Differential-phase-shift keying (DPSK) has recently been used to reach record distances in long-haul lightwave communication systems. This paper will review theoretical, as well as implementation, aspects of DPSK, and discuss experimental results.

Optical phase-shift-keyed transmission

Fiber-optic communication systems form the high-capacity transport infrastructure that enables global broadband data services and advanced Internet applications. The desire for higher per-fiber transport capacities and, at the same time, the drive for lower costs per end-to-end transmitted information bit has led to optically routed networks with high spectral efficiencies. Among other enabling technologies, advanced optical modulation formats have become key to the design of modern wavelength division multiplexed (WDM) fiber systems. In this paper, we review optical modulation formats in the broader context of optically routed WDM networks. We discuss the generation and detection of multigigabit/s intensity- and phase-modulated formats, and highlight their resilience to key impairments found in optical networking, such as optical amplifier noise, multipath interference, chromatic dispersion, polarization-mode dispersion, WDM crosstalk, concatenated optical filtering, and fiber nonlinearity

Advanced Optical Modulation Formats

Advanced optical modulation formats have become a key ingredient to the design of modern wavelength-division-multiplexed (WDM) optically routed networks. In this paper, we review the generation and detection of multigigabit/second intensity- and phase-modulated formats and highlight their resilience to key impairments found in optical networking, such as optical amplifier noise, chromatic dispersion, polarization-mode dispersion, WDM crosstalk, concatenated optical filtering, and fiber nonlinearity

Advanced Modulation Formats for High-Capacity Optical Transport Networks

Dispersion management is becoming paramount in high-speed wavelength-division-multiplexed lightwave systems, that operate at per-channel rates of 40 Gb/s and higher. The dispersion tolerances, in these systems, are small enough that sources of dispersion variation, that are negligible in slower systems, become critically important to network performance. At these high-bit rates, active dispersion compensation modules may be required to respond dynamically to changes occurring in the network, such as variations in the per-channel power, reconfigurations of the channel's path that are caused by add-drop operations, and environmental changes, such as changes in ambient temperature. We present a comprehensive discussion of an emerging tunable dispersion compensating device, based on thermally actuated fiber gratings. These per-channel devices rely on a distributed on-fiber thin film heater, deposited onto the outer surface of a fiber Bragg grating. Current flowing through the thin film generates resistive heating at rates that are governed by the thickness profile of the metal film. A chirp in the grating is obtained by using a thin-film, whose thickness varies with position along the length of the grating in a prescribed manner; the chirp rate is adjusted by varying the applied current. The paper reviews some of the basic characteristics of these devices and their implementation, in a range of different applications, including the mitigation of power penalties associated with optical power variations. We present detailed analysis of the impact of group-delay ripple and polarization-mode dispersion on systems performance, and present results from systems experiments, that demonstrate the performance of these devices at bit rates of 10, 20, 40 and 160 Gb/s. We also discuss advantages and disadvantages of this technology, and compare to other devices.

Integrated tunable fiber gratings for dispersion management in high-bit rate systems

This paper describes coherent optical orthogonal frequency division multiplexing (CO-OFDM) techniques for the long-haul transmission of 100-Gb/s-class channels. First, we discuss the configurations of the transmitter and receiver that implement the optical multiplexing/demultiplexing techniques for high-speed CO-OFDM transmission. Next, we review the no-guard-interval (No-GI) CO-OFDM transmission scheme which utilizes optical multiplexing for OFDM signal generation and the intradyne receiver configuration with digital signal processing (DSP). We examine the transmission characteristics of the proposed scheme, and show that No-GI CO-OFDM offers compact signal spectra and superior performance with regard to tolerance against optical amplifier noise and polarization-mode dispersion (PMD). We then introduce long-haul high-capacity transmission experiments employing No-GI CO-OFDM; 13.4 Tb/s (134 times 111 Gb/s) transmission is successfully demonstrated over 3600 km of ITU-T G.652 single-mode fiber without using optical dispersion compensation.

No-Guard-Interval Coherent Optical OFDM for 100-Gb/s Long-Haul WDM Transmission

We demonstrate the transmission of 256 polarization-division and wavelength-division multiplexed channels at 42.7 Gbit/s rate over 100 km of TeraLight/sup TM/ fiber. An overall capacity of 10 Tbit/s is achieved in C and L bands at a record 1.28 bit/s/Hz spectral efficiency.

10.2 Tbit/s (256x42.7 Gbit/s PDM/WDM) transmission over 100 km TeraLight/sup TM/ fiber with 1.28 bit/s/Hz spectral efficiency

10.2Tb/s capacity is demonstrated over 3/spl times/100km in C and L bands, using 42.7Gb/s channels. The wavelength allocation was chosen while taking into account narrow optical filtering at the transmitter and receiver ends and second-order Raman pumping is used to improve the signal-to-noise ratio.

Transmission of 256 wavelength-division and polarization-division-multiplexed channels at 42.7Gb/s (10.2Tb/s capacity) over 3/spl times/100km of TeraLight/spl trade/ fiber

Vestigial sideband filtering with high crosstalk suppression is demonstrated as optical demux of densely packed 40 Gb/s channels with high spectral efficiency of 0.64 bit/s/Hz. Narrow band optical filters have been applied for separation of 128/spl times/40 Gbit/s channels with alternating spacings of 50 and 75 GHz.

Vestigial side band demultiplexing for ultra high capacity (0.64 bit/s/Hz) transmission of 128/spl times/40 Gb/s channels

In the context of 40 Gbit/s terrestrial networks, we have exhibited a simple design rule to help perform dispersion management of single-channel links. The optimal pre-compensation has been shown to vary linearly with the in-line residual dispersion. Moreover, the dependence of these parameters on span length and fiber type has been assessed. Preliminary results have also shown the relevance of this rule in WDM configurations.

Numerical optimization of pre- and in-line dispersion compensation in dispersion-managed systems at 40 Gbit/s

The tolerance to cumulated residual, and in-line dispersion compensation ratios is evaluated numerically for six modulation formats over TeraLightTM fibre at 43 Gbit/s Practical system implications are discussed

Yann Frignac

Papers

10.2 Tbit/s (256x42.7 Gbit/s PDM/WDM) transmission over 100 km TeraLight/sup TM/ fiber with 1.28 bit/s/Hz spectral efficiency

Transmission of 256 wavelength-division and polarization-division-multiplexed channels at 42.7Gb/s (10.2Tb/s capacity) over 3/spl times/100km of TeraLight/spl trade/ fiber

Vestigial side band demultiplexing for ultra high capacity (0.64 bit/s/Hz) transmission of 128/spl times/40 Gb/s channels

Numerical optimization of pre- and in-line dispersion compensation in dispersion-managed systems at 40 Gbit/s

Tolerance to dispersion compensation parameters of six modulation formats in systems operating at 43 Gbit/s