Polarizing separating device and optical isolator employing the

Details Polarizing separating device and optical isolator employing the Polarizing separating device and optical isolator employing the

1989-10-26

1991-12-31

Arnold, Bruce Y.

Optical: systems and elements

Polarization without modulation

Polarization using a time invariant electric, magnetic, or...

359488, 359589, G02B 530, G02B 2728, G02F 109

Patent

active

050766759

DESCRIPTION:

BRIEF SUMMARY
DESCRIPTION

1. Technical Field
This invention relates to a polarizing separating device employing a polarizer of the open construction and an optical isolator employing such polarizing separating device, and more particularly to a polarizing separating device which is wide in wavelength band with which an extinction ratio higher than a predetermined level can be obtained and besides is suitable in reduction in overall size thereof and to an optical isolator employing such polarizing separating device.
2. Background Art
Generally, in an optical communication system which employs optical fibers as a transmission path, light introduced into an optical fiber from a light source is sometimes reflected at a junction between adjacent optical fibers and partly returns to the light source. If such reflected returning light takes place, then where the light source is a semiconductor laser (for example, a semiconductor laser of the distribution feedback type which is superior in spectrum characteristic), operation of the light source becomes unstable, and the transmission quality is deteriorated. Accordingly, an optical isolator which can allow transmission of light only in a forward direction is required.
A polarizer which forms a common component of optical devices such as an optical isolator and an optical switch has a function to separate polarized light (linearly polarized light) from non-polarized light or to separate polarized light into two polarized light components having planes of polarization orthogonal to each other. Such polarizers are roughly separated, from their constructions, into two types including a type wherein a birefringent crystal of rutile (monocrystal of TiO.sub.2) is used to effect polarizing separation based on a difference in refractive index between a normal light component and an abnormal light component of light passing therethrough and another type wherein an interference film such as a dielectric multilayer film is used to reflect and transmit different polarized components to effect polarizing separation. Of the two types, a polarizer of the type which is constructed using an interference film (polarizing separating film) has a greater separation angle, which is advantageous in construction of an optical device such as an optical isolator. Accordingly, polarizers of the latter type are employed widely.
When it is intended to construct a polarizing separating device using a polarizing separating film, it is common to construct a polarizer of the short construction wherein a polarizing separating film is put on the opposite sides thereof between a pair of transparent substrates in order to assure a high extinction ratio (crosstalk) and assure a wide wavelength band of light with which an extinction ratio higher than a predetermined level can be obtained. However, since the short construction requires at least two transparent substrates, the device obtained has a comparatively large overall size and is complicated in construction. In this regard, a polarizer of the open construction wherein a polarizing separating film is directly exposed to the air is advantageous because it requires only one transparent substrate. However, in order to assure a wide wavelength band of light with which an extinction ratio higher than a predetermined level can be obtained using a polarizer of the open construction, it is necessary to set the incident angle of light to the polarizer to a large angle of, for example, 70 degrees or so. Accordingly, depending upon a diameter of a light beam, the polarizer must have a large size, which is accompanied by a large overall size of the device.


SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide a polarizing separating device wherein the wavelength band with which an extinction ratio higher than a predetermined level can be obtained is wide.
It is another object of the present invention to provide a polarizing separating device which assures a wide wavelength band of light with which an extinction ratio higher than a pred

REFERENCES:
patent: 4553822 (1985-11-01), Mahlein
patent: 4641926 (1987-02-01), Shirasaki
patent: 4725109 (1988-02-01), Wank et al.
patent: 4770505 (1988-09-01), Okazaki
patent: 4854670 (1989-08-01), Mellor
patent: 4900137 (1990-02-01), Carter
patent: 4931315 (1990-06-01), Mellor

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