Alain Destrez

Volterra functional series expansions for semiconductor lasers under modulation

An analytical model based on Volterra nonlinear functionals applied to semiconductor lasers has been developed. Analytical expressions are obtained for different laser diode responses, giving powerful tools for analysis. For harmonic input, the response is given including the gain compression factor /spl epsiv/. Second-harmonic distortion (2HD) shows two maxima at half relaxation oscillation frequency /spl Omega//sub R//2 and at /spl Omega//sub R/, in agreement with experiments; the residual dc component due to nonlinearities is estimated and experimentally verified. Dynamic frequency deviation as function of bias current shows resonant characteristics. Relaxation frequency and damping rate /spl Gamma//sub R/ reveal their precise dependence on /spl epsiv/ and differential gain A. For step input, the turn-on delay t/sub on/ and the overshoot P/sub P//P/sub on/ expressions of our model are only functions of /spl Gamma//sub R/ and /spl Omega//sub R/. P/sub P//P/sub on/, and the ringing phenomena decrease with increasing bias current level. >

Optimization of VCSEL spatiotemporal operation in MMF links for 10-gb ethernet

A complete model of the spatiotemporal behavior of multimode vertical-cavity surface-emitting lasers (VCSELs), through static and dynamic response, noise, thermal effects, and its coupling to multimode fibers (MMF) has been investigated in low-cost 10-Gb Ethernet (10-Gb E) prototype optoelectronic packages using GaAs VCSEL arrays coupled to MMF ribbons for short-distance optical links. Eye diagram simulations compared to measurements allow the analysis of critical parameters, such as launching conditions, in order to maximize the MMF bandwidth as well as VCSEL static and dynamic conditions. A new bit error rate (BER) estimation method is proposed by taking into account not only the Q-factor but random and deterministic jitter and digital pattern effects. Global system optimization is discussed for a BER less than 10 -12 for an aggregate link speed of 120 Gb/s over 300 m of a 12-fiber MMF ribbon

Thermal and optoelectronic model of VCSEL arrays for short-range communication

The integration of different components in optoelectronics modules, such as VCSEL and photodiode arrays, optical guides and electronics, introduces optoelectronical, thermal and mechanical interactions. In this context, a thermal and optoelectronic model of VCSEL array is proposed. The self and cross heating of VCSEL arrays have been simulated. The thermal behavior of VCSEL in the array can be modeled by an equivalent circuit model. A small signal electrical equivalent circuit is also presented. This model is obtained from the electrical effects in the component structure and the identification with the rate equations. The models have been validated with 850nm VCSEL arrays characterization.

Analytical formulation of distortion and chirp in CATV DFB lasers including spatial hole burning

Analytical formulas for distortions permitting the calculation of composite second order (CSO) and composite triple beat (CTB) in distributed feedback (DFB) laser diodes are given, including gain compression and longitudinal spatial hole burning (LSHB). An improved chirp expression including both effects is also proposed. Gain compression is compared to LSHB over the CATV band: LSHB effects on distortion and chirp are found to be dominant in actual CATV lasers. Nonmonotonous behavior (dips) function of frequency and bias current is verified in second- and third-order distortions in agreement with recent results.

Volterra functional series expansions for noise in semiconductor lasers

In this paper, we present a full analysis of noise in semiconductor lasers. Time-covariance and cross-covariance functions of all variables governing single-mode semiconductor laser behavior are given including all Langevin noise sources and considering all terms of the laser rate equations, RIN, carrier noise spectrum, frequency noise spectrum, coherence between the FM and AM noise, variance of the phase change and coupling between amplitude and phase are investigated analytically in their more general form. Spectral line shape has been derived showing dissymmetrical satellite lines centered at multiple integers of relaxation frequency around a central line. It is shown that neglecting the shot noise and considering only the carrier contribution in phase dynamics (common procedure) are too general approximations. >

Fast spectral characterization of tunable laser diodes

Tunable laser diodes are now widely used in dense wavelength division multiplexing (DWDM) optical fiber networks. A wide tunability range and good frequency stability are generally required, without mode hopping. Special applications require fast frequency measurement. Unfortunately, commercially available classical spectral measurement systems are much too slow for that purpose. In this paper, we present a new and low-cost system dedicated to fast spectral measurements based on a Michelson interferometer. The free spectral range (FSR) of the interferometer must be carefully optimized. We have designed optimized and tested an experimental system that can quickly analyze with good accuracy the tunability range of tunable distributed Bragg reflector (DBR) laser diodes, and their possible mode hopping. Our set-up can also be used for other spectral measurements (linewidth, chirp, Henrys alpha enhancement factor, spectral and power monitoring). After theoretical analysis of our experimental set-up, we finally present the fast spectral measurements results obtained with a typical 1550 nm two sections DBR QW (quantum well) laser diode. Our measurements have been obtained within less than 500 ps, which is much faster than limits induced by switching thermal effects in laser diodes, and that speed could still be increased.

An analysis of thermal effects and its influence on the laser dynamics in three-electrode DBR lasers

Static and dynamic thermal processes are incorporated into the modelling and simulation of the three-electrode distributed Bragg reflector (DBR) lasers. An analysis of thermal contribution to bandwidth increase and linewidth decrease in multielectrode DBR lasers is presented. It is theoretically shown that the position of the lasing mode relative to the Bragg reflection peak is influenced by thermal effects, so that if the lasing mode is biased at the long wavelength side of the Bragg reflection peak, a significant increase in 3 dB modulation bandwidth and decrease in spectral linewidth can be obtained.

Fast experimental BER extraction of 40 Gb/s optical signal impacted by jitter, ISI and ASE noise using waveform sampler

We present a new experimental BER extraction method using a sampling oscilloscope and statistical processing on EDFA noise, photoreceiver noise, jitter and ISI successfully tested on a 40 Gb/s network.

Effects of chirped gratings on tunability of multielectrode DBR lasers

A new distributed Bragg reflector (DBR) laser with continuously and arbitrarily chirped gratings is theoretically analysed. The chirped gratings are defined by bent waveguides on homogeneous grating fields. The influence of the chirped gratings on tunability of multielectrode DBR lasers is presented via the study of different bending functions. It is theoretically shown that the tunability of these components can be improved using the appropriate chirping function.