The Effects of Polarization Control on the Transfer Function and the Phase Induced Intensity Noise of a Fiberoptic Recirculating Delay Line

When a fiberoptic recirculating delay line with a midloop 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 may be halved, and the latter may also exhibit maximum noise instead of minimum noise at frequencies which are multiples of l/(loop delay). It is also shown theoretically and experimentally that by proper adjustment of the polarization controllers, the normally observed filtering notches at frequencies /=(n + 0.5)/(loop delay) disappear, making the device a polarization controlled RF filter. Possible applications are also discussed.