Raman effects in a highly nonlinear holey fiber: amplification and modulation

We experimentally demonstrate that a short length of highly nonlinear holey fiber (HF) can be used for strong $L^{+}$-band (1610–1640-nm) Raman amplification and ultrafast signal modulation. We use a pure silica HF with an effective area of just $2.85 \mathit{\mu }{\mathrm{m}}^2$ at 1550 nm, which yields an effective nonlinearity $\sim 15$ times higher than in conventional silica dispersion-shifted fiber. Using a 75-m length of this fiber, we obtained internal Raman gains of more than 42 dB and a noise figure of $\sim 6 \mathrm{dB}$ under a forward single-pump scheme, and the Raman gain coefficient was experimentally estimated to be $7.6\times {10}^{-14} \mathrm{m}/\mathrm{W}$. Also, an 11-dB signal extinction ratio in a Raman-induced all-optical modulation experiment was achieved with the same fiber.