Abstract

We present a technique, based on Raman gain, to generate intense and pure higher-order modes (HOMs) in the core of a H₂-filled hollow-core photonic crystal fiber (PCF). It is based on prism-coupling through the cladding of kagomé-PCF – a species of hollow-core PCF that guides by anti-resonant-reflection (Fig. 1a). This permits precise excitation, through the cladding, of pure individual HOMs, even those with complex multi-lobed transverse intensity profiles [1]. Although a large range of different HOMs (many exhibiting high leakage loss) can be excited and characterised in this way, the inherently low coupling efficiency restricts their practical use. Here we report effective amplification of side-injected HOM Stokes pulses using stimulated Raman gain in H₂, the co-propagating pump pulses being in the fundamental core mode.

© 2015 IEEE