Cryogenic Temperature Measurement Using Rayleigh Backscattering Spectra Shift by OFDR

We present a method to realize temperature variation measurement in the cryogenic environment (e.g., at 76 K) using Rayleigh backscattering spectra (RBS) shift in standard single mode optical fiber by optical frequency-domain reflectometry. By analyzing the relationship of effective sensing segment size of fiber (or sensing spatial resolution), minimal measurable temperature variation, and temperature response of RBS shift, we found minimal measurable temperature variation in the cryogenic environment can be improved by increasing effective sensing segment size. Our experiments show that at a relatively high temperature (e.g., above 195 K), minimal measurable temperature variation is 0.21 K with an effective sensing segment size of 8 cm. When the temperature is very low (e.g., at 76 K), minimal measurable temperature variation can still maintain 0.34 K by simply increasing the effective sensing segment size of fiber to 48 cm.