Dual-Comb Spectroscopy With Enhanced Resolution by Pseudorandom Phase Modulation of Gain-Switched Optical Pulses

We present a dual-comb spectrometer based on gain-switched optical frequency combs which breaks the current spectral resolution limitation of such systems. The external phase modulation of both combs using pseudorandom binary sequences results in a flat dual-comb spectrum that features a line spacing of 3.937 MHz, which can be further reduced. The system, whose acquisition speed is 250 ms, is validated by the measurement of the amplitude response of a narrow (
$\sim$
360 MHz) Fabry-Pérot filter. This approach opens up the possibility of using gain switching dual-comb systems for high-resolution applications with a simple, cost-effective, and integrable perspective.