Description
Multifrequency terahertz (THz) waves with high spectral purity are of pivotal importance to advanced spectroscopy, imaging, and telecommunications. Traditional approaches for producing multifrequency THz waves and THz frequency combs rely on complex setups or sophisticated device structures and are usually limited in bandwidth and efficiency, especially at the spectral range between 0.5 and 1.5 THz. In this work, we use self-injection-locking technique to frequency-lock two chipscale semiconductor lasers to a lithium niobate whispering-gallery-mode microresonator to generate low-noise optical emissions. In contrast to the conventional continuous-wave mode, one of the self-injection-locked lasers is operated in a gain-switching regime by laser current modulation, creating coherent pulses with a repetition rate that is equal to the free-spectral range of the microresonator. By photomixing the two lasers on a photoconductive antenna, we generate a THz frequency comb with 13 comb teeth and a repetition rate of approximately 11 GHz, covering the spectral range from 0.92 to 1.06 THz. Compared with commercial multichannel laser systems, the demonstrated microresonator-based dual-laser system is highly tunable in the THz-range frequency difference and exhibits a high spectral purity and significantly reduced frequency instabilities. With the low-cost components and the prospect of further miniaturization, the self-injection-locked dual-laser source may greatly advance the industrial applications of multichannel THz waves as well as the development of cost-effective THz frequency combs. As a proof-of-principle demonstration, an interferometer-based ranging experiment is carried out, showing the improved measurement resolution by adopting the self-injection-locked gain-switched lasers. Further performance improvement by domain-wall engineering the lithium niobate microresonator is proposed and then demonstrated.
| I am the presenting author | Yes |
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