Passively mode-locked interband cascade optical frequency combs

Abstract

Since their inception, optical frequency combs have transformed a broad range of technical and scientific disciplines, spanning time keeping to navigation. Recently, dual comb spectroscopy has emerged as an attractive alternative to traditional Fourier transform spectroscopy, since it offers higher measurement sensitivity in a fraction of the time. Midwave infrared (mid-IR) frequency combs are especially promising as an effective means for probing the strong fundamental absorption lines of numerous chemical and biological agents. Mid-IR combs have been realized via frequency down-conversion of a near-IR comb, by optical pumping of a micro-resonator, and beyond 7 μm by four-wave mixing in a quantum cascade laser. In this work, we demonstrate an electrically-driven frequency comb source that spans more than 1 THz of bandwidth centered near 3.6 μm. This is achieved by passively mode-locking an interband cascade laser (ICL) with gain and saturable absorber sections monolithically integrated on the same chip. The new source will significantly enhance the capabilities of mid-IR multi-heterodyne frequency comb spectroscopy systems.

The Interband Cascade Laser

“…These characteristics are favorable for compact, broadband, and energy-efficient chemical sensing systems. Princeton U. and NRL had previously applied the same rf beating effect that makes dual- In 2018, JPL and NRL demonstrated the first ICL frequency combs, which were the first electrically-pumped combs to operate in the λ = 3-4 µm range [158]. Using the monolithic geometry illustrated schematically in Figure 17, the gain section (3.7 mm long) and SA section (200 µm) were separated by a gap that prevented electrical cross-talk (100 µm).…”

Mid-Infrared Tunable Laser-Based Broadband Fingerprint Absorption Spectroscopy for Trace Gas Sensing: A Review

“…The spectrum of such a pulse train approximates a series of Dirac delta functions separated by the repetition rate of the laser. In the past decade, there have been hundreds of demonstrations of generating OFC with various lasers including Ti: sapphire solid-state lasers [81], Er: fiber lasers [82], Kerr-lens mode-locked lasers [83], QCLs [84], and ICLs [85] with repetition rates typically between to MHz to 10 GHz. The issues with mode-locked OFC are lower output power, still experimental, and not commercially available.…”

“…Direct Frequency-Modulation Combs. Direct FM combs have been experimentally demonstrated in semiconductor lasers, such as QCLs [91][92][93][94][95][96][97], ICLs [85], quantum dot (QD) [98], and quantum dash lasers [99]. These lasers are passively mode-locked with cw or quasi-cw output.…”

Computational coherent averaging for free-running dual-comb spectroscopy

“…As mentioned earlier, the CoCoA algorithm can be used as a diagnostic tool to indicate the mutual coherence of the two sources contributing to the interferograms. To illustrate this property, two interband cascade lasers [16] centered at ~3.5 µm were used in the DCS configuration, and operated in the comb-regime or high phase-noise regime by altering the bias current. Fig.…”

“…Although the procedure can be applied to any free-running DCS system, e.g. such based on electro-optic modulators, optically pumped microresonators, or fiber lasers, the main motivation for this work is linked to the recent developments in chip-scale frequency combs based on electrically-pumped semiconductor sources such as quantum cascade lasers (QCLs) [4,[10][11][12][13][14] or interband cascade lasers (ICLs) [15,16]. These sources have begun to reach a state of development where they can be considered as the basis for miniaturized, battery-operated, portable spectrometers with small footprints [17], but unfortunately this miniaturization comes at a price.…”