We propose and experimentally demonstrate a continuous-wave (CW) terahertz (THz) imaging system based on microwave photonic signal generation scheme. Compared to the traditional opto-electronic THz imaging by using unmodulated lasers, our proposed system obtains the amplitude information by using microwave photonic optical double sideband modulation (DSB). As a result, the phase noise and frequency drift of the free-running laser sources are negligible. We experimentally demonstrate a THz imaging system for measuring various 3D-printed samples by using a 300 GHz DSB signal. In the experiment, the optical DSB modulation is realized with an in-phase and quadrature Mach-Zehnder modulator, and THz signals are generated by photo-mixing at a uni-traveling-carrier photodiode. The THz signals passing through the sample is received by a self-mixing-based Schottky barrier diode. The experimental results show signal-tonoise ratio (SNR) a ~25 dB . In addition, we verify that the optical DSB system operating in the linear regime is superior to the carrier-suppressed scheme, which is attributed to higher THz power and higher SNR. Therefore, the proposed scheme based on microwave photonic double sideband modulation is potentially promising in high-resolution object recognition.
In this paper, square lattices of air holes were fabricated on a three-layer structure of metal-dielectric-metal using
micromachining technology. The metal-dielectric-metal structure is based on RT/duroid 5870 produced by Rogers
corporation. The square period is 400 μm and the radius of circular hole is 100 μm. The thickness of the structure is
about 863 μm with metal thickness of 39.2 μm and dielectric layer thickness of 785 μm. The loss and dispersion of the
dielectric layer with the dielectric constant of 2.33 are low at microwave frequencies. Terahertz transmission spectra
through the sample were measured by the state-of-the-art THz-TDS system. Experimental results show that there is a
transmittance centered at 1 THz with a wide pass-band exceeding 100 GHz. Transmission spectra calculated by FDTD
method were given for comparisons and showed good agreements with the experimental results. Through analysis, the
extraordinary transmission phenomena are caused by both the Febry-Parot effect and surface plasmon polaritons existing
on the metal arrays.
An experimental research on the wavelength conversion utilizing non-degenerate four-wave mixing in photonic crystal
fiber is presented. Two pumps and a 25 m dispersion flattened and highly nonlinear photonic crystal fiber are used in our
non-degenerate four-wave mixing experimental study. The wavelength conversion bandwidth is about 65 nm. The
wavelength conversion efficiency is -22.7 dB when the powers of two pumps are 17.3 dBm and 13.4 dBm. The
conversion efficiency in the wavelength range of 1 530 to 1 560 nm is stable.
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