All-solid mid-infrared chalcogenide photonic crystal fiber with ultralarge mode area

In this Letter, we report, to the best of our knowledge, the largest effective single-mode mid-infrared chalcogenide (ChG) fiber. Two thermally matched ChG glasses with a large index contrast of ∼0.35 are chosen for constructing all-solid photonic crystal fiber (PCF) with two rings of "holey" microstructured cladding. Single-mode operation is confirmed in the fabricated ChG PCF with a core diameter of 91.2 μm, from both near-field and far-field observation at 4 μm. Ultralow numerical aperture of <0.025 has been observed at wavelengths between 2.5 and 4.0 μm. The fundamental mode area is calculated to be 5200  μm² at 4 μm, where the propagation loss of the ChG PCF is measured to be 5.2 dB/m. Broadband 3.5 and 7.5 μm supercontinuum has been generated in a 35-cm-long ultralarge-mode-area PCF.