Equations for Two-Tone Analog Optical Phase Modulation With an Asymmetric Interferometer

Analytical research is presented for electro-optic phase modulation followed by an asymmetric interferometer that is used for phase-to-intensity conversion. The resulting closed-form equations quantify the performance for arbitrary interferometer bias and input radio-frequency power. Even-order distortions, very important for multi-octave applications, are analyzed. Measured data for a Mach-Zehnder interferometer (MZI) are demonstrated to agree well with the theoretical results. Photodiode-induced even-order distortion is identified as the limiting nonlinearity when the MZI is biased at quadrature.