Abstract
Polycrystalline silicon core fibers (SCFs) fabricated via the molten core drawing (MCD) method are emerging as a flexible optoelectronic platform. Here, the optical transmission properties of MCD SCFs that have been tapered down to a few micrometer-sized core dimensions are characterized from the Telecom band to the mid-infrared spectal regime. The SCFs exhibit low linear losses on the order of a few dB/cm over the entire wavelength range. Characterization of the two-photon absorption coefficient \b{eta}_TPA and nonlinear refractive index n_2 of the SCFs reveals values consistent with previous measurements of single crystal silicon materials, indicating the high optical quality of the polysilicon core material. The high nonlinear figure of merit obtained for wavelengths above 2{\mu}m highlight the potential for these fibers to find application in infrared nonlinear photonics.
Highlights
Nonlinear silicon photonics has attracted growing interest in the past two decades and numerous nonlinear effects in silicon materials have been demonstrated for a wide variety of applications including wavelength conversion, signal amplification and broadband supercontinuum generation [1]
In complement to the chip-based planar structures, low loss polysilicon waveguides can be fabricated within the optical fiber platform using the molten core drawing (MCD) method, which is a derivative of the conventional fiber drawing approach [4]
Measurements of the wavelength dependence of the two-photon absorption (TPA) and Kerr nonlinearity have been reported in bulk materials and SOI waveguides [10,11,12], as of to date, there have been no reports for polysilicon waveguides and/or for silicon core fibers (SCFs) fabricated via the MCD method
Summary
Nonlinear silicon photonics has attracted growing interest in the past two decades and numerous nonlinear effects in silicon materials have been demonstrated for a wide variety of applications including wavelength conversion, signal amplification and broadband supercontinuum generation [1]. Crystalline quality of the core material, resulting in a reduction in optical transmission losses in the telecom band from 12 dB/cm in 10 μm diameter as-drawn fibers, down to 3.5 dB/cm in a 1 μm tapered core fiber [6] This combination of small core size and low loss has allowed for the first observation of nonlinear propagation in a polysilicon material, with the measured nonlinear parameters being comparable with those of single crystal silicon at the telecom wavelength of ∼ 1.55μm [7]. A series of wavelength dependent measurements have been conducted using various continuous wave (CW) and short pulse laser sources to determine both the linear losses and the nonlinear transmission properties related to the βTPA and n2 parameters This characterization provides useful information regarding the quality of our polysilicon core material as well as the dispersion of the FOMNL in the vicinity of the TPA edge. The results indicate the potential for SCFs to find use in nonlinear applications across the mid-infrared region where applications include spectroscopy, imagining and sensing
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