Toward free-running operation of dual-comb fiber lasers for methane sensing

Abstract

The phase information provided by the beat note between frequency combs and two continuous-wave lasers is used to extrapolate the phase evolution of comb modes found in a spectral region obtained via nonlinear broadening. This thereafter enables using interferogram self-correction to fully retrieve the coherence of a dual-comb beat note between two independent fiber lasers. This approach allows the f − 2 f self-referencing of both combs, which is a significant simplification. Broadband near-infrared methane spectroscopy has been conducted to demonstrate the simplified system’s preserved performance.

Photodetector nonlinearity in dual-comb interferometry

“…A gas cell filled with hydrogen cyanide H 13 CN was added in one arm before the output coupler. Due to the requirement of high sampling rate, but also because of memory limitation, only the central portions of the interferograms have been acquired [10].…”

“…Once digitized, the IGMs have been aligned, phase-corrected [11,12] and averaged to limit the noise at a level allowing to clearly distinguish the impact of NL. The spectrum is normalized by fitting a eighth-order polynomial to the smooth spectral baseline instead of using an independent reference measurement [13].…”

“…Transmittance spectrum (top panel) of H13 CN for the P15 to P1 lines in the case of a high power nonlinear measurement and a linear measurement and the difference between the measurements (bottom panel).comb spectroscopy. A model of static NL used in classical FTS has been adapted for DCS where differences mostly due to optical sampling were highlighted.…”

Interleaved electro-optic dual comb generation to expand bandwidth and scan rate for molecular spectroscopy and dynamics studies near 1.6 µm

“…Although typically operated at significantly reduced spectral coverage, electro-optic dual optical frequency combs (EO-DOFC) are an attractive alternative owing to the simplicity of the methods to generate the dual combs from a single free-running laser while maintaining mutual phase coherence in the down-converted radiofrequency (RF) region [9,10,11,12,13,14,15,16]. In many areas, the limited bandwidth of a few cm -1 is advantageous to enhance sensitivity in photon counting applications, to significantly increase comb resolution for quantum state resolved studies of single absorption bands [17,18,19,20], or for the sub-Doppler coherent interrogation of atoms [21,22].…”

Broadband high-resolution molecular spectroscopy with interleaved mid-infrared frequency combs

“…To achieve high resolution, one needs long mutual coherence time between the two combs 3 . If the combs are not fully locked, one can track the relative phase drifts and correct for these in real time, at the expense of having two stable continuous-wave reference lasers, as has been demonstrated in the near-IR 19 – 21 , or perform phase correction by a posteriori data processing, as has been shown in the THz and mid-IR ranges 22 , 23 . However, both of these methods lack the absolute frequency referencing—a setup needs to be calibrated using, for example, a well-known gas absorption feature.…”