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8 February 2008 A combined cavity for high sensitivity THz signal detection
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Detection of signals in the THz frequency region is important for applications of THz waves in many areas, such as in medical imaging, forbidden-combined sensing, weapon monitoring, and wireless communications. Cooling system operating under very low temperature, for eliminating the unwanted background THz radiation that exists everywhere in room temperature, sets an obstacle for applications of conventional THz signal detecting systems. We present a combined cavity that can pick out the useful signal in high sensitivity, while the influence of the background THz radiation can be neglected in the detection. The combined cavity consists of a point-defect photonic-crystal resonator and a photonic-crystal WGR. The two resonators are coupled together through optical tunneling to form the combined cavity. Under proper operating parameters, the two resonators are in simultaneous resonance, and the field intensity in the point-defect resonator can be thousands of times of that of an incoming THz signal for a given frequency, so that the sensitivity of detection can be very high. Since the background THz radiation is not in resonance with the cavity, the influence of it to the detection of THz signals wanted can be neglected, and thus cooling systems can be omitted. Plane wave expansion method is used to determine the resonance wavelengths and mode patterns of the cavity. Finite-difference- time-domain method is used to find the quality factors and to simulate the resonance process. Parameter optimization and the conditions for simultaneous resonance of the two cavities are studied.
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Zhengbiao Ouyang, Xianda Luo, Jong C. Wang, Chung Ping Liu, and Chih Jung Wu "A combined cavity for high sensitivity THz signal detection", Proc. SPIE 6840, Terahertz Photonics, 684008 (8 February 2008);


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