Optical Signal Processing in Highly Nonlinear Fibers

4	Highly Nonlinear Fibers

4.1      INTRODUCTION

Conventional glass fibers for optical communications are made of fused silica and show an attenuation as low as 0.148 dB/km [1] with a broad low-loss optical window, which covers about 60 THz, ranging from 1260 to 1675 µm [2]. As seen in Chapter 2, a number of third-order nonlinear processes can occur in optical fibers [3]; these can grow to appreciable magnitudes over the long lengths available in fibers, even though the nonlinear index of the silica glass is very small ($n_2=2.7\times {10}^{-20}{m}^2/W$) [4].

The nonlinear effects generated in the fibers severely affect the performance of optical communications systems, since they impose limits on the launched power of the signals, channel bit rate, ...