With the rapid development of optical communications and the increasing amount of data exchanged, it has become utterly important to provide effective architectures to protect sensitive data. The use of chaotic optoelectronic devices has already demonstrated great potential in terms of additional computational security at the physical layer of the optical network. However, the determination of the security level and the lack of a multi-user framework are two hurdles which have prevented their deployment on a large scale. In this thesis, we propose to address these two issues. First, we investigate the security of a widely used chaotic generator, the external cavity semiconductor laser (ECSL). This is a time-delay system known for providing complex and high-dimensional chaos, but with a low level of security regarding the identification of its most critical parameter, the time delay. We perform a detailed analysis of the influence of the ECSL parameters to devise how higher levels of security can be achieved and provide a physical interpretation of their origin. Second, we devise new architectures to multiplex optical chaotic signals and realize multi-user communications at high bit rates. We propose two different approaches exploiting known chaotic optoelectronic devices. The first one uses mutually coupled ECSL and extends typical chaos-based encryption strategies, such as chaos-shift keying (CSK) and chaos modulation (CMo). The second one uses an electro-optical oscillator (EOO) with multiple delayed feedback loops and aims first at transposing coded-division multiple access (CDMA) and then at developing novel strategies of encryption and decryption, when the time-delays of each feedback loop are time- dependent.

The focus of this study is the optoelectronic integration of a micro-optical displacement detection architecture with a biomimetic MEMS microphone membrane based on the directional hearing mechanism of the parasitic fly Ormia Ochracea. The micromachined microphones feature optical interferometric displacement detection achieved using a commercially available Vertical Cavity Surface Emitting Laser (VCSEL) coupled with a custom designed silicon photodiode array. This design is shown to have significant advantages over conventional hearing aid microphones, which employ capacitive detection. A Multi-Chip Module (MCM) optoelectronic package is designed to integrate the biomimetic membrane with the optical displacement detection electronics in order to produce a fully integrated acoustic sensor. The modular package components, which are fabricated using high resolution stereolithography apparatus (SLA) equipment, provide accurate optical alignment of the optoelectronic components and allow complete device integration in a package with a total volume under 0.5cc. Characterization of the integrated microphones is described in detail, including measurements of sensitivity, noise floor and directivity. A displacement resolution of 3.5x10⁻¹³ m/√Hz was measured between 4kHz and 16kHz in an anechoic test chamber, corresponding to a dynamic range of 115dB for the optical detection architecture. The total noise SPL of the device is 35.9dBA. Unlike capacitive microphones with similar noise levels, the device developed in this work exhibits first order dipole directivity patterns between 250Hz-1kHz, with an ideal Directivity Index of 4.8dB @ 1kHz and directional attenuation exceeding 25dB. With these results the optoelectronic package presented in this work demonstrates the viability of the integrated optical biomimetic microphones in compact, low power applications, specifically directional hearing aids.

This thesis describes the development of III-Nitride materials for light emitting applications. The goals of this research were to create and optimize a green light emitting diode (LED) and laser diode (LD). Metalorganic chemical vapor deposition (MOCVD) was the technique used to grow the epitaxial structures for these devices. The active regions of III-Nitride based LEDs are composed of InₓGa₁₋ₓN, the bandgap of which can be tuned to attain the desired wavelength depending on the percent composition of Indium. An issue with this design is that the optimal growth temperature of InGaN is lower than that of GaN, making the growth temperature of the top p-layers critical to the device performance. Thus, an InGaN:Mg layer was used as the hole injection and p-contact layers for a green led, which can be grown at a lower temperature than GaN:Mg in order to maintain the integrity of the active region. However, the use of InGaN comes with its own set of drawbacks, specifically the formation of V-defects. Several methods were investigated to suppress these defects such as graded p-layers, short period supper lattices, and native GaN substrates. As a result, LEDs emitting at ~532 nm were realized. The epitaxial structure for a III-Nitride LD is more complicated than that of an LED, and so it faces many of the same technical challenges and then some. Strain engineering and defect reduction were the primary focuses of optimization in this study. Superlattice based cladding layers, native GaN substrates, InGaN waveguides, and doping optimization were all utilized to lower the probability of defect formation. This thesis reports on the realization of a 454 nm LD, with higher wavelength devices to follow the same developmental path.

<p>It is estimated that, between the year 2000 and 2003, thenumber of online Internet users will grow from 250 millions to500 millions. This growth results in rapidly increasing demandfor fibre-optic communication bandwidth, occurring at alllevels: from access and local area networks (LANs) tometro-area networks (MANs). A now established solution for manyapplications such as interconnects and Gigabit Ethernet is thevertical cavity surface emitting laser (VCSEL). The advantagesof VCSELs are numerous: low fabrication and coupling costs,large modulation bandwidth, array integration and tunability.VCSEL-based modules, with speed up to 2.5 Gbit/s are nowcommercially available for multimode fibre (MMF) basedapplications. However, devices operating at long wavelength andhigher transmission rates (10Gbit/s and more) will be needed inthe near future.</p><p>The purpose of the work presented in this thesis was toobtain an understanding of the high-speed properties of VCSELs,in order to extend the modulation frequency at which they canbe used in fibre optical communication systems. An approach forsystematic high-speed characterisation of VCSELs is presentedand both its potential benefits and problems are discussed. Itis shown that the VCSEL dynamics, under certain conditions, canbe well described by a small number of parameters that can beextracted from small signal measurements and used forfurtheroptimisation. The calibrated small-signal modulation responsesof VCSELs have been measured and fitted to an analyticaltransfer function allowing the estimation of the resonancefrequency, damping factor and parasitic cut-off at differentbias points. This data can be used to determine the relativeimportance of different bandwidth limiting effects due todamping, thermal heating and parasitics.</p><p>Small signal analysis and transmission experiments wereperformed with a large sample of VCSELs covering the variousranges of applications. Visible VCSELs and resonant cavitylight emitting diodes (RCLEDs) for very short reach plasticoptical fibre (POF) applications, 850nm datacom VCSELs forshort distance multimode fibre networks, and long wavelengthVCSELs for long haul single mode fibre transmission.</p><p><b>Keywords:</b>Semiconductor lasers, VCSEL, high-speedmodulation, fibre optic networks, datacom, RCLED, plasticoptical fibre</p>

Thesis (Ph.D)--Electrical and Computer Engineering, Georgia Institute of Technology, 2010. / Committee Chair: Yoder, Douglas; Committee Member: Graham, Samuel; Committee Member: Allen, Janet; Committee Member: Klein, Benjamin; Committee Member: Voss, Paul. Part of the SMARTech Electronic Thesis and Dissertation Collection.

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High-power, single-frequency, narrow-linewidth lasers emitting at tailored wavelength are desired for many applications, especially for precision spectroscopy. By way of a free-space resonator, optically pumped semiconductor lasers (OPSLs), a.k.a. vertical external-cavity surface-emitting lasers (VECSELs), can provide near diffraction-limited, high-quality Gaussian beams and are scalable in output power. Free space resonators also allow the insertion of the birefringent filter and the etalon to enforce single-frequency operation. In addition, the emission wavelengths of OPSLs are tailorable through bandgap engineering. These advantages above make OPSL a strong candidate of laser sources for spectroscopic applications including atomic spectroscopy as well as optical lattice clocks. In this research, a single-frequency laser source with high power is demonstrated by applying the injection-locking technique on OPSLs for the first time. The behaviors of the injection-locked OPSL are studied by varying parameters such as output coupling, injection wavelengths and injection power. It was found that the best injection wavelength is by approximately 2 nm shorter than the free-running slave laser at any given pump power. Below the lasing threshold for free-running operation, the laser starts the stimulated emission process as soon as it is pumped, working as a resonant amplifier. With proper parameters, the output power of the injection-locked laser exceeds the output power of its free-running condition. Over 9 W of single-frequency output power at 1015 nm is achieved. The output beam is near-diffraction-limited with Mₓ² = 1.04 and My² = 1.02. By analyzing the surface photoluminescence (PL) and the output performance of the laser, the saturation intensity of OPSLs is estimated to be 100 kW/cm² when the passive loss of 1.4% is assumed. The injection-locked system adds fairly low phase noise to that of the master laser. By measuring the beat note between the master laser and the injection-locked laser, the RMS values of the phase noise are 0.112 rad and 0.081 rad when using the T = 3% and T = 4% output couplers respectively.

We study bifurcations of periodic solutions with spatio-temporal symmetries of functional differential equations (FDEs). The two main results are: (1) a centre manifold reduction around a periodic solution of FDEs with spatio-temporal symmetries, and (2) symmetry-breaking bifurcations for symmetric rings of delay-coupled lasers. For the case of ODEs, symmetry-breaking bifurcations from periodic solutions has already been studied. We extend this result to the case of symmetric FDEs using a Centre Manifold Theorem for symmetric FDEs which reduces FDEs into ODEs on an integral manifold around a periodic solution. We show that the integral manifold is invariant under the spatio-temporal symmetries which guarantees that the symmetry structure of the system of FDEs is preserved by this reduction. We also consider a problem in rings of delay-coupled lasers modeled using the Lang-Kobayashi rate equations. We classify the symmetry of bifurcating branches of solutions from steady-state and Hopf bifurcations that occur in 3-laser systems. This involves finding isotropy subgroups of the symmetry group of the system, and then using the Equivariant Branching Lemma and the Equivariant Hopf Theorem. We then utilize this result to find the bifurcating branches of solutions in DDE-Biftool. Symmetry often causes eigenvalues to have multiplicity, and in some cases, this could lead DDE-Biftool to incorrectly predict the bifurcation points. We address this issue by developing a method of finding bifurcation points which can be used for the general case of n-laser systems with unidirectional and bidirectional coupling. / Thesis (Ph.D, Mathematics & Statistics) -- Queen's University, 2012-04-30 11:25:01.011

Thesis (Ph.D.) -- McMaster University, 1997. / Includes bibliographical references. Also available via World Wide Web.

Thesis (Ph.D.) -- McMaster University, 1997. / Includes bibliographical references (leaves [100]-105. Also available via World Wide Web.