Chip-Scale Optomechanical Frequency Comb with a 1−70 GHz Span

This article presents a compact, chip-scale optomechanical frequency comb based on a silicon carbide (SiC) microdisk resonator, achieving a record frequency span from 1 GHz to 70 GHz. The comb is generated through radiation pressure from a continuous-wave pump laser, which drives phonon lasing in the microdisk and generates 42 phase-locked harmonics with a spacing of 1.655 GHz. The system operates with very low optical power (only 1 mW) and exhibits high phase stability and low noise, making it an attractive solution for applications requiring high-performance microwave sources, such as in communications and quantum information technologies.

Key points include:

1. Optomechanical Frequency Comb: The optomechanical comb is generated by harnessing the strong optomechanical nonlinearity of a 2.5-μm-radius SiC microdisk. The interaction between optical and mechanical modes in the disk results in phonon lasing, producing a comb with harmonics spaced at 1.655 GHz.

2. Broadband Comb with Low Phase Noise: The comb spans 1−70 GHz, with low phase noise of −132 dBc/Hz at a 1 MHz offset frequency. The system achieves excellent frequency stability (<10−7 at 1 s) and exhibits a narrow linewidth (less than 150 Hz) at maximum power, showing promise for applications requiring stable and low-noise frequency sources.

3. Compact and Efficient Design: The SiC microdisk, fabricated on a silicon-on-insulator platform, benefits from SiC's low mechanical losses, making it suitable for high-frequency optomechanical applications. The device uses only 1 mW of dropped optical power to generate a broad comb with minimal losses.

4. Experimental Setup and Characterization: The experimental setup involves a tunable laser and various photodetectors to measure the comb's properties. The setup includes heterodyne detection to extend the measurement range beyond 40 GHz, enabling the observation of harmonics up to 70 GHz.

5. Phase Locking and Frequency Stability: The frequency components of the comb are phase-locked, with a linear relationship between the harmonic frequencies and the fundamental frequency. This phase-locking is critical for maintaining consistent frequency spacing across the entire comb.

6. Performance Benchmark: The performance of the SiC optomechanical comb is compared with other optomechanical combs, highlighting its unique combination of high frequency, broad spectral range, and low phase noise. This makes the SiC microdisk a competitive platform for future applications in high-frequency microwave sources, quantum communications, and other fields.

In conclusion, the demonstrated SiC-based optomechanical frequency comb offers a compact and energy-efficient solution with a broad frequency span, low phase noise, and high stability, making it ideal for demanding applications in microwave photonics and quantum technologies.