Intradyne Detection In Optical Communications With Binary Phase Modulation By Using A Costas Loop In The Domain Of Digital Signal Processing

We report a Costas loop for demodulation of an optical field with binary phase modulation (BPSK). The loop operates in the domain of digital signal processing (DSP) as part of an intradyne coherent digital receiver. The practical implementation of BPSK demodulation in the optical domain is generally not feasible. For this reason, we use techniques based on high-speed digitization of the post-photodetection electrical observable, and the Costas loop in DSP acts on the digitized signal. We chose this loop because it is an optimal structure for both BPSK demodulation and carrier synchronization. Typically, Costas loops for BPSK demodulation operate on a carrier with a frequency higher than the bit rate. However, as we demonstrate in this work, this loop can also perform adequately for a bit rate higher than the carrier frequency (intradyne detection). To the best of our knowledge, the Costas loop in DSP for intradyne BPSK demodulation is reported for the first time in this work. To design the intradyne Costas loop, we used the PLL-equivalent model of a conventional Costas loop. For comparison and performance evaluation, we implemented in simulation, first, a traditional Costas loop and later an intradyne one. We use real-world signals (binary data and additive noise) acquired by digitization for our simulations. Finally, we performed the intradyne Costas loop's characterization using a digitized post-photodetection electrical signal obtained at the output of our digital coherent receiver. We observe a performance very close to that obtained by simulation.