Directly accessing the middle infrared, the molecular functional group spectral region, via supercontinuum generation processes based on turn-key fiber lasers offers the undeniable advantage of simplicity and robustness. Recently, the assessment of the coherence of the mid-IR dispersive wave in silicon nitride (Si 3 N 4 ) waveguides, pumped at telecom wavelength, established an important first step towards mid-IR frequency comb generation based on such compact systems. Yet, the spectral reach and efficiency still fall short for practical implementation. Here, we experimentally demonstrate that large cross-section Si 3 N 4 waveguides pumped with 2 μm fs-fiber laser can reach the important spectroscopic spectral region in the 3–4 μm range, with up to 35% power conversion and milliwatt-level output powers. As a proof of principle, we use this source for detection of C 2 H 2 by absorption spectroscopy. Such result makes these sources suitable candidate for compact, chip-integrated spectroscopic and sensing applications.

Efficient third-order nonlinear optical processes have been successfully integrated on silicon nitride ( S i 3 N 4 ) waveguides. In particular, owing to S i 3 N 4 wide transparency window spanning from the visible to the middle-infrared (mid-IR), efficient mid-IR dispersive-wave (DW) generation from a fiber laser has been recently demonstrated, and its potential as a source for absorption spectroscopy of a single gas has been established. Here we show that the system can be further engineered to broaden the coverage of a single DW without losing efficiency, as to enable simultaneous and discrete detection of several gas-phase molecules within the 2900 and 3380 c m − 1 functional group region. We demonstrate quantitative detection of acetylene, methane, and ethane using a simple direct-absorption spectroscopy scheme, achieving a several hundreds of parts-per-million noise-equivalent detection limit with a 5 cm long gas cell.

We experimentally demonstrate the generation of a short-wave infrared supercontinuum in an uncladded silicon nitride (Si3N4) waveguide with extreme polarization sensitivity at the pumping wavelength of 2.1 µm. The air-clad waveguide is specifically designed to yield anomalous dispersion regime for transverse electric (TE) mode excitation and all-normal-dispersion (ANDi) at near-infrared wavelengths for the transverse magnetic (TM) mode. Dispersion engineering of the polarization modes allows for switching via simple adjustment of the input polarization state from an octave-spanning soliton fission-driven supercontinuum with fine spectral structure to a flat and smooth ANDi supercontinuum dominated by a self-phase modulation mechanism (SPM). Such a polarization sensitive supercontinuum source offers versatile applications such as broadband on-chip sensing to pulse compression and few-cycle pulse generation. Our experimental results are in very good agreement with numerical simulations.

Directly accessing the middle infrared, the molecular functional group spectral region, via supercontinuum generation processes based on turn-key fiber lasers offers the undeniable advantage of simplicity and robustness. Recently, the assessment of the coherence of the mid-IR dispersive wave in silicon nitride waveguides, pumped at telecom wavelength, established an important first step towards mid-IR frequency comb generation based on such compact systems. Yet, the spectral reach and efficiency still fall short for practical implementation. Here, we experimentally demonstrate for the first time to our knowledge, that fs-fiber laser driven systems based on large-cross section silicon nitride waveguides can reach, with powers sufficient to drive dual-comb spectroscopy, the important greenhouse gases spectral region near 4 micron, typically accessed through different frequency generation or more complex approaches. We show, from a 2 µm femtosecond fiber laser, up to 30% power conversion and milliwatt-level output powers, proving that such sources are suitable candidate for compact, chip-integrated spectroscopic and sensing applications.

We demonstrate efficient generation of mid-infrared dispersive wave at 3.5 m in a Si3N4 waveguide pumped by a 2090nm femtosecond mode-locked fiber laser. The 8% maximum efficiency allows for a milliwatt-level average power mid-infrared pulse.

In this contribution, we present how coherent supercontinuum generation in Si3N4 waveguides enabled by fiber laser pumping can be tailored to cover part of the mid-IR spectrum and the use of such sources in spectroscopy. © 2021 The Author(s)

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We demonstrate simultaneous detection of acetylene, methane and ethane using milliwatt-level dispersive-wave generated in a Si3N4 waveguide covering 2900 cm-1 -3380 cm-1 spectral region. This simple mid-IR absorption spectroscopy scheme achieves hundreds of ppm detection limit.