The effects of polarization control of the transfer function and the phase induced intensity noise of a fiber-optic recirculating delay line

When a fiber-optic recirculating delay line with a mid-loop polarization controller is preceded by another polarization controller and followed by a linear polarizer, the system becomes highly polarization-dependent. The periods of the transfer function and of the power spectrum of the phase-induced intensity noise can be halved, and the latter can also exhibit maximum noise instead of minimum noise at frequencies which are multiples of 1/(loop delay). It is also shown theoretically and experimentally that by proper adjustment of the polarisation controllers, the normally observed filtering notches at frequencies f=(n+0.5)/(loop/delay) disappear, making the device a polarization-controlled RF filter. Possible applications are discussed