Wakako Maeda

Ultra fast quantum key distribution over a 97 km installed telecom fiber with wavelength division multiplexing clock synchronization

We demonstrated ultra fast BB84 quantum key distribution (QKD) transmission at 625 MHz clock rate through a 97 km field-installed fiber using practical clock synchronization based on wavelength-division multiplexing (WDM). We succeeded in over-one-hour stable key generation at a high sifted key rate of 2.4 kbps and a low quantum bit error rate (QBER) of 2.9%. The asymptotic secure key rate was estimated to be 0.78- 0.82 kbps from the transmission data with the decoy method of average photon numbers 0, 0.15, and 0.4 photons/pulse.

Practical Quantum Cryptosystem for Metro Area Applications

A practical quantum cryptosystem prototype has been developed for metro area applications. It is of the size of a desktop and incorporates a temperature-independent optical interferometer, a highly reliable photon detector module, and random number generators. It supports various functions, including bit/frame synchronization, BB84 bit reconciliation, error correction and privacy amplification for quantum key generation, and encrypted communication. Two weeks of testing using a commercial fiber in the field demonstrated its ability to continuously generate final keys and to perform crypto communication using the keys.

Technologies for Quantum Key Distribution Networks Integrated With Optical Communication Networks

Secure networks composed of optical networks and quantum key distribution (QKD) are considered in this paper. A network layer structure is defined to focus on issues important with respect to the QKD network layer that controls QKD links and supplies a secure key for message transmission. A multiple-user QKD network layer can be constructed with timing synchronization, secure key sharing between indirectly connected nodes with switched QKD systems and key relays, and key management to control the volume of key generation and supply in response to the demand from optical network nodes.

High-speed QKD system synchronized by automatic phase-alignment mechanism

A high-speed QKD system, which has an automatic modulation-phase-alignment mechanism for compensating for GVD, was developed. Using this system, we confirmed high-speed and stable quantum key distribution with transmission over 40 km was possible.

112Gb/s optical transponder with PM-QPSK and coherent detection employing parallel FPGA-based real-time digital signal processing, FEC and 100GbE Ethernet interface

We demonstrate 112Gb/s transmission using PM-QPSK format and FPGA-based real-time digital signal processing. By employing framed processing architecture for polarization demultiplexing and carrier phase estimation, stable operation of error free after FEC and wide frequency offset have been achieved.

Ensuring Quality of Shared Keys Through Quantum Key Distribution for Practical Application

We investigated the characteristics of shared keys obtained through quantum key distribution (QKD) from the viewpoint of application in cipher communication. We demonstrated that the shared keys at each stage in QKD satisfy the criteria determined by a standardized randomness test by physically compensating for randomness degrading factors. We also examined the increase in the error rate of the shared keys produced by privacy amplification, and succeeded in suppressing the error rate increase by applying a new privacy amplification scheme, which yielded a sufficiently low error rate for the final keys. These investigations showed that the final keys obtained using quantum cryptosystems are available as crypto keys in cipher communication.

Fortnight quantum key generation field trial using QBER monitoring

Frame synchronization and supervisory control scheme were proposed for use in QKD, which all were based on QBER monitoring. Using these techniques proposed here, two weeks of continuous quantum key generation were performed through a field aerial fiber.

Scalable QKD network using simple key-management technique with on-demand crypto-key supply

We propose a simple key-management technique using novel crypto-key supply. We have also successfully demonstrated a five-node QKD network that uses dynamic quantum key generation and on-demand crypto-key supply.

Experimental demonstration of the improvement of system sensitivity using multiple state trellis coded optical modulation with QPSK and 16QAM constellations

We evaluated experimentally 2, 8, 32 state 32Gbaud TCM-QPSK and TCM-16QAM. TCM offers finer configuration for flexible transponders increasing SE, on 1.1dB wider ranges. TCM may also be used with HD-FEC in lower power transceivers.

Long Haul transmission of four-dimensional 64SP-12QAM signal based on 16QAM constellation for longer distance at same spectral efficiency as PM-8QAM

We propose a new 4D coded modulation format, 64SP-12QAM, with same SE as PM-8QAM and straightforwardly-switchable with PM-16QAM. We experimentally demonstrated over 0.2 dB better sensitivity for 64SP-12QAM compared to PM-8QAM, enabling a transmission reach extension to 6,000 km at 6b/s/Hz.