Fundamentals of parametric processing in highly nonlinear optical fiber are reviewed. Experimental procedures necessary for construction of one- and two-pump parametric amplifier architectures are described. Pump phase broadening, dispersion fluctuation and birefringence form basic impairment mechanisms in fiber parametric devices and are analyzed in two-pump parametric devices. Parametric signal processing is introduced with specific applications in all-optical regeneration, band conjugation, multicasting, packet switching and signal distortion reversal.

Wavelength-division multiplexing (WDM) technique employing broadband erbium-doped fiber amplifiers (EDFAs) is considered to be the most effective solution to respond to the increasing demand for transmission capacity. As a means to extend the optical bandwidth outside the conventional band (C-band) ranging from 1530 to 1565 nm, silica-based EDFAs (EDSFAs) operating within the long-wavelength band (L-band) ranging form 1570 to 1600 nm seem to be the most attractive candidate because they can be composed of the same material as C-band EDSFAs, i. e. silica-based Al codoped EDF. However, there exist several discrepancies between C-band and L-band EDSFAs which originate inevitably from the difference in the inversion level and the band location. This paper reviews the basic characteristics of L-band EDSFAs, which have been a controversial issue for practical application of the L-band EDSFAs, such as required EDSF lengths, power conversion efficiency, noise performances, and optical bandwidth. We will also describe L-band EDSFAs' behavior under circumstantial changes, such as the variation of the span-loss, the temperature of the EDSF, and the number of wavelengths, which are expected in the field WDM systems. The dynamic-gain-tilt and temperature-induced change in the gain spectra of L-band EDSFAs are more significant than those of C-band EDSFAs are. Moreover, L-band EDSFAs exhibit a greater apparent inhomogeneous broadening effect, which may hinder the precise gain control when the number of wavelengths is dynamically changed. All of these characteristics must be considered for future designs of broadband WDM networks.

Wavelength-division multiplexing (WDM) transmission systems have been intensely researched in order to increase the transmission capacity. One of the most important key devices for this use is erbium-doped fiber amplifiers (EDFAs) which feature a flattened gain, a high pumping efficiency and a low noise figure (NF), simultaneously. To fulfill these requirements, hybrid silica-based EDFAs (EDSFAs) composed of Al codoped and P/Al codoped EDSFs have been proposed so far. They are also attractive from the viewpoint of productivity, reliability, and cost-effectiveness. On the other hand, the optical bandwidth has been around 15 nm at most. In this paper, we have proposed newly designed hybrid EDSFAs for more than 25 nm optical bandwidth. The gain peak around 1. 53 µm can be suppressed through the saturation degree control in both EDSFs. The remaining obstacle is the diparound 1. 54 µm, which results in the relative gain non-uniformity of 10. 7% over the wavelength range from 1535 to 1560 nm. Owing to the glass composition optimization, the relative gain non-uniformity has been reduced to 5.8% without gain equalizers(GEQs), which is comparable to that of EDFFAs. As another solution, the hybrid EDSFA including two-stage Fabry Perot etalons as the GEQ has been proposed. In this configuration, the hybrid EDSFA has been designed to exhibit the gain profile similar to the summation of two sinusoidal curves, and the relative gain non-uniformity has been reduced to 3. 7%, which is almost equal to that of the hybrid EDFAs composed of EDSF and EDFF. Moreover, it has been demonstrated that newly developed hybrid EDSFAs exhibit a higher pumping efficiency and a lower NF than EDFFAs and hybrid EDSF/EDFFAs.