Hadrien Louchet

Improved DSP algorithms for coherent 16-QAM transmission

We propose new algorithms for adaptive mitigation of coherent 16-QAM constellation distortions. We show that 16-QAM is a potential candidate for the implementation of 100 Gb/s transmission.

Analytical model for the performance evaluation of DWDM transmission systems

We present a novel analytical model to assess the signal quality in nonlinear dense wavelength-division-multiplexed (DWDM) transmission. The nonlinear impairment dependence on various system parameters is reported. The good agreement with numerical simulations indicates that the proposed model can be of significant value in the search for optimized DWDM systems.

Simple criterion for the characterization of nonlinear impairments in dispersion-managed optical transmission systems

We report a novel simple metric for the characterization of nonlinear impairments for both single-channel and wavelength-division-multiplexed dispersion-managed transmission systems. We show that transmission lines having identical nonlinear diffusion bandwidth lead to similar nonlinear degradation.

Analytical model for the design of multispan DWDM transmission systems

We present a novel analytical model to characterize the nonlinear impairments in dispersion-managed amplitude-modulated dense wavelength-division-multiplexing systems. Though this top-down approach is less accurate than numerical simulations, it enables the definition of general rules for the design of transmission lines, which are modulation format and bit-rate independent.

Adaptive nonlinear Volterra equalizer for mitigation of chirp-induced distortions in cost effective IMDD OFDM systems

We report experimental validations of an adaptive 2nd order Volterra equalization scheme for cost effective IMDD OFDM systems. This equalization scheme was applied to both uplink and downlink transmission. Downlink settings were optimized for maximum bitrate where we achieved 34 Gb/s over 10 km of SSMF using an EML with 10 GHz bandwidth. For the uplink, maximum reach was optimized achieving 14 Gb/s using a low-cost DML with 2.5 GHz bandwidth.

High Speed Direct Modulation of a Heterogeneously Integrated InP/SOI DFB Laser

An integrated laser source to a silicon photonics circuit is an important requirement for optical interconnects. We present direct modulation of a heterogeneously integrated distributed feedback laser on and coupled to a silicon waveguide. We demonstrate a 28 Gb/s pseudo-random bit sequence non-return-to-zero data transmission over 2 km non-zero dispersion shifted fiber with a 1-dB power penalty. Additionally, we show 40-Gb/s duobinary modulation generated using the bandwidth limitation of the laser for both back-to-back and fiber transmission configurations. Furthermore, we investigate the device performance for the pulse amplitude modulation (PAM-4) at 20 GBd for high-speed short-reach applications.

Impact of local oscillator frequency noise on coherent optical systems with electronic dispersion compensation

A theoretical investigation of the equalization-enhanced phase noise (EEPN) and its mitigation is presented. We show with a frequency domain analysis that the EEPN results from the non-linear inter-mixing between the sidebands of the dispersed signal and the noise sidebands of the local oscillator. It is further shown and validated with system simulations that the transmission penalty is mainly due to the slow optical frequency fluctuations of the local oscillator. Hence, elimination of the frequency noise below a certain cut-off frequency significantly reduces the transmission penalty, even when frequency noise would otherwise cause an error floor. The required cut-off frequency increases linearly with the white frequency noise level and hence the linewidth of the local oscillator laser, but is virtually independent of the symbol rate and the accumulated dispersion.

Analytical Formulation for SNR Prediction in DMDD OFDM-Based Access Systems

In multicarrier direct modulation direct detection systems, interaction between laser chirp and fiber group velocity dispersion induces subcarrier-to-subcarrier intermixing interferences (SSII) after detection. Such SSII become a major impairment in orthogonal frequency division multiplexing-based access systems, where a high modulation index, leading to large chirp, is required to maximize the system power budget. In this letter, we present and experimentally verify an analytical formulation to predict the level of signal and SSII and estimate the signal to noise ratio of each subcarrier, enabling improved bit-and-power loading and subcarrier attribution. The reported model is compact, and only requires the knowledge of basic link characteristics and laser parameters that can easily be measured.

Joint Carrier-Phase and Polarization Rotation Recovery for Arbitrary Signal Constellations

We introduce a framework where the combined impact of phase noise and fast polarization rotation can be described by a rotation in a four-dimensional space. Based on this outcome, we propose an equalization scheme performing joint carrier-phase and polarization rotation recovery that can be applied to arbitrary two- or four-dimensional signal constellations. After discussing practical implementation issues for this scheme, we show by means of numerical simulations that the performance of the proposed scheme is comparable with state-of-the-art equalization algorithms for the DP-QPSK, PS-QPSK, and 4D-32QAM modulation formats.

Efficient BER Estimation for Electrical QAM Signal in Radio-Over-Fiber Transmission

We present a novel bit-error-rate estimation method for electrical subcarrier multiplexed signals using quadrature amplitude modulation. This method accounts for noise and intermodulation distortions occurring in fiber-based transmissions and thus provides a quick and reliable alternative to Monte Carlo simulations to assess the performance of radio-over-fiber transmission with numerical simulation.