Applications of Nonlinear Fiber Optics , Govind P.Agrawal Academic Press, San Diego, Calif., 2001. $84.95 (458 pp.) ISBN 0-12-045144-1

Govind P. Agrawal’s Applications of Nonlinear Fiber Optics is an extension of his Nonlinear Fiber Optics (3rd edition, Academic, 2001), an earlier successful text, and much of the theory in the new book is taken from that reference. Applications of Nonlinear Fiber Optics covers important technical topics in fiber optics and optical communications, with emphasis on nonlinear effects.

Agrawal first describes fiber gratings, along with phenomena associated with Bragg diffraction. He covers various fabrication techniques for producing fiber gratings, explaining how irradiation changes the index. A description of fiber gratings as optical filters, and supporting experimental data, follow. Next, Agrawal analyzes nonlinear effects in fiber gratings; some of these effects result in optical bistability. The book discusses Bragg solitons—pulses formed by the combined action of the Kerr effect and fiber grating dispersion at a carrier frequency near the grating bandgap— along with their experimental verification. Other subjects include photonic crystal fibers, fiber couplers as optical switches, and nonlinear switching.

The author gives the impression that nonlinear switching is approaching practical applications. A critical reading of the evidence presented, however, suggests otherwise, in view of the high pulse energies required and the poor response of the switches. The switches could prove useful only if major performance improvements are achieved; one would have expected that Agrawal would be more critical of their present state.

Nonlinear effects are enhanced by resonance, thus it is natural that particular attention is paid to Fabry–Perot and ring resonators, especially to nonlinear phenomena in such resonators. Sagnac interferometers are studied along with their nonlinear switching properties. The book states that parametric amplification in a Sagnac interferometer can occur below the 3-dB quantum limit. What should have been pointed out in this connection is that the amplification is phase sensitive, the quadrature phase is attenuated in the process, and the concept of noise figure must be approached with care. The discussion of nonlinear phenomena in interferometers concludes with the Mach–Zehnder and Michelson interferometers. The author’s enthusiasm for nonlinear processes may have led him to overstate their practicality. The responses of nonlinear devices are poor and will limit their use, unless unknown and untried methods provide substantial improvement.

Central topics of optical communications are optical amplification, its spectral response, the associated noise, and the noise figure of the amplifier. I found an error in the noise figure (4.1.17): The expression should read F n = 1/G + 2n sp (G − 1)/G ≈ 2n sp ; with out the 1/G term we would have noise figures of less than unity for G → 1. Dispersive and nonlinear effects are taken up. The Maxwell–Bloch equations for amplification of pulses that are short when compared to the transverse relaxation time are introduced, followed by the Ginzburg–Landau equation. The author gives attention to the amplification of autosolitons, pulses that are amplified without change of shape. In the discussion of amplifiers, as in most of the book, the author faces the challenges to notation posed by his vast coverage, derived from many sources in the literature. The same symbols are used to designate different quantities. A list of symbols and their meaning would be a welcome addition to the next edition.

The discussion of fiber amplifiers is followed by coverage of laser action caused by the application of feedback to amplifiers. Cavity designs are discussed, those that achieve single-mode operation on the one hand and mode-locked operation on the other. Different rare earth lasers are mentioned, but the main emphasis is on erbium-doped fiber lasers. Active mode-locking, harmonic mode-locking, and the vast literature on realizations of such lasers are reviewed.

Passive mode-locking using saturable absorbers and additive-pulse mode-locking, with polarization rotation or with the figure-eight laser, are described in detail. The author states his belief that the limit on the pulse-width with either method is set by the “Kelly sidebands.” This may be true for soliton lasers, but it is not for stretched pulse lasers. The sidebands are hardly noticeable in the latter; the changing character of the pulse along the ring prevents the coherent superposition of the different sources of continuum generation. The shortest pulses (63 fs, ref [241]) have a bandwidth considerably wider than the gain bandwidth.

Pulses emitted from mode-locked lasers can be compressed using self-phase modulation. Criteria for optimum compression with the avoidance of pulse pedestals are described, as are compression schemes based on higher-order soliton excitation and use of dispersion-decreasing fiber. The book concludes with extensive coverage of fiberoptic communications of on the one hand “linear” systems, in which the nonlinearities have to be circumvented, and on the other soliton communications, in which at least the main effect of the Kerr nonlinearity is used to provide stability for pulse propagation in the presence of anomalous dispersion.

Agrawal next discusses dispersion management, as used in all long-span terrestrial and transoceanic transmission. He also covers the ability of dispersion management to overcome cross-talk induced by four-wave mixing. A discussion of stimulated Brillouin scattering (SBS) follows, along with ways of overcoming it by raising its threshold. Four-wave mixing and its deleterious effect on the signal-to-noise ratio in a wavelength-division multiplexed system is explained by simple analytic arguments.

The author touches on design issues confronted by a lightwave-system designer, and the issues of noise and timing jitter, along with means of controlling them, are addressed in the soliton discussion. Dispersion-managed soliton propagation, a scheme that has received a great deal of attention in the last few years, is characterized theoretically, and ample experimental evidence of its efficacy is presented.

The book, and its predecessor Nonlinear Fiber Optics , can serve well in a two-term sequence of graduate courses in fiber optics. The new book is devoted to applications, as the title suggests, and is of interest to practitioners who want to gain an overview of a vast set of phenomena. One important feature of the book is the extraordinarily extensive list of references. The total adds up precisely to 1500 (with some references repeated in different chapters). For years they will serve readers who want to go back to the sources of the devices described. The downside of this approach is that the fundamental concepts and equations are often lifted from the references without a detailed derivation that would let the reader understand all aspects.

The text has remarkably few typos and errors for coverage as ambitious as this one. The reader may disagree with a conclusion here and there, as I did in the few cited examples. On the whole, the work is a welcome addition to the literature of this important and rapidly expanding field.