Millimeter-Wave Vector Signal Generation Based on a Bi-Directional Use of a Polarization Modulator in a Sagnac Loop

A novel technique to generate a frequency-doubled millimeter-wave (mm-W) vector signal that is immune to fiber chromatic-dispersion-induced power fading and free from interband beating interferences (IBBIs) based on a bi-directional use of a polarization modulator (PolM) in a Sagnac loop is proposed and experimentally demonstrated. The fundamental concept of the proposed approach is to use a PolM that is incorporated in a Sagnac loop at which a light wave is modulated by an intermediate-frequency vector signal along one direction and with no modulation along the opposite direction due to the traveling-wave nature of the PolM. The combination of the modulated and un-modulated signals at a photodetector will generate an mm-W signal that is immune to the fiber chromatic-dispersion-induced power fading and free from the IBBIs. The generation of a 100 and a 500 MSym/s 16-QAM signal at 31.5 GHz and the transmission of the signals over a 25-km single-mode fiber are evaluated. An error-free transmission of the 100 MSym/s signal and the transmission of the 500 MSym/s signal with a bit-error-rate below the forward error correction threshold of 3.8 × 10^-3 are achieved.