Thin-Film Lithium Niobate Acoustic Delay Line Oscillators

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In this work, thin-film lithium niobate (LiNbO3) acoustic delay line (ADL) based oscillators are experimentally investigated for the first time for the application of single-mode oscillators and frequency comb generation. The design space for the ADL-based oscillator is first analyzed, illustrating that the key to low phase noise lies in high center frequency (fo), large delay (τ G), and low insertion loss (IL) of the delay. Therefore, two self-sustained oscillators employing low noise amplifiers (LNA) and a low IL, long delay (fo=157MHz, IL =2.9dB, τG= 200-440ns) SH0 mode ADLs are designed for a case study. The two SH0 ADL oscillators show measured phase noise of -109 dBc/Hz and -127 dBc/Hz at 10-kHz offset while consuming 16 mA and 48 mA supply currents, respectively. Although the carrier power of the proposed oscillator is lower than published state-of-the-art ADL oscillators, competitive phase noise performance is still attained thanks to the low IL. Finally, frequency comb generation is also demonstrated with the same delay line and a commercial RF feedback amplifier, showing a comb spacing of 3.4 MHz that matches the open-loop characterization.