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

Organisations as complex adaptive systems : implications for the design of information systems

Today a paradigm shift in the field of organisation and management theories is no longer disputed and the need to switch from the Command-and-Control to the Leaming Organisation Paradigm (LOP) in the area of organisational theory is well understood. However, it is less well appreciated that learning organisations cannot operate effectively if supported by centralised databases and tailor-made application programs. LOP emphasises adaptability, flexibility, participation and learning. It is important to understand that the changes in organisational and management strategies will not on their own be able to produce the desired effects unless they are supported by appropriate changes in organisational culture, and by effective information systems. This research demonstrates that conventional information system strategies and development methods are no longer adequate. Information system strategies must respond to these needs of the LOP and incorporate new information systems that are capable of evolving, adapting and responding to the constantly changing business environment. The desired adaptability, flexibility and agility in information systems for LOP can be achieved by exploiting the technologies of the Internet, World Wide Web, intelligent agents and intranets. This research establishes that there is a need for synergy between organisational structures and organisational information systems. To obtain this desired synergy it is essential that new information systems be designed as an integral part of the learning organisational structure itself. Complexity theory provides a new set of metaphors and a host of concepts for the understanding of organisations as complex adaptive systems. This research introduces the principles of Complex Adaptive Systems and draws on their significance for designing the information systems needed to support the new generation of learning organisations. The search for new models of information system strategies for today's dynamic world of business points to the 'swarm models' observed in Nature

Research Reports: 1989 NASA/ASEE Summer Faculty Fellowship Program

For the twenty-fifth consecutive year, a NASA/ASEE Summer Faculty Fellowship Program was conducted at the Marshall Space Flight Center (MSFC). The basic objectives of the programs are: (1) to further the professional knowledge of qualified engineering and science faculty members; (2) to stimulate an exchange of ideas between participants and NASA; (3) to enrich and refresh the research and teaching activities of the participants' institutions; and (4) to contribute to the research objectives of the NASA Centers. The Faculty Fellows spent ten weeks at MSFC engaged in a research project compatible with their interests and background and worked in collaboration with a NASA/MSFC colleague