Chalcogenide glasses have the advantages of a wide transparency window (over 20 μm) and high optical nonlinearity (up to a thousand times greater than that of silica glasses), making them good candidates for mid-infrared supercontinuum generation. In this review, we describe both the history and recent developments in mid-infrared supercontinuum generation from chalcogenide fibers according to three kinds of fiber structures: step-index, microstructured and tapered fibers. We also review the coherence properties of mid-infrared supercontinuum generation and all-fiber supercontinuum sources based on chalcogenide fibers.

A novel π-phase-shifted (PS) long-period fiber-grating (LPFG) sensor operating near the phase-matching turning point (PMTP) was proposed. The PS-LPFG sensor can simultaneously detect temperature, strain, refractive index (RI), and pH. Due to the introduction of π phase shift, the double resonance peak of the selected cladding mode was divided into four loss peaks, which is convenient for multiparameter measurement. By monitoring the resonant-wavelength shifts of four dips of PS-LPFG, simultaneous detection of temperature, strain, RI, and pH can be achieved. Moreover, using a simple LPFG design on one fiber and a multiparameter matrix algorithm, the crosstalk between multiple signals was eliminated. Graphene oxide/polyvinyl alcohol (GO/PVA) hydrogel was coated onto the grating sensing area to measure the change in pH, and the sensitivity was higher than that of the same type of fiber-grating sensor. Results showed that the maximum sensitivity of temperature, strain, RI, and pH of the fabricated phase-shifted grating sensing structure were 0.2128 nm/°C, 0.1225 nm/μϵ, 718 nm/RIU, and -1.0166 nm/pH, respectively. Overall, the proposed sensor had great potential applications in monitoring marine environments and biochemistry sensing.

A geometrical optimization study of Ge-Sb-Se chalcogenide glass tapered fiber sensors for concentration sensing of methanol is presented. The effects of the geometrical parameters such as taper waist diameter and transition region lengths on the evanescent wave penetration depth are discussed based on the ray-tracing theory. Numerical analysis results demonstrate that the performance of the tapered fiber sensor can be enhanced by decreasing the transition length of the down-taper combined with increasing the transition length of the up-taper. A homemade tapering platform enables controlling the taper waist diameter and transition region length of the tapered fiber accurately. An experimental study using tapered fiber sensors with different transition region lengths is carried out to detect the concentration of methanol aqueous solution. The highest sensitivity of 0.0120 a.u./% is obtained from the tapered fiber with a down-taper transition length of 5.4 mm and an up-taper transition length of 7.9 mm, which agrees with the trend presented by the simulation results. The effects of symmetric and asymmetric tapered fiber structure on the sensing characteristics are also investigated.