Paul D. Townsend

Hybrid DWDM-TDM long-reach PON for next-generation optical access

A novel long-reach passive optical network (PON) architecture based on hybrid dense wavelength-division multiplexing (DWDM) and time-division multiplexing (TDM) is presented as a possible candidate for the next generation of optical access networks. The approach combines access and backhaul functions in a single optical network infrastructure that links end customers directly to core networks without the need for intermediate electronic conversions. A centralized optical carrier distribution and wavelength-independent remote modulation scheme is employed to avoid the potential inventory and deployment costs associated with the use of wavelength-specific lasers in the customer transmitter (TX). The customer TX is based on an electroabsorption modulator (EAM) monolithically integrated with two semiconductor optical amplifiers (SOAs), providing sufficient net gain and bandwidth to support large splitting factors and upstream bit rates up to 10 Gb/s. The experimental results reported show that the network, with a total reach of 100 km and an upstream bit rate of 10 Gb/s, can potentially support 17 TDM PONs operating at different wavelengths each with up to 256 customers, giving an aggregate number of 4352 customers in total.

Quantum key distribution over distances as long as 30 km

We report the secure transmission of cryptographic keys over as long as 30 km of optical fiber, using an interferometric quantum cryptography scheme. Low error rates in the range 1.2–4% were obtained for the quantum transmissions, and error-free secret keys were distilled from the raw data by use of secure error-correction and privacy-amplification protocols.

A short wavelength GigaHertz clocked fiber-optic quantum key distribution system

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.

Wave equations for arbitrary spin from quantization of the extended supersymmetric spinning particle

Abstract We present the action for a relativistic particle with a gauged N-extended line supersymmetry and show that, upon quantization, it yields a relativistic wave equation for pure spin 1 2 N . A curved-space background is compatible with worldline supersymmetry only for N⩽2.

Observation of nonlinear optical transmission and switching phenomena in polydiacetylene‐based directional couplers

Nonlinear optical transmission and switching phenomena have been observed in directional coupler devices fabricated from soluble polydiacetylenes. Effects due to both slow thermal nonlinearities and ultrafast (picosecond) electronic nonlinearities were identified. At the operating wavelength of 1.06 μm used here, the ultrafast electronic nonlinear phenomena originated from intensity‐dependent changes in the imaginary part of the refractive index due to two‐photon absorption effects.

DISCUS: an end-to-end solution for ubiquitous broadband optical access

Fiber to the premises has promised to increase the capacity in telecommunications access networks for well over 30 years. While it is widely recognized that optical-fiber-based access networks will be a necessity in the short to medium-term future, its large upfront cost and regulatory issues are pushing many operators to further postpone its deployment, while installing intermediate unambitious solutions such as fiber to the cabinet. Such high investment cost of both network access and core capacity upgrade often derives from poor planning strategies that do not consider the necessity to adequately modify the network architecture to fully exploit the cost benefit that a fiber-centric solution can bring. DISCUS is a European Framework 7 Integrated Project that, building on optical-centric solutions such as long-reach passive optical access and flat optical core, aims to deliver a cost-effective architecture for ubiquitous broadband services. DISCUS analyzes, designs, and demonstrates end-to-end architectures and technologies capable of saving cost and energy by reducing the number of electronic terminations in the network and sharing the deployment costs among a larger number of users compared to current fiber access systems. This article describes the network architecture and the supporting technologies behind DISCUS, giving an overview of the concepts and methodologies that will be used to deliver our end-to-end network solution.

Rayleigh noise mitigation in long-reach hybrid DWDM-TDM PONs

Feature Issue on Passive Optical Network Architectures and TechnologiesAn architecture employing a centralized light source and reflective modulator at the customer is proposed and demonstrated for a long-reach, hybrid dense wavelength division multiplexed (DWDM)-time-division multiplexed (TDM) passive optical network (PON). Impairments to the upstream channel caused by Rayleigh backscattering in the network are mitigated using a dual-feeder-fiber approach in conjunction with a novel detuned filtering and spectral-broadening scheme. The experimental results show that the network, with a total reach of 116km and an upstream bit rate of 10Gbits/s, can support up to 256 customers on each TDM PON. The potential performance improvements obtainable from an optimized architecture are also discussed.

Multi-user Quantum Cryptography on Optical Networks

Abstract Quantum cryptography has been shown to be an effective technology for the secure distribution of keys on point-to-point optical links. We show how the existing techniques can be extended to allow multi-user secure key distribution on optical networks. We demonstrate that using network configurations typical of those found in passive optical network architectures any of the current quantum key distribution protocols can be adapted to implement secure key distribution from any user to any other user. An important feature of these adapted protocols is that the broadcaster, or service provider on the network, does not have to be trusted by the two users who wish to establish a key.

A 135-km 8192-Split Carrier Distributed DWDM-TDMA PON With 2

We present a hybrid dense wavelength-division-multiplexed time-division multiple access passive optical network (DWDM-TDMA PON) with record performance in terms of reach (135.1 km of which 124 km were field-installed fibers), number of supported optical network units (ONUs-8192) and capacity (symmetric 320 Gb/s). This was done using 32-, 50-GHz-spaced downstream wavelengths and another 32-, 50-GHz-spaced upstream wavelengths, each carrying 10 Gb/s traffic (256 ONUs per wavelength, upstream operated in burst mode). The 10 Gb/s downstream channels were based upon DFB lasers (arranged in a DWDM grid), whose outputs were modulated using a electro-absorption modulator (EAM). The downstream channels were terminated using avalanche photodiodes in the optical networks units (ONUs). Erbium-doped fiber amplifiers (EDFAs) provided the gain to overcome the large fiber and splitting losses. The 10 Gb/s upstream channels were based upon seed carriers (arranged in a DWDM grid) distributed from the service node towards the optical network units (ONUs) located in the users premises. The ONUs boosted, modulated, and reflected these seed carriers back toward the service node using integrated 10 Gb/s reflective EAM-SOAs (EAM-semiconductor optical amplifier). This seed carrier distribution scheme offers the advantage that all wavelength referencing is done in the well-controlled environment of the service node. The bursty upstream channels were further supported by gain stabilized EDFAs and a 3R 10 Gb/s burst-mode receiver with electronic dispersion compensation. The demonstrated network concept allows integration of metro and optical access networks into a single all-optical system, which has potential for capital and operational expenditure savings for operators.

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An improved quantum key distribution test system operating at clock rates of up to 2GHz using a specially adapted commercially-available silicon single-photon counting module is presented. The use of an enhanced detector has improved the fiber-based quantum key distribution test system performance in terms of transmission distance and quantum bit error rate.