Time-bin encoding is a technique used in Quantum information science to encode a qubit of information on a photon. Wikipedia
Is there a generalization for $n$-th level qudits?
Yes! The first application of time bin photonic qudits that comes to mind is for quantum key distribution. Here's an example: https://arxiv.org/abs/1611.01139. I am sure there are more references out there though!
There is a number of groups using time-bin encoding to realise computation/communication protocols.
One example is Furusawa's group in Japan, which among other things works on measurement-based QC with time-bin encoding (e.g. 1706.06312). Another example that comes to mind is Silberhorn's group in Paderborn. They use time-bin encoding for various things, a random example of which is 1710.06103.