Nec Corporation

Kaijo Corporation

Other

Japan Science and Technology Agency

Nec C Orporation

Seigo Takahashi

Akio Tajima

Akihiro Tanaka

Wakako Maeda

Naoya Henmi

Yoshiharu Maeno

Toshiharu Ito

Yoshihiko Suemura

Kohei Hosokawa

Soichiro Araki

Manabu Arikawa

Takashi Ishikawa

Yoshimasa Ono

Hirofumi Shimomura

Takeshi Takeuchi

Kazuo Nakamura

Kazunari Suzuki

Hiroaki Takahashi

Akihisa Tomita

Shuji Suzuki

Toshiaki Eguchi

Yasuaki Ohkubo

Norihisa Takahashi

Yoshihiro Nanbu

Shuuji Suzuki

Junpei Ohkawara

Hironobu Suzuki

The objective of the present invention is to reduce the size of a receiving device circuit in an optical space communication system while maintaining communication stability. A data receiving device which decodes one item of data from a plurality of input signals includes: two or more digital signal processing means for subjecting the plurality of input signals to signal processing; a first recording means for temporarily recording the plurality of input signals; a SN ratio estimating means for estimating S/N ratios of each of the plurality of input signals and determining the number of the plurality of input signals to be combined, and the signals to be combined; and a scheduling means for carrying out overall control on the basis of the results from the SN ratio estimating means.

Free-space optical communication receiving device and method of controlling the same

An appropriate synthesized signal cannot be obtained by only correcting relative phase errors of a plurality of received signals; therefore, a received signal processor according to an exemplary aspect of the present invention includes a plurality of signal-to-noise ratio estimation means for estimating respective signal-to-noise ratios of a plurality of digital signal sequences in which relative phase errors of a plurality of received signal sequences having been corrected; a plurality of temporary decision means for performing symbol decisions of the plurality of digital signal sequences and outputting symbol signal sequences; symbol-map-rotation determination means for determining respective phase rotation amounts of the plurality of digital signal sequences from the plurality of symbol signal sequences and the respective signal-to-noise ratios of the plurality of digital signal sequences; and a plurality of phase rotation means for rotating phases of the plurality of digital signal sequences respectively based on the phase rotation amounts.

Received signal processor and method for processing received signal

It is difficult in a free space optical transmitter to transmit a beacon beam stably at low cost, and that it is impossible to maintain stable tracking; therefore, a free space optical transmitter according to an exemplary aspect of the present invention includes a laser beam transmitting means for transmitting a plurality of laser beams capable of interfering with each other and differing in one of an optical frequency and a time variation in a phase difference; and a wavefront control beam transmitting means for transmitting, to a free space, a plurality of wavefront control beams obtained by making each of the plurality of laser beams have a different wavefront.

Free space optical transmitter and free space optical communication method

A receiving-side splitterthat constitutes part of an optical communication devicesplits a receiving-side signal light into a plurality of lights at a splitting ratio according to the intensity distribution of mutually different propagation modes included in the receiving-side signal light passed through a transmission medium. A transmission-side splittersplits a transmission-side signal light into a plurality of-lights. A signal processing devicedetects the light intensity and/or the phase of the receiving-side signal light, and sets a control target value for the light intensity and/or the phase of the transmission-side signal light to a value according to the result of the detection. A modulatoradjusts the light intensity or the phase of a the transmission-side signal light so that the light intensity or phase equals the set value. A multiplexermultiplexes the plurality of transmission-side signal lights.

Optical communication device, optical communication system, and optical communication method

It is difficult in a free space optical receiver to satisfy both of the stable receiving and the highly sensitive receiving; therefore, a free space optical receiver according to an exemplary aspect of the present invention includes a light collecting means for collecting laser light having propagated through a free space transmission path; a multimode light generating means for receiving input of the laser light collected by the light collecting means, exciting multimode light, and outputting multimode propagation light including a plurality of propagation mode light beams with a number smaller than a number of multimode light beams possible to be excited; and a mode separating means for separating the multimode propagation light into the plurality of propagation mode light beams and outputting the plurality of propagation mode light beams.

Free space optical receiver and free space optical receiving method

The circuit size of a signal processing circuit increases in a free space optical receiver, which increases in cost, because the signal processing becomes complex attempting to improve the coupling efficiency between received light and a fiber; therefore, a free space optical receiver according to an exemplary aspect of the present invention includes a light collecting means for collecting laser light having propagated through a free space transmission path; a multi-mode transmission medium for receiving input of the laser light and outputting multi-mode light; a multi-mode signal processing means for outputting a plurality of received electrical signals based on part of the multi-mode light; a monitor means for monitoring signal information based on the multi-mode light; a control means for controlling an operation of the multi-mode signal processing means based on the signal information; and a signal processing means for performing signal processing on the plurality of received electrical signals and outputting an output signal synthesized from the plurality of received electrical signals.

It is impossible to prevent the deterioration of the coupling efficiency between received light and a single mode fiber, and difficult to achieve a higher transmission rate, with respect to a free space optical communication receiver; therefore, a free space optical receiver according to an exemplary aspect of the present invention includes light collecting means for collecting laser light having propagated through a free space transmission path; mode controlling means for separating the laser light collected by the light collecting means into a plurality of propagation mode beams depending on a wave-front fluctuation of the laser light and outputting the propagation mode beams; a plurality of single mode transmission media for guiding the plurality of propagation mode beams, respectively; and a plurality of light receiving means for receiving the plurality of propagation mode beams respectively through the plurality of single mode transmission media.

A user request can be reflected in the degree of security of an updated key in quantum key distribution. A sender and a receiver are connected through optical fiber. A quantum transmitter in the sender and a quantum receiver in the receiver carry out basis reconciliation and error correction through a quantum channel, based on a source of a key sent from the quantum transmitter and on a raw key received by the quantum receiver. Under the control of security control sections in the sender and receiver, the amount of information having the possibility of being intercepted, which is determined in accordance with a degree of security requested by a user, is removed from the key information after error correction, whereby a final cryptographic key is generated. Secret communication is performed between encryption/decryption sections in the sender and receiver by using the cryptographic key thus updated.

Secret communication system and method for generating shared secret information

A random number quality control circuit capable of fast control of the level of random number quality is present. When a '0' output section and a '1' output section generate random numbers by individually receiving a random number signal, a random number quality monitor monitors an unbalance between the numbers of &#x201c;0&#x201d;s and &#x201c;1&#x201d;s. If a deviation from a desired ratio is found, a drive controller controls the reception characteristics of the &#x201c;0&#x201d; output section and &#x201c;1&#x201d; output section individually so that the deviation will be compensated for. The amount of information intercepted between a sender and a receiver can be reduced by maintaining the mark ratio of shared random numbers at 50%.

Circuit and method for controlling quality of random numbers

In a quantum cryptographic transmitter (), a phase modulator () and an LN intensity modulator () apply optical phase modulation and light intensity modulation to an optical signal based on desired data to generate a desired optical signal to be transmitted to a quantum cryptographic receiver (). Based on the number of photons detected from the desired optical signal, a bias control circuit () controls an operating point in light intensity modulation of the LN intensity modulator ().

Quantum key distribution system, optical transmitter, optical modulation control circuit, and optical modulation control method

A method for managing shared random numbers in a secret communication network including at least one center node and a plurality of remote nodes connected to the center node, includes: sharing random number sequences between the center node and respective ones of the plurality of remote nodes; when performing random numbers sharing between a first remote node storing a first random number sequence shared with the center node and a second remote node storing a second random number sequence shared with the center node, distributing a part of the second random number sequence from the center node to the first remote node; and sharing the part of the second random number sequence between the first remote node and the second remote node.

Method and system for managing shared random numbers in secret communication network

A sender transmits to a receiver an optical signal that is phase-modulated in accordance with source data and a basis stored in a memory. The receiver phase-modulates the received optical signal in accordance with a basis, obtains detection data through interference, and stores the detection data in a memory. An inter-device address difference (G) and an intra-device address difference (D) are provisionally set. The detection data are checked against the source data while sequentially changing the values of Gand Dwithin a predetermined adjustment range. Based on the result of this checking, Gand Dare determined.

Communication system and synchronization control method

A cryptographic key management method and device are provided by which cryptographic keys of multiple nodes can be managed easily and stably. A system includes at least one first node and a plurality of second nodes connected to the first node, and the first node individually generates and consumes a cryptographic key with each of the second nodes connected to the first node itself. A cryptographic key management device in such a system has a monitor that monitors the stored key amounts of cryptographic keys of the individual second nodes, stored at the first node, and a key management control section that performs key generation control on the first node, based on the stored key amounts.

Method and device for managing cryptographic keys in secret communications network

A communication system and a timing control method are proposed that optimize timing in a sender and thereby enable information to be stably transmitted at the right timing. Under instructions from a timing controller in a receiver, the timing of driving a phase modulator in a sender is shifted by one step after another, and the then amount of clock shift and result of interference are monitored at the receiver and stored in a memory. The optimum timing is determined based on the stored data. Thus, a clock for driving the phase modulator in the sender can be set at the right timing. This is equivalent to compensating for group velocity dispersion due to wavelength dispersion that occurs when an optical signal channel and a clock signal channel are transmitted by wavelength division multiplexing transmission.

Communication system and timing control method

For an error rate QBER, threshold values are preset, including a threshold value Qfor frame synchronization processing, a threshold value Qfor phase correction processing, and a threshold value Qfor eavesdropping detection. Upon the distribution of a quantum key from a sender to a receiver, when the measurement value of QBER is deteriorated more than Q, frame synchronization processing is performed. When the measurement value of QBER is deteriorated more than Q, phase correction processing and frame synchronization processing are performed. When QBER does not become better than Qeven after these recovery-processing steps are repeated N times, it is determined that there is a possibility of eavesdropping, and the processing is stopped.

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Tokyo, Japan

Seigo Takahashi