Noise floor analysis of the phase demodulation scheme using a 3×3 coupler

The noise floor of the phase demodulation scheme using a 3×3 coupler was analyzed, where the signal was demodulated by linear combination of the three outputs and digital inverse arctangent approach. According to our study, the noise floor has connection with the noise intensity, noise correlation and initial phase. The approximate expressions to calculate the noise floor were deduced and validated by simulations with input Gaussian white noise. Experiment results show that the predicted noise floor distribution as a function of initial phase agreed well with the experiment results. The noise floor of the experiment system was below 0.70 μrad/√Hz@1kHz.