Thin-film optical filters are created by placing alternating thin layers of materials which possess certain optical characteristics onto a substrate, like optical-grade glass.
As light travels through the optical filter, its course adjusts as it passes through each layer, which leads to internal interference. This is because of the contrast between the refractive indices of the materials found in the dielectric thin-film coating.
An optical filter which influences different wavelengths of light in different ways is created due to the way the layers are configured. Light can be transmitted through the filter, reflected off of it, or absorbed by it – depending on the type and wavelength of the optical filter.
Optical filters can be tailored to reflect, transmit, or block light at any wavelength from the UV to the IR range. Established by their spectral shape, they are typically categorized into five basic groups:
1. Bandpass filters transmit a range of wavelengths while blocking the adjacent light on either side.
2. Notch filters block a range of wavelengths while transmitting the light on either side.
3. Shortpass edge filters transmit shorter wavelengths while blocking longer ones.
4. Longpass edge filters block shorter wavelengths while transmitting longer ones.
5. Dichroic filters reflect specific wavelength ranges while transmitting others.
Typically, notch, bandpass, and edge filters are created to work at 0 ° or other small angles of incidence (AOI). In contrast, dichroic filters are intended for use at 45 ° or other large AOI and can be designed in notch, bandpass, or edge configurations.
It is also possible to design optical filters in multiband configurations. Multiband filters are bandpass filters with multiple regions of high transmission or passbands. Polychroic filters are dichroic filters which possess numerous bands or notches. Multi-notch filters possess multiple blocking regions and transmit all adjacent light.
Custom filters can be designed with any spectral shape imaginable, although the majority of optical filters fall into the categories above. For example, when transmitted through a custom filter which has been specifically designed, the light emitted from a xenon lamp can be altered to simulate the spectrum of the sun. Further custom filters are created to match arbitrary spectral shapes.
Due to their adaptability, optical filters are utilized in a number of applications. Remote sensing, solar imaging, Raman spectroscopy, astronomy, fluorescence microscopy, and telecommunications are just a few applications that depend on optical filters as one of the main aspects of their systems.
Alluxa’s team of experts have produced key innovations in the field of optical thin-films. Further to inventing a novel plasma deposition coating process that increases the performance of their optical filters and also decreases the time it takes to create them, they have also designed and manufactured all of their own custom optical thin-film coating equipment.
By integrating these innovations with proprietary control algorithms, state-of-the-art automation, and precision monitoring during the coating process, they can provide high-performance, low-cost, custom thin-film optical filters for any application.
This information has been sourced, reviewed and adapted from materials provided by Alluxa.
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