All-optical switching in long-period fiber grating with highly nonlinear chalcogenide fibers

All-optical switching in long-period fiber grating (LPFG) with Ge-As-Se chalcogenide fibers was proposed. The switching performances at different resonant wavelengths and cladding modes were systematically investigated using coupled-mode theory. By utilizing the ultra-high nonlinearity of chalcogenide glass, the switching power threshold of the proposed LPFG switching at 1.55 μm was 105  MW/cm² with power coupling for the low-order LP₀₉ cladding mode, which was approximately 200 times lower than that of silica LPFG. Furthermore, the temperature stability of the proposed LPFG switching was examined. The optical switching instability due to the laser thermal effect can be well suppressed by optimizing the cladding radius and grating period. Considering the balance between temperature sensitivity and switching power threshold, an all-optical switch with temperature sensitivity of 51 pm/°C was finally realized by selecting the LP₀₅₁ mode with a cladding radius of 39 μm.