Case Study: 4900 - 5750 nm Wide Band Pass Filter

Case Study: Reducing Coating Duration with Careful Substrate Selection

Customer Challenge: Vortex undertook a project to develop a wide bandpass filter that transmits light in the 4900-5750 nm range with out of band blocking from the UV to 4700 nm and 7000 nm to 20000 nm. The challenge was to achieve this broad blocking range while maintaining cost efficiency. In optical filter manufacturing, the substrate often represents a smaller portion of the cost, and the coating process is typically more expensive, emphasising the importance of careful substrate choice to minimise coating time and cost.

Vortex’s Solution: For this project, we used the properties of 0.5mm Sapphire to enhance the blocking performance of the wide bandpass filter, the absorption off the sapphire acts as the short pass edge of the filter and blocks all the way to 20000nm and beyond. This dramatically reduces the cost of the filter, as all of the blocking in the far infrared is taken care of by the sapphire substrate. This means that only a long pass coating is required to block the near and mid infrared. A general rule for the length of a coating is the further out into the infrared it is, the longer the coating takes. However, this isn’t always possible as the material starts to drop off in performance long before 7000 nm and this then acts as a barrier to high peak transmission, however for this application transmission only had to be above 60%.

The Result: A cost effective, robust filter was designed and manufactured for this application for a long-standing customer. The development samples were turned around in quick time, helped due to the fact that we hold a wide range of substrates in stock ready for immediate coating such as sapphire wafers in this instance. We also have a network of trusted optics suppliers for more bespoke optics allowing us to provide a one stop shop for your optical components needs.