How A Filter Is Specified

In order to achieved a desired optical functionality in an application, it is critical that key use parameters are communicated.  Understanding the filter function and use conditions allows the filter design team to create a filter specification that will ensure the functional requirements are met by a filter that is manufacturable under the commercial constraints (cost, lead-time, volume) of the customer (see our technical note “Filter vs Functional Specs”).

Spectral Bandshape:

 In general, the desired functional spectral performance over the full operational wavelength range must be defined for an optical filter.  The spectral information required varies for different types of filters including band pass filters (BPF), edge pass filters (long pass and short pass, LPF and SPF), notch filters, dichroic filters (long pass dichroic and short pass dichroic, DLP and DSP) and telecom filters including BPF, LPF, gain flattening filters (GFF), and solid or single cavity etalons (SEF or SCF).

The following spectral parameters must be specified in addition to the other parameters discussed in detail below such as AOI, CHA, substrate type, substrate thickness and tolerance, filter dimensions (un-mounted or mounted and mount size) and tolerance, polarization requirement, filter clear aperture, surface quality, surface figure, as well as the environmental operating conditions.