Optical path length measurement using frequency-chirped laser pulses and an optical Doppler frequency sensor

Summary form only given. Coherent frequency domain reflectometry (CFDR) uses a light source whose frequency is linearly chirped in time and encodes target distance information onto the optical frequency domain. Continuous-wave lasers are typically used in CFDR systems as the light source and the linear-chirping in laser frequency can be achieved by using external-cavity acousto-optical frequency shifters or intra-cavity frequency tuning elements. We have demonstrated a new kind of optical displacement measurement apparatus by incorporating a novel optical Doppler frequency sensor into coherent frequency domain reflectometry systems. This new approach allows precise determination of optical beat note frequencies within a duration only fractions of the period of the optical beat notes. This enables the adoption of light sources with significantly higher frequency chirp rates and leads to improved spatial resolution of optical path length measurements.