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Optical Filter Coatings: Comparison of Traditional and Hard-Sputtered

Confused about the differences between traditional-coated and hard-coated optical filters? Join Monica Rainey, Optical Engineer, as she reviews fabrication techniques and benefits of these two filter coating types. To learn more about optical filter coatings and other optical coatings, read our An Introduction to Optical Coatings application note.

Hi, I am Monica, one of the Optical Engineers here at Edmund Optics. Today, I would like to go over the differences between hard- and traditional-coated filters. Some of our filters, such as bandpass filters, are offered with either coating option, while some components just have one coating type. First, let's talk about how these different filters are manufactured. Hard-coated filters are fabricated using our state-of-the-art advanced plasma reactive sputtering coating platform, which means they end up with hundreds of very accurate layers on a single substrate during a single coating run. Traditional filters are fabricated in three sections, each of which determines particular properties of the filter. One coating determines essential wavelength, bandwidth and shape of the curve, while the other two determine the range of blocked wavelengths. This coating is made by vacuum deposition of very thin layers of partially reflective compound onto a glass substrate. The differences in these coatings for bandpass filters are illustrated here. Beyond understanding how these filter coatings are made, it is important to note the benefits of using one type over another in your application. Hard-coated filters are typically better suited for high humidity environments and tend to have a longer shelf life. They provide deeper blocking, higher transmission and steeper sloped transmission curves, but also tend to be more expensive. Traditional-coated filters, in general, are able to block wavelengths from x-ray to far infrared, which is an extremely large wavelength range. Edmund Optics offers more size and wavelength options with traditional-coated filters. However, transmission in the pass band is lower and the coating is less durable with these filters. If your application is high precision, hard-coated might be your best option. But for standard R&D applications, traditional filters offer a more cost effective alternative. I hope this helps you understand the differences between some of our coating options. For more information on filters, please visit our Optical Filters application note on our website. While you are there, you can browse more of our technical application notes and videos to learn more key concepts and find answers to common questions.