Raman amplification at 2.2 mu m in silicon core fibers with prospects for extended mid-infrared source generation

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 similar to 2 mu m, great opportunities exist for Raman systems that extend operation further into the mid-infrared 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 mu m. The SCF has been tapered to obtain a micrometer-sized core diameter (similar to 1.6 mu m) over a length of 6 cm, with losses as low as 0.2 dB cm(-1). A maximum on-off peak gain of 30.4 dB was obtained using 10W of peak pump power at 1.99 mu m, with simulations indicating that the gain could be increased to up to similar 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 mu m range.

Automated summary

Raman scattering provides a mechanism to generate or amplify light at wavelengths without available gain, and with recent advancements in high-power fiber lasers operating at 2 mu m wavelengths, there are opportunities to extend Raman systems into the mid-infrared regime for various applications. This study demonstrates Raman emission and amplification using a thulium-doped fiber laser on a highly nonlinear silicon core fiber platform beyond 2 mu m wavelengths. The results suggest that cascaded Raman processes can achieve practical tunable systems with output powers across the 2-5 mu m range by exploiting the large Raman gain and extended mid-infrared transparency of the silicon core fiber.