Mid-infrared Raman Amplification in Silicon Core Fiber

Abstract Raman scattering provides a convenient mechanism to generate or amplify light at wavelengths where gain is not otherwise available. When combined with recent advancements in high power fiber lasers that operate at wavelengths ~2 μm, great opportunities exist for Raman systems that extend operation further into the mid-infrared (IR) regime for applications such as gas sensing, spectroscopy, and biomedical analyses. Here, a thulium-doped fiber laser is used to demonstrate Raman emission and amplification from a highly nonlinear silicon core fiber (SCF) platform at wavelengths beyond 2 μm . The SCF has been tapered to obtain a micrometer sized core diameter (~1.6 μm) over a length of 6 cm, with losses as low as 0.2 dB/cm. A maximum on-off peak gain of 30.4 dB was obtained with a modest average pump power of 12.4 mW, with simulations indicating that the gain could be increased to up to ~50 dB by extending the SCF length. Simulations also show that by exploiting the large Raman gain and extended mid-infrared transparency of the SCF, cascaded Raman processes could yield tunable systems with practical output powers across the 2-5 μm range.