SWIR Cameras And Their Applications

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High-speed turbulence imaging of a point source at 1.5 µm using a high-speed SWIR camera and telescope. Acquisition made at 10 kHz with an exposure time of 85 µs and 14-bit pixel depth. In this example, the turbulence consists of induced scintillation with a heat source that changes the refraction index of air. Our high-speed SWIR InGaAs camera solutions are the ideal solution for use in fast adaptive optics and other setups used in FSO (Free-Space Optics) telecommunications. 

Video made with: C-RED 3 High-Speed Uncooled InGaAs Camera

What is SWIR or Shortwave Infrared?

SWIR is the acronym for shortwave infrared and refers to non-visible light falling roughly between 1400 and 3000 nanometers (nm) in wavelength. The visible spectrum ranges from 400nm to 700nm, therefore SWIR light is invisible to the human eye. In order to detect SWIR wavelengths, we need dedicated sensors made of In GaAs (Indium Gallium Arsenide) or MCT (mercury cadmium Telluride) as silicon detectors are no longer sensitive to wavelengths larger than 1100 nm. In GaAs sensors are the primary sensors used in typical SWIR range. MCT is also an option and can extend the SWIR range, but these sensors are usually more costly and application dependent.

SWIR light interacts with objects similarly to visible light as it is reflective, consequently it exhibits shadows and contrasts in its imagery. Images from a SWIR camera are comparable to visible images in terms of resolution and detail.

Objects that are almost the same color while imaging in visible region can be easily differentiated using SWIR light, making objects easily recognizable. This is one tactical advantage of imaging in SWIR compared to visible region. Some of the natural emitters of SWIR are ambient star light and background radiance, therefore SWIR is an excellent application for outdoor imaging. Conventional quartz/halogen bulbs also act as a SWIR light source. Depending on the application, some sensors in SWIR cameras can be adjusted to have linear or logarithmic response to avoid saturation.

There are many advantages of using SWIR over a conventional visible sensor. Some applications that are not possible to image in visible range can be imaged using SWIR range. One example, is silicon wafer inspection, which is only possible due to silicon being transparent in the SWIR range. Other examples of materials that are transparent in SWIR region are; Sodium Chloride (NaCl) and Quartz (SiO2). Water vapor is also transparent in SWIR, making SWIR cameras more desirable when imaging through haze or fog. Applications where using SWIR is crucial are detailed in the following section.

Rich results on Google's SERP when searching for 'SWIR spectrum definition'

SWIR vs eSWIR vs vSWIR

Because standard silicon-based sensors are typically sensitive up to 1000 nm only, SWIR cameras require sensors capable of imaging beyond the upper limit of silicon. InGaAs (indium gallium arsenide) sensors are conventionally used for SWIR imaging and cover the 900 nm to 1700 nm spectral range with high quantum efficiency (typically > 70%). Recent improvements to InGaAs sensors enable imaging both visible and SWIR (400 nm to 1700 nm using SenSWIR™ technology from Sony©, for example) or beyond the standard 1.7 µm cut-off with extended range solutions up to 2.2 µm. 

To summarize, when it comes to short-wave infrared cameras: 

– SWIR typically corresponds to the 900 – 1700 nm spectral range

-vSWIR or VIS-SWIR refers to the 400 – 1700 nm spectral range

– eSWIR or XSWIR or extended range InGaAs refers to cameras with a cut-off beyond 1.7µm; typically 1.9 or 2.2 µm. 

Resolution and pixel pitch

InGaAs cameras bridge t