As it is the middle of the night, I'm enjoying a cup or two of Tennessee's finest, and not above boosting my post count by one although the question has been answered...
Yes, a photo interrupter - an IR LED and photo-transistor pair. in printers used from everything to detect the presence of paper in the tray, to registration (where to begin printing the image on the paper leading edge)
They work splendidly on machines feeding under ~35-45 pages per minute, but above that can be a nightmare. Not the actual electronics that work into (at least) the tens of MHz, but the "arm" - called a flag.
They physically wear - either flattening the contact surface, or the paper actually smashing a groove into them. respectively either throwing off the printer timing which will declare a misfeed, or rolling up the leading edge of the paper and causing a jam.
Due to (IMO) skulduggery - they range in manufacture part number price from a buck fifty to over $300! Because they can. Electronically, pretty much identical - but there are 3 wires that can be in one of three positions each for any given outline and modern techs are trained to replace parts by number, not work out solutions that require a meter, soldering iron, and a bit of heat shrink to make replacements as needed.
Yes, I spent over 20 years in that industry and watched it go from skilled labour to screwdriver (read the flow chart) jockey.
I once designed a circuit for my techs. 6 rectifiers in 3P configuration powering a 555, 3 bi-coloured LEDs, and a handful of passives. You'd plug the thing into the sensor harness and it would identify the Vcc, GND, and signal pin positions indicating red, green, and yellowish respectively.