Electronic Military & Defense magazine was developed for engineers, program managers, project managers, and those involved in the design and development of electronic and electro-optic systems for military, defense, and aerospace applications.
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Techniques Electronic Military & Defense Annual Resource, 4th Edition 43 Notice how close all three cameras are, despite the fact that the 640 Vis-SWIR has four times smaller pixels thanks to a lower readout noise and dark current. General Comparison We can also compare cameras equipped with silicon and InGaAs FPA detectors using wavelengths where both technologies are sensitive. Figure 3 represents the NEI vs. exposure time at 950 nm. Of course, this wavelength puts the silicon cameras at a disadvantage, as they have a much reduced quantum efficiency compared to InGaAs cameras, as you can see in Table 4. As shown in Figure 3, in the NIR range with up to 1 sec- ond exposure time, EMCCD is the most sensitive technol- ogy. It is followed by Vis-SWIR and SWIR cameras. Finally, CMOS and CCD differentiate mostly in QE. Otherwise, they have very similar specifications. Conclusion Noise equivalent irradiance allows you to precisely evaluate the sensitivity of wildly differing cameras and to rank them for a given exposure time and wavelength. In the visible wavelength with short exposure times, EMCCD is the most sensitive technology, followed by CCD and CMOS. In the NIR range, InGaAs cameras have the edge over CMOS and CCD. Finally, in the SWIR spec- trum, InGaAs is still the only possibility. While evaluating the various sensors using NEI can be a tremendously helpful tool for determining the ideal sensor for your application, it is only the first step in the engineering process. Defining camera performance and functionality and building it to meet SWaP requirements then leads to designing a camera that drives the best performance from the sensor. References (Endnotes) [1] P.L. Richards, "Bolometers for infrared and millimeter waves," Journal of Applied Physics 76, 1 (1994), doi:10.1063/1.357128. [2] R. C. Jones, "Quantum efficiency of photoconductors," Proc. IRIS 2, 9 (1957). [3] R. C. Jones, "Proposal of the detectivity D** for detectors limited by radiation noise," J. Opt. Soc. Am. 50, 1058 (1960), doi:10.1364/JOSA.50.001058. [4] Malacara, Daniel (1988). Physical Optics and Light Measurements. Academic Press. p. 247. ISBN 9780124759718. Dr. Jean-Edouard Communal is sales manager at Raptor Photonics Ltd. with over 10 years' experience in the photonics industry encompassing high-end imaging, spectros- copy, and laser processing, which combined with his academic background gives him a unique transversal vision of photonics systems. QE Pixel size (µm) Readout noise (e-) Dark current (e-/pixel/ sec) EMCCD 5.2% 8 <1 1 CMOS 8.9% 5.5 7 9 CCD 6.0% 4.54 7 0.08 320 SWIR 18.5% 30 150 190,000 320 Vis- SWIR 83.8% 30 150 190,000 640 Vis- SWIR 72.0% 15 150 15,000 Table 4: Sensor specification at 950 nm. F igure 3: NEI of silicon and InGaAs cameras at 950 nm Figure 2: NEI of InGaAs cameras at 1550 nm