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

Raman amplification at 2.2 μm in silicon core fibers with prospects for extended mid-infrared source generation
a. Concept of using SCFs to generate light at new mid-infrared wavelengths. b. Molten core method for fiber fabrication, with an inset showing the post-processed taper design. c. Stimulated Raman gain profile for a 2 μm pulse pump. d Spectral evolution of spontaneous cascaded Raman scattering when using an optimized pump source. Credit: Meng Huang, Shiyu Sun, Than S. Saini, Qiang Fu, Lin Xu, Dong Wu, Haonan Ren, Li Shen, Thomas W. Hawkins, John Ballato & Anna C. Peacock

The mid-infrared spectral region has attracted great research interest over the past decade, as it is important for many biomedical and sensing applications. However, there is still a major challenge to develop compact and tunable fiber-based light sources that operate at wavelengths beyond 2 μm.

Raman scattering is a nonlinear process that can be used to generate or amplify optical signals in wavelength regions where traditional light sources are limited or unavailable. Thus, when constructed from and waveguides with broad transmission windows, Raman systems can be used to translate near-infrared pump sources into the mid-infrared to help fill the wavelength gaps in this region.

In a new paper published in Light: Science & Applications, an international research team, led by Professor Anna C. Peacock from Optoelectronics Research Centre, University of Southampton, United Kingdom, have demonstrated high levels of Raman amplification at wavelengths extending beyond 2 μm by making use of a highly nonlinear silicon core fiber (SCF) platform.

Compared to planar silicon systems, SCFs have emerged as an exciting platform for mid-infrared Raman amplification as they offer extended propagation lengths, low propagation losses and efficient coupling to fiber lasers. The SCF used in this work was fabricated by a molten core drawing method, which allows for the rapid production of long lengths of fiber.

The fiber was then post-processed via a tapering procedure, which acts to enhance the nonlinear performance through optimization of the core material and size. The resulting SCF was produced with a transmission loss of only 0.2 dB/cm, with a consistent micrometer-sized tapered waist diameter over a length of 6 cm.

By pumping the optimized SCF with a thulium-doped fiber laser, the team have demonstrated Raman emission and amplification at 2.2 μm. For the case of stimulated Raman amplification, an on-off peak gain of ~30 dB was achieved for a pump power of only ~10 mW, thanks to the large Raman gain coefficient of the crystalline core material.

Importantly, the low losses of the SCF also open a route to extend the reach of the Raman shifting out to 4 μm and beyond via cascaded processes. This work represents the first demonstration of mid-infrared Raman scattering in any silicon waveguide system—either fiber or chip-based—and thus provides a crucial step towards the development of robust, compact and tunable systems in this spectral band.

More information: Meng Huang et al, Raman amplification at 2.2 μm in silicon core fibers with prospects for extended mid-infrared source generation, Light: Science & Applications (2023). DOI: 10.1038/s41377-023-01250-y

Journal information: Light: Science & Applications

Citation: Raman amplification at 2.2 μm in silicon core fibers with prospects for extended mid-infrared source generation (2023, September 1) retrieved 27 May 2024 from https://phys.org/news/2023-09-raman-amplification-silicon-core-fibers.html
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