Extended range fiber-optic temperature sensor

A wide range temperature sensor, comprising:

• two light sources of different wavelengths, a first wavelength being selected to provide a temperature measurement for a lower temperature range of from −100° C. to 400° C. and a second wavelength being selected to provide a temperature measurement for a higher temperature range of from 400° C. to 900° C.;
• an optical fiber having a first end and an opposite second end;
• means for applying light from the two light sources to the first end of the optical fiber for passage of light at the two different wavelengths along the optical fiber to the second end;
• an etalon connected to the second end of the optical fiber for reflecting light from the optical fiber striking the etalon, back into the optical fiber;
• a 2×2 coupler optically coupled to the optical fiber at an intermediate location between the first and second ends thereof for diverting a portion of the light from the first end of the optical fiber to a first end of the 2×2 coupler, and for diverting a portion of the reflected light from the second end of the optical fiber to a second end of the 2×2 coupler;
• reference detector means connected to the first end of the 2×2 coupler for generating a reference signal corresponding to the light from the light sources diverted to the first end of the 2×2 coupler;
• signal detector means connected to the second end of the 2×2 coupler for generating a reflected signal corresponding to reflected light diverted to the second end of the 2×2 coupler;
• signal processing means connected to the reference detector means and to the signal detector means for taking a ratio of the reflected signal to the reference signal for light at each of the different wavelengths which is indicative of temperature;
• and
• discriminator means connected to the reference detector means and to the signal processing means for discriminating between the ratios, the discriminator means including means for applying a switching signal from the signal processing means to the two light sources for activating one of the light sources at a time to supply light to the first end of the optical fiber, each of the reference detector means and signal detector means comprising a single detector.