Filter Specs vs Functional Specs – The Pitfall of Double Margining
In designing a filter solution, the filter manufacturer takes the values requested by the user and adds additional design margin to account for both functional effects (such as wavelength shift due to angle variation, thermal induced wavelength shift, etc.) and filter manufacturing effects (such as edge steepness, non-uniformity, wavelength targeting – see Iridian’s technical note “Wavelength budgeting for optical filters”).
Often customers translate the actual functional requirements of their system (such as pass light source wavelength and block light source wavelength) and then add wavelength “padding” (such as CWL, FWHM, etc.) to these values. Typically the filter manufacturer will pad the customer’s spec to ensure meeting the design requirements. However, if the customer has already added “padding,” the result is a more costly solution with compromised performance.
By providing the true requirements of your system, Iridian’s expert designers can produce a filter that will meet expectations for your application and budget.
Do’s and Don’t’s When Specifying Filters
- Provide the spectral bands of your application (including all uncertainties).
- Provide the AOI range and cone angle of your beam.
- Provide the functional requirement for spectral width and depth of blocking bands.
- Do not make assumptions about manufacturing margin, when specifiying a CWL, FWHM, etc.
- Do not assume AOI shifts when specifying spectral widths.
- Do not add margin to spectral width or depth (which adds unnecessary cost and can degrade overall performance).
Iridian Spectral Technologies
Iridian Spectral Technologies is a diversified optical filter manufacturer that is an international leader in filter design and manufacture, especially for application in the fields of fiber optic communications, biomedical optical spectroscopy, 3D entertainment, and aerospace. Iridian is a global supplier with distributors in many countries.
To request more information or a quotation for Iridian products, contact IL Photonics.