Relations among gain, refractive index and group index in Brillouin slow light. When a pump wave at frequency νo propagates in the fibre, a probe wave propagating in the opposite direction experiences a narrowband gain if its frequency is νo-Δν and a narrowband loss if its frequency is νo+Δν. The associated refractive index change strongly modifies the group index and thus the signal velocity at the centre of the gain/loss spectral line. |
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