A ring-pattern liquid-filled photonic crystal fiber (R-LPCF) scheme, in which the first-ring holes (the six holes adjacent to the core) are filled with high-index inclusions, has been experimentally demonstrated to extend over a wide-guided spectral range. In such new fiber, the bandgap-like core mode is investigated, among which the telecommunication bandgap exhibits confinement losses five orders of magnitude smaller than those of the corresponding fully liquid-filled photonic bandgap fibers. Besides, the R-LPCF serving the thermal tunability when filled with index-matching liquid enables guided bandwidth switching from the 1.5-µm-band to the 1.3-µm-band communication window. Moreover, the structural parameters for two commercial photonic crystal fiber are quantified to confirm the feasibility of the proposed method.
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National Natural Science Foundation of China (91950105, 62175116); The Outstanding Chinese and Foreign Youth Exchange Program of China Association for Science and Technology; Association Youth Science and Technology Talent Promotion; 1311 Talents Program of Nanjing University of Posts and Telecommunications (Dingxin); H2020 Marie Sk?odowska-Curie Actions (891685). .