Optical Correlation Domain Reflectometry Based on Coherence Synchronization: Theoretical Analysis and Proof-of-Concept

We describe a novel optical correlation domain reflectometry technique based on coherence synchronization between probe and local lights. Coherence synchronization is realized by using artificially generated low coherence lights, which are controlled by arbitrary waveform generators. Thanks to the flexibility of the electronics, we can easily design the coherence characteristics of the artificially generated low coherence lights to yield a correlation gating that filters an autocorrelation of an original laser at an arbitrary delay. The correlation gating realized by coherence synchronization is effective as long as the measurement length is less than the coherence length of the original laser. We demonstrate the measurement of the Fresnel reflection at the end of an optical fiber by using coherence-synchronized optical frequency combs that have only one correlation peak in the fiber under test (FUT). The FUT is 100 m long, and the repetition rate of the optical frequency comb generated by cascaded electro-optic modulators is 9.5 GHz, which corresponds to a 10.5 mm spacing between the periodic correlation peaks. The proposed technique removes the restriction imposed by the periodic correlation peaks present in correlation-based measurement using an optical frequency comb.