OptiBPM and OptiFiber share a file format *.f3d which is proprietary to Optiwave Corporation. ZEMAX can read this data via Tools...Miscellaneous...Convert File Format.



The details are described in the manual, but note the following points:

• ZBF files have a number of pixels in x and y which must be a power of 2: the .f3d files do not. ZEMAX will therefore zero-pad the .f3d data to make it equal the nearest larger power of 2
• .f3d files do not contain the wavelength of the data, which must therefore be entered separately
• The .f3d E-field phase data is referenced to a local plane. ZEMAX will fit a Gaussian beam to the E-field data to estimate the pilot beam properties required for subsequent propagation in ZEMAX, and store this data in the ZBF file.

The zip file at the end of this article contains two OptiBPM simulations of SMF-28. One is measured with no tilt,and the other contains a tilt that represents a cleaved fiber end. The untilted beam can be converted and then read into ZEMAX like so:

Inputing this beam and analyzing it with the POPD operand shows the following:

• effective width in x: 4.492 microns 
• M² in x: 1.022
• effective width in y: 4.479 microns 
• M² in y: 1.021

The modal field as computed by OptiBPM is therefore very slightly asymmetric, and very slightly non-Gaussian (the M² parameter = 1 for any pure TEM_x,y mode). The simulation is certainly within the specification of a modal field diameter of 9.2 ± 0.4 µm.

The real use of this capability is when the input file is not a good Gaussian, of course. The second file contains a tilt, and analysis with POPD shows:

• effective width in x: 6.64 microns
• M² in x: 1.3
• effective width in y: 6.59 microns
• M² in y: 1.3