B. Chance, J.N. Thurston, P.L. Richman. / "Reprinted from the Review of scientific instruments, v. 18, no. 9, 610-616, Sept., 1947." / Includes bibliographical references.

Thesis (Ph. D.)--Ohio State University, 2006. / Title from first page of PDF file. Includes bibliographical references (p. 95-99).

Thesis (M.S.)--Brigham Young University. Dept. of Electrical and Computer Engineering, 2006. / Includes bibliographical references (p. 53-54).

Thesis (Ph. D.)--University of Washington, 2006. / Vita. Includes bibliographical references (p. 97-101).

RESUME Parmi les divers processus permettant l'amplification optique indispensable aux systèmes de télécommunications par fibre, l'effet Raman, basé sur l'échange de puissance entre un signal et un laser de pompe de fréquence supérieure à travers un couplage avec les vibrations moléculaires de la silice, permet d'amplifier à n'importe quelle longueur d'onde avec une grande bande passante. Un des inconvénients majeurs de cette technique est la forte puissance optique nécessaire à sa réalisation qui génère l'apparition de nombreux effets non linéaires potentiellement dommageables pour la bonne transmission du signal. L'interaction des effets Kerr ou de la diffusion Brillouin avec les autres caractéristiques de la propagation dans les fibres peut entraîner une diminution des performances. Dans la première partie de cette thèse, nous décrivons un nouveau processus d'élargissement spectral induit par l'effet Kerr dans les amplificateurs Raman fibrés. Nous avons également mis à jour ce même processus dans les lasers Raman. L'application de ce phénomène à la suppression de la diffusion Brillouin est ensuite démontrée avec succès. La deuxième partie de ce travail démontre comment tirer avantage des effets non linéaires afin de générer des impulsions optiques de haute puissance dans un laser Raman fibré. Enfin, dans la troisième partie, nous proposons et démontrons l'application de deux nouvelles méthodes de caractérisation à la mesure de la distribution des effets Raman et Kerr le long des fibres optiques grâce à une technique de réflectométrie optique cohérente. SUMMARY Among the various processes that allow optical amplification that is required for fiber telecommunication systems, the Raman effect, based on the power exchange between a signal and a pump laser with higher frequency through a coupling with molecular vibrations of silica, enables to amplify at any wavelength with a large bandwidth. One of the major drawbacks of this technique is the high power required to realize it, generating the appearance of numerous nonlinear effects, potentially harmful for the quality transmission. The interplay between Kerr effects or Brillouin scattering and other propagation characteristics of optical fibers can lead to a decrease of the performances. In the first part of this thesis we describe a new broadening mechanism induced by the Kerr effect in Raman fiber amplifiers. This effect was also discovered in Raman fiber lasers. An application of this phenomenon as an efficient way to suppress Brillouin scattering is then successfully demonstrated. The second part of this work demonstrated how to take advantage of optical nonlinearities to generate high peak power pulses with a Raman fiber laser. Finally, in the third part, we propose and demonstrate the application of two new methods to measure the spatial distribution of Raman and Kerr effects along optical fibers thanks to a coherent optical reflectometry technique.

A compact low-frequency projector is of crucial importance especially in underwater acoustics due to the frequency dependence of the absorption. To improve the efficiency of an omnidirectional acoustic source at low frequencies, parametric amplification may be used by adding a thin layer of nonlinear medium around a spherical transducer. The parametric effect is based on the interaction of two acoustic waves propagating through a nonlinear medium to produce a difference frequency wave. If both primary frequencies are sufficiently close enough, the result is the creation of a low frequency wave. Investigation is required to find the optimal medium, that is to say, one with a large nonlinear coefficient and a low sound speed. Such a source has already been built using a medium composed of a gel and microsphere mixture. In this case, the nonlinear coefficient is highly pressure dependent reaching a maximum when the microspheres buckle. The need is to optimize the material layer to increase the range of hydrostatic pressures over which the projector is useful.

The objective of this work is to investigate the suitability of applying silicon-germanium (SiGe) heterojunction bipolar transistor (HBT) bipolar complementary metal oxide semiconductor (BiCMOS) technology to extreme environments and to design high-speed circuits in this technology to demonstrate their reliable operation under these conditions. This research focuses on exploring techniques for hardening SiGe HBT digital logic for single event upset (SEU) based on principles of radiation hardening by design (RHBD) as well as on the cryogenic characterization of SiGe HBTs and designing broadband amplifiers for operation at cryogenic temperatures. Representative circuits ranging from shift registers featuring multiple architectures to broadband analog circuits have been implemented in various generations of this technology to enable this effort.

This thesis presents a compact femtosecond laser amplifier design for optical preamplifiers and power amplifiers consist of theoretical perspective, simulations to analyze and optimize beam performance. The propagation through optical media is simulated for every optical component such as mirrors and nonlinear crystal separately and suggested realignment of these components required increasing amplifier performance. Finally Gaussian beam propagation and aberration compensation has been conducted.

Optical communications is expanding into new applications such as infrared wireless communications; therefore, designing high performance circuits has gained considerable importance. In this dissertation a wide dynamic-range variable-gain transimpedance amplifier (TIA) is introduced. It adopts a regulated cascode (RGC) amplifier and an operational transconductance amplifier (OTA) as the feed forward gain element to control gain and improve the overload of the optical receiver. A fully-differential variable-gain TIA in a 0.35µm CMOS technology is realized. It provides a bit error rate (BER) less than 10-12 for an input current from 6µA-3mA at 3.3V power supply. For the transimpedance gain variation, from 0.1kΩ to 3kΩ, -3dB bandwidth is higher than 1.7GHz for a 0.6pF photodiode capacitance. The power dissipations for the highest and the lowest gains are 8.2mW and 24.9mW respectively. A new technique for designing uniform multistage amplifiers (MA) for high frequency applications is introduced. The proposed method uses the multi-peak bandwidth enhancement technique while it employs identical, simple and inductorless stages. It has several advantages, such as tunability of bandwidth and decreased sensitivity of amplifier stages, to process variations. While all stages of the proposed MA topology are identical, the gain-bandwidth product can be extended several times. Two six-stage amplifiers in a TSMC 0.35µm CMOS process were designed using the proposed topology. Measurements show that the gain can be varied for the first one between 16dB and 44dB within the 0.7-3.2GHz bandwidth and for the second one between 13dB and 44dB within a 1.9-3.7GHz bandwidth with less than 5.2nV/√Hz noise. Although the second amplifier has a higher gain bandwidth product, it consumes more power and occupies a wider area. A technique for capacitance multiplication is utilized to design a tunable loop filter. Current and voltage mode techniques are combined to increase the multiplication factor (M). At a high input dynamic range, M is adjustable and the capacitance multiplier performs linearly at high frequencies. Drain-source voltages of paired transistors are equalized to improve matching in the current mirrors. Measurement of a prototype loop filter IC in a 0.5µm CMOS technology shows 50µA current consumption for M=50. Where 80pF capacitance is employed, the capacitance multiplier realizes an effective capacitance varying from 1.22nF up to 8.5nF.

Thesis (Ph. D.)--School of Electrical and Computer Engineering, Georgia Institute of Technology, 2004. Directed by J. Stevenson Kenney. / Vita. Includes bibliographical references (leaves 157-165).