This page explains the basic idea of exporting near field electromagnetic data to a rayset for further simulation with a ray tracing tool.
In some applications, it is necessary to use a combination of tools to simulate your entire device. For example, FDTD might be used to simulate scattering from a nano-particle. Additionally, it may be necessary to calculate the fraction of scattered fields that can be collected by a macroscopic detector with a complex lens system. The length scales involved in a macroscopic lens system are not suitable for FDTD simulation. Instead, the near field scattering data from the FDTD simulation can be exported to a ray tracer, which is more suitable for simulating macroscopic systems.
The Zemax interoperability feature offers a seamless exchange of E field data between Lumerical and Zemax via both GUI and script commands. To export data to other ray tracing tools a more general process must be used. This process can be be broken into two main steps:
Decompose near field data into a ray set
Most ray tracing tools are not able to import near field data. Instead, the near field data must first be converted into a rayset, which can then be understood by the ray tracer. Fortunately, it is easy to decompose the near field data from FDTD using the far field projection functions. Basically, these functions decompose the near field data using a set of plane waves (rays) propagating at different angles as the basis for the decomposition. Each plane wave can be considered to be one 'ray' in the ray set. The far field projections provide the amplitude, phase, polarization, etc of each ray.
The far field projection functions are always used to do the near field to ray set conversion. However, the precise details of the analysis depend on the application. For example, the ray 'phase' may or may not be important. Similarly, it may or may not be necessary to combine the results of several FDTD simulations to obtain an incoherent ray set.
For more information on these functions, see the far field projection pages.
Export ray data to a text file
There are many ray tracing products (ASAP TM, FRED TM, ZEMAX TM, etc), and each uses a different file format. In fact, a single software often uses different file formats for different types of ray sets.
Once the far field projections have been calculated, it will be necessary to write the data to a text file in a format that can be imported into your ray tracer. This will require knowledge of the file format. See your ray tracer product documentation or contact their technical support.
An example script for exporting OLED simulation data from FDTD to ASAP can be found at this link . Please see the scripting section for asapimport and asapexport commands.