Analysis of Photonics-Enabled FMCW THz Spectrometers for Non-Destructive Thickness Measurements

Photonics-enabled frequency modulated continuous wave (FMCW) THz spectrometers have been identified as the technology able to provide at least the same functionality as the currently used time domain spectrometers, but with reduced complexity, size and cost. In this paper, we perform for the very first time a thorough analysis of the performance of two architectures of an FCMW THz spectrometer for single-layer thickness measurement in reflection geometry. Key components in both architectures are the laser sources, optical amplifiers and THz emitter and THz receiver based on a PIN diode and photomixing receiver, respectively. The first architecture refers to a homodyne scheme where the same pair of laser sources is used for both the generation and reception of the THz signals while the second refers to a heterodyne scheme where two different pairs of laser sources are used at the transmitter and receiver. The two architectures are compared with respect to the magnitude of the generated photocurrent at transmitter, the emitted power of the THz FMCW signal and the power of the recovered signals at the receiver.