JPH09265009A - Polarizer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a low-cost polarizer capable of easily increasing the area, not causing the peeling of thin films and excellent in durability by satisfying specified conditions between the wavelength of light incident on a multilayered film and the thickness of each metallic thin film and between the wavelength and the thickness of each dielectric thin film. SOLUTION: A mlultilayered film is formed on a plate-shaped dielectric substrate 2 by alternately laminating islanded metallic thin films 3 having a dielectric constant ε1 and dielectric thin films 4 having a dielectric constant ε2 to obtain the objective polarizer 1. The wavelength λ of light incident on the multilayered film and the thickness dm of each of the metallic thin films 3 satisfy the relation of λ/1,000<dm<λ/50 and the wavelength λ and the thickness dd of each of the dielectric thin films 4 satisfy the relation of λ/27<dd<λ/2. The dielectric substrate 2 is made of quartz glass, BK-7 glass, etc., the metallic thin films 3 are made of a metal such as Ag or Cu and the dielectric thin films 4 are preferably made of the same material as the substrate 2 so as not to produce difference in the coefft. of thermal expansion between the thin films 4 and the substrate 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarizer used for optical fiber communication or optical fiber sensor parts.

[0002]

2. Description of the Related Art As a conventional main polarizer, (1) a polarizing prism represented by a Glan-Thompson prism composed of a crystal having a large birefringence, and (2) a polarized component is separated by utilizing Brewster conditions. PBS (polarizing beam splitter), (3) a polarizing film that orients a polymer material in a certain direction and absorbs polarized components in one direction, (4) uses transparent glass as a transparent solid medium, and has an elliptical shape in this medium. Polarized glass in which silver particles are dispersed while aligning in a certain direction to give anisotropy, and (5) a device in which a large number of dielectric thin films are laminated on a substrate and the interference of the multilayer thin films is used, etc. There is.

[0003]

Among these various polarizers, the polarizing prism of (1) uses naturally occurring crystals such as calcite, but natural crystals are limited in size. However, it is difficult to obtain a large-sized one, and thus it is difficult to increase the area of the polarizer, and moreover, it is very expensive. The PBS of (2) and the polarizing film of (3) are inexpensive, but on the other hand, the extinction ratio is low and the durability is poor. In the polarizing glass of (4), the metal particles are dispersed in an optically transparent medium and extruded at a predetermined temperature and pressure to elongate the metal particles so that they have polarization characteristics. There is a problem that the manufacturing temperature control is extremely strict and the stability of the characteristics is low.
The polarizer of (5) has a structure in which dielectric thin films and complex dielectric thin films are alternately laminated. To increase the area, the number of laminated layers must be increased, but actually at most 2
Since only about 00 layers can be laminated, it is difficult to increase the area, and there is a defect in peeling of a thin film, which causes a problem in durability.

As a result of earnest research in view of the above circumstances, the inventor of the present invention alternately stacks different thin films similarly to the polarizer of (5), but replaces with a multilayer film of a dielectric thin film and a complex dielectric thin film. When a plurality of island-shaped discontinuous metal thin films and a plurality of dielectric thin films are alternately laminated to form a multilayer film, the wavelength λ of incident light on the multilayer film and the thickness dm of the metal thin film It has been found that by satisfying a certain relationship with the film thickness dd of the dielectric thin film, it is possible to easily increase the area of the polarizer and to prevent peeling of the thin film.

Therefore, the present invention has been completed based on the above findings, and it is an object of the present invention to easily increase the area of a polarizer provided with a multilayer film, and at a low cost without peeling of the thin film. It is to provide a high-performance polarizer having excellent durability.

[0006]

A polarizer of the present invention has a multilayer film in which a plurality of island-shaped discontinuous metal thin films and a plurality of dielectric thin films are alternately laminated on a dielectric substrate. The wavelength λ of incident light with respect to the multilayer film, the film thickness dm of the metal thin film, and the film thickness dd of the dielectric thin film are set in the following relationship.

Λ / 1000 <dm <λ / 50 λ / 27 <dd <λ / 2

[0008]

1 is a perspective view of a polarizer 1 of the present invention, and FIG. 2 is an operation principle diagram of the polarizer 1. Polarizer 1
Is a plate-type dielectric substrate 2 made of quartz glass or the like.
In this structure, an island-shaped metal thin film 3 having a permittivity ε1 and a dielectric thin film 4 having a permittivity ε2 are alternately laminated in this order to form a multilayer film. In each of these figures, each of the layers 3 and 4 simply represents a stack of several layers, but in reality, it has a structure in which a large number of layers are stacked, and the metal thin film 3 is further included.
When the is sandwiched, it is displayed as a black layer.

This multi-layer film is provided by a thin film forming means such as sputtering or vacuum deposition. At this time, when the metal thin film 3 is formed to be a very thin film, the film is discontinuously formed into islands at the initial stage of film formation. , It was confirmed that such a metal thin film absorbs light of a specific wavelength, unlike the usual bulk.

The light wavelength of the light absorption depends on the shape of the metal particles (in the present invention, particles composed of a large number of metal atoms are referred to as metal particles) forming the metal thin film. When stretched and oriented in the direction perpendicular to the stacking direction (over the film formation surface), the polarized component in the stretching direction of the metal particles is largely absorbed, whereby the transmitted light has a specific polarized component and As a result, a polarizer is formed.

The dielectric substrate 2 is made of quartz glass, BK-
The thin metal film 3 is made of Ag, Cu, Au, Fe, Ni, Cr, or the like. Furthermore, it is desirable to use the same material for the dielectric thin film 4 by forming it with BK-7 glass or Pyrex glass similar to that of the dielectric substrate 2, whereby the dielectric thin film 4 and the dielectric substrate 2 can be used. There is no difference in the coefficient of thermal expansion between the two, so that no stress is generated in the dielectric thin film 4 and film peeling does not occur.

The present inventor repeatedly conducted a number of experiments based on theoretical considerations. As a result, the wavelength λ of incident light with respect to the multilayer film, the film thickness dm of the metal thin film 3, and the film thickness of the dielectric thin film 4 were obtained. It has been found that when dd is set to the following relationship, the heat stretching can be stably performed, and thereby the polarizer 1 having excellent polarization characteristics can be obtained. λ / 1000 <dm <λ / 50 λ / 27 <dd <λ / 2 Next, theoretical consideration according to the present invention will be described. There are conduction electrons in the metal thin film 3, and these electrons have a function of connecting a large number of positive ions to each other, but the electrons move around in the metal particles forming the metal thin film 3 (the metal thin film 3 is a continuous film). Rather, it is a discontinuous film called an island-shaped metal thin film, which results in a film in which metal particles are independently spread on a substrate). When the electric field is not acting on the metal thin film 3, the metal particles become electrically neutral because the stationary sphere of ions and the stationary sphere of electrons overlap.

On the other hand, when a uniform electric field having the same size and direction is applied to each metal particle, ions (Au ⁺ , Ag ²⁺ , Al ³⁺ , Cu depending on the type of the metal particle are used).
²⁺ , Ni ^+, etc.), the electrons start moving in the direction opposite to the direction of the electric field.

That is, under such a uniform electric field,
In any metal particle, the electrons that make up it move the same distance, so that these electrons move in a direction opposite to the direction of the electric field, while maintaining their spherical shape.
The centers of both the sphere consisting of ions and the sphere consisting of electrons are displaced, and as a result, there are portions where only electrons exist and portions where only left-over ions exist, and the surface of each metal particle is negative. There is a positively charged part and a positively charged part,
There is an induced charge.

[0015] Incidentally, when an electric field is applied as described above, when the electric field is varied per second 10 ¹⁵ times direction, so that electrons of the sphere also move up and down per ¹⁰¹⁵ times.

Thus, when the incident light passes through each metal particle of the metal thin film 3 under such an electric field, the electron is shaken by the oscillating electric field, and when the incident light continues to hit the metal particle, the electron Is swayed by an oscillating electric field, on the other hand, it continues to oscillate with an amplitude that is blocked by electrical resistance and finally reaches equilibrium.

That is, the electrons vibrating while receiving electric resistance release heat due to Joule loss, and the vibration decays. However, since the vibration energy is continuously supplied from the incident light, the vibration continues. As a result, the energy of the light that has passed through the metal particles is reduced as compared with the energy of the incident light before hitting the metal particles, and the emitted light is weakened.

However, incident light of all wavelengths is not weakened at the same rate, and when incident light of various wavelengths (incident light of various frequencies) hits a metal particle, it is equal to the plasma frequency of electrons. Incident light at a frequency loses most energy and becomes heavily attenuated, even if the frequency is not exactly equal to the plasma frequency,
A large energy loss occurs.

Therefore, as a result of further diligent research based on the above theoretical consideration, the present inventor has found that the above-described phenomenon occurring in the metal particles has a shape (for example, an ellipse) peculiar to the metal particles constituting the metal thin film 3. It has been found that the polarization is remarkable in the case of having a body shape and a cylindrical body shape, and that a specific polarization occurs depending on the shape of the metal particles.

Further, the present inventor sets the metal thin film 3 and the dielectric thin film 4 under a certain film thickness condition and heat-stretches them to form metal particles having a major axis radius RL and a minor axis radius RS. Along with this, in the major axis direction and the minor axis direction (corresponding to the Y axis direction and the X axis direction in FIG. 2, respectively), resonance vibrations are caused for incident lights having different specific wavelengths, respectively, and thereby, Resonant absorption of light occurs in each direction, and as a result, the absorption amount of the polarized component in the major axis direction and the polarized component in the minor axis direction of the incident light with respect to the metal particles in the metal thin film 3 is different. It was found that it has the function of.

Therefore, based on such knowledge, the following relationship has been derived. λ / 1000 <dm <λ / 50 λ / 27 <dd <λ / 2 When the film thickness dm of the metal thin film 3 is λ / 10000 or less, the metal particles in the metal thin film do not grow and the metal particles When the anisotropy is not given and the thickness is λ / 50 or more, the metal thin film does not become a discontinuous island-shaped thin film but becomes a continuous thin film and serves as a reflective film.

When the film thickness dd of the dielectric thin film 4 is λ / 27 or less, metal particles cannot be embedded,
When the metal particles cannot be anisotropic and have a thickness of λ / 2 or more, the film thickness is large, so that stress is generated in the film and peeling occurs, resulting in an increase in loss.

[0023]

【Example】

(Example 1) In the polarizer 1 of this example, a plate-type dielectric substrate 2 made of BK-7 glass (refractive index 1.51) is used.
An Ag layer (having a refractive index of 0.392-j
8.06) as a dielectric thin film 4 and BK-7 glass layers (refractive index 1.51) are alternately laminated in this order to form a multilayer film.

In order to manufacture the polarizer 1 having this structure, first, a vacuum degree of 1.0 × 10 is formed on the dielectric substrate 2 by vacuum vapor deposition.
^-3 Torr, an Ag layer having a film thickness of 5 nm is formed under the conditions of a vapor deposition rate of 0.02 nm / sec, and after the vapor deposition, the Ag layer is heated at about 400 ° C. by a radiant heat heating method, thereby forming an island shape. The Ag particle shape is adjusted to be spherical (the diameter of this spherical is, for example, 100 nm to 500 nm). Then, a vacuum degree of 1.0 × is formed on the Ag layer by sputtering.
Film thickness 1 at 10 ^-3 Torr and deposition rate 0.2 nm / sec
A BK-7 glass layer of 00 nm is formed.

The above series of steps are repeated several times to alternately stack Ag layers and BK-7 glass layers to form a multilayer film. The multilayer film is stretched while being heated at a temperature (600 ° C.) near the softening point of the BK-7 glass substrate so that the island-shaped metal particles have anisotropy and the particles are oriented at the same time. .

According to the polarizer 1 having this structure, when the wavelength λ is 1310 nm, λ / 1000 to λ / 5.
Within the range of 1.31 nm to 26.2 nm corresponding to 0,
There is dm (5 nm). Further, within the range of 48.5 nm to 655 nm corresponding to λ / 27 to λ / 2, dd (10
0 nm).

According to the thus-obtained polarizer 1, a large area can be easily achieved, and the film thicknesses dm and dd of the metal thin film 3 and the dielectric thin film 4 satisfy the conditions of the present invention. The shapes of the metal particles were extremely well aligned, the extinction ratio was 45 dB or more, and the polarization characteristics were stably obtained at the desired wavelength. Moreover, the thin film was not peeled off, and the durability was remarkably improved.

(Example 2) In the polarizer 1 of (Example 1),
Although the Ag layer is formed as the metal thin film 3, in this example, an Au layer is arranged instead of the Ag layer, and the other configurations are the same.

The Au layer is vacuum-deposited at a vacuum degree of 1.0 × 10 −3 Torr and a deposition rate of 0.015 nm / s.
The film thickness is 5 nm under the film forming conditions of ec. In addition, as with the Ag film, the film after vapor deposition is subjected to radiant heat
It is heated to around 00 ° C., and thereby the island-shaped Au particle shape is made spherical. Then, a BK-7 glass layer having a film thickness of 100 nm is formed on the Ag layer by sputtering at a vacuum degree of 1.0 × 10 ⁻³ Torr and a deposition rate of 0.2 nm / sec. Then, similarly, a series of steps are repeated several times to alternately stack Au layers and BK-7 glass layers to form a multilayer film.
-7 While heating at a temperature (600 ° C.) near the softening point of the glass substrate, stretching is performed so that the shape of the island-shaped metal particles has anisotropy and the particles are simultaneously oriented.

According to the thus obtained polarizer 1, the film thicknesses of the metal thin film 3 and the dielectric thin film 4 satisfy the conditions of the present invention as in the case of (Example 1). Therefore, it is easy to increase the area. In addition, the shapes of the metal particles were extremely well aligned, the extinction ratio was 45 dB or more, and the polarization characteristics were stably obtained at the desired wavelength. Further, since the peeling of the thin film is eliminated, the durability is also improved.

The present invention is not limited to the above-described embodiments and examples, and various modifications and improvements may be made without departing from the gist of the present invention.

[0032]

As described above, according to the present invention, a plurality of island-shaped discontinuous metal thin films and a plurality of dielectric thin films are alternately laminated to form a multilayer film, and the incident light is applied to the multilayer film. By satisfying the required conditions among the wavelength of light, the film thickness of the metal thin film, and the film thickness of the dielectric thin film, it is possible to easily increase the area of the polarizer and remove the thin film. As a result, it is possible to provide a high-performance and highly-reliable polarizer that is low in cost and excellent in durability.

Further, according to the present invention, under the required conditions, the kind of the dielectric material and the film thickness of the dielectric thin film,
Since various properties can be easily designed by controlling the stretching ratio and the like, a high-performance polarizer with low cost and excellent durability can be easily provided as desired depending on the application.

[Brief description of drawings]

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

FIG. 2 is a schematic perspective view showing the operating principle of the polarizer of the present invention.

[Explanation of symbols]

 1 Polarizer 2 Dielectric Substrate 3 Metal Thin Film 4 Dielectric Thin Film

Claims (1)

[Claims] 1. A multilayer film in which a plurality of island-shaped discontinuous metal thin films and a plurality of dielectric thin films are alternately laminated on a dielectric substrate, and a wavelength λ of incident light to the multilayer film is provided.
And a film thickness dm of the metal thin film and a film thickness dd of the dielectric thin film are set in the following relationship. λ / 1000 <dm <λ / 50 λ / 27 <dd <λ / 2