Optical: systems and elements – Optical modulator – Light wave temporal modulation
Patent
1995-10-02
1998-05-26
Ben, Loha
Optical: systems and elements
Optical modulator
Light wave temporal modulation
359281, 359484, G02F 109
Patent
active
057575380
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to an optical isolator for use in optical communication, broadcast wave transmission using light, measurement by light, and so on to prevent a light wave emitted from a laser as a light source from returning to the light source due to various causes.
BACKGROUND ART
FIG. 1 shows a structure of an optical isolator in the prior art which basically comprises a Faraday element 1, a first polarizer 4a, a second polarizer 4b, and a permanent magnet 3. The Faraday element 1 used herein is a rare earth-bismuth-iron-garnet single crystal thick film prepared by the LPE (liquid phase epitaxial) method. The Faraday element 1 is practically used, for instance, in optical communication. The polarizers 2a and 2b (which are collectively referred to as 2 alone) used herein are polarizing prisms, polarizing glass plates, and the like. In addition, the permanent magnet 3, is made of a ferrite magnet, a rare-earth metal, or the like, which has a cylindrical shape and is magnetized in an axial direction.
In order to ensure desired characteristics of the optical isolator, accurate positioning of the optical isolator in a plane perpendicular to an optical axis is necessary such that an angles is formed between the first polarizer 4a and the Faraday element 1 and another angles formed between the first and the second polarizers 4a and 4b. Accordingly, in production, it is extremely important to fix, with high precision, these components by the use of an organic adhesive, an inorganic adhesive, or metal such as solder.
The polarizer may be made of metallic thin films which have recently been known to have a polarization characteristic. The metallic thin films are formed so as to have narrow stripe shapes in a substrate, for example, glass and spaced from each other by an interval not greater than one tenth of the wavelength of light. Such a metallic thin film is also used as the polarizer in the optical isolator. Even in this case, however, it is inevitable to carry out a production process similar to that mentioned above.
As mentioned above, the prior art optical isolator is produced by mechanically fixing the individual components or by use of an adhesive. During production, the locational and angular positioning must be established with high precision as mentioned above. Therefore, it is not easy to maintain good quality at a low cost. Additionally, with a miniaturization of the apparatus on which the optical isolator is mounted, the optical isolator is required to be of a smaller size which is hardly achieved by the conventional technique of the prior art.
It is therefore an object of the present invention to solve the above-mentioned problems and to provide an optical isolator which is small in size, light in weight, and simple to produce.
SUMMARY OF THE INVENTION
In accordance with one form of the present invention, an optical isolator includes a Faraday element having polarization films formed on a light incident surface and a light outgoing surface thereof and which is for rotating a polarization plane of incident light by an angle approximately equal to 45.degree., and a magnetic field applying mechanism for applying a magnetic field to the Faraday element. Each of the polarization films includes a thin film made of a conductive material, and the polarization films are formed on the light incident surface and the light outgoing surface of the Faraday element, respectively, in the form of a unidirectional grating with an interval not greater than one tenth of the wavelength of light. One of the polarization films formed on the light outgoing surface forms, in a plane perpendicular to an optical axis, an angle with respect to the other polarization film formed on the light incident surface, wherein the angle is approximately equal to 45.degree. in a direction similar to that of rotation of the polarization plane by the Faraday element.
A preferred form of the optical isolator, as well as other embodiments, objects, features and advantages of this invention, will be apparent from
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Ben Loha
Tokin Corporation
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