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Using single-stage C-band EDFAs equalized to 41 nm, we transmit 152 x 200 Gb/s PDM 16QAM channels with 6.0 b/s/Hz spectral efficiency over 9,748 km enabled by Nyquist spectral shaping and digital back propagation. 76 x 400 Gb/s channels are also transmitted over 8,665 km detecting two 200 Gb/s channels simultaneously using a single wideband receiver. Digital back propagation benefit versus channel pre-emphasis, transmission distance and wavelength are experimentally investigated.

We transmit 250x100G PDM RZ-16QAM channels with 5.2 b/s/Hz spectral efficiency over 5,530 km using single-stage C-band EDFAs equalized to 40 nm. We use single parity check coded modulation and all channels are decoded with no errors after iterative decoding between a MAP decoder and an LDPC based FEC algorithm. We also observe that the optimum power spectral density is nearly independent of SE, signal baud rate or modulation format in a dispersion uncompensated system.

We transmit 160 x 100 G PDM RZ 16 QAM channels with 5.2 bits/s/Hz spectral efficiency over 6,860 km. There are more than 3 billion 16 QAM symbols, i.e., 12 billion bits, processed in total. Using coded modulation and iterative decoding between a MAP decoder and an LDPC based FEC all channels are decoded with no remaining errors.

We investigate the spectral efficiency (SE) limit of pre-filtered modulation in optical fiber communication systems. We show that pre-filtering induced symbol correlation generates a modulation with memory and, thus, a higher SE limit than that of the original memoryless modulation. The SE limits of a series of modulation formats with varying number L of correlated symbols producing 50% of the original bandwidth are evaluated, which approach the SE limit of a modulation format with 50% pre-filtering as L --> ∞. We show that the SE limit of a modulation format with L correlated symbols approximates a lower bound for the SE limit of the corresponding pre-filtered format.

We found by using Monte Carlo simulations that the timing jitter in a dispersion-managed soliton system decreases as the strength of the dispersion management and hence the ratio of the pulse energy to the pulse bandwidth increases. The results are in qualitative but not quantitative agreement with earlier predictions that the decrease is inversely proportional to the square root of the pulse energy. Using an improved semi-analytical theory, we obtained quantitative agreement with the simulations.

We obtain and solve algebraic eigenvalue equations that predict the dependence of the pulse energy of a dispersion-managed soliton on pulse duration, chirp, and dispersion-map parameters. We demonstrate that a variational ansatz based on a Gaussian pulse shape remains useful even when the actual pulse shape is not Gaussian, and we show that the enhancement factor saturates as the pulse duration decreases.

We compare the performance of dispersion-managed fibers with that of dispersion-decreasing fibers and of fibers with uniform dispersion in filtered soliton wavelength-division multiplexing transmission. Alternating-sign dispersion management allows us to achieve values of collision-induced timing jitter that are comparable with what can be achieved by use of dispersion-decreasing fiber and are lower for some parameter values.

A numerical simulation of the switching characteristics of a polarization multiplexed nonlinear-optical loop mirror demultiplexer is presented and compared with experiment. The model assumes that the optical fiber that composes the loop has a randomly varying birefringence, that the signal and the control pulses have the same frequency, and that these pulses are nearly solitons. Factors that affect the shape and the width of the switching window curve are discussed. A phase-dependent modulation of the switching window curve, which is due to incomplete averaging of the light polarization state, is observed both experimentally and numerically. Models in which the randomness is neglected are not able to describe this modulation adequately.

We simulated dispersion-managed soliton propagation and interaction in optical fibers. The energy-enhancement factor, together with the time-bandwidth product and the stretching factor, were calculated as a function of the difference in absolute values of accumulated dispersion in the fiber spans. The interaction strength of the dispersion-managed solitons was found to depend on the stretching factor. When this factor is less than 1.5, the interaction is weaker than for ideal solitons. When it is more than 1.5, there is a strong interaction between the pulses, which constrains the energy enhancement for practical applications.

We have measured the timing jitter for dispersion-managed solitons in a recirculating loop for distances up to 20,000 km. The data were obtained with modulated data, 2(7) - 1 and 2(23) - 1 pseudorandom binary sequence patterns, at 10-Gbit/s rates and with an unmodulated pulse train at 10 GHz. We have obtained good agreement with our data, using a filtered Gordon-Haus model for the timing jitter reduced by the energy enhancement of our solitons relative to solitons in a fiber with a constant dispersion equal to our map's path-average dispersion. We have also measured a bit-error rate of <10(-9) at a distance of 15,000 km.

We investigate both numerically and experimentally soliton propagation in a fiber loop with dispersion management, in-line filters, and frequency shifting. More than 90% of the fiber in the loop is in the normal-dispersion regime, but the net dispersion is anomalous. Stable pulses in the loop have an enhanced power relative to solitons in a fiber with uniform dispersion equal to the loop's path-averaged dispersion. Because the loop's path-averaged dispersion is small, the in-line filtering and the frequency shifting play an important role in pulse shaping. Recirculating loop experiments that demonstrate stable pulse propagation over 28,000 km are consistent with results from computer modeling.

The acoustic effect significantly increases the timing jitter of solitons and the bit-error rates in communication lines. We suggest the transmission of information with fixed-length blocks that contain an equal number of ones and zeros to suppress acoustically induced timing jitter. It is shown theoretically that this approach will significantly enhance the performance of systems with bit rates per channel higher than 20 Gbits/s.

We study a soliton transmission line with sliding-frequency filters, and we determine the limits on soliton stability imposed by the value of the free spectral range of Fabry-Perot étalon filters. From these limits, we infer the minimum channel spacing that is possible in a soliton wavelength-division-multiplexing system.

The acoustic effect signif icantly increases the timing jitter of solitons in communication lines. We calculate the correlation in near-neighbor soliton time shifts that result from the acoustic interaction and show that the acoustic effect can cause correlated errors that cannot be corrected with standard, simple error-correction codes such as the Hamming code.

We present a theory of acoustically induced pulse interaction in a ring fiber laser cavity. In most cases the acoustic interaction leads to pulse bunching, but in some cases it leads to regular pulse spacing. Our results compare well with the experimental data.

We analyze the effect of the third-order guiding filter term on soliton transmission in optical fibers. We find that this term causes a significant difference between the regimes of up- and down-sliding of filter frequency. In particular, the use of up-sliding requires less additional amplifier gain than down-sliding does, which is preferable in real systems.