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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