Average atmosphere temperature measurement by a Frequency-Shifted Feedback laser

A Frequency-Shifted Feedback (FSF) laser has an intracavity acousto-optic modulator (AOM) and the spectral output consists of a chirped frequency comb evenly spaced at the cavity free spectral range (FSR). An FSF laser is a useful source for optical frequency domain reflectometry (OFDR). We present a new average atmospheric temperature sensor by OFDR using an FSF laser for the first time. The beat signal, which is detected through the self-delayed heterodyne detection of an FSF laser, is proportional to the path difference, and measurements can be done within the frequency bandwidth of a cavity FSR. Furthermore, the beat frequency characteristics are unrelated to the beat order. Therefore, the path measurement resolution is consist and unrelated to the path difference. Changes in atmospheric refractive index primarily depend on variation of temperature and pressure. Observing variation in path difference with an FSF laser should allow calculation of the average atmospheric temperature along the path if the change in pressure is known. As the path difference increases, the temperature resolution improves. This paper outlines the principle of the average atmospheric temperature measurement using an FSF laser and presents preliminary experimental result.