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September, 2021


Using NIR and SWIR Light in Machine Vision Applications


By Darren Bessette, Category Manager — Devices, FRAMOS Technologies, Inc.


of near and short wavelength infrared (NIR and SWIR) light to gather information that is not visible to the human eye. Many times, the information


O


gathered in these wavelengths augment the data seen in the visi- ble, 350 to 750 nm, spectrum. NIR wavelengths are in the range of 780 to 1400 nm, while SWIR is in the range of 900 to 2,500 nm. Though NIR light has been


used extensively in many machine vision applications, many of the sensors that are deployed do not have a very high quantum efficiency in this range and are more often a byproduct of standard vision sensors and cameras. CMOS based sensors are


sensitive to these wavelengths but can only see 10 to 30 percent of this and have a spectrum range limited to between 400 and 1,000 nm, typically. To see deeper into the NIR


and SWIR wavelengths, an InGaAs sensor, made of an alloy of indium arsenide (InAs) and gallium arsenide (GaAs), is used.


Wavelength spectrum bands from UV to IR.


devices more challenging with the final solution being more expen- sive. On top of this, the pixel sizes for a CMOS based camera are smaller (typically 1-5µ) than cam- eras using InGaAs sensors (typi- cally 10-20µ) which further com- plicates the data merging between


calibrated and aligned with each other before data analysis can really start. A drawback to these systems is that they are highly susceptible to vibration and mis- alignment. To maintain factory calibra- tions, camera mounting systems


ne exciting area showing a lot of promise for industri- al applications is the use


This sensor has spectral re - sponse ranges that can vary between 900 and 1,700 nm to 1,100 and 2,600 nm. The desired wavelength response for these sensors is defined during manu- facturing process by adjusting the ratio of InAs and GaAs ele- ments in the sensor. For applications requiring


data in the visible, NIR and SWIR ranges, multiple cameras need to be deployed with different optical paths and optics. This makes overlapping the data from both


the two captured images, at the pixel level.


Multi-Spectral Systems Applications targeting a


broader wavelength spectrum often require multiple cameras to capture all the image data across the targeted range. Each spectrum band utilizes, in many cases, specialized cameras with different fields of view, optics, and pixel sizes. The snapshots produced by these cameras then need to be


must be very robust to withstand stress during shipping, installa- tion, and use that might put them out of alignment and require additional calibration. When a recalibration is need-


ed, the vision system is taken offline to perform the task while the inspection station is out of service, reducing the efficiency and output of the factory or pro- cessing plant. Camera manufac- turers integrating SWIR sensors also need to deal with their imple- mentation challenges such as assessing dark current levels, heavy shading, fixed pattern noise, and large defective pixels. All these items reduce the


signal quality put out by the camera and need to be addressed within the camera’s hardware and software. To add to this, many of these cameras require analog based sensors which, on their own, are expensive and require additional hardware components to control and read out the data.


Enter Sony Sony is a relatively new play-


er to the industrial SWIR sensor Continued on next page


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