Why simulate photonics before building a prototype
In photonic projects many parameters can be analysed numerically before a physical component exists. This does not mean simulation replaces laboratory measurements — its role is to reduce the number of iterations and to catch design problems earlier.
Depending on the application, simulation can allow you to:
- analyse light propagation in the designed structure;
- determine the modes and effective refractive index of a waveguide;
- analyse coupling, splitting, and switching of optical signals;
- study reflection, transmission, diffraction, and polarisation in photonic structures;
- analyse nonlinear phenomena in selected component models;
- combine photonic and electronic models at the circuit level;
- assess the parameters of the whole optical link, not just a single component.
- analyse light propagation in the designed structure;
- determine the modes and effective refractive index of a waveguide;
- analyse coupling, splitting, and switching of optical signals;
- study reflection, transmission, diffraction, and polarisation in photonic structures;
- analyse nonlinear phenomena in selected component models;
- combine photonic and electronic models at the circuit level;
- assess the parameters of the whole optical link, not just a single component.
In practice this means being able to move from the question „how does the structure behave?” to „how will this component affect the operation of the whole system?”. We review the numerical methods themselves — ray tracing, FDTD, BPM, EME, RCWA — in the article Methods for modelling optical phenomena.
From component to whole system
One of the most important criteria for choosing a tool is the modelling level. In industrial photonics several connected levels can be distinguished.
Structure and photonic component
At this level you analyse waveguides, couplers, splitters, switches, and other photonic structures. Here Optiwave offers, among others, OptiFDTD, OptiBPM, and OptiMode. OptiFDTD is used for designing and analysing photonic components with the FDTD method, OptiBPM is an environment for designing complex waveguides, and OptiMode is for mode analysis of waveguide structures.
Optoelectronic circuit
If a photonic component works together with electronics, modelling light propagation alone is not enough — the electrical part of the circuit has to be taken into account as well. This level is served by OptiSPICE, which lets you simulate circuits containing optical and electrical components, including at the transistor level. The vendor lists applications such as laser drivers, transimpedance amplifiers, optical interconnects, and electronic equalizers.
Transmission system
At the highest level the analysis covers the whole optical system: transmitter, channel, receiver, and the components used. OptiSystem is an environment for designing, testing, and simulating optical links at the transmission level, with the ability to build models from individual components to complete systems.
Good practice is not to try to answer every design question with one model. The component model and the whole-system model should pass to each other only the parameters that matter at the next level of analysis.
Mode analysis: understand how the waveguide behaves
Before moving to a propagation simulation of a device, you often need the answer to a more basic question: which modes can the designed waveguide support? That is a task for mode analysis.
OptiMode enables analysis of waveguide structures and the determination of, among others:
- the supported modes;
- the mode profiles;
- the effective refractive index;
- the group index.
OptiMode can run as a standalone application and be integrated with OptiFDTD and OptiBPM, where the results of the mode analysis are used to prepare sources for further simulation.
- the supported modes;
- the mode profiles;
- the effective refractive index;
- the group index.
OptiMode can run as a standalone application and be integrated with OptiFDTD and OptiBPM, where the results of the mode analysis are used to prepare sources for further simulation.
It is important that OptiMode is not exclusively an FEM solver — the vendor lists among others ADI, AnIso, FD Complex, FEM solvers, and the LP and Vector fiber solvers. That is why the term mode analysis is more appropriate for this tool than simply „FEM solver”.
BPM: designing and analysing propagation in waveguides
BPM — Beam Propagation Method is intended for analysing light propagation in waveguide structures. OptiBPM is a CAD environment for designing complex waveguides; the vendor lists applications related to guiding, coupling, switching, splitting, multiplexing, and demultiplexing of optical signals.
BPM is particularly useful when the main design question is how the field propagates along the designed structure. An example workflow:
- you define the waveguide geometry;
- you set the optical properties of the materials;
- you determine the input conditions;
- you analyse the propagation;
- you change the geometry parameters;
- you compare the results of successive variants.
- you define the waveguide geometry;
- you set the optical properties of the materials;
- you determine the input conditions;
- you analyse the propagation;
- you change the geometry parameters;
- you compare the results of successive variants.
BPM should not, however, be treated as a universal replacement for FDTD. The two methods solve light-propagation problems in different ways and have different assumptions and areas of application.
FDTD: full-wave analysis of photonic components
When a project requires a direct, full-wave analysis of the electromagnetic field, the FDTD — Finite-Difference Time-Domain method is used. OptiFDTD is an Optiwave tool for designing and analysing passive and nonlinear photonic components; the vendor lists applications including wave propagation, scattering, reflection, diffraction, polarisation, and nonlinear phenomena. In the OptiFDTD documentation the basis of the computation is the FDTD algorithm with second-order numerical accuracy and the UPML (Uniaxial Perfectly Matched Layer) boundary condition.
FDTD is particularly interesting for designing structures in which the wave nature of light cannot be neglected. Typical areas of application indicated by Optiwave:
- waveguides and photonic components;
- small-scale photonic structures;
- photonic crystals;
- nanostructures;
- selected sensing applications;
- telecommunications components.
- waveguides and photonic components;
- small-scale photonic structures;
- photonic crystals;
- nanostructures;
- selected sensing applications;
- telecommunications components.
The computational cost of FDTD grows with the scale and resolution of the modelled domain. That is why a full-wave model should not automatically be applied to an entire industrial system — in practice it is more effective to combine models of different levels of detail. How the method works and when exactly to use it is described in the article How does the FDTD method work, and when should you use it?.
OptiOmega: GPU FDTD and mode analysis
For projects that require intensive full-wave computation, Optiwave also offers OptiOmega. The tool includes:
- a GPU-accelerated 3D FDTD solver;
- a Vector Finite Difference (VFD) mode solver running on the CPU;
- a Python-based working environment;
- mechanisms such as automatic port detection;
- calculation and export of S-parameters.
- a GPU-accelerated 3D FDTD solver;
- a Vector Finite Difference (VFD) mode solver running on the CPU;
- a Python-based working environment;
- mechanisms such as automatic port detection;
- calculation and export of S-parameters.
This is an important terminological distinction: OptiOmega is not exclusively an FDTD solver — it contains both an FDTD solver and a VFD mode solver. In practice it can be used to move from mode analysis of a structure to analysis of a photonic device. Results such as the effective refractive index or S-parameters can then be used in other Optiwave tools — the vendor indicates that OptiOmega can work with OptiSPICE and OptiSystem.
PIC and the integration of photonics with electronics
For PIC — photonic integrated circuits the design problem often does not end at the photonic device itself. A modulator or another photonic component is frequently part of a circuit that also contains an electrical signal source, a driver, optical elements, a receiver, and electronic circuits that process the signal.
In such a case you need a model that lets you analyse the interaction between the optical and electrical domains. OptiSPICE is intended precisely for simulating optoelectronic circuits — the vendor describes its use for circuits containing optical and electrical components and for analysing their behaviour at the circuit level.
In practice this lets you separate two problems: photonic component model → optoelectronic circuit model — instead of trying to run one huge simulation covering all the physical details of the device. We cover the fundamentals of PIC in the article PIC — photonic integrated circuit: the basics.
System simulation of optical links
At the whole-system level we are interested in different parameters than when designing a waveguide cross-section. In an optical link you analyse, among others:
- the behaviour of the transmitter;
- transmission through the channel;
- the effect of the optical components;
- the receiver;
- signal quality and BER;
- parameters related to transmission quality;
- the effect of changes in system parameters.
- the behaviour of the transmitter;
- transmission through the channel;
- the effect of the optical components;
- the receiver;
- signal quality and BER;
- parameters related to transmission quality;
- the effect of changes in system parameters.
OptiSystem is intended for such tasks — a tool for designing and simulating optical links at the transmission level, from components to complete systems. It also enables parametric analyses; the vendor's materials include examples such as parameter sweeps and BER analysis as a function of input power.
It is at this level that you can check whether a component designed at the device level actually meets the requirements of the whole system.
Optical fibers and Bragg gratings
Not every photonic problem requires FDTD. For optical fibers, parameters such as dispersion, loss, birefringence, PMD, or modal properties can be important. OptiFiber uses numerical mode solvers and fiber-specific models to calculate, among others, dispersion, loss, birefringence, and PMD. OptiGrating, in turn, is intended for modelling and designing devices that use optical gratings — both in integrated and in fiber structures.
This is a good example of a principle that should apply in industrial photonic design: first determine the phenomenon and the modelling level, and only then choose the solver.
Automation and data flow between models
In larger projects the ability to run a single simulation is not enough — what matters is the repeatability of the computation, the ability to change parameters, and passing results between modelling levels. OptiOmega uses Python as the basis of its workflow, which lets you automate simulations and post-processing using Python libraries.
The ability to pass results between tools is also important — Optiwave indicates the use of OptiOmega results (effective refractive index, S-parameters) in OptiSPICE and OptiSystem. In practice this creates a multi-level workflow: mode analysis → component model → circuit model → system model.
Not every project requires all of these stages. Their use depends on whether you are designing a single device, an optoelectronic module, or a complete system.
Matching the tool to the task
| Task | Modelling level | Method / model | Optiwave tool |
|---|---|---|---|
| Waveguide mode analysis | component | mode analysis | OptiMode |
| Designing complex waveguides | component | BPM | OptiBPM |
| Propagation, diffraction, and reflection analysis | component | FDTD | OptiFDTD |
| Full-wave 3D analysis + mode analysis | component / PIC | GPU FDTD + VFD | OptiOmega |
| Optical fiber design | component / fiber | mode solvers and fiber models | OptiFiber |
| Optical gratings | component | grating modelling | OptiGrating |
| Optoelectronic circuit | circuit level | circuit simulation | OptiSPICE |
| Optical link | system | system simulation | OptiSystem |
This split does not mean that each tool is limited to a single application — it is above all a practical map of modelling levels derived from the functions described by Optiwave. We set out the software-selection criteria more broadly in the guide How to choose optical simulation software?.
The most common mistakes in photonic design
- Choosing the method from geometric scale alone — there is no universal rule such as „micrometres = BPM, nanometres = FDTD”. The choice of method is decided by the nature of the problem, the significant physical phenomena, and the required level of accuracy.
- Trying to apply one model to the whole system — a full-wave model may be appropriate for a single component, but need not be the right tool for simulating the whole link.
- Skipping mode analysis — for waveguides, knowing the geometry alone is not enough; information about the supported modes, their profile, and the effective refractive index is often the basis for further analysis.
- No transition from the component level to the system level — a good component simulation result does not automatically mean the whole system will meet the requirements.
- Over-detailing the model — greater complexity does not always mean a better design answer; the model should be as detailed as the specific engineering question requires.
- No automation of repetitive computations — if a project requires recalculating variants many times, automation is often more important than the mere ability to run a single simulation.
- Trying to apply one model to the whole system — a full-wave model may be appropriate for a single component, but need not be the right tool for simulating the whole link.
- Skipping mode analysis — for waveguides, knowing the geometry alone is not enough; information about the supported modes, their profile, and the effective refractive index is often the basis for further analysis.
- No transition from the component level to the system level — a good component simulation result does not automatically mean the whole system will meet the requirements.
- Over-detailing the model — greater complexity does not always mean a better design answer; the model should be as detailed as the specific engineering question requires.
- No automation of repetitive computations — if a project requires recalculating variants many times, automation is often more important than the mere ability to run a single simulation.
Modelling vs. prototyping
Simulation does not replace measurements. Its industrial value lies above all in letting you move part of the design iterations ahead of the prototype-build stage. A typical process: requirements → model → simulation → parameter optimisation → prototype → measurement → model correction → next iteration.
In more complex projects the individual levels can be linked: OptiMode / OptiBPM / OptiFDTD / OptiOmega → OptiSPICE → OptiSystem. This is not a mandatory scheme for every project — it is a way of organising modelling when a project requires moving from the physical photonic structure to a circuit or a whole system. The ability of OptiOmega to work with OptiSPICE and OptiSystem is indicated directly by Optiwave.
Industrial photonics: how to start?
The best starting point is not the name of a program, but the design question:
- „Which modes does my waveguide support?” → mode analysis, e.g. OptiMode.
- „How does light propagate through the designed waveguide?” → BPM, e.g. OptiBPM.
- „How does the structure interact with the electromagnetic field when wave phenomena matter?” → FDTD, e.g. OptiFDTD or OptiOmega.
- „How does the photonic component work together with electronics?” → OptiSPICE.
- „How does the whole component or chain of components affect transmission?” → OptiSystem.
- „What are the properties of the designed optical fiber?” → OptiFiber.
- „How does an optical grating behave?” → OptiGrating.
- „Which modes does my waveguide support?” → mode analysis, e.g. OptiMode.
- „How does light propagate through the designed waveguide?” → BPM, e.g. OptiBPM.
- „How does the structure interact with the electromagnetic field when wave phenomena matter?” → FDTD, e.g. OptiFDTD or OptiOmega.
- „How does the photonic component work together with electronics?” → OptiSPICE.
- „How does the whole component or chain of components affect transmission?” → OptiSystem.
- „What are the properties of the designed optical fiber?” → OptiFiber.
- „How does an optical grating behave?” → OptiGrating.
This approach reduces the risk of choosing a tool solely from a list of features. First you define the physical problem and the modelling level, and then you match the method and the software. iSymulacje — a brand of SPECTROPOL, the Polish distributor of Optiwave and Lambda Research Corporation — helps match modules to real needs and start a trial version.