Boundless-range optical phase modulator for high-speed frequency-shift and heterodyne applications

Optical phase modulators are used for many applications in optical communication systems and signal processing, but they are fundamentally limited in the amount of a monotonic phase change that can be induced due to practical physical limits on the drive-signal magnitude. In this paper, the necessary drive conditions are derived to achieve a boundless monotonic phase change on the output while keeping the drive inputs within practical physical bounds, i.e., comparable to an amplitude modulator. A simulation of a three-section modulator with two distinct drive signals is provided whereby a continuous phase change on the output is achieved with only a maximum phase shift of π/2 created in any individual section. The architecture has two outputs, therefore a design tradeoff can be made in choosing the power splitting ratio between the outputs. The amplitudes are kept constant as the phase is modulated. The other output is not frequency shifted and may provide a convenient heterodyne signal for subsequent coherent processing.