Thin-Film Lithium Niobate Acoustic Delay Line Oscillators

In this work, thin-film lithium niobate (LiNbO 3 ) 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 ( $f_{o}$ ), large delay ( $\tau_{G}$ ), and low insertion loss (IL) of the delay. Therefore, two self-sustained oscillators employing low noise amplifiers (LNA) and a low IL, long delay ( $f_{o}=157\ \mathrm{MHz},\ \mathrm{IL} =2.9\ \mathrm{dB},\ \tau_{G}= 200-440\mathrm{ns}$ ) SH 0 mode ADLs are designed for a case study. The two SH 0 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.