Optical generation of millimeter-wave signals up to 330 GHz by means of cascadingly phase locking three semiconductor lasers

We developed a technique for the optical generation of high-purity millimeter-wave signals by synthesizing the outputs from three cascadingly phase-locked semiconductor lasers. A semiconductor optical amplifier was used to generate four-wave mixing (FWM) signals from the three laser fields. One of the degenerating FWM pairs was used to construct an optical phase-locked loop (OPLL), which ensured that the frequency separations of the three lasers were kept at a ratio of 1 : 2. Using a commercially available p-i-n photodetector, we also developed a conventional OPLL capable of operating at frequencies up to 110 GHz. By combining these techniques, we generated high-purity millimeter-wave optical-beat signals at frequencies up to 330.566 GHz.