Fig. 8From: Autocompensating measurement-device-independent quantum cryptography in space division multiplexing optical fibersBell-state measurement device for codirectional modes. A four port optical integrated circuit serves as a Bell-state measurement device for codirectional modes. Photons coming from Charlie’s OC enter the device, where three DCs and two phase shifters implement the suitable operations. When light reaches the detectors the Bell states |Ψ−〉 and |Φ+〉 are unambiguously identified, as required by MDI-QKDBack to article page