Picometer-resolution dual-comb spectroscopy with a free-running fiber laser

Abstract

Dual-comb spectroscopy utilizes two sets of comb lines with slightly different comb-tooth-spacings, and optical spectral information is acquired by measuring the radio-frequency beat notes between the sets of comb lines. It holds the promise as a real-time, high-resolution analytical spectroscopy tool for a range of applications. However, the stringent requirement on the coherence between comb lines from two separate lasers and the sophisticated control system to achieve that have confined the technology to the top metrology laboratories. By replacing control electronics with an all-optical dualcomb lasing scheme, a simplified dual-comb spectroscopy scheme is demonstrated using just one dual-wavelength, passively mode-locked fiber laser.Dual-comb pulses with a repetition-frequency difference determined by the intracavity dispersion are shown to be sufficiently stable against common-mode cavity drifts and noises. As sufficiently low relative linewidth is maintained between two sets of comb lines, capability to resolve RF beat notes between comb teeth and picometer-wide optical spectral features is demonstrated using a simple data acquisition and processing system in an all-fiber setup. Possibility to use energy-efficient, free-running fiber lasers with a small comb-toothspacing could enable the realization of low-cost dual-comb spectroscopy systems affordable to more applications.

Computational Doppler-limited dual-comb spectroscopy with a free-running all-fiber laser

“…This is several orders of magnitude lower compared to the absolute linewidth (coarsely estimated to be 3 MHz) and proves that the laser shows mutual coherence on time scales much greater than 1/Δf r , as required by computational correction. Such narrow free-running relative line widths have been previously reported only in dual-wavelength configurations [21][22][23][24][25] , and may suggest that the large repetition rate difference of several kilohertz is not necessary. Unfortunately, the opposite is true.…”

“…The burgeoning field of single-cavity dual-comb (SCDC) lasers is constantly being enriched with new concepts. To date, the most popular fiber-based SCDC generation mechanisms employ bidirectional mode-locking of a ring cavity [17][18][19][20] , dual-wavelength lasing [21][22][23][24][25] , and non-linear pulse shaping mechanisms 26 . Their full spectroscopic potential, however, has been weakly exploited to date.…”

Combination of Adaptive Sampling Terahertz Dual-Comb Spectroscopy with a Free-Running Single-Cavity Dual-Comb Fiber Laser

“…2, the comb-mode-resolved adaptive sampling THz-DCS setup is seeded by a free-running single-cavity dual-comb fiber laser, which has an all-fiber ring cavity in which the dual-comb light beams propagate along a commonpath route. The dual-comb light beams with different center wavelengths were obtained by multiplexing the mode-locking operation in the wavelength region [32,34,37]. The cavity consists of a hybrid wavelength division multiplexer and isolator The other important part of the setup compared to our previous THz-DCS system [37] is the adaptive clock generator, which suppresses the long-term drift and timing jitter in the repetition rate difference ∆frep of the free-running, dual-comb laser.…”

“…By propagating through the same cavity, the dual optical combs experience almost the same disturbances, and the commonmode fluctuations thereby prevent the decline of the mutual coherence between the dual combs. Such a single-cavity dual-comb laser has been applied to THz and microwave frequency measurements [32,33] and optical spectroscopy [28,[34][35][36].…”

Dual-comb modelocked lasers

“…Besides these two laser technologies, there are also other approaches with the goal to simplify dual-comb spectroscopy sources such as a bidirectional fiber-ring laser [47] or frequency agile modulation of a cw laser with electro-optic modulators [48]. These methods have different drawbacks at this point in time but show a lot of potential and could evolve to interesting alternatives.…”