Variable optical attenuator which applies a magnetic field to a

Details Variable optical attenuator which applies a magnetic field to a Variable optical attenuator which applies a magnetic field to a

1997-02-21

1999-02-02

Ben, Loha

Optical: systems and elements

Optical modulator

Light wave temporal modulation

359280, 359246, 359324, 359484, 3242441, G02F 109

Patent

active

058673008

ABSTRACT:
An apparatus which attenuates a light signal polarized in a first direction. The apparatus includes a polarization rotation unit and an output unit. The polarization rotation unit rotates the polarization of the light signal to produce a polarization rotated light signal having a polarization component in the first direction and a polarization component in a second direction which is substantially 90 degrees with respect to the first direction. The output unit passes, as an output signal, the polarization component in the second direction of the polarization rotated light signal and blocks the polarization component in the first direction. The polarization rotation unit includes an electromagnet and a permanent magnet which apply magnetic fields in specific directions with respect to the light path. Various yoke constructions are provided for the electromagnet and the permanent magnet. A control circuit maintains the output power of the output signal at a constant level, or maintains a constant ratio between the power level of the output signal and the power level of the light signal before the polarization is rotated. The apparatus can have a wavelength dependent attenuation which compensates for the wavelength dependent gain of an optical amplifier.

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