All You Need to Know About Thin Film Optical Filters

Thin-film optical filters are made by layering thin layers of material with specific optical properties on a surface, similar to optical-grade glass.When light passes across the filter, the course of light changes during every layer, leading to internal interference. This is due to the sharp contrast between the different components’ refractive indexes within the dielectric’s thin-film coating.

An optical filter that influences the different light wavelengths is created by how the layers are set up. Light can pass by the filter, bounce off it, or be absorbed into it, based on the kind and wavelength the filter is made of.

Optical filters can be customized to transmit, reflect and block light in any wavelength from UV up to IR range. Based on their spectral shape and shape, they are usually classified into five categories:

• Bandpass filters. These optical filters from Flourescence filter sets emit different wavelengths and block out nearby light.
• Notch filters. These optical filters block the spectrum of wavelengths while transmitting light on both sides.
• Shortpass edge filters. The optical filters that fall under this category emit short wavelengths of light while blocking out longer wavelengths.
• Longpass edge filters. The shorter wavelengths of light can be blocked through longpass edge filters while longer wavelengths are reflected.
• Dichroic filters. Certain wavelengths reflect off dichroic filters. They reflect other wavelengths.

Custom filters can be created using any shape of spectral imaginable, but most optical filters fit within the categories listed above. For instance, if they’re you transmit a custom filter that has been specially developed, the light emission from a xenon bulb can be modified to mimic the spectrum of sunlight. Custom filters can also be created to conform to arbitrary spectral patterns.

Because of their flexibility, optical filters are used in many different applications. Remote sensors, solar imaging, astronomy fluorescence microscopy, Raman spectroscopy, and telecoms are just some of the applications that rely on optical filters for the primary components of their equipment.

Different Types of Optical Filters

There are a variety of thin optical films, and each kind of film has specific purposes

Anti-Reflection

Anti-reflection films help improve transmittance, enhance contrast, and remove ghost images. Because these films are extremely robust, almost all transmissive optics come with some form of anti-reflection film.

High-Reflective

High-reflective films are mirrors that have been calibrated to maximize reflectance either in single wavelengths or over the entire spectrum.

Beamsplitter

Beamsplitter films split light into multiple output beams. They can be found in projectors, cameras and lasers.

Filter

Filter films can block light at certain wavelengths. The thin films reflect light and absorb or transmit it.

Optic thin films are produced for specific incident angles and a certain polarization light, such as P-polarization, or S-polarization. If the angle of the incident is changed in an optical system, the internal angles and optical path lengths will also be altered, affecting the change in phase of the light beams that result through the films. If a non-normal incidence is used, S-polarized and P-polarized light behave differently at the respective interfaces and result in different optical effects for both Polarizations. This phenomenon is utilized to design beamsplitter films.