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Abstract-A quantum key distribution system has been developed, using standard telecommunications optical fiber, which is capable of operating at clock rates of greater than 1 GHz. The quantum key distribution 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 µ µ µ µm, and a linear gain germanium avalanche photodiode was used to optically synchronize individual photons over the standard telecommunications fiber. The 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. For a 10 km fiber range a quantum bit error rate of 2.1%, and estimated net bit rate of greater than 7,000 bits -1 was achieved.

An improved quantum key distribution test system operating at clock rates of up to 2GHz using a specially adapted commercially available silicon single photon avalanche diode is presented. The use of improved detectors has improved the fibrebased test system performance in terms of transmission distance and quantum bit error rate.

Abstract-We present the application of quantum key distribution technologies to fiber-based broadband passive optical access networks. This application is based on our 850 nm wavelength gigahertz clock-rate single-receiver system, is compatible with existing telecommunications fiber and exploits a wavelength band not currently utilized in access networks. The developed quantum key distribution networks are capable of transmitting over distances consistent with the span of access links for metropolitan networks (10 km), at clock frequencies ranging up to 3 GHz.Index Terms-Communications systems, cryptography, data security, optical fiber communications, quantum cryptography, quantum key distribution I. INTRODUCTION UANTUM KEY DISTRIBUTION (QKD) [1] exploits fundamental physical principles to achieve information security on optical communications links. To date, much of the work on fiber-based QKD has focused on extending the achievable transmission distance on point-topoint (P2P) links to beyond 100 km [2]. Operation over this length scale would open the possibility of applications in secure, metropolitan-area-sized networks. However, comparatively less attention has been given to the question of how QKD could best be implemented on the access links to such networks. If based on current network topologies and technologies then these access links are likely to have a span of up to around 10 km and to be based on either multiple P2P links or point-to-multipoint passive optical networks (PONs). Optical access solutions of these types are currently in deployment in a number of regions of the world, where However, in practice each end-user would also contain a transmitter to enable upstream communication to a receiver in the central node. Wavelength division multiplexing (WDM) is usually employed to allow the two channels to share the same fiber without interference, with the upstream channel typically operating in the wavelength band around 1300 nm and the downstream channel (or channels) operating in the wavelength band around 1500 nm [3]. In the case of the PON, the passive optical splitter is shown as a single "star", but other architectures with, for example, distributed splitters in "tree-" or "bus-" type configurations are also possible. In this paper we address the question of how QKD could be best implemented in a secure network application employing these typical access topologies and wavelength allocation plans. We have previously developed a single-receiver QKD system using the B92 protocol [4] with polarization encoding that is capable of transmission at gigahertz clock rates through the use of mature silicon single-photon avalanche diodes (Si-SPADs) and 850 nm light in standard telecommunications fiber [5][6]. Here we demonstrate the feasibility of extending the application of this system to multi-user access networks. In this scenario the 850 nm operating wavelength brings a number of potential advantages. For example, the use of both 1300 nm and 1500 nm wavelength bands for conventional channels in acc...

Objective Medication‐related problems can adversely affect patients' health and treatment outcomes. While many authors have investigated the frequency of different types of medication‐related problem, no studies have described the development and validation of a screening tool to identify patients who are experiencing medication‐related problems. The aim of this study was to develop and validate a screening tool for the identification of patients experiencing medication‐related problems. Methods Based on the literature, a screening tool was developed for this purpose. Patients prescribed a cardiovascular medicine, who were aged over 18 years, were recruited from four community pharmacies and five general practice surgeries in South London. Patients were interviewed with the screening tool in the pharmacies and surgeries. Subsequently in‐depth interviews in patients' own homes were conducted to validate the findings and assess the effectiveness of the tool. Key findings Ninety‐nine patients in the pharmacies and 122 in the surgeries were recruited and interviewed using the screening tool; 74 of these were identified with at least one medication‐related problem. Seventy‐eight participants (43 identified with at least one problem and 35 with no apparent problems) agreed to be interviewed in their own homes. In 83% of cases the screening tool correctly distinguished between patients with at least one medication‐related problem and those identified with none. The screening tool was less likely than the home interview to pick up problems which required the patient to comment on the service of the surgery or pharmacy. Conclusion The screening tool could have a valuable role in identifying patients experiencing medication‐related problems. Its focus on patients' perspectives is important in ensuring that service developments are responsive to the needs of consumers.