Critical study of the vertical-cavity surface emitting laser electrical access for integrated optical sub-assembly

The proposal contribution aims at highlighting the consequence of the impedance mismatching in Vertical-Cavity Surface-Emitting laser (VCSEL)-based optical subassembly for optical interconnection applications. The integration of this micro laser diode needs a particular care to avoid electromagnetic coupling which could transform the advantage of the VCSEL technology in a weakness. Indeed, the vertical emission perpendicular to the active layer gives the possibility to achieve the need of planarization of the optoelectronic circuits and the design of VCSEL arrays. That is why it is of great interest to develop an optoelectronic model including the electrical access effect. This model is based on the VCSEL rate equation comparison with a behavioural small-signal equivalent circuit. Scattering parameters of various VCSEL structures and various VCSEL chip submounts are tested. This characterization allows the validation of the laser model and emphasizes the influence of the electrical access in the light transmission. In a particular VCSEL array structure, a crosstalk phenomenon is also observed. In other cases, the frequency rise involves modification of the laser frequency response. Consequently the electrical access of the VCSEL needs to be improved in order to avoid an inadequate utilization of the VCSEL

Spectral behavior of long wavelength VCSELs

For a long time, only a small wavelength range of Vertical-Cavity Surface-Emitting Lasers (VCSEL) was available. The current evolution in process technology allows the fabrication of long wavelength VCSEL that is interesting for Telecom systems because they offer a higher integration level than the existing optical sources at lower costs since they are fabricated in arrays. We propose to focus our investigation on the behavior of singlemode 1.55μm VCSEL. We aim at precisely knowing their spectral properties under direct modulation. We present a study about the linewidth measurement and the linewidth enhancement factor, also called the Henry - or the alpha - factor. Many studies have been reported but only a few of them are really efficient. Two different set-ups are presented here to extract alpha factor. The first one uses an interferometer based on the heterodyne technique and the second uses the dispersive properties of an optical fiber. We compare both results and discuss about each set-up

Multimode VCSEL model for wide frequency-range RIN simulation

In this paper, we present an equivalent circuit model for oxide-confined AlGaAs/GaAs VCSEL with the noise contribution adapted to optomicrowave links applications. This model is derived from the multimode rate equations. In order to understand the modal competition process, we restrain our description to a two-modes rate equations system affected by the spectral hole-burning. The relative intensity noise (RIN) measurements which were achieved on a prober in Faraday cage confirm the low frequency enhancement described by the model. We validate our model for a wide frequency-range [1 MHz–10 GHz] and high bias level up to six times the threshold current

2.49 GHz low phase-noise optoelectronic oscillator using 1.55μm VCSEL for avionics and aerospace applications

We present here a 1.55 μm single mode Vertical-Cavity Surface-Emitting Laser (VCSEL) based low phasenoise ring optoelectronic (OEO) oscillator operating at 2.49 GHz for aerospace, avionics and embedded systems applications. Experiments using optical fibers of different lengths have been carried out to obtain optimal results. A phase-noise measurement of -107 dBc/Hz at an offset of 10 kHz from the carrier is obtained. A 3-dB linewidth of 16 Hz for this oscillator signal has been measured. An analysis of lateral mode spacing or Free Spectral Range (FSR) as a function of fiber length has been carried out. A parametric comparison with DFB Laser-based and multimode VCSEL-based opto-electronic oscillators is also presented

Comparaison de la diaphonie présentée par deux technologies d'intégration de barrettes de VCSEL

Nous présentons les résultats de simulations et caractérisations de diodes lasers VCSEL (Vertical Cavity Surface Emitting Laser) montées en barrettes selon 2 technologies distinctes: l'une de type microruban développée par Avalon Photonics, et l'autre de type coplanaire fournie par Ulm Photonics

Optimization of an avionic VCSEL-based optical link through large signal characterization

Optical communication systems have been widely preferred for network communications, especially for Datacoms Local Area Network links. The optical technology is an excellent candidate for on-board systems due to the potential weight saving and EMC immunity. According to the short length of the link and a cost saving, Vertical Cavity Surface Emitting Laser (VCSEL) and multimode fiber are the best solution for gigabit systems. In this context, we propose a modeling of 850nm VCSEL based on the rate equations analysis to predict the optical interconnect performances (jitter, bit error rate). Our aim is to define the operation conditions of VCSEL under large signal modulation in order to maximize the Extinction Ratio (current IOFF below threshold) without affecting link performances. The VCSEL model is developed to provide large signal modulation response. Biasing below threshold causes stochastic turn-on delay. Fluctuations of this delay occur, due to the spontaneous emission. This leads to additional turn-on jitter. These stochastic effects are included in the model by adding the Langevin photon and electron noise sources. The VCSEL behavior under high-speed modulation is studied to observe the transient response and extract the resonance frequency, overshoot and turn-on delay. The associated jitter is evaluated with the standard deviation of the turn-on delay probability density function. Simulations of stochastic and deterministic jitters are realized under different conditions of modulation (OFF current levels). Comparing simulations with measurement results carried out on VCSEL and a short haul gigabit link validates the approach

Noise and signal modeling of various VCSEL structures

Current evolution in Datacoms and Gigabit Ethernet have made 850nm Vertical Cavity Surface Emitting Lasers(VCSEL) the most important and promising emitter. Numerous different structures have been growth, to obtain bestcurrent confinement and then to control the emitted light modal behavior. We have developed a small signal equivalent electrical model of VCSEL including Bragg reflectors, active area, chip connection and noise behavior. Easy tointegrate with classical software for circuit studies, this model which is widely adaptable for different structures takesinto account the complete electrical environment of the chip. An experimental validation for RF modulation up to 10GHz has been realized on oxide confined VCSEL, demonstrating that the model could be used to get realistic valuesfor the VCSEL intrinsic parameters.Including Langevin noise sources into the rate equations and using the same electrical analogy, noise current andvoltage sources can be added to the model. It allows good prediction for the RIN function shape up to 10GHz formonomodal emitter

Bidirectional link mock-up for avionics applications

Copper-based networks have been extensively employed on aircraft to ensure the avionics data-communications. Since the Airbus A380 development, Avionic Data Communication Network (ADCN) has been implemented to ensure transmissions between avionic equipment. This system is based on the Avionic Full Duplex Ethernet (AFDX), and transfers data at rates up to 100 Mb/s. The need of faster communications systems, up to 1Gb/s, has led to great interest in fiber optic based networks. Beyond higher data rates capabilities, the fiber optics have additional benefits, compared to electrical cables, in terms of weight saving and electromagnetic interference immunity which is strongly needed at gigahertz bandwidths. Multimode fibers (MMF) are becoming increasingly attractive for short-haul (<300m) high-speed interconnections. Besides, Vertical Cavity Surface Emitting Lasers (VCSELs) present interesting performances in comparison to edge-emitting lasers, cost effective and are widely chosen in this type of applications. We aim at achieving an entirely optical fiber Gigabit Ethernet (GbE) link based on 850nm VCSELs to interconnect avionic equipments. To meet IEEE 802.3 standards [1] and ADCN requirements [2], the fiber optic link must be full-duplex, bi-directional, on a single wavelength, and on the same fiber on up to 100m-distance. We have used, at each side of the link, a transceiver module developed for harsh environment applications. Also, there are multiple connections due to production breaks. These connections give birth to return loss (RL) and consequently crosstalk. One might pay attention to the impact of the RL on the link. We present the characterization of a mock-up and the comparison of experimental results with the GbE requirements

Modeling and characterization of VCSEL-based avionics full-duplex ethernet (AFDX) gigabit links

Low cost and intrinsic performances of 850 nm Vertical Cavity Surface Emitting Lasers (VCSELs) compared to Light Emitting Diodes make them very attractive for high speed and short distances data communication links through optical fibers. Weight saving and Electromagnetic Interference withstanding requirements have led to the need of a reliable solution to improve existing avionics high speed buses (e.g. AFDX) up to 1Gbps over 100m. To predict and optimize the performance of the link, the physical behavior of the VCSEL must be well understood. First, a theoretical study is performed through the rate equations adapted to VCSEL in large signal modulation. Averaged turn-on delays and oscillation effects are analytically computed and analyzed for different values of the on - and off state currents. This will affect the eye pattern, timing jitter and Bit Error Rate (BER) of the signal that must remain within IEEE 802.3 standard limits. In particular, the off-state current is minimized below the threshold to allow the highest possible Extinction Ratio. At this level, the spontaneous emission is dominating and leads to significant turn-on delay, turn-on jitter and bit pattern effects. Also, the transverse multimode behavior of VCSELs, caused by Spatial Hole Burning leads to some dispersion in the fiber and degradation of BER. VCSEL to Multimode Fiber coupling model is provided for prediction and optimization of modal dispersion. Lastly, turn-on delay measurements are performed on a real mock-up and results are compared with calculations

Systèmes opto-hyper à base de VCSEL

Face au développement des communications haut débit, la génération optique de signaux hyperfréquences, devenue incontournable, doit faire face aux besoins d’intégration. C’est dans ce contexte que le groupe MOSE mène des recherches sur l’application des VCSEL dans les systèmes opto-microondes pour des applications embarquées. L’étude et la réalisation d’un oscillateur opto-microonde à base de VCSEL (VBO) a fourni des résultats permettant d’envisager la conception d’un système générant des signaux hyperfréquences par voie optique très intégré et de faible coût. Un signal à 2.49GHz a été généré par un VBO utilisant un VCSEL émettant à 1550nm. Un bruit de phase de -107dBc/Hz à 10kHz de la porteuse pour 1000m de fibre a été mesuré. Compte tenu des avancées technologiques des VCSELs à grande longueur d’onde et de la possibilité d’optimiser le dispositif en vue d’une intégration, le bruit de phase pourra être considérablement diminué. Dans le cadre d’un projet transnational franco-suisse (en partenariat avec D-lightsys, BeamExpress, l’Ecole Polytechnique Fédérale de Lausanne), le laboratoire développe des modèles optoélectroniques et caractérise de nouvelles générations de VCSELs afin d’améliorer les performances du composant et d’optimiser son intégration. La modélisation basée sur la confrontation des éléments d’un schéma électrique équivalent et des équations d’évolution en accord avec l’expérience a permis d’extraire des valeurs de paramètres intrinsèques du VCSEL utiles au fabriquant (BeamExpress). Cette étude porte également sur les accès électriques du VCSEL et leurs effets sur les paramètres S11 et S21, ce qui permet d’adapter au mieux le composant dans des modules optoélectroniques intégrés. Le verrouillage optique de deux VCSELs en configuration maître-suiveur a également été réalisé afin de repousser la fréquence de coupure du VCSEL. Grâce à la constante progression des performances des VCSELs, de nouvelles applications dans les systèmes opto-hyperfréquences sont en perspectives