Direct Detection and Coherent Optical Time-Domain Reflectometry With Golay Complementary Codes

We extend the Golay coded Optical Time Domain Reflectometry OTDR technique for the first time from direct-detection to coherent OTDR, investigating the unique issues arising in the coherent setting regarding signal processing operations and efficient real-time implementation of the DSP in practical coherent OTDR receivers and the resulting OTDR performance. We also derive detailed signal flow block diagrams for direct-detection and coherent OTDRs and use an intuitive analogy between spatial speckle and temporal coherent fading noise to guide the selection of OTDR system parameters. We present extensive simulations of the OTDR signal and noise flow accounting for all major effects including the optical source coherence and the backscatter random fading.