Continuous wave terahertz system with optical switch and coaxial DFB LD

We have proposed and presented tunable beat source with optical switch for CW THz spectroscopy system. By connecting coaxial DFB LDs to optical switch, we could implement a tunable beat source for the CW THz spectroscopy system. As changing optical path, THz frequency was rapidly changed without frequency drifts. The THz signal at CW THz receiver was measured using a lock-in-amplifier through pre-amplifier, while changing the delay line and also was calculated to obtain peaks of THz frequency by taking FFT of measured THz waveforms. We could see that the FFT peak of experimental results are well matched with the interval frequency of the optical beat source. By equipping the implemented tunable beat source with optical switch and DFB LDs, CW THz spectroscopy system was made and used to THz spectrum of two type wafer with different resistance. Through THz spectrum of Si wafer, we can say that the proposed tunable beat source has great potential as a key module of THz spectroscopy system in nondestructive inspection.