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 partial derivative n/partial derivative 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 etalon 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 partial derivative n/partial derivative T data. The reported results are in agreement with the previously reported research at the lower < 600 K temperatures. (c) 2005 American Institute of Physics.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 partial derivative n/partial derivative 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 etalon 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 partial derivative n/partial derivative T data. The reported results are in agreement with the previously reported research at the lower < 600 K temperatures. (c) 2005 American Institute of Physics.