Quantum cryptography systems can operate over relatively long distances in standard telecommunications fiber by taking advantage of the low transmission losses in these fibers at 1.3 or 1.5 microns. Although there has been much progress toward the development of highly efficient and low-noise detectors for these wavelengths, silicon avalanche photodiodes currently offer superior single photon counting performance, but only at visible and near IR wavelengths where the fiber transmission is poor. For ranges typical of local area networks, it is possible that a quantum key distribution (QKD) system operating below 850nm could be optimal, even though standard telecommunications fiber supports multiple optical modes at these wavelengths. We have recently developed an optical mode filter that allows efficient higher order mode rejection from standard telecommunications fiber near 830nm. We have used this type of filter to launch and recover QKD signals from a polarization-based system implementing the BB84 quantum cryptography protocol. Here we present results from testing and operation in installed fiber links ranging up to 3km. These results demonstrate that the filters can attenuate the higher order modes over 35dB while having a minimal (<1dB) impact on the fundamental mode carrying the QKD signal.
Quantum cryptography systems can operate over relatively long distances in standard telecommunications fiber by taking advantage of the low transmission losses in these fibers at 1.3 or 1.5 microns. Although there has been much progress toward the development of highly efficient and low-noise detectors for these wavelengths, silicon avalanche photodiodes currently offer superior single photon counting performance, but only at visible and near IR wavelengths where the fiber transmission is poor. For ranges typical of local area networks, it is possible that a quantum key distribution (QKD) system operating below 850nm could be optimal, even though standard telecommunications fiber supports multiple optical modes at these wavelengths. We have recently developed an optical mode filter that allows efficient higher order mode rejection from standard telecommunications fiber near 830nm. We have used this type of filter to launch and recover QKD signals from a polarization-based system implementing the BB84 quantum cryptography protocol. Here we present results from testing and operation in installed fiber links ranging up to 3km. These results demonstrate that the filters can attenuate the higher order modes over 35dB while having a minimal (<1dB) impact on the fundamental mode carrying the QKD signal.
A quantum key distribution (QKD) system has been developed, using a standard telecommunications optical fiber, which is capable of operating at clock rates of greater than 1 GHz. The QKD system implements a polarization encoded version of the B92 protocol. The system employs vertical-cavity surface-emitting lasers with emission wavelengths of 850 nm as weak coherent light sources, and silicon single photon avalanche diodes as the single photon detectors. A distributed feedback laser of emission wavelength 1.3 /spl mu/m, and a linear gain germanium avalanche photodiode was used to optically synchronize individual photons over the standard telecommunications fiber. The QKD system exhibited a quantum bit error rate (QBER) of 1.4%, and an estimated net bit rate (NBR) greater than 100 000 bits/sup -1/ for a 4.2-km transmission range. For a 10-km fiber range, a QBER of 2.1%, and an estimated NBR of greater than 7000 bits/sup -1/ was achieved.
One of our major target is quantum key distribution (QKD,) which is closest to the practical use. Though QKD can be performed only with current technology, there still remain many thing to be improved. One of the most important devices that determine the system performance is photon detectors. It limits the transmission distance in optical fiber communication wavelength. A photon detector combining the two avalanche photon diodes (APD) has been demonstrated for qubit discrimination in 1550 nm. Spikes accompanied with the signals in gated-mode were canceled by balanced output from the two APDs. The balanced APD photon detector shows very low dark count rate (2x10-7) counts/pulse) with 10 % detection efficiency. We have also developed a highly stable interferometer on a planer-lightwave-circuit (PLC.) We have achieved single-photon interference over 150 km using time-division interferometers for quantum cryptography, which were composed of the two integrated-optic asymmetric Mach-Zehnder interferometers, and the balanced gated-mode photon detectors. The observed visibility was more than 80 % after 150-km transmission, which refers to a quantum bit error rate of less than 10 %. We will also describe temperature insensible QKD system and high speed (100 bps) key transmission over 40 km fiber.
Quantum cryptography offers the unique possibility of certifiably secure key distribution between remote locations, practical systems require efficient, low noise, single photon avalanche photodiodes (SPADs) to achieve this goal. This letter reports experimental results from a polarization-encoded system utilizing a state-of-the-art silicon SPAD. The system is used to investigate the performance limits of quantum cryptography systems operating in the first optical fiber communication window at wavelengths around 0.8 μm. The results demonstrate the potential for secure quantum key distribution at Mb/spl middot/s1rates over fiber LANs also carrying conventional high-speed (Gb/spl middot/s1) data channels at a wavelength of 1.3 μm.
In recent years quantum information research has lead to the discovery of a number of remarkable new paradigms for information processing and communication. These developments include quantum cryptography schemes that offer unconditionally secure information transport guaranteed by quantum-mechanical laws. Such potentially disruptive security technologies could be of high strategic and economic value in the future. Two major issues confronting researchers in this field are the transmission range (typically <100km) and the key exchange rate, which can be as low as a few bits per second at long optical fiber distances. This paper describes further research of an approach to significantly enhance the key exchange rate in an optical fiber system at distances in the range of 1-20km. We will present results on a number of application scenarios, including point-to-point links and multi-user networks. Quantum key distribution systems have been developed, which use standard telecommunications optical fiber, and which are capable of operating at clock rates of up to 2GHz. They implement a polarization-encoded version of the B92 protocol and employ vertical-cavity surface-emitting lasers with emission wavelengths of 850 nm as weak coherent light sources, as well as silicon single-photon avalanche diodes as the single photon detectors. The point-to-point quantum key distribution system exhibited a quantum bit error rate of 1.4%, and an estimated net bit rate greater than 100,000 bits-1 for a 4.2 km transmission range.
The access network portion of a telecommunications system in the last years demands ever-increasing bandwidth to serve not only residential and commercial customers but also other telecommunications operators, as is the case with back-haul in mobile infrastructure.To achieve this, technologies using fiber optics as a transmission medium are being developed.Passive Optical Network (PON) protocols such as ITU-T G.9804.1 provides new schemes of multiplexing that improve higher speed offered both in the downstream channel (operator to user) and in the upstream channel (user to operator).In some cases a symmetrical optical link is required to support new services, applications and terminals from users side because their profiles and demands has changed in the last decade with new challenges to maintain network parameters within the established contracted values.On the other hand, information security has also been a topic of interest in recent years, so quantum cryptography offers an alternative to increase robustness compared to the mechanisms available in electronic systems that could be vulnerable to the development of quantum computing.Although quantum cryptography protocols were defined in the last century, their application is of interest today, as they can exploit the properties of photons to make it more difficult for an intruder to obtain the private key of an information system that uses optical fiber as a transmission medium.This work shows the computational application of the BB84 quantum key distribution (QKD) protocol on an operating model of a 50G passive optical network, demonstrating both the cryptography performance and network quality parameters such as the bit error rate (BER) and the eye diagram.
We have developed a system for quantum key distribution (QKD), based on standard telecommunication lasers, detectors, and optical fiber, that passively compensates for time-dependent variations of the fiber-optic path due to stress, temperature changes, or birefringence. This approach allows information encoded in phase shifts imposed on single-photon-level pulses to be accurately read out after transmission over many kilometers of uncontrolled fiber. Cooled InGaAs avalanche photodiodes, pulse-biased using a special noise canceling circuit, are used to detect single 1.31-/spl mu/m infrared photons with a high efficiency, low dark-count rate, and subnanosecond time resolution. A single optical fiber carries both the quantum information and precise 1.55 /spl mu/m timing pulses between the two end stations. Overall synchronization of end-station activities, public discussion of basis choices, error correction, and privacy amplification have all been implemented over a local area network (LAN). The system at present generates raw, error-corrected, and privacy-amplified key data at rates of /spl sim/1000, 600, and 200 bits/s, respectively, over a 10-km single-mode fiber link.