Fiber-optic frequency encoder for high-resolution OFDR

A fiber-optic frequency encoder indispensable to optical frequency sampling used in the OFDR (optical frequency domain reflectometer) is reported. The encoder is stabilized using a feedback technique to minimize optical frequency tracking error resulting from environmental perturbations. The encoder can discriminate between an increase and a decrease in optical frequency at a zigzag or repeated chirp and can generate clock pulses at any integer multiple of half the beat period. These functions enable the coherent averaging of beat signals during repeated chirps in order to increase the SNR, and allow optical frequency sampling at any desired period to minimize the number of sampled points without the occurrence of the aliasing effect.<>