Single-mode antiresonant terahertz fiber based on mode coupling between core and cladding* *Project supported by the National Natural Science Foundation of China (Grant No. 62075159), the National Key Research and Development Program of China (Grant No. 2017YFF0104603), the 111 Project of China (Grant No. B17031), and the Major Scientific and Technological Innovation Projects of Key Research and Development Plans in

Abstract

Based on the index-induced mode coupling between the higher-order mode in core and the fundamental mode in cladding tubes, the single-mode operation can be realized in any antiresonant fibers (ARFs) when satisfying that the area ratio of cladding tube and core is about 0.46:1, and this area ratio also should be modified according to the shape and the number of cladding tubes. In the ARF with nodal core boundary, the mode in core also can couple with the mode in the wall of core boundary, which can further enhance the suppression of high-order mode. Accordingly, an ARF with conjoint semi-elliptical cladding tubes realizes a loss of higher-order mode larger than 30 dB/m; simultaneously, a loss of fundamental mode loss less than 0.4 dB/m.