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RP Fiber Calculator is a convenient tool for calculations on optical fibers.
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RP Coating – Advanced Software for
Designing Optical Multilayer Structures

Demo File: Short-pass and Long-pass Filters

This demo file provides a custom form with which one can easily design optical filters which have a high transmission at short wavelengths and high reflectivity at long wavelengths (short pass) or vice versa (long pass). The design is essentially that of a Bragg mirror, but with added λ/8 layers at the top and the bottom. If required, the performance can be further improved with an optional local numerical optimization.

form for short-pass and long-pass filters

It is instructive to see the used script code for the definition of the coating, based on various variables which are entered in the form:

beam from superstrate
substrate: (material_s$)
if DesignType$ = "Bragg" then
begin
  for j := 1 to N_Bragg do
  begin
    * (material_l$), l/4 at l_Bragg
    * (material_h$), l/4 at l_Bragg
  end
end
else if DesignType$ = "short-pass" then
begin
  * (material_l$), l/8 at l_Bragg
  for j := 1 to N_Bragg do
  begin
    * (material_h$), l/4 at l_Bragg
    * (material_l$), l/4 at l_Bragg
  end
  * (material_h$), l/4 at l_Bragg
  * (material_l$), l/8 at l_Bragg
end
else if DesignType$ = "long-pass" then
begin
  * (material_h$), l/8 at l_Bragg
  for j := 1 to N_Bragg do
  begin
    * (material_l$), l/4 at l_Bragg
    * (material_h$), l/4 at l_Bragg
  end
  * (material_l$), l/4 at l_Bragg
  * (material_h$), l/8 at l_Bragg
end
superstrate: air

The first diagram shows the reflectivity profile of a short-pass filter, designed for transmitting pump light at 808 nm into a laser operating at 1064 nm:

reflectivity profile of short-pass filter

A second diagram shows the reflectivity as a function of wavelength and angle of incidence:

reflectivity of optical filter vs. wavelength and angle

As we are using a custom form, both the form and the underlying calculations can be modified by the user according to specific requirements.

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