Hoya B370 Color Glass Filter

This article describes how to construct a FRED model for the Hoya B370 color filter as sold by Edmund Optics using a material definition. In order to build this model there are a few pieces of information that we need; the refractive index of the substrate, the internal transmission of the bulk material, and the thickness of the blank used for the internal transmission figure; these are available in the data sheet provided by Hoya:

A material definition called Hoya B370 features in the example FRED model.

Download the FRED file here: B370+Color+Filter.frd

In the model, a new material was added using the "Sampled Material" option which defines the dispersion from a simple list of refractive index vs wavelength. The information from the Hoya datasheet has been entered into the Material tab of the material definition:

The internal transmission is input into the material's Absorption tab using the Internal Transmittance option.

The datasheet doesn't supply the tabular form of this data, so it needs to be to extracted from the plot. In this case the data has been extracted into a text file that has a header that allows it to be read into FRED's Absorption tab by right mouse clicking in the spreadsheet of the Absorption tab and choosing the option to "Replace Data with File Data". More information on the file formatting is available in the FRED help system, within the Materials > Absorption topic.

For reference the text file is available here: B370_ColorFilter.txt

To see the effect of the color filter a ray trace can be ran where wavelength selection is performed via ray selection filters on your analysis surfaces (Analysis Surface Ray Filters). In the FRED model, there are two analysis surfaces. The one labeled Detector_Surface_BlockingBandpass uses ray selection filters to isolate rays within the blocking bandpass of the B-370 glass (0.4 to 0.7 microns). The other analysis surface includes all rays that pass through the filter.

We can retrieve the power within the specified bandpass limits by using any number of FRED's energy based analyses functions, such as the Irradiance Spread Function analysis, and then checking the output window for the reported Integrated Power value. If the "bandpass" analysis surface is used with the irradiance spread function analysis, FRED will report the integrated power value as 0.0187 watts for this particular example.