Abstract
The nonlinear transmission properties of hydrogenated amorphous silicon (a-Si:H) core fibers are characterized from the near-infrared up to the edge of the mid-infrared regime. The results show that this material exhibits linear losses on the order of a few dB/cm, or less, over the entire wavelength range, decreasing down to a value of 0.29 dB/cm at 2.7μm, and negligible nonlinear losses beyond the two-photon absorption (TPA) edge ~ 1.7μm. By measuring the dispersion of the nonlinear Kerr and TPA parameters we have found that the nonlinear figure of merit (FOM(NL)) increases dramatically over this region, with FOM(NL) > 20 around 2μm and above. This characterization demonstrates the potential for a-Si:H fibers and waveguides to find use in nonlinear applications extending beyond telecoms and into the mid-infrared regime.
Highlights
Hydrogenated amorphous silicon (a-Si:H) is becoming an increasingly popular material for nonlinear silicon photonics due to its low transmission losses, high Kerr nonlinear coefficient n2, and low fabrication costs [1]
Compared to crystalline silicon (c-Si), a-Si:H has a larger bandgap energy (Eg ∼ 1.7 eV), which suggests that the nonlinear absorption should be modest at telecoms wavelengths that are past the two-photon absorption (TPA) edge
We have previously reported on the nonlinear optical properties and the associated FOMNL of these a-Si:H fibers at the telecoms wavelength of 1.54 μm, and by exploiting the ultrafast βTPA and large n2, demonstrated all-optical modulation and wavelength switching schemes [6, 14]
Summary
Hydrogenated amorphous silicon (a-Si:H) is becoming an increasingly popular material for nonlinear silicon photonics due to its low transmission losses, high Kerr nonlinear coefficient n2, and low fabrication costs [1]. In complement to the research that is currently being undertaken on-chip, we have been investigating a new class of a-Si:H core optical fiber that is fabricated using a high pressure chemical vapour deposition (HPCVD) method [12] This method differs from the plasma enhanced CVD technique used for the fabrication of the on-chip waveguides, in terms of the way that the hydrogen is incorporated, yet the resulting materials have similar nonlinear parameters [2, 4]. A series of wavelength dependent measurements spanning ∼ 1.5 − 2.3 μm have been conducted using various continuous wave and short pulse laser sources to determine both the linear losses and the nonlinear transmission properties related to the βTPA and n2 coefficients This characterization provides useful information regarding the dispersion of the FOMNL in the vicinity of the TPA edge. The combination of the lower linear losses ( 1 dB/cm) and the negligible nonlinear absorption for wavelengths > 1.7 μm indicate the potential for these a-Si:H fibers to find use for nonlinear applications in areas such as broadband and/or free-space communications, as well as some mid-IR gas sensing and medical applications
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