System sniffs out hardware trojans in electromagnetic emissions

If you send a beam of light into it from the side, the beam splitter will allow half that light to pass straight through it, while the other half is reflected from the angled mirror, causing it to bounce off at 90 degrees from the incoming beam. Now shine a second beam of light, perpendicular to the first, into this beam splitter so that it impinges on the other side of the angled mirror. The two output beams will combine with the two outputs from the first beam. Let's call these field intensities x and y. Shine those two beams into the beam splitter, which will combine these two beams. In addition to the beam splitter, this analog multiplier requires two simple electronic components-photodetectors-to measure the two output beams. Another promising scheme is based on something called a Mach-Zehnder interferometer, which combines two beam splitters and two fully reflecting mirrors. That's because these optical processors suffer from various sources of noise and because the digital-to-analog and analog-to-digital converters used to get the data in and out are of limited accuracy.