Abstract
Transmission properties of circular dielectric- coated metallicwaveguides for infrared transmissionMitsunobu Miyagi, Kazuhide Harada, Yoshizo Aizawa, and Shojiro KawakamiResearch Institute of Electrical Communication, Tohoku University,2 -1 -1 Katahira, Sendai, 980 JapanAbstractSeveral kinds of dielectric- coated metallic waveguides such as germanium- coated nickelor silicon- coated aluminum hollow waveguides are fabricated by using a method based on rfsputtering, plating, and etching techniques. Transmission losses of 0.34 dB /m are achievedfor straight waveguides at 10.6 pm. Measurements of bending losses of several kinds ofhollow waveguides are conducted, which reveal that dielectric- coated metallic waveguideshave smaller bending losses than conventional metallic waveguides. Edge -guided modes orwhispering gallery modes in circular metallic waveguides are also observed. A design theoryfor reducing bending losses of circular dielectric- coated waveguides has been presented byusing a new theory' different from that used previously.2 Theoretical and experimentalresults have been compared.IntroductionDevelopment of low -loss flexible waveguides is of great concern for transmitting infraredCO2 laser light in medical and industr_al applications. Although significant progress hasbeen made for dielectric fibers as cited in our previous paper,' hollow -core waveguides seemto be potential media from the viewpoint of high power operation. So far there have beenproposed and fabricated several types of hollow -core waveguides for practical use.3 -7 Amongthem, there are two types of circular waveguides which can transmit the HE1, mode with low
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