Enhanced Spurious Suppression in Fiber-Optic Pulse Repetition Rate Multiplication and Its Application in Robust Microwave Photonic Frequency Synthesis

In microwave photonic frequency synthesis, pulse-repetition-rate multiplication (PRRM) mitigates photodetection saturation of optical frequency combs (OFCs), yet spurious-tone suppression is seldom quantified, especially at high frequencies. We present a PRRM model for asymmetric fiber-optic Mach–Zehnder interferometers (MZIs) that incorporates amplitude and delay mismatches and predicts spurious levels accurately. Devices fabricated on a high-precision platform yield spurious tones of -37.8 dBc, -36.4 dBc and -34.6 dBc for 12 GHz, 20 GHz and 32 GHz carriers, respectively, deviating no more than 1.6 dB from theoretical simulations. To assess field deployability and engineering potential, we assembled a compact synthesis system from standard telecom components. The synthesized 33.8 GHz carrier exhibits -121.7 dBc/Hz phase noise at 1 kHz offset and spurious suppression exceeding -70 dBc. After 10 g random vibration and 1000 g shock, performance is unchanged, demonstrating, to our knowledge, the first mechanically robust microwave photonic frequency synthesizer.