Photomixer Systems as Submillimeter Oscillators and Coherent Test Sources

The development of widely tunable coherent frequency sources for application as local oscillators or simply as test equipment above 1 THz remains an impediment in receiver development and characterization. Photomixer sources have demonstrated sufficient power to pump SIS mixers to over 600 GHz and have demonstrated over 2.5 THz of bandwidth in a single device. First generation photomixer system solved the problem of frequency calibration, but failed to fully address the needed spectral purity required for heterodyne applications. A number of improved laser technologies are greatly simplifying the implementation and improving the spectral purity of photomixer systems, however a full system demonstration in the THz frequency range remains elusive. The current state of the art for photomixer based sources is explored in light of heterodyne local oscillator and coherent tests sources for antenna and component characterization at THz frequencies.