Electro-optically tunable narrow-linewidth single-frequency microlasers and low-phase-noise microwave signal synthesizer on single active lithium niobate microdisks

Single-frequency microlasers and photonic generation of microwave signal with a fast tuning are highly in demand for lots of applications, including high-resolution spectroscopy, precision metrology, coherent communication, and so on. Design and fabrication of narrow-linewidth microlasers and low-phase-noise microwave signal are challenging. Here, we fabricated high-Q erbium ion doped lithium niobate microcavities for single frequency lasing through simultaneous excitation of high-Q polygon modes at both pump and laser wavelengths. Tunable single-mode microlasers with linewidth as narrow as 454 Hz was demonstrated. Moreover, photonic generation of low-phase-noise microwave signals were synthesized from dual-wavelength microlasers on single active LNOI microdisks. The dual-wavelength microlasers were generated from high-Q nearly degenerate polygon modes with spatial intensity distributions almost the same but a π-phase difference. Due to the suppression of the gain competition, dual-wavelength lasing and in turn the low noise microwave source are stable. The phase noise of the microwave signal was measured to -123 dBc/Hz.