6-H single-crystal silicon carbide thermo-optic coefficient measurements for ultrahigh temperatures up to 1273 K in the telecommunications infrared band

6H single-crystal silicon carbide (SiC) is an excellent optical material for extremely high temperature applications. Furthermore, the telecommunication infrared band (e.g., 1500–1600 nm) is an eye safe and high commercial maturity optical technology. With this motivation, the thermo-optic coefficient $∂n∕∂T$ for 6H single-crystal SiC is experimentally measured and analyzed from near room temperature to a high temperature of 1273 K with data taken at the 1550 nm wavelength. Specifically, the natural étalon behavior of 6-H single-crystal SiC is exploited within a simple polarization-insensitive hybrid fiber-free-space optical interferometric system to take accurate and rapid optical power measurements leading to $∂n∕∂T$ data. The reported results are in agreement with the previously reported research at the lower $<600K$ temperatures.