We propose a transmission-based dispersion compensator employing an apodized, unchirped fiber Bragg grating (FBG). A theoretical model for dispersion compensation in transmission based on the dispersive properties of the periodic structure is developed. A figure of merit is defined for optimization of the grating parameters for maximum recompression of dispersion-broadened optical pulses in long-haul communication systems. Numerical examples confirm that nearly perfect compensation with very low insertion losses can be achieved for many practical cases of interest.

Fiber Bragg gratings for dispersion compensation in transmission: theoretical model and design criteria for nearly ideal pulse recompression

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

The dispersion characteristics of apodized, linearly chirped fiber Bragg gratings and their potential as dispersion compensators have been studied systematically. It is shown that the positive hyperbolic-tangent profile results in an overall superior performance, as it provides highly linearized time-delay characteristics with minimum reduction in the linear dispersion. To compensate for the linear dispersion of 100 km of standard telecom fiber over certain bandwidth (in nanometers), the required grating length is 19.24 cm/nm.

Optimization of apodized linearly chirped fiber gratings for optical communications

We demonstrate the higher temperature sensitivity of a fiber Bragg grating (FBG) sensor when it is clad with a metal of a large thermal expansion coefficient. With lead (solder) cladding, the sensitivity of Bragg wavelength shift can be enhanced by about five (four) times. A theoretical model was adopted to show quite consistent results. It was found that thermal annealing was crucial for preparing high-quality fiber Bragg grating sensors with metal claddings.

Thermal performance of metal-clad fiber Bragg grating sensors

Publisher Summary
This chapter examines different aspects chirped fiber Bragg gratings. Gratings that have a non-uniform period along their length are known as chirped. Chirp in gratings take different forms. The period varies symmetrically, either increasing or decreasing in period around a pitch in the middle of a grating. The chirp is linear and the period varies linearly with length of the grating, may be quadratic, or may even have jumps in the period. The performance of chirped gratings as a dispersive filter specifically for the compensation of chromatic dispersion is analyzed. An important feature of a dispersion-compensating device is the figure of merit. There are several parameters that affect the performance of chirped fiber Bragg gratings for dispersion compensation. These are the insertion loss, dispersion, bandwidth, polarization mode-dispersion, and deviations from linearity of the group delay and group delay ripple. It is found that the transfer matrix method is ideally suited to chirped gratings, since the grating is broken up into smaller sections of uniform period and/or refractive index profile. It is observed that the role played by the rear end of the grating is apparent when the coupling constant is apodized asymmetrically.

Chapter 7 – Chirped Fiber Bragg Gratings

We report on results of a system trial involving dispersion compensating chirped fiber gratings, demonstrating that transmission up to 537 km of standard telecommunications fiber is now feasible at 10 Gb/s, with a pair of 10-cm-long gratings cascaded together.

Dispersion compensation over distances in excess of 500 km for 10-Gb/s systems using chirped fiber gratings

An ISO 9001 audit can be seen as an independent risk assessment on the business, where each ‘Nonconformity” or “Opportunity For Improvement” is considered as a potential risk. Nevertheless, their actual impact on the business remains difficult to determine; as a consequence, the urgency of a mitigation plan at corporate level can sometimes be underestimated. This paper proposes a semi-quantitative risk assessment methodology on the ISO 9001 findings relying on a selected panel of experts. The experts’ responses are analyzed and validated using a specific statistics test for inter-rater reliability. The proposed methodology has been applied on real findings coming from ISO 9001 internal audits, involving 10 subject matter experts of 7 different countries. 

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A. Cavaciuti

Papers

Dispersion compensation over distances in excess of 500 km for 10-Gb/s systems using chirped fiber gratings

Inter-rater Agreement Based Risk Assessment Scheme for ICT Corporates