Optical: systems and elements – Polarization without modulation – Polarization by optical activity
Reexamination Certificate
1997-09-29
2001-06-26
Spyrou, Cassandra (Department: 2872)
Optical: systems and elements
Polarization without modulation
Polarization by optical activity
C359S490020, C427S163100
Reexamination Certificate
active
06252709
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a polarizer that is used in optical communication equipment, optical recording equipment, optical sensors, etc., and in particular, to a polarizer of high extinction ratio and high reliability that can be used effectively in optical isolators used in optical communication equipment.
PRIOR ART
For a long time polarizers have existed that use optical anisotropy obtained by stretching a material. For example, polarizing films and the like have been well known that use polymer films.
Polarizers are also known that exhibit polarization in infrared ranges due to minute anisotropic metal particulates dispersed in a glass. Such polarizers are used extensively in the field of optical communication because these polarizers have smaller losses and higher durability than those polarizers that use polymer films. The former polarizers are produced in the following manner. A glass piece containing silver halide is heat-treated to coagulate silver halide. Then the glass piece is heated and stretched to deform minute coagulated silver halide particles into spheroids, and at the same time, to orient a large number of spheroidal particles in the direction of the longer axis. After that, the silver halide is reduced to metallic silver to impart a polarizing property and produce a polarizer (please refer to Japanese Provisional Patent SHO 56-169140, etc.; hereinafter the process is referred to as the melting method).
As shown in
FIG. 7
, in a polarizer P, metallic particulates
13
in the shape of spheroid are dispersed in a glass piece
11
, and the metallic particulates
13
absorb a polarized component
14
of a transmitted/incident light ray
12
in the direction of the longer axis of the metallic particulates
13
and transmit a polarized component
15
of the light ray
12
in the direction of the shorter axis thereof. As a result, the device works as a polarizer P.
Polarizers produced by the melting method, however, require introduction of a reducing gas to reduce silver halide into metallic silver. As this reducing gas tends to react with other materials, careful handling is required. Moreover, the reducing gas is expensive.
The reduction proceeds from the surface of silver halide, and the final depth of the reduced portion is about several tens of micrometers from the surface. Hence most of the silver will remain unchanged, in the form of silver halide. Accordingly, in terms of utilization of the materials, the efficiency of use of silver halide is extremely low. Moreover, in terms of optical characteristics, silver halide, that does not involve in the polarizing property, increases the insertion loss.
In response to these problems, the following polarizer has been proposed, wherein, just like those mentioned above, metal particles are dispersed in a glass. In this polarizer, to disperse metal particles, a thin film making process such as vacuum evaporation is used to alternately form metal films and dielectric films on a dielectric substrate such as a glass piece. In the metal films the metal is dispersed insularly to form films of insular metal particles. The dielectric films are made from, for example, a glass. Anisotropy is imparted to the insular metal particles by heating and stretching the substrate after the film formation (hereinafter the process is called the thin film method). In comparison with the melting method, this thin film method has some merits, for example, that reduction is not required and the production process is easy (for example, Denshi Joho Tsushin Gakkai, Autumn General Meeting of 1990, Preprints C-212).
However, in polarizers produced by the thin film method, surface deformation such as swell, and surface roughness may be generated as a result of the heating and stretching processes. The surface deformation, in turn, will deflect the incident light ray, and the surface roughness will increase the insertion loss; both deformation and roughness will deteriorate the polarizing property of the finished product.
Furthermore, generally speaking, it is necessary, for optical devices, to form antireflection films on the surface. To this end, the surface must have high cleanliness and smoothness. Adjustment of the device thickness may be required in some cases. It, therefore, is necessary to polish the surface by chemical polishing, mechanical polishing, etc. The conventional thin film method, however, does not expect or anticipate any working after the heating and stretching. Hence polishing may damage a layer that generates polarization.
Methods for giving thermal plastic deformation to the dielectric substrate include, other than the stretching, extrusion with a mold, drawing with a mold, rolling with rollers, etc. According to the working methods other than stretching, the work proper will contact the mold or rollers, and the surface layers of the work proper will be degraded by pressurization. Hence thermal plastic deformation has been limited to the stretching method. In the thin film method, relative to the melting method, it is difficult to raise the density of the dielectric glass, and the external atmosphere may penetrate and deteriorate the polarizing property.
SUMMARY OF THE INVENTION
The present invention is intended to provide a polarizer that is produced by the thin film method, that can undergo thermal plastic deformation given by some -methods other than the stretching method, that has durability even when the surface is polished after thermal plastic deformation, and that has a very good long-term reliability, and a production method thereof.
To accomplish the above objective, according to the present invention, between the major surfaces of at least two dielectric substrates having transparency, at least a polarizing layer wherein a large number of particles having morphological anisotropy are oriented in at least a dielectric layer is placed, and at least said two dielectric substrates are jointed to form a polarizer. Preferably, an antireflection film is provided on the outer major surface of each of at least two dielectric substrates.
According to the production method of the polarizer of the present invention, metal particle layers comprising a large number of metal particles and dielectric layers are alternately built up to form a laminated layer on one major surface of at least one of two dielectric substrates having transparency, then the above two dielectric substrates are jointed, in such a way that the above laminated layer is put between the two dielectric substrates, to form a jointed substrate, after that, the jointed substrate is subjected to thermal plastic deformation in a certain direction to give the metal particles in the above laminated layer morphological anisotropy and orientation, and in turn, to turn the laminated layer into a polarizing layer held between the two dielectric substrates. Preferably, before jointing, the surface of the laminated layer is chemical-polished by CMP (chemical-mechano polishing), etc. Furthermore, preferably, to reduce the insertion loss, both the major surfaces of the jointed substrate are polished, after the thermal plastic deformation, by mechanical polishing, etc. and antireflection films are provided.
According to the production method of the polarizer of the present invention, metal particle layers comprising a large number of metal particles and dielectric layers are alternately built up on one major surface of at least one of two dielectric substrates having transparency to form a laminated layer, then the dielectric substrate on which the laminated layer has been built up is subjected to thermal plastic deformation in a direction to give the metal particles of the laminated layer morphological anisotropy and orientation, and in turn, to turn the laminated layer into a polarizing layer, after that, the above two dielectric substrates are jointed in such a way that the polarizing layer is sandwiched between the two substrates.
According to the polarizer and the production method thereof of the present invention, the polarizing layer, wh
Hogan & Hartson LLP
Kyocera Corporation
Spyrou Cassandra
Treas Jared
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