In the Spotlight: Interference Bandpass Filters

11th May 2021

Here, Knight Optical – the leading supplier of custom-made and stock premium-quality optical components – uncovers all you need to know about Interference Bandpass Filters.

How do Interference Bandpass Filters Work?

Used for a wide range of uses and across a broad spectrum of industries, Interference Bandpass Filters are extremely useful for applications that require selective transmission of specific wavelengths whilst blocking undesired bands. In other words, these filters are designed to pass desired frequencies and reject wavelengths outside that particular range. For example, if you’re after an optical component that transmits a portion of the infrared (IR) wavelength and blocks an amount of the ultraviolet (UV) waveband, Interference Bandpass Filters are the optics that you’re looking for.

There are two key points to examine when considering Interference Bandpass Filters for your application. Firstly, as we’ve discussed, desired wavelengths are rejected by these Filters, meaning this frequency is reflected. It is, therefore, essential to think about the location that these reflected wavelengths will end up in. The second element centres around the performance of Interference Bandpass Filters. These Filters are sensitive to incidence angles, which move to shorter wavelengths as the incidence angle is increased.

What Are Interference Bandpass Filters Used For?

Due to their selective benefits, Interference Bandpass Filters are used for a variety of applications. What’s more, here at Knight Optical, we offer Customisable Interference Bandpass Filters, meaning these helpful optical components can be custom-manufactured for seamless integration with your end application. Popular within imaging applications, you can find Interference Bandpass Filters in all corners of the world.

Here are a couple of examples:

The Food Sector

Interference Bandpass Filters are commonly found within the food industry – particularly near-infrared (NIR) Interference Bandpass Filters for food spectroscopy. For example, the research paper ‘Simulation of NIR Interference Bandpass Filters for Spectroscopic Applications’ explores how these optical components can be used to “detect the quality and differentiate between meat samples¹”. In this project, “three bandpass filters were designed and optimised…for three different wavelength ranges using the needle synthesis method¹”.

Extragalactic Astronomy

On the ground, Interference Bandpass Filters are also being used for imaging-based applications for extragalactic astronomy. One particular project that explores the use of these filters for such purposes is described in the 2020 paper, ‘Wide-field ultra-narrow-bandpass imaging with the Dragonfly Telephoto Array’. The paper looks at adding a “wide-field narrow-band imaging capability to the Dragon y Telephoto Array²” – a ground-based optical telescope array developed at the Dunlap Institute for Astronomy & Astrophysics of the University of Toronto³. It also focuses on the “development of a ‘Dragon y Filter-Tilter’ – a device that places ultra-narrow bandpass interference filters (Δλ ≈1 nm) in front of each of the lenses that make up the array².”

These are just a couple of diverse examples of applications that make use of the benefits offered by Interference Bandpass Filters, and new innovations are popping up continuously. In a more recent paper, the next generation of Interference Bandpass Filters is explored. It’s what’s described as: “A new class of miniaturised signal-interference bandpass filters (BPFs) using resonant signal-interference (RSI) stages⁴“.

Knight Optical’s High-Quality, Metrology-Tested Interference Bandpass Filters

Here at Knight Optical, our extensive range of Interference Bandpass Filters are widely recognised for their premium quality. Many Interference Bandpass Filters are simply sealed into a metal housing with resin. This makes them susceptible to leakage and vulnerable to moisture damage. Our Filters are individually CNC scribed and hermetically sealed. This forms a secure stack in the filters’ rings to ensure maximum long-term stability.

Our stock range of Interference Bandpass Filters is available from 214nm to 2000nm in various bandwidths from narrow 3nm FIN type up to 65 to 100nm FIW types.

They are also available in a range of types, including:

What’s more, as well as a comprehensive stock portfolio, we also offer Interference Bandpass Filters as custom-made optics.

Click here to enquire about customised Interference Bandpass Filters.

Why Choose Knight Optical for your Application?

Here at Knight Optical, we supply a range of both Interference Bandpass Filters. Discerning customers rely Knight Optical not only for the premium quality of our output and in-house state-of-the-art Metrology Laboratory and QA Department‘s capabilities but because – as well as a range of Stock Optics (available for next-day dispatch) – we also offer a range of sought-after Custom-Made Optical Components.

This year, we’re celebrating 30 years in business. With three decades’ experience under our belt and a whole host of long-standing world-renowned customers on our books, we are proud to have worked on some of the most ground-breaking innovations.

If you are looking for premium-quality, bespoke optical components, please do not hesitate to get in touch with a member of the Technical Sales Team today.

FOOTNOTES:

¹https://www.researchgate.net/publication/303072763_Simulation_of_Near_Infrared_Interference_Bandpass_Filters_for_Spectroscopic_Applications

²https://www.spiedigitallibrary.org/conference-proceedings-of-spie/11445/1144527/Wide-field-ultra-narrow-bandpass-imaging-with-the-Dragonfly-Telephoto/10.1117/12.2561162.short?SSO=1

³https://en.wikipedia.org/wiki/Dragonfly_Telephoto_Array

⁴https://ieeexplore.ieee.org/abstract/document/9338040