A Short Wavelength GigaHertz Clocked Fiber-Optic Quantum Key Distribution System

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 micro-metres, 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-per-second 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-per-second was achieved.Comment: Pre-press versio

Sigma-model soliton intersections from exceptional calibrations

A first-order `BPS' equation is obtained for 1/8 supersymmetric intersections of soliton-membranes (lumps) of supersymmetric (4+1)-dimensional massless sigma models, and a special non-singular solution is found that preserves 1/4 supersymmetry. For 4-dimensional hyper-K\"ahler target spaces ($HK_4$) the BPS equation is shown to be the low-energy limit of the equation for a Cayley-calibrated 4-surface in \bE^4\times HK_4. Similar first-order equations are found for stationary intersections of Q-lump-membranes of the massive sigma model, but now generic solutions preserve either 1/8 supersymmetry or no supersymmetry, depending on the time orientation.Comment: 21 pages. Version 3: Minor corrections and one further reference: version published in JHE

3.3 Gigahertz Clocked Quantum Key Distribution System

A fibre-based quantum key distribution system operating up to a clock frequency of 3.3GHz is presented. The system demonstrates significantly increased key exchange rate potential and operates at a wavelength of 850nm.Comment: Presented at ECOC 05, Glasgow, UK, (September 2005

Dilaton Domain Walls and Dynamical Systems

Domain wall solutions of $d$-dimensional gravity coupled to a dilaton field $\sigma$ with an exponential potential $\Lambda e^{-\lambda\sigma}$ are shown to be governed by an autonomous dynamical system, with a transcritical bifurcation as a function of the parameter $\lambda$ when $\Lambda<0$. All phase-plane trajectories are found exactly for $\lambda=0$, including separatrices corresponding to walls that interpolate between $adS_d$ and adS_{d-1} \times\bR, and the exact solution is found for $d=3$. Janus-type solutions are interpreted as marginal bound states of these ``separatrix walls''. All flat domain wall solutions, which are given exactly for any $\lambda$, are shown to be supersymmetric for some superpotential $W$, determined by the solution.Comment: 30 pp, 11 figs, significant revision of original. Minor additional corrections in version to appear in journa

High intensity luminescence from pulsed laser annealed europium implanted sapphire

Sapphire samples (Al2O3) were implanted with 400-keV ions at a dose of 1×1016 ions cm-2. A comparison was made between furnace annealing and pulsed laser annealing of the implanted samples. Furnace annealing to 1200°C, followed by excimer laser anneals, resulted in an increase of the cathodoluminescence emission intensity of the implanted europium by a factor of ∼20. This enhanced intensity is ∼50 times that of the signal prior to any form annealing treatment. It is proposed that the laser anneals dissociate Eu related clusters. The Eu 622-nm lifetime reached 1.53 ms compared with an original postimplant value of 0.14 ms. © 1994 American Institue of Physics.Peer Reviewe

25Gb/s PAM4 adaptive receiver equalisation requirements for burst-mode transmission systems

Requirements for burst-mode equalisation in a 25Gb/s PAM4 system for passive optical network upstream traffic are analysed for different linear equaliser solutions, with transmission over 40km of fibre. The impact of chromatic dispersion, transmitter bandwidth restriction and non-linearities is considered

Chirp control in directly modulated 25G PAM4 transmitters for optical access networks

Narrowband filtering chirp control is demonstrated for a 25Gb/s PAM4 signal in directly modulated transmitters for next generation optical access systems, allowing 50km transmission without chromatic dispersion compensation with blue-shift filtering offering the best performance

Tachyons, Supertubes and Brane/Anti-Brane Systems

We find supertubes with arbitrary (and not necessarily planar) cross section; the stability against the D2-brane tension is due to a compensation by the local momentum generated by Born-Infeld fields. Stability against long-range supergravity forces is also established. We find the corresponding solutions of the infinite-N M(atrix) model. The supersymmetric D2/anti-D2 system is a special case of the general supertube, and we show that there are no open-string tachyons in this system via a computation of the open-string one-loop vacuum energy.Comment: 1+23 pages, 2 figures, LaTeX. V2, 1+28 pages: Further generalization to non-planar cross-sections and addition of an entirely new section with the explicit supergravity solutions. V3, 1+30 pages: Bound on the angular momentum added, other minor changes in Section

Detection and equalization of set-partitioned offset-QAM OFDM in IMDD systems

We design the detection algorithm for orthogonal frequency division multiplexing (OFDM) based on set-partitioned offset quadrature amplitude modulation (SP-offset-QAM) in adaptively-loaded intensity modulation and direct detection (IMDD) systems. The algorithm mitigates signal-signal beating interference (SSBI), improves the equalization capability of conventional one-tap equalizers, and reduces the complexity and the required length of training sequence in the decoding of multi-dimensional SP-QAM signals. We experimentally demonstrate adaptively-loaded SP-offset-QAM OFDM over 50-km single-mode fiber to verify the proposed algorithm. It is shown that the modified equalization significantly improves the performance while the SSBI mitigation brings benefits after transmission. The proposed decoding scheme reduces the complexity comparable to that in conventional QAM. It is also shown that SP-offset-QAM OFDM outperforms SP-based conventional QAM and conventional offset-QAM OFDM both at back-to-back and after 50-km transmission, when the algorithm is applied to all schemes