|Precisely filters specific wavelengths.||High cost.|
|Can be designed to work at any of a wide range of specific wavelengths, can be used to significantly narrow a specific wavelength band.||Angle dependent.|
|Suitable for high power applications.||Less durable than absorptive filters. Care must be taken when cleaning.|
|Hard coatings provide a longer life time than conventional colored glass filters as the color cannot be bleached out over time.||Coatings tend to separate from the glass surface over time when subjected to thermal cycling and humidity.|
|As light is reflected and not absorbed, they are not as heat sensitive as absorptive filters and can be used with higher intensity light sources.|
Dichroic filters can be manufactured from several materials including BOROFLOAT®33, N-BK7®, B270® and fused silica. Substrate selection is based on how well a specific material transmits light in a specific wavelength region. Advanced Optics can precision polish all of these substrates in almost any configuration and provide custom coatings to meet your requirements.
For further technical information and tutorials on dichroic filters please visit: Florida State Research Foundation
Specifying the Correct Optical Filter
Optical filters are classified by their construction, which determines the way they filter light. There are many types of absorptive and reflective filters and careful selection should be based on the specific application in which they will be used. One should consider the following when selecting an optical filter for a specific application: wavelength range of interest as well as cut-on and cut-off properties, AOI of incoming light, energy of incoming light and operating environment.
Whether your application requires an absorptive filter, dichroic filter or neutral density filter, carefully considering your requirements is critical. Specific consideration should be given to the physical size, shape and tolerances of the substrate as tighter tolerances may require additional manufacturing which can add cost. The same applies to the surface quality of the filter which is expressed by a scratch and dig number. The lower the scratch and dig number, the more potential there is for a reduction in yield which drives up the cost of the filter.
Selecting the proper optical filter for your application is essential to saving manufacturing time, which translates to reduced costs. Advanced Optics can help you define your requirements.