More than just a few colours

Hyperspectral imaging (HSI) has been used for a couple of decades in applications such as satellite imaging, air reconnaissance and other markets that are not overly price sensitive. Classical hyperspectral-imaging cameras use prisms or gratings as dispersive elements. These cameras are bulky, sensitive to misalignment and very expensive. The advent of alternative approaches makes HSI attractive for volume markets or even consumer products and applications–for example, cancer detection, precision farming, food testing in supermarkets and many more.

Delta Optical Thin Film A/S develops and manufactures custom Bifrost Continuously Variable Bandpass Filters (CVBPF) for mid-size and full-frame CCD/CMOS sensors (e.g., 30 mm x 25 mm or 24 mm x 36 mm). These filters offer very high transmission and are fully blocked in the light-sensitive wavelength range of silicon-based detectors (200 nm to 1150 nm). The combination of CVBPFs with silicon detectors allows the design of very compact, robust and affordable HSI detectors that offer several advantages and benefits over conventional approaches:

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

Ask us for your custom designed Bifrost Continuously Variable Bandpass Filter! Available for immediate testing are filters with the following specifications:

• Centre wavelength range 450 nm to 950 nm, bandwidth approximately 2% of centre wavelength, exponential dispersion, transmission 60% to 90%, blocking range 200 nm to 1200 nm, blocking level OD4, for sensor size 30 mm x 36 mm

  

• Centre wavelength range 450 nm to 850 nm, bandwidth approximately 4% of centre wavelength, transmission 70% to 90%, blocking range 200 nm to 1100 nm, blocking level OD4, for sensor size 30 mm x 25 mm

  

• Centre wavelength range 796 nm to 1084 nm, bandwidth approximately 1% of centre wavelength, transmission >85%, blocking range 200 nm to 1150 nm, blocking level OD4, for sensor size 23 mm x 18 mm

  

The sizes are given as height x length, where height is perpendicular to the wavelength gradient and length is along the wavelength gradient. The filters can be diced to smaller sizes.

Learn more about these filters by downloading our presentation, or watch a recording of the presentation that was shown at Photonics West 2016. An article comparing our filter solution with classical Hyperspectral Imaging cameras and other new approaches is published in Optik & Photonik, DOI: 10.1002/opph.201600012.

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

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