Abstract: The authentication system comprises: the authentication side unit configured to include the intensity modulated weak light source, the first reading unit, the decrypting unit, and the determining unit; and the client side unit configured to include the detecting unit, the second reading unit, and the encrypting unit. The intensity modulated weak light source generates intensity modulated weak light. The first reading unit reads the transmission time information. The detecting unit detects the intensity modulated weak light, and records the detected time in the second storage medium as reception time information. The encrypting unit encrypts all or part of the reception time information and generates encrypted information. The decrypting unit decrypts the encrypted information, and acquires all or part of the reception time information.

Abstract: The authentication system comprises: the authentication side unit configured to include the intensity modulated weak light source, the first reading unit, the decrypting unit, and the determining unit; and the client side unit configured to include the detecting unit, the second reading unit, and the encrypting unit. The intensity modulated weak light source generates intensity modulated weak light. The first reading unit reads the transmission time information. The detecting unit detects the intensity modulated weak light, and records the detected time in the second storage medium as reception time information. The encrypting unit encrypts all or part of the reception time information and generates encrypted information. The decrypting unit decrypts the encrypted information, and acquires all or part of the reception time information.

Abstract: There is provided a quantum-key-distribution receiving device used in a quantum key distribution system that utilizes a pair of quantum-entangled photons including a signal photon and an idler photon, the quantum-key-distribution receiving device including a single-photon detector in which a secure-key generation rate is dependent on a first performance index ?/(1+Pa), ? denoting a detection efficiency and Pa denoting an after-pulse probability.

Abstract: In a quantum entangled photon pair generator selectively generating polarization entangled photon pairs and time-bin entangled photon pairs, an excitation optical pulse shaper receives a linearly polarized optical pulse, and selectively outputs either one of a polarization excitation optical pulse pair to be a seedlight pulse for a polarization entangled photon pair and a consecutive excitation optical pulse pair to be a seedlight pulse for a time-bin entangled photon pair. An optical interferometer receives the polarization excitation optical pulse pair or the consecutive excitation optical pulse pair, and outputs a correlated photon pair forming signal and idler photons through a parametric fluorescence process. A quantum entangled photon pair extractor spatially extracting wavelength components corresponding to photons of the quantum entangled photon pair to output the components as the polarization entangled photon pair or the time-bin entangled photon pair.

Abstract: There is provided a quantum-key-distribution receiving device used in a quantum key distribution system that utilizes a pair of quantum-entangled photons including a signal photon and an idler photon, the quantum-key-distribution receiving device including a single-photon detector in which a secure-key generation rate is dependent on a first performance index ?/(1+Pa), ? denoting a detection efficiency and Pa denoting an after-pulse probability.

Abstract: A quantum entangled photon pair generating device, an optical frequency dividing filter, a 2N-input/2N-output optical switch, a 2N number of quantum key receiving devices, an optical transmission path and a control unit are provided. The quantum entangled photon pair generating device generates quantum entangled photon pairs. The optical frequency dividing filter receives the quantum entangled photon pairs, divides an optical frequency region by 2N, and performs output. The 2N-input/2N-output optical switch allocates photons of the 2N number of optical frequency regions to any one of a 2N number of output ports, and outputs the photons.

Abstract: A quantum entangled photon pair generating device, an optical frequency dividing filter, a 2N-input/2N-output optical switch, a 2N number of quantum key receiving devices, an optical transmission path and a control unit are provided. The quantum entangled photon pair generating device generates quantum entangled photon pairs. The optical frequency dividing filter receives the quantum entangled photon pairs, divides an optical frequency region by 2N, and performs output. The 2N-input/2N-output optical switch allocates photons of the 2N number of optical frequency regions to any one of a 2N number of output ports, and outputs the photons.

Abstract: A quantum correlated photon pair generating device includes a nonlinear optical medium that generates quantum correlated photon pairs from excitation light by spontaneous parametric fluorescence and generates auxiliary idler light from the excitation light and auxiliary signal light by stimulated parametric conversion. The excitation light and auxiliary signal light are generated separately, combined, and input simultaneously to the nonlinear optical medium. An optical demultiplexer separates the auxiliary signal light and the auxiliary idler light output from the nonlinear optical medium. The intensities of the output auxiliary signal light and auxiliary idler light are detected, and the intensity or wavelength of the excitation light or the temperature of the nonlinear optical medium is controlled to maintain the ratio of the detected intensities at a preset value. The rate at which the quantum correlated photon pairs are generated is thereby held steady.

Abstract: In a quantum entangled photon pair generator selectively generating polarization entangled photon pairs and time-bin entangled photon pairs, an excitation optical pulse shaper receives a linearly polarized optical pulse, and selectively outputs either one of a polarization excitation optical pulse pair to be a seedlight pulse for a polarization entangled photon pair and a consecutive excitation optical pulse pair to be a seedlight pulse for a time-bin entangled photon pair. An optical interferometer receives the polarization excitation optical pulse pair or the consecutive excitation optical pulse pair, and outputs a correlated photon pair forming signal and idler photons through a parametric fluorescence process. A quantum entangled photon pair extractor spatially extracting wavelength components corresponding to photons of the quantum entangled photon pair to output the components as the polarization entangled photon pair or the time-bin entangled photon pair.

Abstract: A quantum key delivery system includes an optical circulator, an optical low-pass filter, optical splitters, and first and second optical couplers arranged for outputting various wavelength components including correlated-photon pair wavelength components outputted from an optical loop path. The first and second optical couplers output light beams, which are sent over first and second quantum channels to first and second recipients, respectively. Other optical splitters are adapted to output light rays, from which first and second control signals are produced. From auxiliary idler light components transmitted over the first and second quantum channels, clock signals are extracted. The system thus extracts a clock signal for detecting arrival of photons, and stably operates with an expected value of the number of generated correlated photon pairs maintained at a substantially constant value.

Abstract: An optical m-ary modulator includes an optical loop forming a polarization maintaining closed optical path. A loop input-output unit splits linearly polarized input signal light into a first component and a second component and feeds the first and second components into the optical loop in opposite directions. A pair of phase modulators modulate the first and second components according to respective control signals. The loop input-output unit recombines the modulated first and second components. The optical phase bias unit creates a phase difference between the first and second components so that they combine to form an m-ary modulated optical signal. Since the first and second components travel around the same optical path, when they recombine their phases are correctly aligned, making the modulator immune to environmental effects and permitting the use of high-speed optical modulation techniques.

Abstract: The device is structured to have a first electric modulation signal generator, a second electric modulation signal generator, a two-mode beat light source and an optical intensity modulator. The first electric modulation signal generator generates and outputs a first electric modulation signal. The second electric modulation signal generator generates and outputs a second electric modulation signal of a same frequency as the first electric modulation signal and to which a phase difference of ? radians is provided (? is a real number satisfying 0????). The two-mode beat light source is driven by the first electric modulation signal, and generates and outputs two-mode beat light. The two-mode beat light is inputted to the optical intensity modulator, and the optical intensity modulator generates and outputs a CS optical pulse train. Light transmittance of the optical intensity modulator is modulated by the second electric modulation signal.

Abstract: Excitation light is split into two components with mutually orthogonal polarization. One component is fed clockwise and the other component is fed counterclockwise into a polarization maintaining loop. An optical conversion generation unit including two second-order nonlinear optical media disposed on opposite sides of a half-wave plate in the loop generates up-converted light from each excitation component by second harmonic generation, and generates down-converted light from the up-converted light by spontaneous parametric down conversion. A polarization manipulation unit manipulates the polarization direction of at least one of the excitation or down-converted components. The clockwise and counterclockwise components of the down-converted light are recombined and output as quantum entangled photon pairs having substantially the same wavelength as the excitation light.

Abstract: Excitation light is split into two components with mutually orthogonal polarization. One component is fed clockwise and the other component is fed counterclockwise into a polarization maintaining loop. A second-order nonlinear optical medium disposed in the loop generates up-converted light from each excitation component by second harmonic generation, and generates down-converted light from the up-converted light by spontaneous parametric down conversion. A polarization manipulation unit manipulates the polarization direction of at least one of the excitation or down-converted components. The clockwise and counterclockwise components of the down-converted light are recombined and output as quantum entangled photon pairs having substantially the same wavelength as the excitation light. The optical components can be optimized for operation at this wavelength without the need to consider the shorter wavelength of the up-converted light.

Abstract: The device is structured to have a first electric modulation signal generator, a second electric modulation signal generator, a two-mode beat light source and an optical intensity modulator. The first electric modulation signal generator generates and outputs a first electric modulation signal. The second electric modulation signal generator generates and outputs a second electric modulation signal of a same frequency as the first electric modulation signal and to which a phase difference of ? radians is provided (? is a real number satisfying 0????). The two-mode beat light source is driven by the first electric modulation signal, and generates and outputs two-mode beat light. The two-mode beat light is inputted to the optical intensity modulator, and the optical intensity modulator generates and outputs a CS optical pulse train. Light transmittance of the optical intensity modulator is modulated by the second electric modulation signal.

Abstract: A quantum correlated photon pair generating device includes a nonlinear optical medium that generates quantum correlated photon pairs from excitation light by spontaneous parametric fluorescence and generates auxiliary idler light from the excitation light and auxiliary signal light by stimulated parametric conversion. The excitation light and auxiliary signal light are generated separately, combined, and input simultaneously to the nonlinear optical medium. An optical demultiplexer separates the auxiliary signal light and the auxiliary idler light output from the nonlinear optical medium. The intensities of the output auxiliary signal light and auxiliary idler light are detected, and the intensity or wavelength of the excitation light or the temperature of the nonlinear optical medium is controlled to maintain the ratio of the detected intensities at a preset value. The rate at which the quantum correlated photon pairs are generated is thereby held steady.

Abstract: A quantum key delivery system includes an optical circulator, an optical low-pass filter, optical splitters, and first and second optical couplers arranged for outputting various wavelength components including correlated-photon pair wavelength components outputted from an optical loop path. The first and second optical couplers output light beams, which are sent over first and second quantum channels to first and second recipients, respectively. Other optical splitters are adapted to output light rays, from which first and second control signals are produced. From auxiliary idler light components transmitted over the first and second quantum channels, clock signals are extracted. The system thus extracts a clock signal for detecting arrival of photons, and stably operates with an expected value of the number of generated correlated photon pairs maintained at a substantially constant value.

Abstract: An optical modulator includes, a first polarization separation and combination portion, a second polarization separation and combination portion, a first polarization plane-maintaining optical fiber, a second polarization plane-maintaining optical fiber, a third polarization plane-maintaining optical fiber of which a first end is coupled with the second input and output terminal of the second polarization separation and combination portion, the third polarization plane-maintaining optical fiber including a first optical coupler, to which control light that is linearly polarized light is input, a fourth polarization plane-maintaining optical fiber of which a first end is coupled with the third input and output terminal of the second polarization separation and combination portion; and a first polarization plane conversion portion that optically communicates with a second end of the third polarization plane-maintaining optical fiber and a second end of the fourth polarization plane-maintaining optical fiber.

Abstract: The device is structured to have a first electric modulation signal generator, a second electric modulation signal generator, a two-mode beat light source and an optical intensity modulator. The first electric modulation signal generator generates and outputs a first electric modulation signal. The second electric modulation signal generator generates and outputs a second electric modulation signal of a same frequency as the first electric modulation signal and to which a phase difference of ? radians is provided (? is a real number satisfying 0????). The two-mode beat light source is driven by the first electric modulation signal, and generates and outputs two-mode beat light. The two-mode beat light is inputted to the optical intensity modulator, and the optical intensity modulator generates and outputs a CS optical pulse train. Light transmittance of the optical intensity modulator is modulated by the second electric modulation signal.

Abstract: An optical clock signal recovery apparatus includes a mode-locked semiconductor laser that generates an optical pulse train polarized in a first direction. Optical components of the apparatus transmit a component of an input optical signal polarized in a second direction, perpendicular to the first direction, into the mode-locked semiconductor laser while blocking the component of the input optical signal polarized in the first direction, and transmit light exiting the mode-locked semiconductor laser polarized in the first direction, while blocking light exiting the mode-locked semiconductor laser polarized in the second direction. The transmitted exiting light is output as a recovered optical clock signal.