Abstract
Broadband mid-infrared light sources are highly desired for wide-ranging applications that span free-space communications to spectroscopy. In recent years, silicon has attracted great interest as a platform for nonlinear optical wavelength conversion in this region, owing to its low losses (linear and nonlinear) and high stability. However, most research in this area has made use of small core waveguides fabricated from silicon-on-insulator platforms, which suffer from high absorption losses of the use of silica cladding, limiting their ability to generate light beyond 3 µm. Here, we design and demonstrate a compact silicon core, silica-clad waveguide platform that has low losses across the entire silicon transparency window. The waveguides are fabricated from a silicon core fibre that is tapered to engineer mode properties to ensure efficient nonlinear propagation in the core with minimal interaction of the mid-infrared light with the cladding. These waveguides exhibit many of the benefits of fibre platforms, such as a high coupling efficiency and power handling capability, allowing for the generation of mid-infrared supercontinuum spectra with high brightness and coherence spanning almost two octaves (1.6–5.3 µm).
Highlights
The mid-infrared region is an important spectral region in which strong molecular absorption bands and atmospheric transmission windows can be exploited for practical use in medicine, food production, imaging, environmental monitoring, and security[1,2]
We demonstrate a compact Silicon core fibres (SCFs) platform capable of achieving a high-brightness SC spectrum spanning almost two octaves, from the near infrared into the mid-IR
The SCFs used in this work were fabricated using the molten core method (MCM) followed by tapering; both procedures were adapted from conventional silica fibre processing
Summary
The mid-infrared (mid-IR) region is an important spectral region in which strong molecular absorption bands and atmospheric transmission windows can be exploited for practical use in medicine, food production, imaging, environmental monitoring, and security[1,2]. Planar-based SC systems employing highly nonlinear group IV materials (e.g., silicon) and compound III–V semiconductors (e.g., GaAs and AlGaAs) can avoid these issues and offer advantages in terms of compactness and on-chip integration[9,10], which are important considerations for the development of portable systems. In this case, the trade-off is that these small core waveguides suffer from low power conversion efficiency due to both the high on-chip coupling losses (typically 5–10 dB per facet) and propagation losses associated with increased core/cladding interactions[11]. The best demonstrations of SC generation in silicon-on-insulator (SOI) waveguides, which are the most common
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