Tsinghua University and Capital Normal University (both in Beijing, China) researchers have demonstrated that large-diameter polymer light pipes can transmit singlemode terahertz radiation when fabricated with the proper physical parameters.
Fabrication begins with a single polymethylmethacrylate (PMMA) hollow tube that is filled with seven small PMMA hollow tubes and drawn into polymer light pipes with two layers. The outer pipes are 3–4 mm in diameter with 200 μm wall thickness, which support the hexagonal inner pipe by six thin walls. Experimental and theoretical modeling of the configuration as a function of the radius of the inner pipe (r) show that singlemode guiding of a terahertz wave is accomplished when the radius value is near 1 mm. This is because in this condition, only the HE11 mode field concentrates in the inner pipe, whereas the fields of all the higher modes expand to the space between the inner and outer pipes leading to high attenuations in these modes. For a 15-cm-long sample of the polymer pipe transmitting a 3.1 THz light beam, the insertion loss was measured at 5.34 dB including the coupling loss at the input end. Contact Wei Zhang at zwei@tsinghua.edu.cn.
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