Optical thin film filters are devices that are used to selectively transmit, or reflect different parts of the electromagnetic spectrum, and they are used for a range of different applications. Standard optical filters include longwave and shortwave pass filters, bandpass filters, and dichroic and polarization beamsplitters.
What is an Optical Filter Coating?
Optical thin film coatings are one of the things used to enable optical filters to achieve these different application requirements. They are composed of a number of thin film layers, which create interference effects that will improve the reflection or transmission properties of the optical filter.
The number of layers in a coating and the thickness of individual layers directly affect the performance, and these coatings are often used in precision optics.
‘Soft coatings’ were the first type of optical filter coatings. These coatings are still available today at low prices, but they are susceptible to degradation as they are not dense and mechanically not very stable.
‘Hard coatings’ were the next evolution of optical filter coatings. One issue with these coatings was that the layers were not fully densified and they contain voids, where water vapor can be absorbed. This can have a negative effect on the refractive index of the coating and the filter can shift.
Ultra-Hard-Coated Optical Filters from Delta Optical Thin Film
In 2005 Delta Optical Thin Film started to successfully develop optical filters with Ultra-Hard-Coating (UHC) technology, which they continue to use for their optical filters today.
These coatings are produced with an advanced plasma process that deposits layers with a much higher packing density than hard coatings. Glue is not used for UHC optical filters, as the coating is deposited on one single substrate. This results in a coating with an exceptionally smooth surface, reducing stray light. Additionally, no filter performance is lost when it is exposed to intense humidity and light.
Compared to soft and hard coatings, UHC optical filters have many benefits. Due to the higher packing density, the water uptake in these coatings is minimal which reduces the risk of any unwanted effects in the optical system. This also results in an optical filter with an increased lifetime – reducing the overall costs for customers.
The deposition technique of these filters also provides the possibility of very thick layers being produced, which could have increased and complex functions, not achievable in other types of filters. Customers also have the option to dice the filters to smaller sizes, while still maintaining 100% clear aperture after coating.
UHC optical filters are a popular choice for many biomedical and analytical applications, these include hyperspectral imaging, flow cytometry, biomedical laser systems, color separation systems and many more.
If you have any questions about our range of UHC filters and how they can help your applications please contact us.