TERAHERTZ SOURCES

Tunable comb

Opt. Lett. 43, 2507–2510 (2018)

Broadband optical frequency combs in the terahertz region with comb lines that are continuously tunable and exactly referenced would be highly beneficial as a source. Now, Lalitha Ponnampalam and co-workers report stable, phase-coherent optical comb lines spanning over 3.8 THz using only a single phase modulator optical frequency comb generator (OFCG). The OFCG consists of a LiNbO3 phase modulator with a 3-dB bandwidth of 22 GHz, a 980-nm pump laser and a 5-m-long erbium-doped fibre that gives a relatively flat gain spectrum over the entire C-band. An amplified loop incorporating a variable optical delay line allows the spacing between the comb lines to be continuously tuned from 17.5 to 20 GHz. By heterodyning two lines, the team obtained a continuously tunable electrical signal from 122.5 GHz to >2.7 THz. The team says that the scheme is potentially realizable in a monolithic platform.

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Correspondence to Rachel Won.

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Won, R. Tunable comb. Nature Photon 12, 377 (2018). https://doi.org/10.1038/s41566-018-0212-6

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