The Omron E3C-LDA6 is a separate digital amplifier meant to work with compatible photoelectric sensor heads — the type you'd find in discrete-parts detection on conveyor lines or in packaging machinery. It takes the signal from the remote sensor head, conditions it, and gives you a switched output. Out here in the grease, having the amplifier away from the sensing point means you can fit a smaller head in tight spots and keep the electronics somewhere cleaner and cooler.
This part is listed at a mature lifecycle stage — meaning it's been around long enough that production should be steady, and the supply chain knows it.