A Fabry-Perot like two-photon interferometer for high-dimensional   time-bin entanglement
  We generate high-dimensional time-bin entanglement using a mode-locked laser and analyze it with a 2-photon Fabry-Perot interferometer. The dimension of the entangled state is limited only by the phase coherence between subsequent pulses and is practically infinite. In our experiment a pico-second mode-locked laser at 532 nm pumps a non-linear potassium niobate crystal to produce photon pairs by spontaneous parametric down-conversion at 810 and 1550 nm. 
Damien Stucki, Hugo Zbinden and Nicolas Gisin