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he chief goal of any designproject is to produce anoptimized design that hasthe highest possible per-

formance given any requireddesign constraints, whether physicalor financial. RSoft Design Grouptools have always supported optimiza-tion through automated parameterscanning and by user-created pro-grams using the scripting interface.However, with the increasing impor-tance of optimization across thedevice and system levels, RSoft isnow releasing a Multi-variableOptimization and Scanning Tool,(MOST ), solely dedicated to theautomation and analysis of parameter

scanning and optimization. This toolis designed to work with RSoft’s exist-ing line of design and simulation soft-ware packages including BeamPROP,

F u l l W A V E ,B a n d S O L V E ,G r a t i n g M O D ,D i f f r ac tMOD,LaserMOD, andOptSIM .

While a proto-type can usuallybe improved bya trial and errorsearch for betterdesigns, themost efficient

and effective means to approachdesign evolution is to utilize optimization algorithms. Optimization algorithms enable engineers to quickly

find design solutions that satisfyspecific requirements. For example, the cross-section of a microstructured fibecan be designedsuch that the fibehas specific desired dispersioncharacteristics oa taper-based modeconverter can be

E C O C 2 0 0 4 S t o c k h o l m , S w e d e n B o o t h 2 1 8 S e p t e m b e r 2 0 0 4

Volume 3 Number 2 

RSoft Introduces Advanced Optimizer andComplete VCSEL Design Solution

T 

continued on page i

n the current design para-digm, VCSEL designs andthe optical systems that use

them are simulated sepa-rately. However, it is

important for cost and time-to-marketreduction, as well as performanceoptimization, that VCSEL designersare able to simulate their new deviceswithin the context of a system, andthat system designers have thoroughand accurate VCSEL models. It is alsoimportant that laser driver circuitdesigners have accurate VCSEL mod-els due to the tight nonlinear couplingbetween the VCSEL and the laser driv-er circuit.

While thorough and accurate VCSELmodels do exist for system simula-tions, these models have many param-

eters, making them difficult to cali-brate for real devices and to includeeffects such as jitter, self-heating, andspatial hole burning. To tackle thisproblem, RSoft introduces a newhybrid simulation methodology thatnot only allows the extraction of realis-tic system-level VCSEL models fromboth measured and simulated devicedata, but can also provide the equiva-lent circuit-level models for use withSPICE and other EDA tools.

The hybrid simulation procedure

begins either with RSoft’s activdevice tool, LaserMOD™ , which simulates the VCSEL at the microscopi

level or measured data. Next, thOptSim™ Best-Fit Laser Toolkit™directly extracts the system modeparameters from this data. RSoftsystem tool, OptSim, is then used tsimulate the system performance witthe extracted VCSEL model. Once thdesired performance criteria arachieved, a circuit model for thVCSEL can be exported for use ielectronic circuit simulations wittools such as SPICE. This is extremely valuable for accurate laser driver cicuit simulations and design optimization

A Complete Design Strategy: Using Comprehensive Mixed-level Design 

and Simulation for VCSEL-based Optical Transmission Systems 

I 

continued on page

The MOST TM  Advanced Optimizer for Photonic Design 

Evolution of a 40 variable system using a Genetic Algorithm 

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created which has the lowest couplingoss within a maximum device length.

Optimization algorithms also allowengineers to explore systems which arehighly complicated and have either a

ocal or a broad parameter space.Local optimization routines allow theuser to quickly find an optimal designgiven a few initial guesses at parame-ter values. Global optimization rou-tines, though computationally moredemanding than local algorithms,allow the identification of global maxi-ma/minima in a broad parameter spaceand allow the user to create non-obvi-ous solutions to difficult problems.

MOST  includes a number of excitingfeatures: It is fully integrated withexisting RSoft products and providesdialogs for specifying optimizationsand scans over an arbitrary number ofvariables. The package includes aarge number of single and multi-

dimensional optimization algorithmsincluding root-finders, minimizers,simplex search routines, genetic algo-rithms, and other stochastic routines.Moreover, a simple but flexible APIallows users to add custom algorithms

through their own C++ DLL’s or load-able Python scripts. It is fully integrat-ed with existing RSoft software andprovides dialogs for specifying opti-mizations and scans over an arbitrarynumber of variables. A graphical dis-play indicates the overall convergenceof the algorithm and current values ofthe parameters.

MOST is highly flexible not only in themanner of optimization but also in thetarget to be optimized. While it is easyto optimize simple scalar quantitiessuch as coupled power, the tool can beconfigured to optimize any vector ormatrix-like quantity in terms of a “met-ric” or figure-of-merit. For instance,the integrated difference between a

target and a simulated transmissiospectrum can be minimized.

Perhaps most significantly, MOST fully ready for clustered computatioGlobal optimization problems, in pa

ticular, can be hugely demanding computational resources. Users wimultiple copies of RSoft tools can usMOST to automatically distribute largscans and certain optimizations acroa network. This effectively extendcluster capabilities beyond FullWAVto the entire RSoft device suite on boWindows and UNIX platformThrough load-balancing, it is not evenecessary for the various machines have the same performance.

While nothing can replace the knowedge and experience of a good opticengineer, optimization routines alloexperienced engineers to explore neand untried solutions to theproblems.

Introducing MOST continued from page i 

The LaserMOD simulation engine pro-

vides a self-consistent solution of theelectro-thermal transport and opticalfield propagation in semiconductorlasers such as VCSELs. The devicestructure and material parame-ters are digitized on a non-uni-form mesh. Many importanteffects such as self-heating,gain guiding and saturation,multi-mode competition, andpackaging parasitics are allaccounted for in such ascheme. Simulation resultsinclude steady-state solutionsfor analyzing CW performance,and transient solutions for ana-lyzing the modulation responseof the device.

The OptSim Best-Fit Laser Toolkit extracts a corresponding system-levellaser model from LaserMOD simulationresults, such as the material gain ver-sus temperature and carrier density,via a proprietary parameter optimiza-

tion procedure. Measured results or

manufacturer data sheets can also beused to generate the system-levelmodel. At this point, a comprehensivenonlinear electrical circuit model can

be exported to many popular EDA toolson the market such as SPICE3,PSpice, ADS, Spectre, and Hspice.

After the calibrated parameters are inplace, the OptSim VCSEL model, themost advanced model of its kind, isavailable for VCSEL-based optical sys-

tem simulation. This model is base

on multimode rate equations whicconsider the thermal dependence anspatial distribution of carrier densitVarious performance analyses such

eye diagrams, Q and BER estmates, and spatial couplineffects are provided when usein conjunction with ModeSYS ,multimode simulation tool.

This compressive mixed-levmethodology allows, for the firtime in a commercial tool suitthe accurate and consistedescription of a VCSEL at bodevice-and system-levels anprovides an interface to ele

tronic circuit design. It enables prevously unavailable design paths, anthus make the overall design and optmization cycle of VCSEL-based optictransmission systems much more efcient.

A Complete Design Strategy continued from page i 

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RSoft Design Group Interview with Dr.Kurt Hingerl, University of Linz

Professor Kurt Hingerl is a researcher at the University of Linz in Linz,

Austria. After earning his PhD at the

University of Linz, Prof. Hingerl did his

post-doctoral research at the University of

llinois and Bellcore. After this, his career

path has taken him from environmentalengineering to surface physics and now to

photonics.

RSoft: Professor Hingerl, please tell us a little bit about your position and

he research you do at the University of Linz.

My group is working on basic problems related to a new kind of mate-

ial, photonic crystals, also called PhCs (or photonic band-gap materi-

als). PhCs are periodic dielectric (or sometimes metallic) structures

hat have a photonic band gap (PBG) for photons, i.e. that light propa-gation is forbidden at certain frequencies. By scaling the size of the

periodicity, the PBG can be tuned from the microwave to the UV region.

This property enables one to control (guide and split) light in a way that

s almost impossible with conventional optics or with conventional inte-

grated optics.

We are active in theoretical and numerical techniques of light propaga-

ion, but also performing experimental work as one of the major users

of the clean room at the University of Linz, especially electron beam

ithography and structural processing.

One of our recent achievements is the “invention” of curvilinear pho-

onic crystals, as recently published in Appl. Phys. Lett, issue 7th of

une 2004. Other works in progress are concerned with add- dropMultiplexers with PhCs, the fabrication of 3D PhCs, the use of nanoim-

print-lithography, etc.

RSoft: Now, we understand that you and the university are part of a large

collaboration among researchers throughout Europe. Please tell us more

about this.

We have been very active in measuring (with ellipsometric methods)

and calculating (with FDTD, plane wave expansion, etc.) the polariza-

ion optical response of nano-structured surfaces and all this is done

either in international projects. So we are currently involved in two

European Community projects (5th and 6th Framework program) and

ndependently also pursue co-operations with groups at CREOL,

Florida, Univ. Brno, Czech republic, Univ. Rome III, Italy, and Univ.Bath, UK.

RSoft: What made you chose RSoft Design Group as the vendor of choice for

design and simulation software?

Basically three reasons were the important ones for us:

RSoft FDTD code runs on 64 bit supercomputers, in our case Altix and

SGI Origin machines, and especially for 3D computations the 2GB limit

of Pentium based systems can be overcome easily. The fully integrated

CAD system allows one to switch to BandSOLVE , DiffractMOD ,

BeamPROP , FullWAVE , GratingMOD , all within the same structure.

The really good support and continued development!

RSoft: In what way has RSoft’s line of design and simulation software aid

in these collaborative efforts? Given this research, what ways h

BeamPROP  and FullWAVE  been utilized for specific designs of photon

devices?

One example is e.g. – for curvilinear PhCs- the integrated user interfa

and the scanning property: after obtaining the band gap maps for th

curvilinear PhCs it was a simple change to obtain the FDTD simulati

results.

BeamPROP  is currently used for student education. Novel photon

devices are difficult to be understood and optimized by analytical tec

niques alone. Although it is of utmost importance for students

understand the basic equations, they only get a feeling for photonics

they are able to work “hands on” with simulation software to see, ho

their designs really perform.

RSoft: What types of research have you been pursuing with LaserMOD ?

We plan to enter into VCSELs out of IV-VI compounds, (PbTe and rela

ed materials), where the thermal management is of high importance

RSoft: Your research is targeted toward photonic bandgap structures a

devices. How has RSoft’s products helped you pursue this research?

I can only highlight it again: the integration of FullWAVE  wi

BandSOLVE within one CAD layout is really helpful!

It is not our vision to develop software, but to apply this softwa

towards innovative designs and RSoft turned out to be the ideal par

ner for these goals.

RSoft: How do you see the need and demand for photonic software in futu

applications?

Especially if one works with high index materials and low index mat

rials with high index contrasts, like the Si/SiO2, but also with th

AlGaAs/Al2O3 oxide system, fast BPM techniques which are able

handle this high index contrast will become important for industrpurposes. Approaches beyond effective index approximations shou

be developed by close collaboration between mathematicians a

users.

At the same time optimization tools integrated into the existing sof

ware will become important in industrial environments to automa

design projects.

Nevertheless, creative new approaches, where the computer code

then used to verify and respectively falsify, these models will alwa

demand new extensions of the available software tools.

RSoft: Yes, in fact at ECOC 2004 we plan to present a new integrated opmizer and new capabilities to handle high index contrast structures. A

final thoughts regarding RSoft’s products and their integration with yo

research?

Just continue with your kind of customer support and development

continue to aid the industry!

RSoft: Thank you for your time and we wish you good luck in your researc

i

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2 0 0 E x e c u t i v e B o u l e v a r d

O s s i n i n g , N Y 1 0 5 6 2 U S A

P h o n e : 9 1 4 . 9 2 3 . 2 1 6 4

E m a i l : i n f o @ r s o f t d e s i g n . c o m

W e b : w w w . r s o f t d e s i g n . c o m

U K O f f i c e :

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4 4 1 7 8 7 4 7 7 9 7 8

i n f o @ r s o f t d e s i g n . c o . u k

I N B R I E F

Application papers on our website

RSoft Design Group has developed a collect

technical papers authored by both our tecstaff and our customers which describe many

of design applications using our software. Ple

to our website www.rsoftdesign.com to access

references. If you would like to submit a pape

listed on our site, please

info@rsoftdesign.com.

ATS in Turino Italy has referenced its use of O

in a talk at ECOC 2004, entitled “Imp

Electronic Equalization on Advanced Modu

Formats in Dispersion-Limited Systems” by V.

R. Gaudino and A. Napoli.

ecently this year RSoftDesign Group announcedthe release of its newestcomponent level package,DiffractMOD TM , a powerful,

easy to use tool for the design andanalysis of periodic and diffractivestructures. The software is based onthe well-known Rigorous CoupledWave Analysis (RCWA) algorithm.While RCWA is currently an industrystandard, DiffractMOD has been pow-erfully enhanced with the latestbreakthroughs and state of the arttechniques, including ModalTransmission Line (MTL) and FastFourier Factorization (FFF). Theseunique new features allow the soft-

ware to converge quickly and providefor the greatest stability. An exten-sive range of materials and devicescan be designed using this advancedsimulation technology.

One important application area thatwill benefit fromDiffractMOD  is opticalmetrology where theprofile of a periodicstructure can becharacterized by usingoptical scatterometryand spectrometry.The RCWA algorithmprovides the neces-sary accuracy andefficiency for suchoptical metrology toolsespecially as the Critical Dimension(CD) decreases for semiconductormanufacturing. Additionally more andmore manufacturers are now makingstandard advanced process controls(APCs) based on real time opticalmetrology where software holds animportant role. DiffractMOD  can beutilized for both the design andimplementation of metrology systemsby utilizing the RCWA algorithm as anefficient way of addressing theseneeds.

DiffractMOD  is integrated directlyinto the RSoft CAD in order to simu-late these structures types in astraightforward and easy manner.

Once the structure is created in theCAD tool, the powerful RCWA tool willoutput all of the spectral informationat any order, and can even output thefields at various positions throughout

the device. This type of analysisallows for the “fine-tuning” of metrol-ogy devices where the line-widths andpositions of spectral response peaksare critical.

Another important use of DiffractMOD is to simulate photonic bandgap(PBG) applications. PBG devices arean exciting area of research wherescientists and engineers are lookingto create structures which benefitfrom their low loss and dispersion

capabilities. DiffractMOD  can ana-lyze an incoming beam on a diffrac-tive structure and quickly give theresponse of the device. This is veryuseful for a fast and accurate analysisof the propagation of a field through aPBG device acting either as a diffrac-

tive structure or as afilter. To furtherextend this analysis,DiffractMOD  can beused with other RSoftsimulation tools. Resultsfrom DiffractMOD can be used in conjunc-tion with FullWAVE’s ability to producetime dependent resultsof the field andBandSOLVE’s  simu-

lations of the complete bandgap ofthe device. The results of these threetools, can be combined to produce acomplete solution for PBG baseddevices.

In addition to metrology and PBGapplications, DiffractMOD  can beused for many other periodic and dif-fractive structures. The software isapplicable to optical signal process-ing, sub-wavelength gratings, anti-reflection structures, filters, diffrac-tive optical elements (DOEs), andbeam splitting, and other such opti-cal devices. For further informationon these or the previous applications,please contact RSoft.

R 

–

RSoft Design Group Includes Software in New B

by Govind P. Agrawal

Furthering its strong relationships with the

demic community, RSoft Design Group is incl

a demonstration version of its award-winning

ware, the RSoft Photonics CAD Suite™, incl

system design, in a new book by fiber-optics

nary Dr. Govind P. Agrawal. The first book in a

volume engineering resource, Ligh

Technology: Components and Devices, pub

by John Wiley and Sons, describes a multitu

today’s silica- and semiconductor-based o

devices. Conceived and written by the fore

expert and bestselling author in the fiber

field, the text provides detailed, in-depth cov

of both theoretical and practical aspects of th

ence, including fiber optics, passive and

fiber components, planar waveguides, semico

tor lasers and amplifiers, optical modulators,

todetectors, WDM components, and space

time-domain switching. Included with this b

a CD-ROM containing simulation examples

on RSoft’s software that accompany and illu

the concepts discussed in each of the book’s

ters. The wide range of examples make u

BeamPROP™, FullWAVE™, GratingMO

BandSOLVE™, LaserMOD™, and OptSproducts.

v 

DiffractMOD: The Tool of Choice for Optical Metrologyand a Complementary Solution for

Photonic Crystal Design