Soliton transmission at 10 Gbit/s over 2022 km of standard fibre with dispersion compensation

We present experimental results of 10 Gbit/s, 20 ps soliton data transmission over standard fibre, dispersion compensated to 0.5 ps/nm/km. Acceptable Q values were measured to a distance of 2022 km.

Optical phase conjugation for dispersion and nonlinearity compensation in a 1600km, 42 Gb/s quasi-lossless system

We experimentally investigate a long-distance, high-bit-rate transmission system which combines optical-phase-conjugation with quasi-lossless amplification. Comparison with a conventional system configuration demonstrates the possibility of obtaining both dispersion compensation and improved nonlinear tolerance using proposed scheme.

Digital fiber nonlinearity compensation:toward 1-Tb/s transport

The world is connected by a core network of long-haul optical communication systems that link countries and continents, enabling long-distance phone calls, data-center communications, and the Internet. The demands on information rates have been constantly driven up by applications such as online gaming, high-definition video, and cloud computing. All over the world, end-user connection speeds are being increased by replacing conventional digital subscriber line (DSL) and asymmetric DSL (ADSL) with fiber to the home. Clearly, the capacity of the core network must also increase proportionally. © 1991-2012 IEEE.

Intra-channel nonlinearity compensation for PM-16QAM traffic co-propagating with 28Gbaud m-ary QAM neighbours

We quantify the benefits of intra-channel nonlinear compensation in meshed optical networks, in view of network configuration, fibre design aspect, and dispersion management. We report that for a WDM optical transport network employing flexible 28Gbaud PM-mQAM transponders with no in-line dispersion compensation, intrachannel nonlinear compensation, for PM-16QAM through traffic, offers significant improvements of up to 4dB in nonlinear tolerance (Q-factor) irrespective of the co-propagating modulation format, and that this benefit is further enhanced (1.5dB) by increasing local link dispersion. For dispersion managed links, we further report that advantages of intra-channel nonlinear compensation increase with in-line dispersion compensation ratio, with 1.5dB improvements after 95% in-line dispersion compensation, compared to uncompensated transmission. © 2012 Optical Society of America.

Study of EEPN mitigation using modified RF pilot and Viterbi-Viterbi based phase noise compensation

We propose - as a modification of the optical (RF) pilot scheme -a balanced phase modulation between two polarizations of the optical signal in order to generate correlated equalization enhanced phase noise (EEPN) contributions in the two polarizations. The method is applicable for n-level PSK system. The EEPN can be compensated, the carrier phase extracted and the nPSK signal regenerated by complex conjugation and multiplication in the receiver. The method is tested by system simulations in a single channel QPSK system at 56 Gb/s system rate. It is found that the conjugation and multiplication scheme in the Rx can mitigate the EEPN to within 1/2 orders of magnitude. Results are compared to using the Viterbi-Viterbi algorithm to mitigate the EEPN. The latter method improves the sensitivity more than two orders of magnitude. Important novel insight into the statistical properties of EEPN is identified and discussed in the paper. © 2013 Optical Society of America.

Nonlinearity compensation via spectral inversion and digital back-propagation:a practical approach

We report performance enhancements enabled by pre-dispersed spectral inversion equivalent to that of ideal back-propagation, with further x2 increase in reach from multi-channel compensation, with spectral inversion employed upto 400km (from mid-link) with <1dB penalties. © 2012 OSA.

Extra compensation for inventive employees:is our system equitable, unbiased and motivating?

There is a presumption that invention is good. It provides us with innovative goods, services and ways of doing things leading to greater employment, wealth and health. This article looks at the two recent UK cases regarding statutory extra compensation that may be awarded to employee inventors under the Patents Act 1977. Most universities worldwide and many companies have individual inventor reward schemes. Researchers now work in teams made up of both industry and academic researchers who are often based in different countries where different legal regimes apply. Is leaving the decision to award employees extra financial compensation up to individual companies unfair, unequal and de-motivating? Is having differing legislative systems in different European countries counter productive and a barrier to economic growth? There must be a balance between the inventor and the innovator. Do we have it right and if not what should it be? Legislation: Patents Act 1977 s.39 , s.40 , s.41 Cases: Kelly v GE Healthcare Ltd [2009] EWHC 181 (Pat); [2009] R.P.C. 12 (Ch D (Patents Ct)) Shanks v Unilever Plc [2010] EWCA Civ 1283; [2011] R.P.C. 12 (CA (Civ Div))

In situ aberration corrected-transmission electron microscopy of magnesium oxide nanocatalysts for biodiesels

Biofuels are promising renewable energy sources and can be derived from vegetable oil feedstocks. Although solid catalysts show great promise in plant oil triglyceride transesterification to biodiesel, the identification of active sites and operating surface nanostructures created during their processing is essential for the development of efficient heterogeneous catalysts. Systematic, direct observations of dynamic MgO nanocatalysts from a magnesium hydroxide-methoxide precursor were performed under controlled calcination conditions using novel in situ aberration corrected-transmission electron microscopy at the 0.1 nm level and quantified with catalytic reactivity and physico-chemical studies. Surface structural modifications and the evolution of extended atomic scale glide defects implicate coplanar anion vacancies in active sites in the transesterification of triglycerides to biodiesel. The linear correlation between surface defect density (and therefore polarisability) and activity affords a simple means to fine tune new, energy efficient nanocatalysts for biofuel synthesis. © 2009 Springer Science+Business Media, LLC.

Experimental comparison of fibre and grating-based dispersion compensation schemes for 40 channel 10Gb/s DWDM systems

We report an experimental comparison between broadband fibre Bragg gratings (FBGs) and conventional dispersion compensating fibre (DCF) for a 40 x 10Gb/s DWDM system over 525km. A performanceoptimised configuration using FBG compensators is presented.

Phase-conjugated pilots for fibre nonlinearity compensation in CO-OFDM transmission

We experimentally demonstrate a novel fibre nonlinearity compensation technique for CO-OFDM based on phase-conjugated pilots (PCPs), showing that, by varying the PCP overhead a performance improvement up to 4 dB can be achieved allowing highly flexible adaptation to link characteristics.

Channel estimation and compensation in chromatic dispersion limited optical fast OFDM systems

We experimentally investigate the channel estimation and compensation in a chromatic dispersion (CD) limited 20Gbit/s optical fast orthogonal frequency division multiplexing (F-OFDM) system with up to 840km transmission. It is shown that symmetric extension based guard interval (GI) is required to enable CD compensation using one-tap equalizers. As few as one optical F-OFDM symbol with four and six pilot tones per symbol can achieve near-optimal channel estimation and compensation performance for 600km and 840km respectively.

Phase noise influence in coherent optical DnPSK systems with DSP based dispersion compensation

We present a comparative study of the influence of dispersion induced phase noise for n-level PSK systems. From the analysis, we conclude that the phase noise influence for classical homodyne/heterodyne PSK systems is entirely determined by the modulation complexity (expressed in terms of constellation diagram) and the analogue demodulation format. On the other hand, the use of digital signal processing (DSP) in homodyne/intradyne systems renders a fiber length dependence originating from the generation of equalization enhanced phase noise. For future high capacity systems, high constellations must be used in order to lower the symbol rate to practically manageable speeds, and this fact puts severe requirements to the signal and local oscillator (LO) linewidths. Our results for the bit-error-rate (BER) floor caused by the phase noise influence in the case of QPSK, 16PSK and 64PSK systems outline tolerance limitations for the LO performance: 5 MHz linewidth (at 3-dB level) for 100 Gbit/s QPSK; 1 MHz for 400 Gbit/s QPSK; 0.1 MHz for 400 Gbit/s 16PSK and 1 Tbit/s 64PSK systems. This defines design constrains for the phase noise impact in distributed-feed-back (DFB) or distributed-Bragg-reflector (DBR) semiconductor lasers, that would allow moving the system capacity from 100 Gbit/s system capacity to 400 Gbit/s in 3 years (1 Tbit/s in 5 years). It is imperative at the same time to increase the analogue to digital conversion (ADC) speed such that the single quadrature symbol rate goes from today's 25 GS/s to 100 GS/s (using two samples per symbol). © 2014 by Walter de Gruyter Berlin/Boston.

Repeatability of ocular aberration measurements in patients with keratoconus

Purpose: To explore the repeatability of lower-order and higher-order ocular aberrations measured in patients with keratoconus. Methods: The IRX-3 (Imagine Eyes, Paris, France) aberrometer was used to record lower-order and higher-order aberrations in 31 eyes of 31 patients with keratoconus. Four monocular measurements were taken consecutively for each patient. The aberrometry data were analysed up to the 5th Zernike order for a 4-mm pupil diameter. The data were evaluated using repeated-measures anova and Friedman analyses. Repeatability was analysed using within-subject standard deviation (SW) and the repeatability limit (r) calculated as 1.96 ×√2×Sw. Results: Of the 11 aberration terms evaluated, the repeatability of Z (2,0) (mean= 1.36μm; SW=0.09μm; r=0.26μm); Z (2,±2) RMS (mean=1.05μm; SW= 0.09μm; r=0.24μm) and Z (4,0) aberrations (mean=0.34μm; SW=0.09 μm; r=0.24μm) showed the highest variability. In contrast, Z (3,±1) RMS aberrations (mean=0.85μm; SW=0.06μm; r=0.16μm) and Z (4,±2) RMS aberrations (mean=0.40μm; SW=0.07μm; r=0.18μm) showed comparatively better repeatability. Conclusions: The lower-order and higher-order aberrations measured in this group of keratoconic patients showed higher levels of variability compared to previous investigations of visually-normal subjects. These results may be of interest to eyecare practitioners involved in the design and fitting of aberration-controlling contact lenses for patients with keratoconus. © 2011 The College of Optometrists.

Mitigation of pattern sensitivity in full-field electronic dispersion compensation

We investigate the pattern-dependent decoding failures in full-field electronic dispersion compensation (EDC) by offline processing of experimental signals, and find that the performance of such an EDC receiver may be degraded by an isolated "1" bit surrounded by long strings of consecutive "0s". By reducing the probability of occurrence of this kind of isolated "1" and using a novel adaptive threshold decoding method, we greatly improve the compensation performance to achieve 10-Gb/s on-off keyed signal transmission over 496-km field-installed single-mode fiber without optical dispersion compensation.