Presence Of Optical Noise Research Articles

Calculation of Receiver Sensitivities in (Orthogonal) Subcarrier Multiplexing Microwave-Optical Links

Microwave-based all-analogue (orthogonal) subcarrier multiplexing (SCM) permits a direct processing of baseband data at Gbit/s while achieving low power consumption, low latency, low cost, and tolerance to dispersion. A key figure of merit in any SCM link is the sensitivity in the receiver, which depends on the transmitter, the link and the receiver. By analysing the impact of the nonlinearities of an optical IQ modulator in the presence of optical noise, sensitivities are mathematically estimated as a function of the optical modulation index (OMI) at the transmitter. The results are verified with simulations achieving a good agreement with the mathematical model. The theoretical model provided can be employed as a tool to predict the best achievable sensitivities and the optimum OMI in broadband SCM and orthogonal SCM links.

Digital Postcompensation Using Volterra Series Transfer Function

We propose a noniterative digital backward propagation technique, based on an inverse modified Volterra series transfer function to postcompensate transmission linear and nonlinear impairments in the presence of optical noise. Using a single-channel 40-Gb/s nonreturn-to-zero quadrature phase-shift-keying optical signal propagated over 20 × 80 km of standard single-mode fiber, and performing digital postcompensation around the Nyquist rate, our compensation algorithm is able to surpass the maximum accuracy obtained with a symmetric split-step Fourier method, enabling us to increase the nonlinear tolerance by approximately 2 dB.

Optical Equalization: System Modeling and Performance Evaluation

Optical equalization in fiber-optic systems is theoretically investigated. First, a wide variety of optical equalizers is presented by giving their equivalent models, by describing the basic principles of operation, and by showing analogies and differences among different structures and configurations. Then, evaluation of the bit error rate and outage probability, in the presence of optical noise, chromatic dispersion (CD), and polarization mode dispersion (PMD), is discussed by comparing different methods based either on the PMD vector and its related statistics or on Markov chain Monte Carlo (MCMC) simulations applied to a random waveplate model. As the first relevant result, the accuracy and complexity of different PMD models in compensated systems are tested and compared, and a novel reduced Bruyegravere-Kogelnik (BK) model, which is more accurate and simple than the complete BK model or other second-order models, is proposed. As an additional result, the ultimate theoretical performance for different configurations and numbers of stages of the equalizers is given, and it is shown that when a single equalizer is used for a pair of polarization-multiplexed channels, the system tolerance to PMD is highly increased