The development of negative curvature fibers is an exciting advance in optical fiber technology that combines relatively low loss over a broad bandwidth with relatively high tolerance for fabrication imperfections. Tolerance of fabrication imperfections is particularly important for chalcogenide fibers, and negative curvature geometries have made it possible to fabricate hollow-core chalcogenide fibers that can transmit light at 10 μm with a loss of 2.1 dB/m. We review theoretical and experimental work that we have carried out to determine the performance limits and to design and fabricate chalcogenide negative curvature fibers.
Recent computational work to optimize the output spectrum of As2Se3 and As2S3 chalcogenide photonic crystal fibers is summarized. Design procedures for both maximizing the output bandwidth and maximizing the power spectral density in the 3-5 μm range are described. With a 2.5μm pulsed pump source, it is possible to obtain a bandwidth of 4 μm in As2Se3 fibers, and, with a 2.0 μm pulsed pump source, it is possible to shift 25% of the input power to the 3-5 μm range in As2S3. With a source at 2.8 μm, it is possible to obtain an output power spectral density in As2S3 that extends between 2.5 μm and 6.5 μm. The single-shot output power spectral density exhibits rapid 10-20 dB fluctuations as the wavelength varies. Moreover, when the pump pulse duration and peak power vary, there are substantial shot-to-shot fluctuations in both the output bandwidth and spectral power density. With 10% variations of the pump pulse duration and peak power, the output spectrum averaged over 5000 shots exhibits less than 5 dB of variation in the intermediate wavelength range of 2.8-4.6 μm and has a reproducible bandwidth of slightly less than 3 μm. The average over 5000 shots yields the same output spectrum with 106 shots, indicating that the spectrum has converged.