Fig. 4From: Autocompensating measurement-device-independent quantum cryptography in space division multiplexing optical fibersA-MDI-QKD system for polarization encoding. Charlies generates suitable polarization states and launches them towards Alice and Bob. They autocompensate and modulate the relative phase between the horizontal and vertical components so as to encode their information. Light comes back to Charlie. Circulators redirect it to a polarization Bell-state analyser (Innsbruck scheme)Back to article page