New algorithm for digital phase locking of a phase-modulation I/Q-demodulation optical link

We propose a new algorithm for digital phase locking of a high-linearity analog optical link using phase modulation and In-phase/Quadrature (I/Q) demodulation. Due to the imperfect physical implementation, the timing of the signals to the I and Q photoreceivers is not properly matched leading to the phase loss. An algorithm is proposed to embed into digital signal processing (DSP) blocks for digital phase locking without using a complex optical-phase-lock-loop (OPLL). A numerical simulation is carried out to show the effectiveness of the proposed algorithm. Moreover, a linear phase demodulation of an analog signal even exceeding unity modulation depth is also demonstrated showing ~ 40-dB.Hz^2/3 spurious-free dynamic range (SFDR) improvement thanks to the proposed DSP.