Optical phase modulation method and apparatus for quantum key distribution

• US 8,477,947 B2
• Filed: 10/06/2010
• Issued: 07/02/2013
• Est. Priority Date: 12/21/2009
• Status: Active Grant

• Current Assignee: Electronics and Telecommunications Research Institute
• Original Assignee: Electronics and Telecommunications Research Institute
• Inventors: Cho, Jeong-sik
• Primary Examiner(s): Arani, Taghi
• Assistant Examiner(s): VICTORIA, NARCISO F
• Application Number:
  US12/899,128
• Publication Number:
  US 20110150226A1
• Time in Patent Office: 1,000 Days
• Field of Search: 380/263, 380/278
• US Class Current: 380/278
• CPC Class Codes: H04B 10/70 Photonic quantum communication
• CPC Class Codes: H04L 9/0858 Details about key distillation or coding, e.g. reconciliation, error correction, privacy amplification, polarisation coding or phase coding

Abstract

Provided is an optical phase modulating method and apparatus for a quantum key distribution. When an optical phase modulator is arranged outside an optical interferometer, a configuration of the optical interferometer may be simplified, and an extension of an optical path caused by the optical phase modulator, instability and an insertion loss increased in the optical interferometer, and the like, may be overcome. An output feature may be improved by adjusting an applied voltage of the optical phase modulator arranged outside the optical interferometer.

Claims

1. A transmitting apparatus of a quantum key distribution system, the transmitting apparatus comprising:

an optical interferometer to receive a single photon inputted from a light source, and to divide a path into a plurality of paths to enable a probability of existence of the inputted single photon to be distributed in a plurality of coordinates in a time domain; and

an optical phase modulator being connected to an outside of the optical interferometer, and modulating a phase of a single photon corresponding to at least one path from among the plurality of paths,

wherein the optical phase modulator includes successively connected at least two optical phase modulators wherein one of the at least two optical phase modulators modulates the phase of the single photon based on bit information and the other one of the at least two optical phase modulators modulates the phase of the single photon based on basis information.

2. The transmitting apparatus of claim 1, wherein the optical interferometer includes one of an optical fiber-based Mach-Zehnder interferometer and an optical fiber-based Michelson interferometer.

3. The transmitting apparatus of claim 2, wherein the optical interferometer is the optical fiber-based Mach-Zehnder interferometer, and further includes a polarization controller.

4. The transmitting apparatus of claim 2, wherein the optical interferometer is the optical fiber-based Mach-Zehnder interferometer, and is constituted of polarization maintaining fibers.

5. The transmitting apparatus of claim 1, wherein the optical interferometer includes one of an optical system-based Mach-Zehnder interferometer and an optical system-based Michelson interferometer.

6. A receiving apparatus of a quantum key distribution system, the receiving apparatus comprising:

an optical phase modulator to receive a single photon from a transmitting apparatus of a quantum key distribution system, and to modulate a phase of a single photon that is not modulated from the received single photon; and

an optical interferometer to divide a path of the single photon received from the optical phase modulator to enable a probability of existence of the single photon received from the optical phase modulator to be distributed in a plurality of coordinates in a time domain,

wherein the optical phase modulator is connected to an outside of the optical interferometer,

wherein the optical phase modulator includes successively connected at least two optical phase modulators wherein one of the at least two optical phase modulators modulates the phase of the single photon based on bit information and the other one of the at least two optical phase modulators modulates the phase of the single photon based on basis information.

7. The receiving apparatus of claim 6, wherein the optical interferometer includes one of an optical fiber-based Mach-Zehnder interferometer and an optical fiber-based Michelson interferometer.

8. The receiving apparatus of claim 7, wherein the optical interferometer is the optical fiber-based Mach-Zehnder interferometer, and further includes a polarization controller.

9. The receiving apparatus of claim 6, wherein the optical interferometer is the optical fiber-based Mach-Zehnder interferometer, and is constituted of polarization maintaining fibers.

10. The receiving apparatus of claim 6, wherein the optical interferometer includes one of an optical system-based Mach-Zehnder interferometer and an optical system-based Michelson interferometer.

11. A quantum key distribution system, the system comprising:

a transmitting-end optical phase modulating unit including an optical phase modulator to input, with respect to a single photon, a modulation signal of which a time and a width is adjusted, a path of the single photon being divided into a plurality of paths to enable a probability of existence of the single photon to be distributed in a plurality of different coordinates, and to selectively modulate a phase of a single photon corresponding to at least one path from among the plurality of paths; and

a receiving-end optical phase modulating unit to selectively modulate a phase of a single photon that is not modulated by the transmitting-end optical phase modulating unit from the single photon received via the transmitting-end optical phase modulating unit,

wherein the optical phase modulator includes successively connected at least two optical phase modulators wherein one of the at least two optical phase modulators modulates the phase of the single photon based on bit information and the other one of the at least two optical phase modulators modulates the phase of the single photon based on basis information.

12. The system of claim 11, wherein the transmitting-end optical phase modulating unit comprises a plurality of optical modulators that are successively connected.

13. The system of claim 12, wherein one of the plurality of optical phase modulators of the transmitting-end optical phase modulating unit modulates a phase of a single photon based on bit information, and another one of the plurality of optical phase modulators of the transmitting-end optical phase modulating unit modulates the phase of the single photon based on basis information.

14. The system of claim 11, wherein an applied voltage of the receiving-end optical phase modulating unit is determined based on a phase difference between two optical interferometers respectively established in a transmitting-end and a receiving-end.

15. The system of claim 14, wherein the phase difference is calculated based on a number of single photons detected with a maximal probability and a number of single photons detected with a minimal probability.

16. A transmitting method of a quantum key distribution system, the method comprising:

receiving a single photon inputted from a light source;

performing an optical interfering process that divides a path of the single photon into a plurality of paths to enable a probability of an existence of the single photon to be distributed in a plurality of coordinates in a time domain; and

performing an optical modulating process that modulates a phase of a single photon corresponding to at least one path from among the plurality of paths, outside an apparatus where the optical interfering process is performed,

wherein the optical modulating process is performed by successively connected at least two optical phase modulators wherein one of the at least two optical phase modulators modulates the phase of the single photon based on bit information and the other one of the at least two optical phase modulators modulates the phase of the single photon based on basis information.

17. A receiving method of a quantum key distribution system, the receiving method comprising:

performing an optical phase modulating process that receives a single photon transmitted via a transmitting-end, and modulates a phase of a single photon that is not modulated from the received single photon; and

performing an optical interfering process that divides a probability of existence of the optical phase modulated-single photon to be distributed, with a plurality of different probabilities, in a time domain,

wherein optical modulating process is performed separately from the optical interfering process,

wherein the optical modulating process is performed by successively connected at least two optical phase modulators wherein one of the at least two optical phase modulators modulates the phase of the single photon based on bit information and the other one of the at least two optical phase modulators modulates the phase of the single photon based on basis information.

18. An optical phase modulating method of a quantum key distribution system, the method comprising:

a transmitting-end optical phase modulating process of inputting, with respect to a single photon, a modulation signal of which a time and a width is adjusted, a path of the single photon being divided into a plurality of paths to enable a probability of existence of the single photon to be distributed in a plurality of different coordinates, and of selectively modulating a phase of a single photon corresponding to at least one path from among the plurality of paths; and

a receiving-end optical phase modulating process of selectively modulating a phase of a single photon that is not modulated by the transmitting-end optical phase modulating process from the single photon received via the transmitting-end optical phase modulating process,

wherein the transmitting-end optical phase modulating process is performed by successively connected at least two optical phase modulators wherein one of the at least two optical phase modulators modulates the phase of the single photon based on bit information and the other one of the at least two optical phase modulators modulates the phase of the single photon based on basis information.