Dispersion measurements of fiber-optic components and applications of a novel tunable filter for optical communications

Optical communications has experienced a rapid development during the last decade. More bandwidth can be acquired by decreasing the spacing of the optical channels or by increasing the data rate. Characterization of the optical components and active monitoring of the network calls for accurate measurement methods. The objective of this thesis is to investigate and develop measurement methods and instruments for measuring important parameters of the components used in optical communications. Chromatic dispersion of optical fibers and frequency chirp of the laser transmitters set limits for the data rate and transmission distance. Measurements of dispersion have traditionally been performed using a phase-shift method. When high modulation frequencies are applied to achieve high resolution an error could be introduced. In this thesis, the measurement accuracy of this method is analyzed in detail and a novel method for estimating the accuracy and correcting the measurement result is developed. A Fabry-Perot interferometer finds numerous applications in many fields of optics. In this thesis, tunable Fabry-Perot etalon filters made of silicon were developed and several applications for these devices are demonstrated. A new device for measurements of time-resolved frequency chirp of directly modulated laser diodes in real time is developed. Interaction between the dispersion and frequency chirp limits the use of directly modulated lasers in long-haul optical links. Another application is monitoring of the wavelength of optical transmitters. The wavelength of the laser diode may shift due to aging and active monitoring and controlling of the wavelength is required. In addition, the filter improves the performance of the directly modulated transmitter by temporal reshaping of the pulses. The filter is also applied in reducing the frequency chirp of gain-switched pulses generated with a diode laser. These pulses can then be made transform limited and can for example be used in generation of optical solitons. Finally, the etalon is employed in realization of a compact wavelength reference for calibration of the wavelength scale of the optical spectrum analyzers and wavemeters. The transmission spectrum of the etalon consists of equidistant fringes. Each of these fringes can be applied as an accurate reference over a large wavelength range once the temperature of the filter is stabilized. This reference was developed to be automatic and it has an adequate accuracy for performing calibrations of field instruments.reviewe

GPU in Physics Computation: Case Geant4 Navigation

General purpose computing on graphic processing units (GPU) is a potential method of speeding up scientific computation with low cost and high energy efficiency. We experimented with the particle physics simulation toolkit Geant4 used at CERN to benchmark its geometry navigation functionality on a GPU. The goal was to find out whether Geant4 physics simulations could benefit from GPU acceleration and how difficult it is to modify Geant4 code to run in a GPU. We ported selected parts of Geant4 code to C99 & CUDA and implemented a simple gamma physics simulation utilizing this code to measure efficiency. The performance of the program was tested by running it on two different platforms: NVIDIA GeForce 470 GTX GPU and a 12-core AMD CPU system. Our conclusion was that GPUs can be a competitive alternate for multi-core computers but porting existing software in an efficient way is challenging

DC –Furnace control philosophy in ferroalloys applications

In this Master thesis is investigated the development of control system for ferroalloys applications. In the DC EAF technology is about to having a break through due to treason that more of the customers are ending up to invest in DC furnace instead of traditional AC furnaces. Also the continuously increasing environmental emission regulations are favoring the DC furnaces in addition to the fact that at mostly the smelters are located in very remote areas where electrical networks are often unstable. The work is divided into two parts. In the literature survey is firstly considered the history and comparing the difference of EAF furnaces which has been divided to AC and DC furnaces. In the chapter also the most common control practices and the function of DC furnace control philosophy is studied which then has work as the basis for developing the Pori ORC DC-furnace pilot project. Global markets for the electric arc furnaces are very small and few major companies has been developing DC furnaces continuously and therefore also lot of experience has been gained from these applications. In the second part of the thesis functional description and the equipments of Pori ORC are taken under the loop. At the end, final conclusions of the test trial are presented only from logic and control point of view and all the mechanical and metallurgical results are excluded

Energy efficiency of dynamic management of virtual cluster with heterogeneous hardware

Cloud computing is an essential part of today's computing world. Continuously increasing amount of computation with varying resource requirements is placed in large data centers. The variation among computing tasks, both in their resource requirements and time of processing, makes it possible to optimize the usage of physical hardware by applying cloud technologies. In this work, we develop a prototype system for load-based management of virtual machines in an OpenStack computing cluster. Our prototype is based on an idea of 'packing' idle virtual machines into special park servers optimized for this purpose. We evaluate the method by running real high-energy physics analysis software in an OpenStack test cluster and by simulating the same principle using the Cloudsim simulator software. The results show a clear improvement, 9-48 %, in the total energy efficiency when using our method together with resource overbooking and heterogeneous hardware.Peer reviewe

Guided-mode resonance gratings for enhanced mid-infrared absorption in quantum dot intermediate-band solar cells

Achieving strong absorption of low-energy photons is one of the key issues to demonstrate quantum dot solar cells working in the intermediate band regime at practical concentration factors and operating temperatures. Guided-mode resonance effects may enable large enhancement of quantum dot intraband optical transitions. We propose quantum dot thin-film cells designed to have significant field waveguiding in the quantum dot stack region and patterned at the rear-side with a sub-wavelength diffraction grating. Remarkable increase of the optical path length at mid-infrared wavelengths is shown owing to guided-mode resonances. Design guidelines are presented for energy and strength of the second-photon absorption for III-V quantum dots, such as InAs/GaAs and GaSb/GaAs, whose intraband and intersubband transitions roughly extends over the 2 − 8 µm range. The proposed design can also be applied to quantum dot infrared detectors. Angle-selectivity is discussed in view of applications in concentrator photovoltaic systems and infrared imaging systems

The Effect of Networking Performance on High Energy Physics Computing

High Energy Physics (HEP) data analysis consists of simulating and analysing events in particle physics. In order to understand physics phenomena, one must collect and go through a very large quantity of data generated by particle accelerators and software simulations. This data analysis can be done using the cloud computing paradigm in distributed computing environment where data and computation can be located in different, geographically distant, data centres. This adds complexity and overhead to networking. In this paper, we study how the networking solution and its performance affects the efficiency and energy consumption of HEP computing. Our results indicate that higher latency both prolongs the processing time and increases the energy consumption.Peer reviewe

Nanoimprint Lithography - Next Generation Nanopatterning Methods for Nanophotonics Fabrication

The application of different electrochemical techniques to surfactant systems, namely polarography and cyclic voltammetry, differential capacitance, chronocoulometry and electrochemical impedance spectroscopy, is reviewed

Light case study : Improving dairy production in Senegal

Ref. Ares(2016)6357987 - 10/11/201

Structured metal/polymer back reflectors for III-V solar cells

We report on fabrication of microstructured metal/polymer back reflectors for light trapping in III-V solar cells. The asymmetric triangular grating provided the highest diffraction of the light when compared to half sphere and cylinder reflectors