This article describes how to use the polar detector and import/export source IESNA and EULUMDAT data. It also contains a description of the NSDP optimization operand and ZPL numeric function. An encapsulated LED is used to illustrate these features.

Authored By Akash Arora

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Introduction

OpticStudio has numerous built-in, Non-Sequential source types for simulating various spatial and angular source ray distributions. The polar detector can be used to measure the radiant intensity of any of those sources, including imported sources, such as IESNA or EULUMDAT sources. Once the source is chosen and an optical system is modeled and optimized, the polar detector may also be used to export individual source data or system optical output to a standard format for use in another software.

In this article, we will show how to export angular source data and how to import it back into OpticStudio to verify the proper energy distribution.

The polar detector

The polar detector is a spherical shaped detector that displays radiant intensity data on a polar plot. It can show both power and tristimulus (i.e. true color) data from NSC rays that hit the detector. This type of detector can be considered a “far-field” detector, as opposed to “near-field” detector types that display data in spatial coordinates. For source characterization, far-field intensity data is often the most informative way to display the intensity profile; polar plots are the most intuitive way to look at angular data.

The polar detector has the following unique parameters:

• Maximum Angle: the maximum polar angle in degrees from 0 to 180. As this is a polar angle, a sphere can be defined.
• Radial Size: the maximum radial size of the detector. This determines the radius of the spherical detector.
• #P pixels: the number of polar pixels from 10 to 721.
• #A pixels: the number of azimuthal pixels from 12 to 720.
• Mirroring: allows the detector to exploit symmetry in the incident rays, if appropriate. This is supported for most detector types.

Note that the vertex of the polar detector will be located a distance equal to the radius from the detector’s local coordinate origin. The suggested method for placing the detector is to center it on the source that is being measured. In this case, the radial size determines the distance of the detector vertex from the source and the angular size determines the lateral extent of the detector (the angle it subtends from the source). To fully characterize a source, the detector should be placed and sized to collect all rays from the source.

A unique optimization operand, NSDP, is supported for optimizing data on a polar detector. The syntax for the NSDP operand is as follows:

NSDP   Surf   Det#   Pix#   Data

Surf defines the Non-Sequential group surface (1 in pure NSC), Det# defines the desired polar detector from which to report data (it can also be used to clear one or all detectors), Pix# defines the specific pixel or computed value to return and Data defines whether to return power, flux, radiometric/photometric intensity, chromaticity or tristimulus data. For a detailed description of NSDP capabilities, see the optimization chapter in the OpticStudio user’s guide.

The Zemax Programming Language also has a numeric function, NSDP(), that returns the same data as the optimization operand. This function allows you to return any desired data from a polar detector in a macro. More information about ZPL can be found in the help file at the following location: The Programming Tab...About the ZPL.

IESNA & EULUMDAT data formats

The IESNA and EULUMDAT file formats were developed as standardized methods for representing angular data. Both formats are ASCII text files that list relative intensity at discrete polar and azimuthal angles. IESNA files have a *.IES extension and EULUMDAT files have a *.LDT extension.

For more information on the IESNA format, see this link:

https://www.ies.org/

For more information on the EULUMDAT format, see this link:

https://en.wikipedia.org/wiki/EULUMDAT

OpticStudio has two source types that allow IESNA and EULUMDAT files to be imported into a Non-Sequential system. The “Source IESNA File” and “Source EULUMDAT File” are used for IESNA and EULUMDAT formats, respectively. IES files must be placed in the {Zemax}\Objects\Sources\IESNA directory and LDT files must be placed in the {Zemax}\Objects\Sources\EULUMDAT directory. Once the files have been saved in these directories, they will appear as options for selection in the object properties dialog.

The Export Polar Data as IES/LDT tool

Any radiant intensity data that is recorded on a polar detector may be exported to an IES or LDT file. Once rays have been traced and energy has been registered on the detector, the export source data tool may be used to create an IES or LDT source file. The export tool can be found under Tools...Export...Export Source Data.

The export tool has several options:

• Format: export to IESNA or EULUMDAT format
• Detector: the polar detector from which to export data
• File Name: the name of the source file to save (without the extension)
• Smoothing: apply a smoothing factor to the data before saving

The file will be saved to either the {Zemax}\Objects\Sources\IESNA or EULUMDAT directory depending upon the format. If a full path name is included, the file will be saved to that directory

Note that it is also possible export ray irradiance, intensity and position data simultaneously. The ray database settings contain an option to save rays on a specific object. All that needs to be done is to trace and save rays, open the ray database and select a file to save the rays to, and then define a source file using that *.dat file.

LED example: The Polar Detector

To illustrate the capabilities of the detector polar and the source export tool, we will investigate a sample file that models an LED. You will find the sample file “led_model_poldet.zar” attached to this article; open this file.

The LED in this file is modeled using a source volume for the active region and several geometry objects to simulate the encapsulation and electrical leads of the LED. Note the polar detector is referenced (Ref Object) to the source volume and the maximum angle of acceptance is 60 degrees. The vertex of the detector is located 20 mm from the source itself.

When the detector viewer is defined to show polar detector data, OpticStudio automatically shows a polar plot; this is the most intuitive way to view radiant intensity data. In addition to the polar plot markings, the detector viewer shows the active cursor in polar coordinates rather than Cartesian coordinates.

Trace rays and compare the radiant intensity results on the detector rectangle and detector polar.

The radiant intensity distribution is nearly identical. Note that the polar detector pixels are actually triangular regions sized to have approximately the same area. The detector rectangle has rectangular pixels of equal area. This difference will cause some variation in the appearance of the energy distributions.

The benefit of displaying radiant intensity on a polar plot is clear when comparing the two types of detectors. In addition to the polar plot markings and polar coordinates, the detector polar can capture rays at any angle (even beyond 90 degrees), whereas the detector rectangle cannot because it is planar.

Neither detector is collecting all the energy that is emitted from the LED. A single planar detector cannot detect all the energy emitted from a source with rays beyond 90 degrees; this is where the detector polar truly excels. Define a maximum angle of 180 degrees on the polar detector. Notice that the detector becomes a full sphere and, ideally, all the energy should be registered on the detector. In this example, Fresnel reflections from the PMMA capsule and the mirrored components causes some energy to be lost/absorbed.

The shaded model plot shows the spherical detector polar and its ability to capture rays emitted into a full sphere.

The polar plot shows that little energy is incident beyond 100 degrees.

A log-5 plot shows that there is a small amount of energy up to 180 degrees.

The ability to capture rays emitted into 4*pi steradians enables the detector polar to fully characterize any source. Now that the detector polar has information about the encapsulated LED, we can export this data to an IES or LDT file.

Led example: source export

The export source data tool is used to convert the radiant intensity data stored on a detector polar and convert it to IES or LDT format. Make sure that the energy distribution is still stored on the detector, open the export source data tool located in Analyze...Detector Tools...Export Polar Detector Data as IES/LDT.

Select the following settings and press OK.

That’s all there is to creating an IESNA or EULUMDAT photometric data file! Any Non-Sequential source or combination of sources can be used to create a source file. Simply define a polar detector and trace rays.

To verify the intensity profile that was exported, we can import the LDT file using the Source EULUMDAT File type. The other file attached to this article, “led_model_LDT.zar”, contains only this source and the detector polar; open it now.

Take note that the source EULUMDAT file is modeled as a point source, not as an elliptical volume like the original source. Ray directions are chosen according to the radiant intensity profile recorded by the polar detector. Trace rays and compare the radiant intensity profile with that achieved in the original system.

When comparing results as we just did, keep in mind that the EULUMDAT source should be placed in the original location relative to the polar detector, and the properties of both the source and the polar detector should be the same as were used to record the data.

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