OCT technique for distance measurement using an RTD terahertz oscillator

We propose a method for distance measurement using terahertz waves based on the amplitude modulation of a resonant-tunneling-diode (RTD) oscillator and using a method similar to the optical coherence tomography (OCT). The terahertz output of the RTD oscillator is modulated in amplitude at a series of frequencies and sent to the target. The returning wave is demodulated and homodyne mixed with the original modulation signal at each of those frequencies. The distance to the target is calculated from the inverse Fourier transform of the series of mixer output signals. In principle, the distances to multiple targets can be measured simultaneously; here we report the experimental verification for the case of one and two targets.