# Nonlinear optical properties of polycrystalline silicon core fibers from Telecom wavelengths into the mid-infrared spectral region

## TL;DR

This study investigates the optical transmission and nonlinear properties of polycrystalline silicon core fibers across telecom to mid-infrared wavelengths, demonstrating their high optical quality and potential for nonlinear photonics applications.

## Contribution

It provides the first characterization of the nonlinear optical properties of polycrystalline silicon core fibers over a broad wavelength range, highlighting their suitability for infrared nonlinear photonics.

## Key findings

- Low linear losses (~few dB/cm) across the wavelength range
- Measured nonlinear parameters comparable to single crystal silicon
- High nonlinear figure of merit above 2 μm wavelength

## 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.