Optical waveguides – Polarization without modulation
Patent
1990-04-27
1991-12-10
Lee, John D.
Optical waveguides
Polarization without modulation
385 43, 385 29, G02B 626
Patent
active
050712128
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. TECHNICAL FIELD
This invention relates to a polarizer which is used to obtain linearly polarized light having a particular polarization plane and a process of production of the same, and more particularly to an optical fiber polarizer which is obtained by working an optical fiber and is suitably inserted in and used with an optical transmission line of an optical communication system or is suitably used as a component of an optical isolator and also to a process of production of the same.
2. BACKGROUND ART
A polarizer is used to obtain linearly polarized light having a particular polarization plane from other light such as elliptically polarized light than linearly polarized light or is used to obtain a linearly polarized light component from linearly polarized light which is considered to be a combination of two linearly polarized light components having mutually perpendicular polarization planes. Conventionally, the following polarizers are well known as polarizers of the type mentioned: use of the fact that a birefringent crystal has different refractive indices with respect to ordinary and extraordinary rays of light; dielectric multi-layer film or the like such that a beam of light incident to a thin film is separated into two linearly polarized light components having mutually perpendicular polarization planes and one of the two linearly polarized light components passes through the thin film while the other linearly polarized light component is reflected by the thin film; and and metal layers laminated in an alternate relationship with each other and absorbs and removes, when a beam of light is introduced in parallel to the planes of the layers into the polarizer, one of linearly polarized light components.
Such polarizers are used to the following applications in the field of optical communications: semiconductor laser which emits in a predetermined condition and an external modulator for intensity modulating light from the light source, where the modulation characteristic of the external modulator is varied in response to a polarization condition of light as in the case of a modulator of the Mach-Zehnder type, a polarizer is provided on the light source side of the external modulator so that linearly polarized light having a particular polarization plane may be introduced into the external modulator in order to stabilize the modulation characteristic of the external modulator. there is a gap in refractive index such as a connecting point between optical fibers or an exposed end portion of an optical fiber, light from an optical transmitter is sometimes reflected by the portion and partly returned into the optical transmitter. If such reflected returning light is produced, particularly where the light source is a semiconductor laser, the operation thereof is put into an unstable condition by the reflected returning light. In such an instance, an optical isolator is provided intermediately of an optical transmission line so as to remove reflected returning light. A polarizer is thus used as a component essential to the optical isolator of the type mentioned.
By the way, since a most popular one of optical transmission lines in an optical communication system is an optical fiber, where a polarizer itself or an optical isolator including a polarizer as a component therein is provided in an optical transmission line in any of such applications as described above, it is necessary to cut an intermediate portion of the optical transmission line and provide a parallel light beam system at the location. In other words, while light emitted from an emergent end of one of a pair of cut optical fibers with a predetermined numerical aperture is collimated into a beam by a convex lens and then the beam of light is condensed by another convex lens and introduced to an incident end of the other cut optical fiber, it is necessary to dispose a polarizer at a location of such parallel light beam formed between the two convex lenses. If such parallel light beam system is not constructed, then even if li
REFERENCES:
patent: 4586784 (1986-05-01), Tremblay et al.
patent: 4725113 (1988-02-01), Chang et al.
patent: 4795233 (1989-01-01), Chang et al.
Arima Tadao
Inagaki Shinya
Mesaki Akitoshi
Okamura Kouji
Suzuki Norio
Barns Stephen W.
Fujitsu Limited
Lee John D.
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