Sound-light interactions in PCF
Phonon-photon interactions in photonic crystal fibre (PCF) depend strongly on the detailed fibre microstructure. Interactions can be strongly enhanced in small-core PCFs with high air-filling fractions due to the large discontinuity in acoustic properties between air and glass, which gives rise to phononic band gaps and families of multi-GHz core-guided acoustic modes, creating unusual forward and backward Brillouin spectra. The backward Brillouin spectra display multiple bands arising from different types of core-guided acoustic modes and show higher threshold intensities compared to conventional optical fibres [Dainese (2006)]. On the other hand, forward Brillouin scattering is Raman-like in character, acoustic resonances (ARs) trapped transversely in the core behaving much like artificial nonlinear oscillators whose frequency and lifetime can be designed to suit a particular application [Dainese (2006a)].
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