Two new techniques to form extreme environment minimally invasive freespace targeted optical temperature sensors using preferably single crystal Silicon Carbide (SiC) optical sensor chips. One technique uses wavelength signal processing exploiting the SiC chip's quadratic nature of its Thermo-optic effect. The other sensing method uses spatial signal processing while utilizing the temperature dependent Snell's law effect. A unique multi-sensor temperature measurement system is described using optical switching, fiber-remoting, and wavelength controls.
 This invention was made with United States Government support awarded by the following agencies: U.S. Department of Energy (DOE) Grant No.: DE-FC26-03NT41923. The United States has certain rights in this invention.