Electro‐Optically Tunable Low Phase‐Noise Microwave Synthesizer in an Active Lithium Niobate Microdisk

Abstract

AbstractPhotonic‐based low‐phase‐noise microwave generation with real‐time frequency tuning is crucial for a broad spectrum of subjects, including next‐generation wireless communications, radar, metrology, and modern instrumentation. Here, for the first time to the best of the authors’ knowledge, narrow‐bandwidth dual‐wavelength microlasers are generated from nearly‐degenerate polygon modes in a high‐Q active lithium niobate microdisk. The record‐high‐Q (≈107) nearly‐degenerate polygon modes formation with independently controllable resonant wavelengths and free spectral ranges is enabled by the weak perturbation of the microdisks using a tapered fiber. Moreover, because a high spatial overlap factor between the pump and the dual‐wavelength laser modes is achieved, the gain competition between the two lasing modes spatially separated with a π‐phase difference is suppressed, leading to stable dual‐wavelength laser generation with low threshold, and in turn, the low noise microwave source. The stable beating signal confirms the low phase‐noise achieved in the tunable laser. Without the need of external phase stabilizers, the measured microwave signal shows a phase noise of −123 dBc Hz−1 and an electro‐optic tuning efficiency of −1.66 MHz V−1. The linewidth of the microwave signal is measured as 6.87 kHz, which is more than three orders of magnitude narrower than current records based on integrated dual‐lasers.