Low-complexity low-PAR transmission for MIMO-DSL

This letter considers clip-limited transmission over multiple-input multiple-output digital subscriber lines (MIMO-DSL). We show that a recent low complexity, low peak-to-average-ratio (PAR) single-input modulation technique can be applied to the case of multiple cross-talking channels in a bonded-DSL system. Unfortunately however the direct initialization procedure is computationally infeasible. In this paper, we provide a novel low-complexity initialization procedure. Simulations confirm that the proposed approach has superior performance in clip-limited conditions, compared with both discrete matrix multitone and vectored discrete multitone.

ADSL transceivers applying DSM and their nonstationary noise robustness

Dynamic spectrum management (DSM) comprises a new set of techniques for multiuser power allocation and/or detection in digital subscriber line (DSL) networks. At the Alcatel Research and Innovation Labs, we have recently developed a DSM test bed, which allows the performance of DSM algorithms to be evaluated in practice. With this test bed, we have evaluated the performance of a DSM level-1 algorithm known as iterative water-filling in an ADSL scenario. This paper describes the results of, on the one hand, the performance gains achieved with iterative water-filling, and, on the other hand, the nonstationary noise robustness of DSM-enabled ADSL modems. It will be shown that DSM trades off nonstationary noise robustness for performance improvements. A new bit swap procedure is then introduced to increase the noise robustness when applying DSM.

Fibre-based devices for next generation photonics communication systems

The future broadband information network will undoubtedly integrate the mobility and flexibility of wireless access systems with the huge bandwidth capacity of photonics solutions to enable a communication system capable of handling the anticipated demand for interactive services. Towards wide coverage and low cost implementations of such broadband wireless photonics communication networks, various aspects of the enabling technologies are continuingly generating intense research interest. Among the core technologies, the optical generation and distribution of radio frequency signals over fibres, and the fibre optic signal processing of optical and radio frequency signals, have been the subjects for study in this thesis. Based on the intrinsic properties of single-mode optical fibres, and in conjunction with the concepts of optical fibre delay line filters and fibre Bragg gratings, a number of novel fibre-based devices, potentially suitable for applications in the future wireless photonics communication systems, have been realised. Special single-mode fibres, namely, the high birefringence (Hi-Bi) fibre and the Er/Yb doped fibre have been employed so as to exploit their merits to achieve practical and cost-effective all-fibre architectures. A number of fibre-based complex signal processors for optical and radio frequencies using novel Hi-Bi fibre delay line filter architectures have been illustrated. In particular, operations such as multichannel flattop bandpass filtering, simultaneous complementary outputs and bidirectional nonreciprocal wavelength interleaving, have been demonstrated. The proposed configurations featured greatly reduced environmental sensitivity typical of coherent fibre delay line filter schemes, reconfigurable transfer functions, negligible chromatic dispersions, and ease of implementation, not easily achievable based on other techniques. A number of unique fibre grating devices for signal filtering and fibre laser applications have been realised. The concept of the superimposed fibre Bragg gratings has been extended to non-uniform grating structures and into Hi-Bi fibres to achieve highly useful grating devices such as overwritten phase-shifted fibre grating structure and widely/narrowly spaced polarization-discriminating filters that are not limited by the intrinsic fibre properties. In terms of the-fibre-based optical millimetre wave transmitters, unique approaches based on fibre laser configurations have been proposed and demonstrated. The ability of the dual-mode distributed feedback (DFB) fibre lasers to generate high spectral purity, narrow linewidth heterodyne signals without complex feedback mechanisms has been illustrated. A novel co-located dual DFB fibre laser configuration, based on the proposed superimposed phase-shifted fibre grating structure, has been further realised with highly desired operation characteristics without the need for costly high frequency synthesizers and complex feedback controls. Lastly, a novel cavity mode condition monitoring and optimisation scheme for short length, linear-cavity fibre lasers has been proposed and achieved. Based on the concept and simplicity of the superimposed fibre laser cavities structure, in conjunction with feedback controls, enhanced output performances from the fibre lasers have been achieved. The importance of such cavity mode assessment and feedback control for optimised fibre laser output performance has been illustrated.

Exploitation of fibre characteristics in temperature sensing and radio-over-fibre applications

The development of sensing devices is one of the instrumentation fields that has grown rapidly in the last decade. Corresponding to the swift advance in the development of microelectronic sensors, optical fibre sensors are widely investigated because of their advantageous properties over the electronics sensors such as their wavelength multiplexing capability and high sensitivity to temperature, pressure, strain, vibration and acoustic emission. Moreover, optical fibre sensors are more attractive than the electronics sensors as they can perform distributed sensing, in terms of covering a reasonably large area using a single piece of fibre. Apart from being a responsive element in the sensing field, optical fibre possesses good assets in generating, distributing, processing and transmitting signals in the future broadband information network. These assets include wide bandwidth, high capacity and low loss that grant mobility and flexibility for wireless access systems. Among these core technologies, the fibre optic signal processing and transmission of optical and radio frequency signals have been the subjects of study in this thesis. Based on the intrinsic properties of single-mode optical fibre, this thesis aims to exploit the fibre characteristics such as thermal sensitivity, birefringence, dispersion and nonlinearity, in the applications of temperature sensing and radio-over-fibre systems. By exploiting the fibre thermal sensitivity, a fully distributed temperature sensing system consisting of an apodised chirped fibre Bragg grating has been implemented. The proposed system has proven to be efficient in characterising grating and providing the information of temperature variation, location and width of the heat source applied in the area under test.To exploit the fibre birefringence, a fibre delay line filter using a single high-birefringence optical fibre structure has been presented. The proposed filter can be reconfigured and programmed by adjusting the input azimuth of launched light, as well as the strength and direction of the applied coupling, to meet the requirements of signal processing for different purposes in microwave photonic and optical filtering applications. To exploit the fibre dispersion and nonlinearity, experimental investigations have been carried out to study their joint effect in high power double-sideband and single-sideband modulated links with the presence of fibre loss. The experimental results have been theoretically verified based on the in-house implementation of the split-step Fourier method applied to the generalised nonlinear Schrödinger equation. Further simulation study on the inter-modulation distortion in two-tone signal transmission has also been presented so as to show the effect of nonlinearity of one channel on the other. In addition to the experimental work, numerical simulations have also been carried out in all the proposed systems, to ensure that all the aspects concerned are comprehensively investigated.

A novel sensor interrogation technique using chirped fiber grating based sagnac loop

We demonstrate a novel and simple sensor interrogation scheme for fiber Bragg grating (FBG) based sensing systems. In this scheme, a chirped FBG based Sagnac loop is used as a wavelength-dependent receiver, and a stable and linear readout response is realised. It is a signijkant advantage of this scheme that the sensitivity and the measurement wavelength range can be easily adjhsted by controlling the chirp of the FBG or using an optical delay line in the Sagnac loop.

A novel all-fiber bipolar transversal filter with complementary outputs

A novel all-fiber bipolar delay line filter is realized in a single-line cascaded high birefringence fiber structure. Optically coherent operation is achieved with suppression of interference noise. Complementary filter outputs give simultaneous lowpass and highpass responses.

A novel sensor interrogation technique using chirped fiber grating based Sagnac loop

We demonstrate a novel and simple sensor interrogation scheme for fiber Bragg grating (FBG) based sensing systems. In this scheme, a chirped FBG based Sagnac loop is used as a wavelength-dependent receiver, and a stable and linear readout response is realised. It is a signijkant advantage of this scheme that the sensitivity and the measurement wavelength range can be easily adjhsted by controlling the chirp of the FBG or using an optical delay line in the Sagnac loop.

A novel all fiber microwave transversal filter with complementary outputs

A novel all-fiber bipolar delay line filter is realized in a single-line cascaded high birefringence fiber structure. Optically coherent operation is achieved with suppression of interference noise. Complementary filter outputs give simultaneous lowpass and highpass responses.

Advanced techniques for the improvement of optical transmission systems

This thesis presents the experimental investigation into two novel techniques which can be incorporated into current optical systems. These techniques have the capability to improve the performance of transmission and the recovery of the transmitted signal at the receiver. The experimental objectives are described and the results for each technique are presented in two sections: The first experimental section is on work related to Ultra-long Raman Fibre lasers (ULRFLs). The fibre lasers have become an important research topic in recent years due to the significant improvement they give over lumped Raman amplification and their potential use in the development of system with large bandwidths and very low losses. The experiments involved the use of ASK and DPSK modulation types over a distance of 240km and DPSK over a distance of 320km. These results are compared to the current state of-the-art and against other types of ultra-long transmission amplification techniques. The second technique investigated involves asymmetrical, or offset, filtering. This technique is important because it deals with the strong filtering regimes that are a part of optical systems and networks in modern high-speed communications. It allows the improvement of the received signal by offsetting the central frequency of a filter after the output of a Delay Line Interferometer (DLI), which induces significant improvement in BER and/or Qvalues at the receiver and therefore an increase in signal quality. The experimental results are then concluded against the objectives of the experimental work and potential future work discussed.

Practical and prospective slow light Surface Nanoscale Axial Photonics (SNAP) devices

Miniature slow light Surface Nanoscale Axial Photonics (SNAP) devices are reviewed. The fabrication precision of these devices is two orders of magnitude higher and the transmission losses are two orders of magnitude smaller than for any of the previously reported technologies for fabrication of miniature photonic circuits. In the first part of the report, a SNAP bottle resonator with a few nm high radius variation is demonstrated as the record small, slow light, and low loss 2.6 ns dispersionless delay line of 100 ps pulses. Next, a record small SNAP bottle resonator exhibiting the 20 ns/nm dispersion compensation of 100 ps pulses is demonstrated. In the second part of the report, the prospects of the SNAP technology in applications to telecommunications, optical signal processing, quantum computing, and microfluidics are discussed. © 2014 IEEE.

Tunable photonic elements at the surface of an optical fiber with piezoelectric core

Tunable photonic elements at the surface of an optical fiber with piezoelectric core are proposed and analyzed theoretically. These elements are based on whispering gallery modes whose propagation along the fiber is fully controlled by nanoscale variation of the effective fiber radius, which can be tuned by means of a piezoelectric actuator embedded into the core. The developed theory allows one to express the introduced effective radius variation through the shape of the actuator and the voltage applied to it. In particular, the designs of a miniature tunable optical delay line and a miniature tunable dispersion compensator are presented. The potential application of the suggested model to the design of a miniature optical buffer is also discussed.

Design, construction, and applications of a high-resolution terahertz time-domain spectrometer

This thesis reports on the design, construction, and initial applications of a high-resolution terahertz time-domain ASOPS spectrometer. The instrument employs asynchronous optical sampling (ASOPS) between two Ti:sapphire ultrafast lasers operating at a repetition rate of approximately 80 MHz, and we thus demonstrate a THz frequency resolution approaching the limit of that repetition rate. This is an order of magnitude improvement in resolution over typical THz time-domain spectrometers. The improved resolution is important for our primary effort of collecting THz spectra for far-infrared astronomy. We report on various spectroscopic applications including the THz rotational spectrum of water, where we achieve a mean frequency error, relative to established line centers, of 27.0 MHz. We also demonstrate application of the THz system to the long-duration observation of a coherent magnon mode in a anti-ferromagnetic yttrium iron oxide (YFeO3) crystal. Furthermore, we apply the all-optical virtual delay line of ASOPS to a transient thermoreflectance experiment for quickly measuring the thermal conductivity of semiconductors.

La situación de la venta de contenidos on line en España: un estudio del lector de prensa digital

Actualmente es una realidad la dificultad del cobro por servicios on line. Sobre todo si estos servicios son de carácter generalista y se reproducen en muchos sitios web. Las actuales iniciativas de algunos periódicos para cobrar no tienen todavía el suficiente valor añadido para que los usuarios paguen. Muchas veces el tráfico que pierden, y por lo tanto los ingresos de publicidad on line que dejan de ingresar, representan una mayor cantidad económica que el dinero que les suponen las nuevas suscripciones. En el presente trabajo se pretende estudiar el comportamiento de los lectores de diarios on line, identificando cuales son los principales elementos que este tipo de lectores valoran para posteriormente realizar una buena estrategia de contenidos de pago.

Medical image registration based on random line sampling

One of the key aspects in 3D-image registration is the computation of the joint intensity histogram. We propose a new approach to compute this histogram using uniformly distributed random lines to sample stochastically the overlapping volume between two 3D-images. The intensity values are captured from the lines at evenly spaced positions, taking an initial random offset different for each line. This method provides us with an accurate, robust and fast mutual information-based registration. The interpolation effects are drastically reduced, due to the stochastic nature of the line generation, and the alignment process is also accelerated. The results obtained show a better performance of the introduced method than the classic computation of the joint histogram

An on-line algorithm of uncertain time delay estimation in a continuous system

In this paper, we present an on-line estimation algorithm for an uncertain time delay in a continuous system based on the observational input-output data, subject to observational noise. The first order Pade approximation is used to approximate the time delay. At each time step, the algorithm combines the well known Kalman filter algorithm and the recursive instrumental variable least squares (RIVLS) algorithm in cascade form. The instrumental variable least squares algorithm is used in order to achieve the consistency of the delay parameter estimate, since an error-in-the-variable model is involved. An illustrative example is utilized to demonstrate the efficacy of the proposed approach.