All-optical serrodyne frequency shifter

We describe and demonstrate a method to induce a single-sideband serrodyne-like optical frequency shift in an all-fiber device. The time-varying phase-shift is generated by cross-phase modulation in a nonlinear fiber. Unlike electro-optic based serrodyne methods, which require a high-fidelity and high-bandwidth analog electrical ramp modulation signal, the proposed optical method uses a simple pulsed pump and can be made simultaneously both low-loss and polarization-independent. We demonstrate the technique by shifting a 1550 nm optical signal 150 MHz in a 1.5 dB insertion-loss polarization-independent frequency shifter and show a pathway to multi-GHz shifting frequencies.