RU80637U1 - INTEGRAL OPTICAL SWITCH FOR PHASE CODING QUANTUM CRYPTOGRAPHY SYSTEMS - Google Patents

Abstract

The utility model relates to communication technology, namely to quantum cryptography devices. The purpose of the utility model is to build a quantum cryptographic network with several secret key receivers, and to transmit the key over public fiber optic networks. Integrated optical switch 8 × 8, containing 64 switches connected by directional couplers, characterized in that all the switches of the device are made on the same glass substrate using integrated optics technology. 1 ill.

Description

The proposed device relates to communication technology and can be used as an element in quantum cryptography systems with differential phase modulation of the optical signal.

Known integrated optical switch fiber communication systems based on the Mach-Zehnder interferometer and directional couplers, consisting of waveguide arms of the interferometer connected by optical splitters. To change the refractive index in one of the arms of the interferometer, a thermo-optical effect is used. Depending on the magnitude of the introduced phase shift, the optical radiation is directed to one of the two outputs of the directional coupler of the interferometer. (Espinola RL, Tsu M.-C., Yardley J.T. and Osgood RM "Fast and low-power thermooptic switch on thin silicon-on-insulator," J. IEEE Photon. Technol. Lett, 1999, V.15 , pp. 1366.).

The disadvantages of this device are: the inability to send a quantum cryptographic key to multiple recipients and the construction of an optical network. The integrated optical switch used in quantum cryptography allows transmitting the secret key to only two recipients. If it is necessary to transmit information to a large number of users, it becomes necessary to use a complex connection of several separate switches, which leads to loss of single-photon pulsed radiation and distortion of the transmitted secret key.

The purpose of the proposed device is to build a quantum cryptographic network with several receivers of a quantum key.

The goal is achieved by the fact that from the integrated optical switches based on the Mach-Zehnder interferometer, a switch matrix is formed, consisting of 64 switches connected

directional couplers. The integrated optical switch has 8 inputs and 8 outputs.

As a result of the mathematical analysis, the proposed device allows constructing a quantum cryptographic network for transmitting the key to several users and controlling the optical path with respect to weak signals on optical photons together with high-speed digital data streams using powerful light pulses. The 8 × 8 matrix switch can be used in fiber optic networks in which the optical path must be monitored without conversion to electrical signals.

Figure 1 shows the device of the integrated optical switch 8 × 8 for networks of quantum cryptography with phase coding. The device contains a glass substrate on which are located Mach-Zehnder microwave interferometers. The arms of the interferometers are connected by integrated optical couplers. At the shoulders of the interferometers, phase modulators based on the thermo-optical effect can be integrated.

The device operates as follows. Optical radiation from the laser is introduced at one of the inputs of the switch, using a splitter it is divided into two beams of the same intensity. At the output of the first interferometer, the rays passing through the second splitter form an interference pattern. If a phase modulator is built into the arm of the interferometer, then, depending on the phase shift introduced, the optical radiation leaves the first or second output of the splitter. The choice of phase shifts created in the arms of the interferometers allows directing optical radiation to various outputs of the switch. Each output of the switch can be connected by a fiber communication line to the recipient of a quantum cryptographic key. As is known from quantum optics, when single photons pass through two slits, the same interference pattern is obtained as with interference

light waves. Therefore, for single photons, the switch will work in the same way as for a light wave. When passing through the switching nodes, a single-photon optical signal should not be partially or completely transformed into an electrical signal, since in this case the quantum state of the photon will be destroyed during the passage of the switch. Therefore, the optical path in quantum cryptography systems should be monitored without conversion to electrical signals, which makes it possible to make an 8 × 8 integrated optical switch matrix. When combining weak signals with powerful information flows, they will intersect in the matrix of the switch. There is no need for time diversity of signals. They can be sent simultaneously and independently of each other, and the selection of the signal corresponding to the transmitted key can be done using an optical spectral filter in the reception ports of single pulses. The connection of a large number of switches on a single substrate makes it possible to avoid radiation power losses during the coupling of integrated optical elements, which significantly improves the transmission of weak single-photon pulses.

The use of the 8 × 8 switch in quantum cryptography systems, in comparison with the prototype, makes it possible to transmit the secret key to several recipients, build a quantum information transmission network, and transmit the secret key over public fiber optic networks.

Claims (1)

Integrated optical switch for phase-coding quantum cryptography systems based on Mach-Zehnder interferometers, containing 64 switches connected by directional couplers, characterized in that, in order to build a quantum cryptographic network with several secret key receivers, all device switches are made on one glass substrate using integrated optics technology, the device avoids loss of optical radiation at the junction of a large number of commutators tori in quantum cryptographic networks.