A method for measuring the nonlinear refractive index of optical fibers with an error of less than 5% is demonstrated. The technique is based on measuring the nonlinear phase shift experienced by a dual-frequency beat signal, permitting a simple, highly sensitive, accurate, repeatable, and easily automated measurement procedure and sampling. Measurements of the nonlinear coefficient in standard telecommunication, dispersion-shifted, and a number of dispersion-compensated fibers are presented.

Direct continuous-wave measurement of n(2) in various types of telecommunication fiber at 1.55 microm.

This chapter deals with the properties of highly non-linear fibers. It reviews the techniques used to measure the non-linear parameter ( γ ). The four kinds of fibers that are developed to enhance the non-linear effects are also reviewed. The three major non-linear effects occurring inside the optical fibers—the self-phase modulation (SPM), the cross-phase modulation (XPM), and the four-wave mixing (FWM), are governed by a single non-linear parameter γ. This parameter is fixed for each glass material. The chapter elaborates that the use of the non-silica glasses provides an alternative approach to designing non-linear fibers. The SPM technique uses the broadening of the pulse spectrum. It measures the maximum value of the non-linear phase shift. In place of deducing the SPM-induced phase shift from spectral broadening, a related technique deduces it from the spectral changes occurring when light from two lasers operating at slightly different wavelengths is transmitted through the fiber. Measurements in such an approach can be performed with CW lasers. The chapter summarizes that the combination of unusual dispersive properties and a high value of γ leads to a variety of novel non-linear effects.

Highly Nonlinear Fibers

We discuss experimental results that demonstrate the existence of Bragg grating solitons in fiber gratings at high intensities. These solitons can exist because of the balance of the nonlinearity in the glass and the group-velocity dispersion introduced by the grating. We show that Bragg grating solitons can travel at velocities substantially below that in bare fiber and also how trains of such solitons can be generated.

Nonlinear pulse propagation in Bragg gratings

Publisher Summary
This chapter deals with the properties of highly non-linear fibers. It reviews the techniques used to measure the non-linear parameter (γ). The four kinds of fibers that are developed to enhance the non-linear effects are also reviewed. The three major non-linear effects occurring inside the optical fibers—the self-phase modulation (SPM), the cross-phase modulation (XPM), and the four-wave mixing (FWM), are governed by a single non-linear parameter γ. This parameter is fixed for each glass material. The chapter elaborates that the use of the non-silica glasses provides an alternative approach to designing non-linear fibers. The SPM technique uses the broadening of the pulse spectrum. It measures the maximum value of the non-linear phase shift. In place of deducing the SPM-induced phase shift from spectral broadening, a related technique deduces it from the spectral changes occurring when light from two lasers operating at slightly different wavelengths is transmitted through the fiber. Measurements in such an approach can be performed with CW lasers. The chapter summarizes that the combination of unusual dispersive properties and a high value of γ leads to a variety of novel non-linear effects.

Chapter 11 – Highly Nonlinear Fibers

We propose lightpath establishment techniques for transparent optical networks, valid for both centralized path computation (i.e., performed by a path computation element-PCE) and distributed path computation (i.e., performed by each ingress node). The proposed techniques rely on correlating the end-to-end quality of transmissions (QoT) (e.g., optical-to-signal-noise ratio-OSNR) of lightpaths already set up to evaluate the QoT of lightpaths to be established. The correlation is leveraged by two end-to-end estimation frameworks called “network kriging” and “norm l2 minimization.” Each framework is used in turn to estimate end-to-end parameters that describe the QoT for a lightpath to be established, based on measured parameters from other lightpaths that were previously established or probed. Simulations are carried out for both PCE and distributed networking scenarios on a sample optical transparent network. The proposed lightpath establishment techniques reduce the probability that a setup attempt is unsuccessful due to unacceptable QoT and reduce the number of setup attempts to successfully establish lightpaths. Simulation results are also provided to show that our techniques permit a fast convergence of QoT information at PCE or ingress nodes in the context of dynamic networks.

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Lightpath Establishment Assisted by Offline QoT Estimation in Transparent Optical Networks

Nonlinear coefficient measurements for dispersion shifted fibres (DSFs) using the self-phase modulation (SPM) method at 1.55 mu m are presented for the first time. The nonlinear Kerr refractive index n/sub 2/ for various DSFs is found to be approximately 2.31*10/sup -20/m/sup 2//W (+or-5%) for random polarisation states at 1.55 mu m. >

Y. Namihira

Papers

Nonlinear coefficient measurements for dispersion shifted fibres using self-phase modulation method at 1.55 µm