PASSIVE ELIMINATION OF POLARIZATION SENSITIVITY OF FIBEROPTIC MICROWAVE MODULATORS

The polarization sensitivity of a bidirectional fiberoptic modulator i s passively eliminated by incorporating the modulator in an orthoconju gate loop mirror or in an in-line fiber loop. We describe and analyze these fiber loop configurations which allow remote interrogation of po larization-sensitive devices with either one or two conventional singl emode fibers. For bulk single-drive modulators, the polarization sensi tivity is reduced to +/-0.15 dB out to 2 GHz. By utilizing a balanced, dust-drive feed to a bidirectional traveling-wave modulator, residual polarization sensitivity of +/-2 dB is demonstrated for ultrawideband operation to 25 GHz and +/-0.3 dB for narrowbands.