Does an optical splitter exist with adjustable delay on one output?

[rfbrw]

IMO it sounds trivial until one considers how it could be actually implemented.

As it happens it is relatively trivial. I once worked for a manufacturer of digital video processing devices and delaying the embedded audio was an essential function. It certainly didn't require a DSP. There are times when just want a shovel and not a JCB backhoe loader with every attachment under the sun.