Friedrich-Alexander-Universität Erlangen-Nürnberg

Stimulated Raman scattering in gas-filled hollow-core photonic crystal fibre

Stimulated Raman Scattering in Gas-filled Hollow-core Photonic Crystal Fibre

Gas-filled hollow-core photonic crystal fibre (HC-PCF) is a very efficient system for light-matter interaction as it allows long-distance propagation in a diffractionless manner. Such a system has been successfully used for many different types of non-linear experiments [1].

When filled with Raman-active gas, this can result into ultra-low threshold stimulated Raman scattering [2]. Although the scattering from the pump to the Stokes is usually observed in the same spatial mode, it may happen that the nonlinearity couples two independent fibre modes with different transverse symmetries. This phenomenon has been observed with H2-filled HC-PCF [3]. Whereas the pump laser light and the first-order Stokes signal are guided in the fundamental LP01 mode, the second-order Stokes signal is generated in the double-lobed LP11 mode, although the fundamental mode still exists for this frequency. This arises from the peculiar shape of the dispersion curves of the fundamental and the higher-order mode, which favours intermodal second Stokes generation over a cascaded process in the same mode. The former requires two different phonons: Phonon ph1 couples the pump to the first Stokes in the same spatial mode, whereas phonon ph3 couples the first Stokes to the second Stokes which then appears in the higher-order mode. In our fibre, the nearly phase-matched phonon ph3 leads to the dominant generation of the second Stokes in the LP11 mode.

Fig. 2: Phase-matching condition required to generate the different Stokes components in a stimulated Raman scattering process. ph1 and ph3 are the phonon responsible for the coupling between the pump and the different Stokes components.

 References:

[1]   A. R. Bhagwat and A. L. Gaeta, “Nonlinear optics in hollow-core photonic bandgap fibers,” Opt. Expr. 16:5035 (2008)

[2]F.Benabid,J.C.Knight,G.AntonopoulosandP.St.J.Russell,“StimulatedRamanscatteringinhydrogen-filledhollow-core photonic crystal fiber,” Science 298, 399–402 (2002)

[3]  M. Ziemienczuk, A.M. Walser, A. Abdolvand, A. Nazarkin, C.F. Kaminski, P.St.J. Russell, “Three-wave stimulated Raman scattering in hydrogen-filled photonic crystal fiber,” CD8.1., CLEO Europe (2011)

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