| 摘要 |
An active polarization control system, which provided two dimensional optical waveguide birefringence modulation, provides polarization control in systems such as fiber optic rotation sensors and coherent fiber optic communications systems without the necessity of using costly polarization preserving fiber. In a rotation sensor, the signal output from the sensing loop is used to form feedback signals for correcting polarization state errors. The feedback signals are used to provide the corrective voltage applied to two banks of orthogonally modulated birefringence transducers situated inside the rotation sensing loop. In a coherent fiber optic communications system orthogonal modulation of two banks of birefringence transducers situated in either the communications or local oscillator signal arms at the receiver provides the required feedback signals for polarization control. The polarization of light guided by an optical waveguide is controlled by adjusting the birefringence of the opticla waveguide with a first transducer and a second transducer arranged to act on the optical waveguide along parallel axes and a third transducer being on an axis that is placed between the parallel axes and angularly displaced by 45 DEG therefrom. A first control signal is applied to each of the first and second transducers, and a second control signal in time quadrature with the first control signal is applied to the third transducer.
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