Thesis (M.S.)--Montana State University--Bozeman, 2006. / Typescript. Chairperson, Graduate Committee: James P. Becker. Includes bibliographical references (leaves 84-87).

Thesis (M.S.E.E.)--University of Puerto Rico, Mayagüez Campus, 2005. / Tables. Printout. Includes bibliographical references (leaves 135-138).

Fiber optical parametric amplifiers (OPAs) are based on a highly-efficient four-wave mixing process. Their capability to give very high gain and large bandwidths have made them an attractive candidate for providing higher bandwidths for future telecommunication systems, such as wavelength-division multiplexed (WDM) photonics networks. In dynamic photonic networks a where number of channels are dropped and/or added all the time, the OPA gain for the other channels is affected. In this thesis we employed a well-known gain control technique, all-optical gain clamping (AOGC), and reduced the gain variation of fiber OPAs below 0.5 dB, under varying input conditions. We also showed an improvement in power penalties o at the bit-error rate of 10-8, from 2.5 dB to 0.5 dB for on/off keying modulation. We also investigated fiber optical parametric oscillators (OPOs). Using fiber OPAs as gain medium we realized two different continuous-wave (CW) OPOs, centred at 1561 nm and 1593 nm. One gave us watt-level output power from 1600 nm to 1670 nm, with overall tuning range of 211 nm. The output linewidth of signal and idler was measured to be 0.08 nm and 0.15 nm respectively. The OPO centred at 1593 nm gave us a record tuning range of 254 nm, and with 3 dB output coupling fraction, it gave us large output powers (20-27 dBm) from 1610 nm to 1720 nm. Using a large seed generated by a watt-level fiber OPO in the U-band, and using 3 W of CW pump source in the C-band for Raman amplification, we generated 3 W of CW output power. This gave us nearly 100% conversion efficiency. Launching a high-power CW pump with narrow linewidth into a fiber makes stimulated Brillouin scattering (SBS) a major problem. We investigated an SBS suppressor, based on a common technique of phase dithering of the pump to suppress the SBS. We compared a multitone modulation technique to modulation with a pseudo-random bit sequence (PRBS), and we showed that it can increase the SBS threshold by 4.18 dB, and is less expensive to implement.

M.Ing. / This thesis is about the gain equalization of erbium doped fibre amplifiers (EDFA), which is a key technology for enabling wavelength-division multiplexed (WDM) optical communication systems. In order to flatten dynamically the EDFA gain spectrum, a tuneable long-period grating filter was demonstrated. Long-period gratings were fabricated by using a KrF excimer laser combined with the metal amplitude mask technique. The transmission spectrum characteristic of the long- period grating was simulated theoretically by the coupled-mode theory. The coupling between the core and cladding modes of the long-period grating was investigated both experimentally and theoretically. The EDFA was constructed by using the forward pumping configuration consisting of pump laser source, WDM couplers, an optical isolator, and the erbium-doped fibre. The EDFA was characterized theoretically and experimentally for WDM applications. The tuneable long-period grating filter design is based on the tuneable coupler that uses the Mach-Zehnder interferometer configuration. The tuneable filter was demonstrated by equalizing the EDFA gain spectrum and the amplified spontaneous emission (ASE) source. The main advantage of this filter compared to other optical filters is its tuneability of the attenuation over a wide range of pump power.

No description available.

M.Ing. / Long distance optical communication systems experience a large degree of attenuation due to fibre losses, necessitating signal amplification. Erbium Doped Fibre Amplifiers (EDFAs) have found widespread use as all-fibre optical amplifiers, but exhibit unequal amplification of different wavelengths. Since the gain spectrum is signal-power and pump-power dependent, each EDFA spectrum may differ considerably, and a tuneable gain equalizer is required. A tuneable long-period grating (LPG) can be implemented as a gain equalizer for EDFAs. This dissertation deals with the design of an integrated optic version of the tuneable equalizing filter. The various components of which the device comprises, including optical couplers, Mach-Zehnder interferometers and an LPG, are investigated. The integrated optics designs of these components are then done using the BeamPROP software package. The use and optical properties of germania-doped silica as photosensitive waveguide material is studied. The production of the films for the gain equalizer, using electron-cyclotron resonance plasma-enhanced chemical vapour deposition, is discussed. Characterization of these films was carried out using spectroscopic ellipsometry and infrared spectroscopy. The optical constants, thickness, germania content and hydroxyl absorption was calculated using these measurements.

M.Ing. (Electrical And Electronic Engineering) / Please refer to full text to view abstract

This thesis describes the design of two particular types of conventional distributed amplifiers and treats a proposed split-band amplifier. The method used for the conventional designs is an iterative synthesis process developed at Stanford University in 1952. The objective was to investigate the possibility of producing distributed amplifiers of superior performance. Only amplifiers with a flat amplitude response were considered since the calculating equipment available was inadequate for the computations involved in producing amplifiers with other types of response characteristics. Three designs of one form of conventional distributed amplifier were carried out. These were amplifiers with ladder networks for delay lines and with both delay lines identical except for a possible difference in impedance level. None of the three amplifiers had theoretical characteristics which justified an attempt to construct them. The other conventional amplifier was one employing ladder-like networks for the delay lines with each of the lines symmetrical about the mid-point of its length and with both lines identical except for a possible difference in impedance level. An attempt to design one of these amplifiers produced new information beyond that reported in the original work at Stanford University. Furthermore, when using the iterative technique to design this amplifier, there seemed to be reasonable doubt as to whether or not the process was always convergent. No definite opinion on the matter was formulated since it would have required that the calculations be continued through more cycles of iteration than could reasonably be carried out with the computing equipment at hand. Finally, a proposed split-band amplifier was investigated and its theoretical gain-bandwidth characteristics were compared with those of a conventional distributed amplifier. It showed a slight advantage, but this was far outweighed by certain serious inherent disadvantages and the project was discontinued. The investigation has shown that it is impractical to carry out the calculations involved in the iterative prodecure when using a hand calculator. Also, some doubt as to the general convergence of the iterative synthesis process has been raised. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

Previous research has shown the benefit obtained by hard of hearing people when using inductive means (T-switch) to couple their hearing aids to telephone receivers. Benefit provided by receiver amplification in the telephone handset has also been shown. Informal surveys of hard of hearing people indicate that many of them use telephones having a dual capability: magnetic coupling and receiver amplification. The objective of this investigation was to study user performance with this dual capability. In particular, the effect of receiver amplification on the speech perception ability (as measured by R-SPIN test items) of 10 hard of hearing subjects using inductive means to couple their hearing aid to a telephone receiver was examined under both good and poor telephone line conditions. The influence of the predictability of the speech material presented was also investigated by noting any difference between the subjects' performance on high predictability items and performance on low predictability items (of the R-SPIN test). Results showed that the use of receiver amplification in conjunction with inductive coupling significantly improved the subjects' speech perception scores. Not surprisingly, good telephone line conditions also significantly improved the subjects' scores. Improvement due to receiver amplification was noted, irrespective of line conditions. Similarly, improvement due to good line conditions was observed, irrespective of whether amplification was used or not. Both receiver amplification and good line conditions had significant and positive effects on both low predictability and high predictability scores. We conclude that with speech either in or out of context, receiver amplification will be of benefit to those who use inductive coupling. Clinical implications and recommendations are discussed. / Medicine, Faculty of / Audiology and Speech Sciences, School of / Graduate

Résumé / Abstract