Usually attached to a substrate like glass, thin-film optical filters are layers of materials with optical properties. These filters change the direction of light as it passes through them, creating internal interferences. Filters can be specially designed to transmit, reflect, or block light in any wavelength between ultraviolet (UV) and infrared (IR).

Thin-film optical filters can be used for many optical applications, including astronomy, solar imaging, fluorescence microscopy, telecommunications, and remote sensing. This blog will discuss the mechanics of thin-film optical filters and their five main types.

How Thin-Film Optical Filters Work

To create a thin-film optical filter, we deposit the necessary coating onto the optical glass with extreme precision. One deposition method is ion-assisted e-beam evaporation. During this process, a beam of ions is directed at the substrate at the same time that the evaporated materials are being deposited onto the substrate. The ions contain energy that is released into the evaporative atoms of the materials, creating a thin film.

Physical vapor deposition creates thin films by vaporizing solid material inside a vacuum and then depositing it onto the substrate. This type of deposition results in durable, scratch-resistant coatings. They can also withstand high temperatures.

The specific thickness and number of coatings will affect the wavelength of light that passes through the filter. These methods, along with others, create durable coatings to achieve the intended optical effects. 

Types of Thin-Film Optical Filters

There are five main types of optical filters.

  1. Bandpass Filters. These filters transmit certain wavelengths and block out the surrounding light.
  2. Notch Filters. This type of filter blocks out a variety of wavelengths and transmits light on either side.
  3. Shortpass Edge Filters. Short wavelengths are transmitted through this filter, and longer wavelengths are blocked.
  4. Longpass Edge Filters. Long wavelengths are transmitted through this filter, while short wavelengths are blocked.
  5. Dichroic Filters. A dichroic filter reflects certain wavelengths while others pass through it.

The first four filters are intended for use at 0° or other small angles of incidence. Dichroic filters are best used at 45° or less.

Some of these types can be combined to create multiband filters. We can also create custom filters that have a different spectral shape than those listed above.

Evaporated Coatings Inc.’s Thin-Film Optical Filters

Evaporated Coatings Inc. has over 60 years of experience producing high-precision optical coatings. We have the expertise necessary to design and create thin-film optical filters that will solve your industry-specific problems. We are dedicated to staying up-to-date in the optical filter industry, as we develop our own thin-film designs and processes using advanced deposition methods.

Our experienced engineering staff handles the entire process: design, preparation, and coating. We deliver personalized service to customers in the United States and around the world. Contact us to find out how we can meet your specific thin-film optical filter requirements.