Hyperspectral Imaging Choosing Bandpass Filters for Sensors

For the past 20 years, hyperspectral imaging (HSI) has been applied in air reconnaissance, satellite imaging, and other markets that are not overly price-sensitive. The conventional hyperspectral-imaging cameras employ gratings or prisms as dispersive elements. Other than being sensitive to misalignments and bulky, such cameras are also very expensive.

The introduction of alternative techniques has made HSI well-suited for volume markets or even consumer products and applications such as precision farming, cancer detection, food testing in supermarkets and others.

Bifrost CVBPFs

Custom-made Bifrost Continuously Variable Bandpass Filters (CVBPF) are developed and manufactured by Delta Optical Thin Film A/S for mid-size and full-frame CCD/CMOS sensors (e.g., 25 mm x 25 mm or 24 mm x 36 mm).

Such filters provide very high transmission, and are fully blocked in the light-sensitive wavelength range of silicon-based detectors (200 nm to 1150 nm). CVBPFs in combination with silicon detectors enable designing robust, compact, and affordable HSI detectors. These detectors offer the following benefits and advantages over traditional approaches:

  • Higher transmission than prism and grating
  • Large aperture as compared to prism and grating
  • High suppression of stray light
  • Short measurement time
  • Excellent signal-to-noise ratio

Delta Optical can be contacted for the supply of custom-designed Bifrost CVBPFs. The filters with the following specifications are available for immediate testing:

  • Center wavelength range 450 nm to 850 nm, bandwidth approximately 4% of center wavelength, transmission 70% to 90%, blocking range 200 nm to 1100 nm, blocking level OD4, for sensor size 25 mm x 25 mm
  • Center wavelength range 450 nm to 880 nm, bandwidth approximately 2% of center wavelength, transmission 60% to 90%, blocking range 200 nm to 1150 nm, blocking level OD4, for sensor size 24 mm x 36 mm
  • Center wavelength range 796 nm to 1084 nm, bandwidth approximately 1% of center wavelength, transmission >85%, blocking range 200 nm to 1150 nm, blocking level OD4, for sensor size 32 mm x 18 mm

The sizes are specified as height x length, where height is vertical to the wavelength gradient and length is parallel to the wavelength gradient. The filters can be cut up to smaller sizes.

Learn More

More information on these filters can be obtained by downloading Delta Optical’s presentation, or watching a recording of the presentation made at Photonics West 2016.

A comparison of the company’s filters with classical hyperspectral imaging cameras and other new techniques was published in Optik & Photonik, DOI: 10.1002/opph.201600012.

The article “High spatial resolution hyperspectral camera based on a linear variable filter” was published by Ingmar Renhorn and his collaborators in Optical Engineering. It can be openly accessed through http://opticalengineering.spiedigitallibrary.org/article.aspx?articleid=2587755.

Demo of Hyperspectral Imaging camera developed by LDP LLC. More application examples on YouTube.

This information has been sourced, reviewed and adapted from materials provided by DELTA Optical Thin Film.

For more information on this source, please visit DELTA Optical Thin Film.

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