#technology #products

Crosstalk of the ULTRIS X20

ULTRIS X20 features a blocking capacity of OD4 for all wavelengths

What is the Crosstalk and Interchannel Straylight of the ULTRIS X20?

Crosstalk describes the contribution of light of one wavelength to light with a different wavelength being measured in a specific channel. For example, how much light of the wavelength 500 nm is measured in the channel at 700 nm? Typically, there are two possible ways crosstalk can occur:

Zwei Mitarbeiter von Cubert arbeiten mit einer Hyperspektralkamera.

A) Spectrally Dispersive Element Quality

Spectrally dispersive elements, like prisms, gratings, and filters, have different separation qualities based on their physical properties. For spectral thin-film filters, these qualities can simply be graded by the range of their optical densities (OD). A good filter in an imaging spectrometer will have a quality of OD2, thus blocking 1/100 of light with an unwanted wavelength.
The ULTRIS X20 features a blocking capacity of OD4 for all wavelengths over the complete range of the camera. This leads to an unprecedentedly low crosstalk of 1/10000, or less than 0.01% of unwanted light interfering with spectrum measurements.

Abb. 1: Filterpositionen der ULTRIS X20. Die Filter sind linear von 350 – 1000 nm mit einer Schrittweite von 10 nm und einer FWHM von 10 nm angeordnet.
Fig 1: Filter positions of the ULTRIS X20. The filters are positioned linearly from 350 – 1000 nm with a step width of 10 nm and a FWHM of 10 nm.

B) Interchannel Straylight or Scattering between Channels

All cameras generate some sort of straylight in the optical system. This straylight is generated due to dust, optical defects, reflections on optical surfaces, or suboptimal coatings. Furthermore, the sensor itself scatters parts of the light back, and this light can be reflected from mechanical parts and optical elements back onto the sensor itself.

Some spectrometer designs are more prone to interchannel straylight, where light from one channel is scattered to neighboring channels, than others. This problem is especially typical of filter-on-chip setups since the filters have no physical boundaries between each other.
To reduce this issue, the ULTRIS X20 is equipped not only with sufficient antireflection coatings but also a mechanical surface coating, which offers very high straylight reduction from the visible to the near-infrared. Furthermore, each channel is mechanically and optically sealed against its neighboring channels. The camera features a very low interchannel straylight on a 50% white target of below 1%.

Abb. 2: Messung des interkanalen Streulichts mit einem 50% weißen Ziel. Die Reflexion zeigt eine 100%ige Reflexion auf dem weißen Ziel und eine unter 1% Reflexion auf dem dunklen Ziel. Die Beleuchtung erfolgte durch eine Halogenlichtquelle; daher erreichte nur eine geringe Menge Licht den Sensor in den UV-Wellenlängen (<400 nm), was zu höheren Fehlern durch Rauscheffekte führte.
Fig 2: Measurement of interchannel straylight with a 50% white target. The reflectance shows a 100% reflection on the white target and a sub-1% reflection on the dark target. Illumination was provided by a halogen light source; therefore, only a small amount of light reached the sensor in the UV wavelengths (<400 nm), leading to higher errors due to noise effects.

Conclusion

In conclusion, the ULTRIS X20 offers unprecedentedly low crosstalk, especially when compared to other video spectroscopy setups, like filter-on-chip designs. The amount of unwanted light in neighboring channels is two orders of magnitude lower than what is typically found in hyperspectral cameras, which results in magnificent spectral quality with an unprecedentedly small amount of interchannel straylight and crosstalk.

René Heine, CEO von Cubert, dem Hersteller von Hyperspektralkameras

About the Author

Dr. René Heine is the Co-Founder and CEO of Cubert GmbH, a leader in real-time spectral imaging. Since founding the company in 2012, René has been instrumental in shaping Cubert’s technological direction and growth. He holds a Doctor of Physics degree from the University of Ulm, where he graduated magna cum laude, and completed his diploma thesis at Harvard Medical School. René’s deep expertise in physics and his vision for cutting-edge imaging technologies drive Cubert’s innovations and advancements in hyperspectral solutions.