I guess it could be anything, but the marking is ILD855. What I do know is that the "D" in ILD usually means a dual whatever it is - two opto functions, usually the same kind. It's not a big deal. I have lots of optos of various sorts, but I especially like to find specs for the ones that I have a fair number of, for possible later use. It's really weird that this one fairly modern part is so obscure. I've found data on almost every other part I've looked at recently, even going back to ones from the 1970s. I even just tried 1 (one rather than letter "I") LD855 - no good. It's not all that complicated, so I can figure out the function with some simple experiments, but it's way nicer to just have the datasheet.
Ed
