Measurements and Simulations of nonlinear noise redistribution in an SOA

Measurements and numerical simulations of the noise statistics after a semiconductor optical amplifier (SOA) demonstrate nonlinear noise redistribution. The redistribution, which relies on self-modulation due to gain saturation and carrier dynamics, shows a strong power and bandwidth dependence and can be important for SOA-based regenerators.     

Reduction of intrachannel four-wave mixing using the alternate-phase RZ modulation format

The authors propose a modulation format in which the phase of the signal pulses alternates, in order to reduce the intrachannel four-wave mixing. They demonstrate numerically that the performance of a 40-Gb/s transmission link can be substantially improved.     

Time division multiplexing using optical switches

Design considerations are considered for optical time-division multiplexing in terms of bandwidth requirements for the modulators and switches for a particular multiplexing scheme and the corresponding drive signals are derived using a time-domain approach. It is shown that these requirements are stricter than expected from simple considerations. Different types of multiplexing schemes are analyzed and are shown to behave differently due to varying chirping properties; this chirping is also calculated. A comparison to nonmultiplexed systems is made     

Dynamic stimulated Brillouin scattering analysis

We present a new simple analysis-including the effect of spontaneous emission-of the (dynamic) influence of stimulated Brillouin scattering (SBS) on the detected receiver eye diagram. It applies in principle for general types of modulation formats such as the digital formats of amplitude shift keying (ASK), frequency shift keying (FSK), and phase shift keying (PSK). The analysis is formulated for a determination of the signal power depiction and intersymbol interference (ISI) caused by the combined effect of fiber dispersion, fiber attenuation and nonlinear fiber effects such as the effect of self-phase modulation (SPM) and SBS. The analysis allows a quantification of the dithering influence on the SBS threshold. Representative numerical examples are presented for two single-channel ON-OFF modulated 10-Gh/s systems utilizing Franz-Keldysh and Mach-Zehnder-type modulators     

Direct Detection of Direct Optically Filtered Millimeter-Wave Signals

Good performance of a direct optical microwave filter combined with direct detection consisting of a single superimposed grating used in reflection has been assessed through bit-error-rate (BER) measurement. In the passband with a 3-dB bandwidth of 2GHz, the BER is below 1.2times10^-11, showing nearly on-off behavior of the filter     

Residual chirp in integrated-optic modulators

The authors have analyzed and measured the dispersion effects of residual chirp arising from asymmetry in field overlap in Mach-Zehnder structures. A clear influence of chirp was seen at 7 Gb/s and a propagation length of 75-km nondispersion shifted fiber at λ=1.55 μm. It is shown that a MZ-modulator with field overlap in one arm only and operated in the blue-shift mode is the best choice for single coplanar stripline (CPS) electrode MZ-modulators in this case. Calculations have shown good agreement with measured results. This indicates that a simple model for fiber mode propagation have shown good agreement with measured results. This can be used together with a FFT-algorithm for calculating the effect of residual chirp from external modulators in multigigabit dispersive fiber-optic systems     

On differential group-delay statistics for polarization-modedispersion emulators

We present a theoretical study on differential group-delay (DGD) statistics for common models of polarization-mode dispersion (PMD) emulators. Our study will show, for the first time to our knowledge, that the statistics for the length of the PMD vector will not necessarily behave as a system with three degrees of freedom when the number of sections in the PMD emulator is low. However, when the number of sections is large, i.e., 10 sections or more, the length of the PMD vector is well described with a system with three degrees of freedom     

Asynchronous Phase Modulation for the Suppression of IFWM

Intrachannel four-wave mixing (IFWM) represents main source of impairments in fiber transmission at 40 Gb/s. A number of phase modulation techniques have been proposed to suppress the IFWM. In this paper, we study a cost-effective way of increasing the nonlinear tolerance of a 40-Gb/s wavelength division multiplexing transmission system by asynchronous phase modulation (APM). This can be achieved with one phase modulator placed after the wavelength multiplexer so that cost is shared by all channels. We show, by means of numerical simulations and laboratory experiments, that APM greatly improves the performance of ON-OFF-keying transmission.     

Calculation of signal outage due to polarization mode dispersion

A method to calculate signal outage due to polarization mode dispersion (PMD), i.e., PMD outage, when differential group delay, as well as principal state of polarization are varying is presented. The most common way to analyze this problem has been based on assuming worst case polarization, which will give too high a value for PMD outage     

Mitigation of polarization-mode dispersion in optical multichannel systems

Simulations of first-order polarization-mode dispersion (PMD) mitigation, based on the electrical power spectrum has been performed. We show that, although first-order compensation significantly improves the signal quality for PMD values of a few tenths of the bit-slot, the improvement still is deficient for telecom purposes when the PMD value neighbors a third of the bit-slot. We, therefore, propose and analyze a novel concept for PMD mitigation in optical multichannel systems, which increases the systems reliability at the expense of the total capacity for the same system. With the proposed method, which uses switching to redundant channels based on measurements of signal quality of all channels in the actual system, the PMD value can be increased to a half of the bit-slot while still keeping the probability for signal outage at acceptable low levels. In the appendixes we simulate the statistical impact of different PMD-emulator models and we show that static bit sequences may induce notches in the electrical power spectrum. These notches may obstruct the extraction of feedback signals for PMD-mitigator schemes based on electrical power spectrum.