86-GBaud subcarrier multiplexed 16QAM signal generation using an electrical 90 degree hybrid and IQ mixers.

We experimentally demonstrate an aggregate 86-GBaud (over three sub-bands and one polarization) signal generation based on subcarrier multiplexing technique using IQ mixers, an electrical 90 degree hybrid, and diplexers. The electrical hybrid allows transmitter-side digital signal processing to be simplified to pulse shaping and digital pre-emphasis. We verified the configuration by testing the performance of an 86-GBaud Nyquist-shaped 16 quadrature amplitude modulation signal with differential bit encoding. The implementation penalty assuming 7% hard-decision forward error correction is reduced to 2 dB by utilizing a 31-tap decision-directed least mean square based multiple-input multiple-output equalizer for sideband crosstalk mitigation.

Noise and transmission performance improvement of broadband distributed Raman amplifier using bidirectional Raman pumping with dual order co-pumps.

We demonstrate a low noise bidirectional broadband distributed Raman pumping scheme combining dual order co-propagated pumps without increasing the signal RIN level. The noise performance improvement is compared experimentally and numerically with conventional counter-pumping only and bidirectional pumping with only a 2nd order co-pump for a 70nm bandwidth and 61.5km distributed Raman amplifier. The proposed broadband pumping scheme shows 1.2dB maximum noise figure improvement and extends the long-haul transmission reach up to 6150km with a Q-factor improvement of ~0.7dB compared with counter-pumping only scheme.

Long-distance 40-Gbit/s soliton transmission over standard fiber by use of dispersion management.

We demonstrate, through numerical simulations, the possibility of transmitting solitonlike pulses over 2000 km of standard fiber at a single-channel data rate of 40 Gbits/s. The system used here employs a novel dispersion map to overcome the large fiber dispersion. The longest transmission distance was achieved with pulses that did not exhibit the enhanced energy normally associated with dispersion management and indeed had lower energy than an equivalent average soliton.

Dispersion-managed solitons in the normal dispersion regime: a physical interpretation.

We present an analytic description of dispersion-managed soliton propagation based on split-step and variational models. Using these models, we derive the threshold map strength for the existence of dispersion-managed solitons in the normal dispersion regime and obtain a bound on the maximum normal average dispersion.

Nonlinear focusing of femtosecond pulses as a result of self-reflection from a saturable absorber.

We calculate the spatiotemporal evolution of intense, femtosecond pulses that are incident upon a saturable absorbing interface in the regime of self-reflection, using the finite-difference time-domain computational method. The pulses induce a curved, moving absorption front in the nonlinear medium that acts as a transient focusing mirror for the reflected pulse energy.

Dispersion-managed soliton propagation in short-period dispersion maps.

We show through detailed numerical simulations that stable dispersion-managed solitons exist in short-period dispersion maps characterized by a dispersion-management period that is less than the amplifier spacing. These pulses show regular dynamics within the amplifier span and have greater energy enhancement than the conventional dispersion-managed soliton. We also show that greater interaction is obtained in this regime as a result of this increased enhancement.

Power dependence of dispersion-managed solitons for anomalous, zero, and normal path-average dispersion.

We determine the power dependence of dispersion-managed solitons on map strength and average dispersion, using a combination of numerical simulations and the variational approach. In particular, we investigate the behavior near zero dispersion and identify the region of existence of dispersion-managed solitons in the average normal-dispersion regime.

Soliton collisions with wavelength-division multiplexed systems with strong dispersion management.

We investigate collisions between solitons in a lossless two-channel wavelength-division multiplexed system with strong dispersion management. Numerical results show that the net frequency shift that is due to interchannel collisions is at least 1 order of magnitude smaller than predicted by adiabatic theories. A modified theoretical analysis is presented and shown to be in good agreement with the numerical results.

Dispersion management for wavelength-division-multiplexed soliton transmission.

Residual frequency shifts that are due to two-soliton collisions in stepwise exponentially dispersion-tapered fiber are calculated. Two-step dispersion profiles to minimize the frequency shifts and associated timing jitter are specifically identified. These profiles will improve the performance of wavelength-division-multiplexed soliton systems and permit operation with longer amplifier spans over an increased bandwidth.

Soliton collisions in dispersion-managed wavelength-division-multiplexed systems.

We show that collision-induced frequency shifts in wavelength-division-multiplexed (WDM) soliton transmission systems are strongly suppressed with increasing dispersion management. We predict new oscillations in the residual frequency shift response, owing to the relative motion induced by the dispersion map, and demonstrate a direct correlation between these oscillations and the modified soliton-collision dynamics. Simple analytical expressions for the oscillation minima are obtained, and implications for WDM soliton system design are discussed.

Energy-scaling characteristics of solitons in strongly dispersion-managed fibers.

We present an empirical scaling law that models the increased energy required for launching a soliton into an optical system with sections of both normal and anomalous dispersion fiber. It is shown that the inclusion of periodic attenuation and amplification can be handled as separate problems, provided that the interval between optical amplifiers is substantially different from the period of the dispersion map. These concepts are illustrated by reference to an example system comprising dispersion-shifted fiber combined with anomalous standard fiber.

Soliton switching using cascaded nonlinear-optical loop mirrors.

We demonstrate multiple-peaked switching in a nonlinear-optical loop mirror and present an experimental investigation of device cascading in the soliton regime based on a sequence of two independent nonlinear-optical loop mirrors. Cascading leads to an enhanced switching response with sharper switching edges, flattened peaks, and increased interpeak extinction ratios. We observe that pulses emerging from the cascade retain the sech(2) temporal profile of a soliton with minimal degradation in the spectral characteristics.