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))

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.

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.

Scaling the Advantages of Intra-channel Nonlinearity Compensation in Future Flexible Optical Networks

We report that, contrary to common perception, intra-channel nonlinearity compensation offers significant improvements of up to 4dB, in nonlinear tolerance (Q-factor), in a flexible traffic scenario, and further improvements with increasing local link dispersion, for an optical transport network employing flexible 28Gbaud PM-mQAM transponders.

Fibre impairment compensation using artificial neural network equalizer for high-capacity coherent optical OFDM signals

We propose an artificial neural network (ANN) equalizer for transmission performance enhancement of coherent optical OFDM (C-OOFDM) signals. The ANN equalizer showed more efficiency in combating both chromatic dispersion (CD) and single-mode fibre (SMF)-induced non-linearities compared to the least mean square (LMS). The equalizer can offer a 1.5 dB improvement in optical signal-to-noise ratio (OSNR) compared to LMS algorithm for 40 Gbit/s C-OOFDM signals when considering only CD. It is also revealed that ANN can double the transmission distance up to 320 km of SMF compared to the case of LMS, providing a nonlinearity tolerance improvement of ∼0.7 dB OSNR.

Demonstration of phase-conjugated subcarrier coding for fiber nonlinearity compensation in CO-OFDM transmission

In this paper, we demonstrate through computer simulation and experiment a novel subcarrier coding scheme combined with pre-electrical dispersion compensation (pre-EDC) for fiber nonlinearity mitigation in coherent optical orthogonal frequency division multiplexing (CO-OFDM) systems. As the frequency spacing in CO-OFDM systems is usually small (tens of MHz), neighbouring subcarriers tend to experience correlated nonlinear distortions after propagation over a fiber link. As a consequence, nonlinearity mitigation can be achieved by encoding and processing neighbouring OFDM subcarriers simultaneously. Herein, we propose to adopt the concept of dual phase conjugated twin wave for CO-OFDM transmission. Simulation and experimental results show that this simple technique combined with 50% pre-EDC can effectively offer up to 1.5 and 0.8 dB performance gains in CO-OFDM systems with BPSK and QPSK modulation formats, respectively.

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

In this paper, we demonstrate a novel fiber nonlinearity compensation technique for coherent optical orthogonal frequency-division multiplexing (CO-OFDM) systems based on the transmission of phase-conjugated pilots (PCPs). In this scheme, a portion of OFDM subcarriers (up to 50%) is transmitted with its phase conjugates, which is used at the receiver to estimate the nonlinear distortions in the respective subcarriers and other subcarriers, which are not accompanied by PCPs. Simulation and experimental results show that by varying the PCP overhead, a performance improvement up to 4 dB can be achieved. In addition, the proposed technique can be effectively applied in both single polarization and polarization-division multiplexed systems, in both single channel and wavelength-division multiplexing systems, thus, offering highest flexibility in implementations.

Measurement and compensation of pivot point positional error on five-axis machines

Measuring and compensating the pivot points of five-axis machine tools is always challenging and very time consuming. This paper presents a newly developed approach for automatic measurement and compensation of pivot point positional errors on five-axis machine tools. Machine rotary axis errors are measured using a circular test. This method has been tested on five-axis machine tools with swivel table configuration. Results show that up to 99% of the positional errors of the rotary axis can be compensated by using this approach.

Real-time error compensation of a three-axis machine tool using a laser tracker

The concept of measurement-enabled production is based on integrating metrology systems into production processes and generated significant interest in industry, due to its potential to increase process capability and accuracy, which in turn reduces production times and eliminates defective parts. One of the most promising methods of integrating metrology into production is the usage of external metrology systems to compensate machine tool errors in real time. The development and experimental performance evaluation of a low-cost, prototype three-axis machine tool that is laser tracker assisted are described in this paper. Real-time corrections of the machine tool's absolute volumetric error have been achieved. As a result, significant increases in static repeatability and accuracy have been demonstrated, allowing the low-cost three-axis machine tool to reliably reach static positioning accuracies below 35 μm throughout its working volume without any prior calibration or error mapping. This is a significant technical development that demonstrated the feasibility of the proposed methods and can have wide-scale industrial applications by enabling low-cost and structural integrity machine tools that could be deployed flexibly as end-effectors of robotic automation, to achieve positional accuracies that were the preserve of large, high-precision machine tools.

Techniques for noise and nonlinear impairments compensation in CO-OFDM transmission

In this paper, we discuss recent advances in digital signal processing techniques for compensation of the laser phase noise and fiber nonlinearity impairments in coherent optical orthogonal frequency division multiplexing (CO-OFDM) transmission. For laser phase noise compensation, we focus on quasi-pilot-aided (QPA) and decision-directed-free blind (DDF-blind) phase noise compensation techniques. For fiber nonlinearity compensation, we discuss in details the principle and performance of the phase-conjugated pilots (PCP) scheme.

Optical-phase conjugation nonlinearity compensation in Flexi-Grid optical networks

Optical-phase conjugation nonlinearity compensation (OPC-NLC) in optical networks is evaluated using a built-in tool including self-channel and crosstalk channel interference effects. Though significant improvements are observed, a further refined launch power policy is required to fully take advantage of OPC-NLC capability.