Abstract
Absorption spectroscopy based on supercontinuum generation in the mid-infrared is a powerful technique to analyze the chemical composition of samples. Furthermore, phase-coherent supercontinuum sources can enable fast data acquisition with coherent, stable pulses that allow single-shot measurements. We report here a numerical study of the coherence of an octave-spanning mid-infrared supercontinuum source that was experimentally obtained in an air-clad SiGe/Si waveguide. We show that engineering two closely spaced zero-dispersion wavelengths that enclose an anomalous dispersion band centered around a fixed pump wavelength can produce supercontinuum pulses with high spectral density and full coherence at the extreme ends of the spectrum. This work is important for absorption spectroscopy, on-chip optical frequency metrology, and f -to-2 f interferometry applications.
Highlights
S UPERCONTINUUM (SC) sources are of great interest because of their high spectral brightness over a large spectral bandwidth
The waveguide was pumped in the Transverse Electrical (TE) polarization by a 200 mW tunable OPA laser (MIROPA-fs, Hotlight Systems) delivering 205 fs pulses centered at 4 μm (75 THz frequency) with a repetition rate of 63 MHz [17]
The observed energy transfer might be attributed to degenerate four-wave mixing (FWM) between the remaining redshifted signal in the anomalous dispersion band and the tail of the low energy peak at ∼−20 THz, leading to the generation of a signal at higher frequencies and to an enhancement of the idler [38]
Summary
S UPERCONTINUUM (SC) sources are of great interest because of their high spectral brightness over a large spectral bandwidth. Singh et al generated a SC with a coherence higher than 90%, on average, by pumping a silicon-on-insulator waveguide with sub-100 fs pulses in the short wave infrared (SWIR) This approach is constraining from the technological point of view [27]. These strategies were recently used to numerically demonstrate high coherence of the supercontinuum in mid-IR generated from the germanium-on-silicon waveguide [28]. With this approach, it is possible to achieve a broadband SC with a high degree of coherence irrespectively of the waveguide length and without the need for sub-100 fs pump-pulses or multi-photon absorption
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