A downconverting, linearized phase-modulated fiber optic link optimized for K-band microwave signals

We demonstrate a new technique to simultaneously downconvert and linearize a phase-modulated radio-over-fiber link that does not require a frequency-stabilized optical local oscillator. A 20 GHz microwave signal is downconverted to a 250 MHz intermediate frequency with a 14 dB improvement in spur-free dynamic range over the nonlinearized link configuration. The method uses a single lithium niobate phase modulator at the transmitter, modulating two different wavelengths on orthogonal polarizations. These wavelengths are modulated again in the receiver to impart a local oscillator tone, then each upper sideband is filtered with a fiber bragg grating to present the beat IF at the photodetector.