Abstract
We used a resonant-tunneling-diode (RTD) oscillator as the source of a terahertz-wave radar based on the principle of the swept-source optical coherence tomography (SS-OCT). Unlike similar reports in the terahertz range, we apply the stepwise frequency modulation to a subcarrier obtained by amplitude modulation instead of tuning the terahertz carrier frequency. Additionally, we replace the usual optical interference with electrical mixing and, by using a quadrature mixer, we can discriminate between negative and positive optical path differences, which doubles the measurement range without increasing the measurement time. To measure the distance to multiple targets simultaneously, the terahertz wave is modulated in amplitude at a series of frequencies; the signal returning from the target is detected and homodyne mixed with the original modulation signal. A series of voltages is obtained; by Fourier transformation the distance to each target is retrieved. Experimental results on one and two targets are shown.
Highlights
The terahertz electromagnetic range, with frequencies roughly between 0.1 and 10 THz, has seen an increasing number of applications in imaging, spectroscopy, wireless communication, etc
The detector is a Fermi-level-managed barrier diode (FMBD) with a confirmed sensiThe two outputs of the IQ mixer are connected to two low-frequency amplifiers that tivity from 200 GHz to 1 THz [16]
Compared with our implementation of the amplitude-modulated continuous-wave (AMCW) radar based on an RTD source [5,6], the discrete Fourier transform (DFT) radar has the great advantage of being able to measure more than one distance at a time, despite being only marginally more complex
Summary
The terahertz electromagnetic range, with frequencies roughly between 0.1 and 10 THz, has seen an increasing number of applications in imaging, spectroscopy, wireless communication, etc. While at the same time having a short enough wavelength to allow imaging or detection of small targets or features as well as propagation over long distances by using relatively small optics. The positions and shapes of targets in the propagation direction were determined exclusively by using the time-domain spectroscopy, a time-of-flight technique whereby the arrival time of terahertz radiation pulses was used to measure propagation distances. A new technique has been added to the arsenal of terahertz-wave ranging: the optical coherence tomography (OCT), either in its original form, the time-domain (TD) OCT, in which a low-coherence
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