Injection Locking of Gigahertz‐Frequency Surface Acoustic Wave Phononic Crystal Oscillator

Low‐noise gigahertz (GHz) frequency sources are essential for applications in signal processing, sensing, and telecommunications. Surface acoustic wave (SAW) resonator‐based oscillators offer compact form factors and low‐phase noise due to their short mechanical wavelengths and high‐quality ( Q ) factors. However, their small footprint makes them vulnerable to environmental variation, resulting in their poor long‐term frequency stability. Injection locking is widely used to suppress frequency drift of lasers and oscillators by synchronizing to an ultra‐stable reference. Here, injection locking of a 1‐GHz SAW phononic‐crystal oscillator is demonstrated, achieving 40‐dB phase noise reduction at low offset frequencies and unperturbed low noise at large offset frequencies. Compared to a free‐running SAW oscillator, which typically exhibits frequency drifts of several hundred hertz over minutes, the injection‐locked oscillator reduces the frequency deviation to below 0.35 Hz. The locking range and oscillator dynamics is also investigated in the injection pulling region. The demonstrated injection‐locked SAW oscillator could find applications in high‐performance portable telecommunications and sensing systems.