Comb-referenced photonic 300-GHz-band frequency scanners with high-speed single-sideband sweeping

Frequency-agile signal generation in the sub-terahertz band is important for secure wireless communications, radar, and spectroscopy. However, it remains challenging to simultaneously achieve a wide tuning range, high scanning speed, and frequency referencing. Here, we propose and demonstrate two photonic frequency scanners for the 300-GHz band based on optical injection locking to optical frequency combs and frequency sweeping using a single-sideband modulator. In the first system, an electro-optic comb serves as the frequency reference for injection locking of two distributed-feedback lasers, and continuous frequency scanning is realized by sweeping one of the lasers via single-sideband modulation. We demonstrate discrete frequency tuning from 230 to 330 GHz and continuous scanning at a rate of 250 GHz/µs. Injection locking suppresses the phase noise of the generated 300-GHz signal by 51 dB at 10 kHz offset and reduces the frequency-fluctuation width by approximately a factor of 40. In the second system, a 310-GHz microcomb is used to mitigate the frequency-noise limitation imposed by the single-sideband modulation. Discrete tuning steps as small as 100 MHz are achieved, together with a phase-noise reduction of 62 dB at 10 kHz offset. These results show that comb-referenced photonic sub-THz scanners, combined with single-sideband frequency sweeping, can provide broadband and high-speed frequency agility while remaining compatible with frequency stabilization.