November 1, 2013. Agilent Technologies Inc. has introduced a physics-based model for its opto model library that quickly and accurately solves the challenges posed by signal distortion in vertical cavity surface emitting lasers (VCSELs) used in rack-to-rack opto links. The new VCSEL model, available in the Advanced Design System 2013 Transient Convolution Element and SystemVue 2013 AMI Modeling Kit, is used both for modeling optoelectronic components and designing them into equipment.
Before the multigigabit era, rack-to-rack digital signals propagated tens or even hundreds of meters across CAT-5 twisted pair or co-axial copper cables with little distortion. However, at today’s speeds, rising and falling edges degrade after travelling only a few meters. Laser technologies like VCSELs have pushed down the cost of optoelectronics to the point where optical fiber communication is now replacing traditional copper cabling for spans over about 10 meters in the multigigabit regime.
Up to now, simulation tools used to design these nonlinear devices required engineers to learn a whole new optical paradigm. With the new VCSEL model, however, Agilent is leveraging a technique that high-speed digital engineers are already familiar with—the Input/Output Buffer Information Specification (IBIS) AMI flow. Senior Agilent engineers contributed this innovative model to document BIRD-156 of the IBIS Open Forum. BIRD-156 extends the AMI flow to allow both electrical and optical repeater links to be modeled and was incorporated in the recently ratified IBIS version 6.0. Agilent co-authors will present a paper, “Modeling, Extraction and Verification of VCSEL Model for Optical IBIS AMI,” at DesignCon 2014, to be held in January in Santa Clara.
With the VCSEL model, SystemVue 2013 now offers model builders, such as optoelectronic component vendors, a tool that supports the evolution of IBIS and can build rack-to-rack opto link models. The models run in ADS, the tool that opto component consumers (data center and telecoms equipment manufacturers, for example) use to design these subsystems into their larger systems. SystemVue 2013 also now features an enhanced model for the clock/data recovery circuitry found in both optical and electrical retimers.
“With our previous opto model library release we added a simpler class of VCSEL model with frequency-independent behavior,” said Colin Warwick, product manager for High-Speed Digital Design at Agilent EEsof EDA. “With this release, we’re adding not only a physics-based, frequency-dependent model that uses rate equation techniques, but also a tool to fit the rate equation parameters to measured data, ensuring an accurate model.”