide as a main component (50 wt% or more) are used. Good.

In particular, when the present polarizing element is used as an isolator, borosilicate glass is preferable. This is because the coefficient of thermal expansion of borosilicate glass is close to the metal material used for the holder of the optical isolator. This is because, for example, the body thermal expansion coefficient of the Ni—Fe alloy used as the holder material is close to 90 to 96 × 10 ⁻⁷ / ° C., and sealing in the holder is extremely easy. For example, the body thermal expansion coefficient of BK-7 glass (SiO ₂ is about 69 wt%, B ₂ O ₃ is about 10 wt%) is about 72 to 89 × 10 ⁻⁷ / ° C., and Ni—Fe is used.
It can be preferably used because it is very close to the body thermal expansion coefficient of the alloy.

The dielectric layer 3 is preferably made of the same material as the substrate 1. For example, when Pyrex glass is used for the substrate 1, Pyrex glass is also used for the dielectric layer 3.
It is preferable to match the characteristics such as the coefficient of thermal expansion.

The metal particles 2 are selected such that the standard enthalpy of formation of the metal oxide is larger than the standard enthalpy of formation of silicon oxide. That is, Au, Ag,
Noble metals such as Pt, Rh, Ir, Cu, Ni, Fe, Z
One or more metals selected from transition metals such as n and Cr. Further, among these metals, a metal that does not generate a silicate compound, that is, the above-mentioned noble metal, Cu, Ni, Cr or the like is desirable. Further, it is desirable that the metal is a metal that is poorly wetted with the dielectric layer 3 and easily aggregates, and is hard to be oxidized, and that can exist as the metal particles 2 in the dielectric layer 3. Of these,
Particularly preferred are Au, which has a low melting point and thus easily agglomerates, has poor wetting with glass, and is not easily oxidized, and Cu, which is inexpensive and has poor wetting with glass. The metal particles 2 are not limited to simple metals, but may be alloys.

The metal particles 2 are spheroidal and have anisotropy, and in FIG. 1 (where the traveling direction of light is the Z direction, and the plane perpendicular to this is the XY plane). The major axis direction of the metal particles 2 is the Y direction, and the minor axis direction is the X direction. Further, the ratio of the major axis length to the minor axis length of the metal particles 2 is the aspect ratio, but here, the average value of the aspect ratios of many metal particles 2 is simply referred to as the aspect ratio.

The metal particles 2 have a spheroidal shape because the metal particles 2 are formed together with the substrate 1 during stretching after the polarizing layer H1 is formed.
Is stretched in the stretching direction. The higher the aspect ratio, the higher the extinction ratio, but at the same time, the stretching rate of the substrate 1 increases, making it difficult to stretch. Further, the rate of increase of the extinction ratio decreases in the region with a high aspect ratio. Is preferably 10 to 30, and particularly preferably about 15 to 25. The extinction ratio is a ratio of the loss of polarized light in the X direction to the loss of polarized light in the Y direction when the input light that is not polarized at a predetermined wavelength is used.

As the length of the minor axis of the metal particles 2 increases, the insertion loss with respect to the polarized light in the X direction to be transmitted also increases. From this, the aspect ratio is 10 or more, more preferably 15
As described above, it is preferable that the minor axis length is short and the insertion loss is small. When the long axis average length of the metal particles 2 increases, the absorption peak wavelength in the Y direction increases and approaches the wavelength range (about 1.3 μm) used in optical communication. However, considering that the aspect ratio of the metal particles 2 is limited due to manufacturing and the increase of the minor axis length causes an insertion loss, the major axis length is also limited.

Therefore, the preferable conditions for the metal particles 2 are that the aspect ratio is 10 to 30, the average major axis length is 10 to 300 nm, and the average minor axis length is 1 to 10 nm, more preferably. Aspect ratio is 10 to 30, average length of major axis is 30 to 200 nm, average length of minor axis is 2 to
10 nm, most preferably an aspect ratio of 15-2
5, the average value of the major axis length is 40 to 200 nm, and the average value of the minor axis length is 2 to 10 nm.

In the case of FIG. 1, the incident light incident in the Z direction is
The polarization component in the Y direction is absorbed by resonance with the free electrons of the metal particles 2, and the polarization component in the X direction has a high transmittance and becomes polarized outgoing light. In addition, there is a difference in absorption peak wavelength between the Y direction and the X direction, and there is an absorption peak in the Y direction on the longer wavelength side than the X direction. Unless otherwise specified, the extinction ratio is determined by the wavelength at which the absorption peak in the Y direction occurs.

Next, a method of manufacturing the above polarizing element will be described. For example, it is manufactured as follows. That is, FIG.
As shown in FIG. 2, the polarizing element P1 includes a metal particle layer in which metal particles 2 having anisotropy are dispersed and a dielectric layer 3 made of glass on one main surface or both main surfaces of the dielectric substrate 1. When forming the polarizing layers H1 which are alternately laminated, steps A to C (A: step of depositing metal fine particles on the dielectric film-forming surface made of glass by a sputtering method, B: dielectric film forming) Heating to a temperature below the glass softening point of the dielectric,
Steps of growing metal fine particles to form spheroidal metal particles 2 having a larger diameter, C: forming a dielectric layer 3 in a film shape on the metal particle layer by a sputtering method are repeated a plurality of times. To do. Then, after that, the dielectric substrate 1
Dielectric layer 3 formed on the outermost of one main surface or both main surfaces
While being heated, it is stretched (thermoplastically deformed) by applying stress in a certain direction to impart anisotropy to the metal particles dispersed in the glass layer. Further, in order to make the surface smooth, polishing is performed by a CMP method or the like to form the antireflection film 4. An antireflection film is similarly formed on the back surface of the substrate (not shown) even though the polarizing layer is not formed.

Further, as shown in FIG. 3, a mixture thin film of a dielectric layer and metal fine particles is formed on at least one main surface of a transparent dielectric substrate 1, and then the mixture thin film is heated. As a result, a large number of metal particles 2 are formed in the mixture thin film by agglomeration of metal fine particles, and then the substrate 1 and the mixture thin film are stretched under heating to stretch the metal particles 2 in a spheroidal shape to form a polarizing layer. You may manufacture the polarizing element P2 which has H2.

[0025]

EXAMPLES Next, more specific examples will be described. Example 1 As shown in FIG. 1, BK-7 glass, which is a borosilicate glass having a size of 76 mm × 10 mm × 1 mm (softening point: 72
The glass substrate 1 was prepared by using 4 ° C. and a coefficient of thermal expansion of 72 to 89 × 10 ⁻⁷ / ° C.). Films are formed on the substrate 1 by sputtering using a dual magnetron sputtering device, Cu is used as a target for metal particles, and BK-7 is used as a target for dielectrics.
Glass is used, the sputtering conditions are RF power of 20 W, the sputtering atmosphere is Ar, and the pressure is 2.0 × 10 ⁻³ Too.
The flow rate was r and the flow rate was 10 cc / m. 8 nm film thickness in the first step
Cu film is formed and this is sputtered at 500 ℃.
And heated for 60 minutes to grow Cu particles. At this heating temperature, a dielectric layer made of BK-7 glass was formed to a thickness of 200 nm (intermediate layer) and 1000 nm (top layer). Then, the cycle consisting of the formation of the Cu film, the heat treatment, and the formation of the dielectric film is repeated 5 times, and the polarizing layer H1 is formed on one surface of the substrate 1.
Was provided.

Next, 45 k is applied to both ends of the substrate 1 in the opposite direction.
A substrate having a length of 76 mm was stretched by 50 mm by applying a force of g / mm ² to impart anisotropy to the metal particles 2. The thickness of the dielectric thin film after stretching is about 80 nm in the intermediate layer and 400 in the uppermost layer.
became nm. Here, the preferable range of the stretching ratio is 50 to
It is 400%. The preferable range of the applied force is 10 to 10
The heating temperature during stretching is preferably 550 to 720 ° C., which is lower than the softening point of the substrate 2, and more preferably 59 kg / mm ^2.
The temperature was 0 to 650 ° C, and 625 ° C in the example. The atmosphere during stretching is arbitrary. The extinction ratio of the polarizing element thus obtained was 24 dB as shown in FIG.

Second Embodiment Next, another embodiment will be described with reference to FIG. First, BK-7 glass was used as the substrate 1. The size of the substrate 1 is the same as that in the first embodiment. Next, the polarizing layer H2
Au as a metal material and a dielectric material were obtained by binary magnetron sputtering targeting BK-7 glass (BK-7 which is the same as the substrate 1) and Au so that the metal content therein was 10% by volume. BK-7 glass as a substrate was simultaneously sputter-deposited on the substrate 2. The sputtering conditions were RF power of 20 W, sputtering gas of Ar, pressure of 2.0 × 10 ^-2 Torr, and Ar flow rate of 10 cc / m.

The polarizing layer H2 was formed as a single layer film, and the film thickness thereof was about 0.5 mm before stretching. The substrate 1 after the film formation was heat-treated in the air at 600 ° C. for about 1 hour to aggregate the metal fine particles to obtain the metal particles 2. Here, the metal particles 2 thus produced had an average particle diameter (diameter) of about 120 nm and a particle diameter of about 100 to 150 nm before the stretching.

Further, when the spectral transmission characteristic (extinction characteristic) in this state was measured, it was 20d at a wavelength of around 0.5 μm.
There was a peak of absorption around B. Next, a force of 45 kg / mm ² was applied to both ends of the substrate 1 in opposite directions to stretch the substrate 1. Here, preferred conditions for stretching are that the applied force is 10 to 100 kg / mm ² and the temperature during stretching is 400.
-700 degreeC (more preferably, 600-650 degreeC). The preferred range of the amount of stretching is 40 to 300 mm in terms of the stretching length with respect to the substrate 1 having a length of 76 mm, which means a stretching ratio of 50 to 400%. Then, in the embodiment, at the temperature of 625 ° C. in the atmosphere, the both ends of the substrate 1 are 45
It was stretched by 50 mm by applying a force of kg / mm ² .

As a result, the film thickness of the polarizing layer H2 is about 0.3 μm.
It became m. In the polarizing element thus obtained, the average aspect ratio of the metal particles 2 was 20, the major axis length was about 80 nm ± 10 nm, and the minor axis length was about 4 nm ± 2 nm.

When the extinction characteristic of the obtained polarizing element was measured, an extinction ratio of 20 dB was obtained at a wavelength of 0.55 μm.

In the above embodiment, the case where the polarizing layers H1 and H2 are provided on the one main surface side of the substrate 1 has been described, but the polarizing layers may be provided on both main surfaces of the substrate 1. By doing so, warpage of the substrate 1 can be suppressed, and a highly reliable polarizing element can be provided.

[0033]

As described above, according to the polarizing element of the present invention, even if it is exposed to an external atmosphere or a high temperature state, the metal particles do not oxidize or form a silicic acid compound, It is possible to provide a highly reliable polarizing element capable of maintaining excellent polarization characteristics for a long period of time.

Further, since the selection of the material of the metal particles is not performed simply on the basis of the difficulty of oxidation, the standard enthalpy of formation of silicon oxide is compared with that of the metal oxide, so that the material selection is sure. Can be done.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment according to the present invention.

FIG. 2 is a diagram showing optical characteristics according to the present invention.

FIG. 3 is a perspective view showing another embodiment according to the present invention.

FIG. 4 is a diagram schematically illustrating the operation of a polarizer.

[Explanation of symbols]

 1 ... Dielectric substrate 2 ... Metal particles 3 ... Dielectric layer 4 ... Antireflection film H1, H2 ... Polarizing layer P1, P2 ... Polarizing element

Claims (3)

[Claims] 1. A polarizing layer in which a large number of anisotropic metal particles are dispersed in a dielectric containing silicon oxide is provided on at least one main surface of a transparent dielectric substrate. A polarizing element, wherein the metal particles of the polarizing layer are made of a metal whose standard enthalpy of formation for forming the metal oxide is higher than the standard enthalpy of formation for forming silicon oxide. . 2. The polarizing element according to claim 1, wherein the metal particles do not generate a silicate compound. 3. The polarizing element according to claim 1, wherein the metal particles have an aspect ratio (long-axis average length / short-axis average length) of 10 to 30.