4. Optical Fibers

Chalcogen-based materials in glassy form are popular infrared (IR) fiber materials due to their flexible stoichiometry leading to a broad glass forming region and their ability to be readily drawn into fiber with a broadband IR transmission. Depending upon composition, the sulfide, selenide, and telluride-based fibers transmit between about 0.8 and 7 μm, 1 and 10 μm, and 2 and 12 μm, respectively. The low phonon energy of chalcogenide glasses (~300–450 cm⁻¹) compared to silica glass (~1100 cm⁻¹) and fluoride glass (~560 cm⁻¹) allows many IR transitions that are quenched in silica and fluoride glass to be active. The low phonon energy of the chalcogenide glasses (ChGs) also results in a wide infrared transmission window that allows low loss transmission in the mid-wave infrared (MWIR) and long-wave Infrared (LWIR) bands. In addition, the large refractive index and high degree of covalent bonding in chalcogenide glass results in oscillator strengths and radiative transition probabilities greater than in other host materials. In particular, ChGs doped with rare earth elements (Er³⁺, Pr³⁺, Dy³⁺, and Tb³⁺) are ideal candidates for fiber lasers and amplifiers in MWIR and LWIR regions. Refractive index of sulfur-based materials such as arsenic sulfide (As₂S₃) can be easily tailored by changing the relative amounts of arsenic and sulfur, thus making it the most popular one for application as optic fiber.