Record performance of parametric amplifier constructed with highly nonlinear fibre

Record performance from a two-pump parametric amplifier constructed with highly nonlinear fibre is reported. Equalised continuous-wave parametric gain of 40 dB was achieved over 33.8 nm without any gain-flattening elements. Maximal difference between signal and idler powers was measured to be 1 dB within the equalised gain band.     

Determination of Achievable Information Rates (AIRs) of IM/DD Systems and AIR Loss Due to Chromatic Dispersion and Quantization

The achievable information rates (AIRs) of a nonreturn-to-zero optical transmission system operating at 10Gb/s are determined based on experimentally obtained conditional probability density functions for an amplified spontaneous emission noise-dominated system in the presence of chromatic dispersion (with and without optical dispersion compensation). Specifically, we concentrate on the AIR loss due to the accumulation of chromatic dispersion, as well as the practical constraint of the analog-to-digital conversion and quantization of log-likelihood ratios     

Impact of pump-phase modulation on dual-pump fiber-optic parametric amplifiers and wavelength converters

Modulation of pump phases required for suppressing stimulated-Brillouin scattering is shown to cause large power changes in both the amplified and wavelength-converted signals when dual-pump fiber-optic parametric amplifiers are used. The physical origin of power changes is related to pump-amplitude modulations caused by fiber dispersion. Analytical as well as numerical calculations show that the signal-to-noise ratio of the signal or idler may reduce to below 23 dB when pump phases change rapidly with a sharp rise time.     

A sensitive assay for measuring alpha-Gal epitope expression on cells by a monoclonal anti-Gal antibody

BACKGROUND: The distinction between solitary parathyroid adenoma and hyperplasia can sometimes be difficult during surgery for primary hyperparathyroidism (pHPT), especially in patients who have undergone previous thyroid or parathyroid surgery. The use of intraoperative parathyroid hormone (PTH) monitoring as a possible diagnostic tool was therefore investigated. METHODS: Intraoperative levels of PTH were measured in 119 patients during 121 operations (including 14 reoperations) for pHPT. The mean(s.d.) preoperative serum calcium level was 2.79(0.21) mmol/l. Blood samples were drawn before, and at 5 and 15 min after, excision of the first enlarged parathyroid gland. PTH was analysed electively in 61 patients and on-line by a modified assay for intact PTH in 48 patients. Both procedures were used in ten patients. RESULTS: The mean(s.d.) decline in PTH concentration in 101 patients with primary exploration due to solitary adenoma was 63(17) per cent after 5 min (n=84) and 83(10) per cent after 15 min. The patients with primary exploration because of multiglandular disease (n=6) were correctly predicted not to have parathyroid adenoma. CONCLUSION: Measurement of PTH levels during surgery for pHPT is a highly sensitive method for differentiating between single and multiple gland disease. The on-line monitoring of PTH is clinically useful in patients who have undergone previous neck surgery. Its role in pHPT surgery at primary exploration should be evaluated in prospective trials.     

High bandwidth underwater optical communication

We report error-free underwater optical transmission measurements at 1 Gbit/s (10(9) bits/s) over a 2 m path in a laboratory water pipe with up to 36 dB of extinction. The source at 532 nm was derived from a 1064 nm continuous-wave laser diode that was intensity modulated, amplified, and frequency doubled in periodically poled lithium niobate. Measurements were made over a range of extinction by the addition of a Mg(OH)(2) and Al(OH)(3) suspension to the water path, and we were not able to observe any evidence of temporal pulse broadening. Results of Monte Carlo simulations over ocean water paths of several tens of meters indicate that optical communication data rates >1 Gbit/s can be supported and are compatible with high-capacity data transfer applications that require no physical contact.     

Theoretical analysis of iterative signal reconstruction for impulsive noise mitigation in OFDM systems

In this paper a theoretical analysis of the iterative signal reconstruction algorithm for impulsive noise mitigation in orthogonal frequency‐division multiplexing (OFDM) systems is developed. The following main results are developed: first, analytical model for the total noise in the frequency domain, and second the model for the total noise probability density function (pdf) in the frequency domain, both defined for each step of the iterative reconstruction process. Finally, based on the pdf of the total noise, explicit expressions for BER in kth iteration are defined as well. The main intention of the paper is to present the approach to theoretical analysis of the iterative impulsive noise mitigation algorithm that has not yet been appeared in the literature, because the theoretical analysis of the noise pdf during iterations has been considered as too complex a problem. Analyses and analytical results presented in the paper are given for scenario with a fixed number of noise impulses per frame. However, this is not a handicap of the proposed approach, since all presented models can be used as building blocks for scenarios with other impulsive noise distributions including Bernoulli–Gaussian and Middleton's Class A. Copyright © 2009 John Wiley & Sons, Ltd.     

Optical Demultiplexing of 320 Gb/s to 8 40 Gb/s in Single Parametric Gate

In this paper, we report the experimental demonstration of 320 Gb/s demultiplexing to eight simultaneous always-on 40 Gb/s tributaries with near-zero latency. The single-channel, single-polarization 320 Gb/s optical-time-division-multiplexed signal was processed by a copy-and-sample-all architecture. 1-to-8 wavelength multicasting over more than 10 THz of bandwidth was achieved in a self-seeded two-pump parametric amplifier, and was followed by a single gate, multicolored sampling with equalized response over more than 20 THz. The single gate operation allows for truly scalable real-time processing while avoiding the complexity of parallel pipelines processing. Error-free performance was measured over all extracted 40 Gb/s tributaries with less than 4 dB power penalty compared to conventional single tributary gating.      

Pedestal-Free Pulse Source for High Data Rate Optical Time-Division Multiplexing Based on Fiber-Optical Parametric Processes

In this paper, an RF-driven pedestal-free cavity-less 40 GHz pulse source for generation of high-speed optical time-division multiplexing signal is presented. The pulse source is based on pulse compression by means of self-phase modulation in combination with subsequent filtering. Further compression and pedestal removal of the pulse was achieved in one-pump fiber-optic parametric amplifier seeded by a continuous-wave laser source. The obtained idler pulses were characterized by a full-width at half-maximum pulsewidth of 1.2 ps and an SNR of 36 dB. Generation of 320 Gb/s data stream with a Q-factor of 20 dB is successfully demonstrated using the proposed pulse source.     

Continuous-Wave Band Translation Between the Near-Infrared and Visible Spectral Ranges

Wavelength conversion based on degenerate four-wave mixing in a photonic crystal fiber with two zero-dispersion wavelengths is investigated both theoretically and experimentally. The proposed concept of universal band translation in a single-pass traveling-wave structure offers a wavelength band rather than a single-wavelength mapping between distant spectral ranges. Near-infrared signals are modulated using both harmonic and pseudorandom bit sequences and translated to the visible optical band. Multiple-channel translation, which produces wavelength-division-multiplexed idlers in the visible band, is demonstrated for the first time. The performance of the translation process is measured both spectrally and temporally for both single- and multiple-channel signals     

Rapid binding of a cationic active site inhibitor to wild type and mutant mouse acetylcholinesterase: Brownian dynamics simulation including diffusion in the active site gorge

It is known that anionic surface residues play a role in the long-range electrostatic attraction between acetylcholinesterase and cationic ligands. In our current investigation, we show that anionic residues also play an important role in the behavior of the ligand within the active site gorge of acetylcholinesterase. Negatively charged residues near the gorge opening not only attract positively charged ligands from solution to the enzyme, but can also restrict the motion of the ligand once it is inside of the gorge. We use Brownian dynamics techniques to calculate the rate constant kon, for wild type and mutant acetylcholinesterase with a positively charged ligand. These calculations are performed by allowing the ligand to diffuse within the active site gorge. This is an extension of previously reported work in which a ligand was allowed to diffuse only to the enzyme surface. By setting the reaction criteria for the ligand closer to the active site, better agreement with experimental data is obtained. Although a number of residues influence the movement of the ligand within the gorge, Asp74 is shown to play a particularly important role in this function. Asp74 traps the ligand within the gorge, and in this way helps to ensure a reaction.