An applications-oriented review of optical parametric amplifiers in fiber communications is presented. The emphasis is on parametric amplifiers in general and single pumped parametric amplifiers in particular. While a theoretical framework based on highly efficient four-photon mixing is provided, the focus is on the intriguing applications enabled by the parametric gain, such as all-optical signal sampling, time-demultiplexing, pulse generation, and wavelength conversion. As these amplifiers offer high gain and low noise at arbitrary wavelengths with proper fiber design and pump wavelength allocation, they are also candidate enablers to increase overall wavelength-division-multiplexing system capacities similar to the more well-known Raman amplifiers. Similarities and distinctions between Raman and parametric amplifiers are also addressed. Since the first fiber-based parametric amplifier experiments providing net continuous-wave gain in the for the optical fiber communication applications interesting 1.5-/spl mu/m region were only conducted about two years ago, there is reason to believe that substantial progress may be made in the future, perhaps involving "holey fibers" to further enhance the nonlinearity and thus the gain. This together with the emergence of practical and inexpensive high-power pump lasers may in many cases prove fiber-based parametric amplifiers to be a desired implementation in optical communication systems.

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Fiber-based optical parametric amplifiers and their applications

Raman amplification has enabled dramatic increases in the reach and capacity of lightwave systems. This tutorial explains why, starting with the fundamental properties of gain from stimulated Raman scattering. Next, noise accumulation from amplified spontaneous emission is reviewed, and the merits of distributing Raman gain along a transmission fiber are explained. Other sources of noise that are particularly relevant for Raman amplifiers are summarized. Finally, novel Raman pumping schemes that have recently been developed are highlighted.

https://www.osapublishing.org/viewmedia.cfm?URI=OFC-2003-TuC1&seq=0

Raman amplification for fiber communications systems

Publisher Summary Polarization mode dispersion (PMD) is a linear effect that can be compensated in principle. In an ideal circularly symmetric fiber, the two orthogonally polarized modes have the same group delay. However, in reality, fibers exhibit a certain amount of birefringence because of imperfections in the manufacturing process or mechanical stress on the fiber after manufacture. It is noted that fluctuations in the polarization mode and fiber birefringence produced by the environment lead to dispersion that varies statistically with time and frequency. PMD causes different delays for different polarizations and when the difference in the delays approaches a significant fraction of the bit period, it leads to pulse distortion and system penalties. Environmental changes— including temperature and stress—cause the fiber PMD to vary stochastically in time. PMD, illustrating the basic concepts, the measurement techniques, the PMD measurement, the PMD statistics for first- and higher orders, the PMD simulation and emulation, the system impairments, and the mitigation methods has been summarized in the chapter. Both the optical and the electrical PMD compensations are considered.

Polarization-Mode Dispersion

Differential phase-shift keying (DPSK) has attracted significant attentions in research and development during the last several years. An overview of DPSK for high spectral efficiency optical transmission is presented in this paper. The advantages of DPSK in terms of receiver sensitivity and tolerance to fiber nonlinearity will be discussed in detail. A simplified method for estimating the performance of phase-shift keying in numerical simulations is explained. Results of experimental and numerical investigations of several phase shift keying formats, including polarization division multiplexing and multilevel encoding, will be reviewed. Finally, methods for further enhancing performance of phase-shift keying in long-haul transmissions, specifically the compensation of nonlinear phase jitter, are presented.

Differential phase-shift keying for high spectral efficiency optical transmissions

Dispersion Compensating Fibers

The number of channels in a WDM system can be increased by reducing the channel spacing, or by increasing the system's usable bandwidth.

320 Gb/s WDM Transmission (64x5 Gb/s) over 7,200 km using Large Mode Fiber Spans and Chirped Return-to-Zero Signals

We demonstrate transmission of a record aggregate capacity of 3.28 Tb/s (82/spl times/40 Gb/s PRBS 2/sup 31/-1 NRZ) over 3/spl times/100 km of a demonstration TrueWave(R) fiber with very low dispersion slope. The system for the first time incorporate dual C- and L-band transmission and distributed Raman amplification in addition to the 40 Gb/s line rate.

3.28 Tb/s (82/spl times/40 Gb/s) transmission over 3/spl times/100 km nonzero-dispersion fiber using dual C- and L-band hybrid Raman/erbium doped inline amplifiers

42 × 10 Gbit/s wavelength division multiplexed transmission over 4000 km of UltraWave fibre with 100 km dispersion-managed spans and 50 GHz channel spacing is demonstrated. A new dispersion map and all-Raman distributed amplification are employed to obtain error-free transmission of all 42 channels without the use of forward error correction.

420 Gbit/s (42 × 10 Gbit/s) WDM transmission over 4000 km of UltraWave fibre with 100 km dispersion-managed spans and distributed Raman amplification

Summary form only given. We report results of large volume production of more than 10000 km of dispersion-compensating fibers (DCF). This is equivalent to more than 1000 modules, which each can compensate 60 km of standard fiber. Reproducible large volume production of DCF is a difficult task. The design is very sensitive towards small variations in the index profile. For example, we find for our design that a 1% variation of either the core diameter or core index results in a change in dispersion of 5 and 2.5% respectively. Another challenge is to obtain low polarization-mode dispersion (PMD). DCF is more than one order of magnitude more sensitive to core ovalities than conventional telecommunication fibers due to the high core index used. Therefore extreme care has been taken to avoid core ovalities. At the same time we stimulate the mode coupling by introducing oscillatory twist into the fiber during draw. Enhanced mode coupling not only reduces the PMD, but also gives a more stable PMD value, for example during temperature cycling of DCF modules.

Large volume manufacturing of dispersion compensating fibers

10 Gbit/s unrepeatered transmission is achieved over a distance of 442.5 km by using remotely pumped post and preamplifiers, low loss silica-core fibre combined with dispersion compensation, as well as artificial broadening of the spectrum to eliminate stimulated Brillouin scattering.

D.W. Peckham

Papers

320 Gb/s WDM Transmission (64x5 Gb/s) over 7,200 km using Large Mode Fiber Spans and Chirped Return-to-Zero Signals

3.28 Tb/s (82/spl times/40 Gb/s) transmission over 3/spl times/100 km nonzero-dispersion fiber using dual C- and L-band hybrid Raman/erbium doped inline amplifiers

420 Gbit/s (42 × 10 Gbit/s) WDM transmission over 4000 km of UltraWave fibre with 100 km dispersion-managed spans and distributed Raman amplification

Large volume manufacturing of dispersion compensating fibers

442 km repeaterless transmission in a 10 Gbit/s system experiment