Quantum cryptography transmission system and an optical circuit

Quantum cryptography transmission system of the present invention includes a transmission device (10A), and the receiver (20A), the transmission path for connecting between them and (30). Transmitting device has the light emitting unit for generating a photon serving as a qubit information carrier (11), a transmitting-side optical circuit (12A). Receiving device includes the light receiving unit for detecting a photon is information carrier qubits (21) and a receiving side optical circuit (22A). Transmitting-side optical circuit (12A) and the receiving-side optical circuit (22A) includes an optical delay circuit to one of the arms; asymmetric Mach-Zehnder interference system containing the (123-1 223-1); and (123 223), this asymmetry it is constituted optical circuit by; (227 127) Mach-Zehnder interference system (123; 223) of two transmission-side 3dB coupler which couples to each of the two arms (126 226) and.