Raman Spectral Talbot Amplifier: A Subsystem for Producing Customizable Broadband Optical Frequency Combs

We propose and experimentally demonstrate an all-fiber reconfigurable comb spacing multiplier based on parametric and Raman-assisted spectral Talbot effect. In proof-of-concept experiments, our method transforms a Gaussian-shaped optical frequency comb (OFC) initially spaced at 13.5 GHz into 94.5-GHz and 108-GHz spaced OFCs in a fully programmable fashion, achieving different multiplication factors. This transformation is realized through the collaborative combination of linear Talbot effect and non-linear Raman-assisted four-wave mixing (FWM) in a Kerr medium. The generated OFCs exhibit significantly expanded comb spacing, enhanced carrier-to-noise ratio (CNR) of up to 35 dB, and practical power levels (> −10 dBm) for each frequency tone. These attributes are feasible for high-data-rate coherent communications. We have successfully demonstrated 81-km coherent optical transmission using the widely spaced combs, modulating individual frequency tones with 40 GBaud probabilistic constellation shaping (PCS) 64-QAM signals. Additionally, the reconfigurable comb spacing can benefit other potential applications including broadband spectroscopy, bandwidth-flexible optical networking, and photonic neuromorphic computing.