Sensitivity-enhancing scheme of a polarimetric heterodyne sensor using a birefringent fiber loop

In order to improve the sensitivity of a fiber-optic polarimetric sensor, a new scheme utilizing a birefringent fiber loop with midloop frequency shifters is proposed. In this scheme, heterodyne signals with an integral multiple-phase sensitivity can be obtained in the frequency domain. The validity of the scheme is confirmed experimentally by a bulk-optic configuration. One-order-of-magnitude improvement in sensitivity without changing the dynamic range is expected from the calculation of the signal-to-noise ratio, even in the case of a 40% excess loss in the optical loop.