Optical: systems and elements – Optical modulator – Light wave temporal modulation
Reexamination Certificate
1998-12-04
2001-08-14
Sikder, Mohammad Y. (Department: 2872)
Optical: systems and elements
Optical modulator
Light wave temporal modulation
C359S281000, C359S284000, C359S289000, C359S282000
Reexamination Certificate
active
06275323
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical attenuator including a magneto-optic crystal.
When conducting experiments with or adjustments of an optical communication system, sometimes an optical attenuator is used for adjusting the intensity level of an optical input to any device which is part of the system. As an optical attenuator, one adapted to mechanically vary its attenuation factor is known. However, in the case where an optical attenuator is incorporated in a system with the attenuation factor thereof being one of the objects to be controlled, it is desired that an optical attenuator having no mechanically moving part be put to practical use to improve reliability on the system.
2. Description of the Related Art
As optical attenuators which have so far been in practical use, there is one in which the attenuation factor is changed by a mechanical motion. For example, having an attenuation film with a varying attenuation factor distributed thereon inserted in the optical path, the attenuation factor of the optical attenuator can be adjusted by shifting the attenuation film.
However, it sometimes becomes necessary in practice to use such an optical attenuator incorporated in a control system in which the attenuation factor of the very optical attenuator is an object to be controlled. An example is a case where, in an optical amplifier adapted to amplify a signal light wave by conducting the signal light wave together with an pumping light wave through an optical fiber doped with a rare earth element such as Er (erbium), the power of the signal light and/or pumping light is controlled in accordance with the monitored level to thereby obtain a required characteristic (for example S/N ratio). In such a case, use of an optical attenuator adjusting the attenuation factor mechanically should be avoided in order to secure reliability on the control system.
Accordingly, an object of the present invention is to provide an optical attenuator having no mechanically moving part.
Other objects of the present invention will become apparent from the following description.
SUMMARY OF THE INVENTION
According to the present invention, there is provided an optical attenuator varying an attenuation factor in its optical path in accordance with an input signal thereto comprising a magneto-optic crystal provided in the optical path, a polarizer provided in the optical path on the downstream side of the magneto-optic crystal allowing a light wave having a specific direction of polarization to pass therethrough, magnetic field application means for applying a first and a second magnetic field acting in different directions from each other to the magneto-optic crystal such that the strength of the composition of these magnetic fields exceeds a predetermined value, and magnetic field adjustment means for varying strength of at least one of the first and second magnetic fields in accordance with the input signal.
The above and other objects, features and advantages of the present invention and the manner of realizing them will become more apparent, and the invention itself will best be understood from a study of the following description and appended claims with reference to the attached drawings showing some preferred embodiments of the invention.
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Fujitsu Limited
Sikd-er Mohammad Y.
Staas & Halsey
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