Abstract Single frequency laser has the advantages of high stability in frequency and low noise. Therefore, single frequency laser is now widely used in applications, such as high precision measurement, holography and data storage. Attempts to generate second harmonic radiation using a linear cavity have typically resulted in significant amplitude fluctuations due to longitudinal mode coupling. Various techniques have been proposed for solving the so called ¡§green(blue) problem¡¨ to achieve single longitudinal mode operation, such as inserting optical component in the conventional linear cavity or use ring cavity instead of linear cavity. Uni-directional ring cavity has shown to be the most robust method for producing single frequency laser. The purpose of this study is to develop compact, low-cost and high-efficiency single frequency IR, green and blue lasers. To continue our preview achievement in single frequency IR and green laser systems, shorter wavelength for 946 nm and blue (473 nm) single frequency laser were attempted. In this thesis, we introduced how could only two spherical mirrors to form the laser cavity for traveling wave oscillation and eliminate ¡§spatial hole burning¡¨ caused by the standing wave operation. And we overcome the thermal problem of quasi-three-level laser by multi-wavelength coating on gain medium and input/output couplers, numerical simulation for mode match, and TE-cooling system for laser crystal. Finally, a non-planar figure ¡§8¡¨ 946-nm ring laser were developed using the multi-reentrant ring cavity, and controlled beam path at uni-directional operation. This symmetrical two-mirror figure ¡§8¡¨ ring cavity has the merit of compact, few optical elements, and easy design. The stable single frequency laser output of our ring cavity promises to make the design widely applicable to solid-state lasers.

At the present time, wireless sensor networks are becoming more and more  common and energy consumption is a key factor in the deployment and  maintenance of these networks. This thesis compares non-SFN multi-hop and  a single frequency network (SFN) or cooperative diversity algorithms with  respect to the energy consumed by the nodes. Since the nodes have limited  power capacity it is extremely important to have an efficient algorithm. In  addition, the behaviour of the network when SFN is employed must be  studied and advice offered with regards to improvements in order to achieve  preferential results. The effect on the network regarding macro diversity is  positive but, the battery energy consumption is still higher and has a drainage  effect on the network for simple multi-hop. The report will include  background information regarding mobile ad-hoc networks and the  relationship with cooperative diversity. It will also deal with how different  algorithms affect the energy consumption in multi-hop networks. Simulations  will also be presented in Matlab plots for two single frequency network  scenarios against a simple multi-hop regarding node energy during the  network discovery and decline. Results will include comparative figures which  are followed by a discussion concerning the simulation results and its effects.  The applications for wireless sensor networks include area monitoring,  environmental monitoring, data logging, industrial monitoring, agriculture  and the idea can additionally be used for wireless radio and TV distribution.  The simulations have been conducted for cooperative diversity algorithms  (SFN-A and SFN-D) against an algorithm which does not use cooperative  diversity in Matlab. The node energy consumption is compared for both  scenarios with regards to both  network reachability and decline. The node  power is analysed during the reachability of the network from the start to  attaining 100% of the discovered network. During network decline, the  behaviour of the node energy is studied for algorithms with SFN-A, SFN-D  and non SFN.  Also, the number of times node transmission occurs with  regards to  node discovery is also analysed.

In this dissertation, an all-fiber-based single frequency nanosecond pulsed laser system at ~ 1918.4 nm in master-oscillator-power-amplifier (MOPA) configuration is present. The nanosecond pulse seed is achieved by directly modulating a continuous wave (CW) single frequency fiber laser using a fast electro-optical modulator (EOM) driven by an arbitrary waveform generator (AWG). One piece of single mode, large core, polarization-maintaining (PM) highly thulium-doped (Tm-doped) germanate glass fiber (LC-TGF) is used to boost the pulse power and pulse energy of these modulated pulses in the final power amplifier. This laser system can work in both high power and high energy regime: in high power regime, to the best of our knowledge, the highest average power 16 W and peak power 78.1 kW are achieved for single frequency transform-limited ~2.0 ns pulses at 500 kHz and 100 kHz repetition rate, respectively: In high energy regime, nearly 1 mJ and half mJ pulse energy is obtained for ~15 ns pulses at 1 kHz repetition rate and 5 kHz repetition rate, respectively. Theoretical modeling of the large-core highly Tm-doped germanate glass double-cladding fiber amplifier (LC-TG-DC-FA) is also present for 2&mum nanosecond pulse amplification. A good agreement between the theoretical and experimental results is achieved. The model can simulate the evolution of pump power, signal energy, pulse shape and the amplified stimulated emission (ASE) in the amplifier. It can also be utilized to investigate the dependence of the stored energy in the LC-TGF on the pump power, seed energy and repetition rate, which can be used to design and optimize the LC-TG-DC-FA to achieve higher pulse energy and average power. Two channel of high energy nanosecond pulses (at 1918.4 nm and 1938 nm) are utilized to generate THz wave in a quasi-phase-matched (QPM) gallium arsenide (GaAs) based on difference frequency generation. THz wave with ~ 5.4μW average power and ~18 mW peak power has been achieved. Besides, one model is built to simulate a singly resonated THz parametric oscillator. The threshold, the dependence of output THz energy on pump energy has been investigated through this model. One pump enhanced THz parametric oscillator has been proposed. The enhancement factor of the nanosecond pulses in a bow-tie ring cavity has been calculated for different pulse duration, cavity length and the transmission of the coupler. And the laser resonances in the ring cavity have been observed by using a piezo to periodically adjust the cavity length. We also build an all-fiber thulium-doped wavelength tunable mode-locked laser operating near 2&mum. Reliable self-starting mode locking over a large tuning range (>50 nm) using fiber taper based carbon nanotube (FTCNT) saturable absorber (SA) is observed. Spectral tuning is achieved by stretching another fiber taper. To the best of our knowledge, this is the first demonstration of an all-fiber wavelength tunable mode-locked laser near 2&mum.

Envisioning novel fully monolithic fiber-optical devices, this dissertation investigates four fiber optical devices both, active and passive, that contribute to the goal of further integrating and miniaturizing fiber optics. An all phosphate glass fiber laser was designed in an effort to reduce laser intensity noise by reducing cavity losses and low mechanical strength that arise from intra-cavity fusion splices between silica fiber Bragg gratings (FBG) and phosphate active fiber in state of the art phosphate single frequency fiber lasers. Novel phosphate glass based FBGs have been fabricated utilizing high intensity laser pulses at 193 nm and a phase-mask. Net reflectivities of up to 70 % and a bandwidth of 50 pm have been achieved in the FBGs. The laser design comprised two of the novel FBGs and a short section of Er³⁺Yb³⁺ phosphate fiber to form a distributed Bragg reflector (DBR) laser. The performance of the new laser has been compared to a conventional phosphate fiber laser. Particular focus was put on the laser intensity noise due to its dependence on intra-cavity losses. Relative intensity noise (RIN) amplitudes of -80 dB/Hz have been measured for both lasers when operating at comparable output powers. For similar levels of absorbed pump power the relaxation oscillation frequencies (ROF) were shifted towards lower frequencies in the new laser. ExcessFBG scattering losses and mode-field miss-match between the active and passive fiber limited the output power of the new laser to 16 mW compared to 140 mW in the conventional laser. A monolithic all-phosphate glass fiber laser with up to 550 mW output power that is operating at a single longitudinal mode and exhibiting narrow linewidth is presented. The laser cavity has been formed by inscribing FBGs directly into heavily Er³⁺Yb³⁺ doped phosphate glass fiber using femtosecond laser pulses and a phase mask, completely eliminating the need for intra-cavity fusion splices. A linewidth of less than 60 kHz and relaxation oscillation peak amplitudes below -100 dB/Hz without active suppression of RIN have been measured. The compact form factor and higher output power combined with the low noise and narrow linewidth characteristic make this laser an ideal candidate for ranging, interferometry and sensing applications. Strong and robust Bragg gratings in optical fiber fabricated from highly photosensitive photo-thermo-refractive (PTR) glass are demonstrated. The fibers were drawn at 900 °C from a machined PTR-glass preform. A low power two beam interference pattern from a continuous wave (cw) He-Cd laser with a wavelength of 325 nm was used to write gratings into the fibers, achieving peak grating strengths of 20 dB and a spectral width of 45 pm. The gratings showed no sign of degradation when exposed to a high temperature environment of 425 °C for several hours. This is significantly higher when compared to standard Telecom FBGs which are rated for operation temperatures below 200 °C. A detailed study of novel mode-field adapters (MFA) based on multi-mode interference in graded index multi-mode fibers (GIMF) is presented. MFAs are often used in cases when low coupling losses between single mode fibers with very different mode-field diameters are needed. Here a new type of MFAs has been fabricated and characterized from a selection of commercially available single mode and graded index fibers. Compared to existing techniques the presented MFAs can be fabricated very quickly and are not limited to certain fiber types. Insertion losses of 0:5 dB over a spectral range of several hundred nm have been obtained with an ultra compact MFA with a length of 275 μm.

[pt] Este trabalho tem como objetivo obter a caracterização do canal de propagação para redes de TV Digital de frequência única (SFN) bem como desenvolver modelos para simulação do desempenho dos serviços de radiodifusão e para tanto medições de campo devem ser realizadas. A avaliação do desempenho de redes individuais através de medidas tem duas desvantagens significativas: custo elevado com demanda de tempo considerável e nem sempre é possível aplicar os resultados de campo com a avaliação de desempenho de receptores comerciais. Neste caso, simulações realizadas em laboratório, utilizando modelos condicionados pelas propriedades do canal de rádio, podem ser a resposta ao problema. Estes modelos podem ser usados em diferentes simulações, tornando possível não somente a avaliação de desempenho, bem como a análise e projeto de equipamentos e sistemas de comunicação adequados para uma determinada característica de canal SFN. São apresentadas as campanhas de medições realizadas, incluindo a descrição das regiões e configurações de medição, técnicas de medição e processamento de dados utilizados. Em sequência, é apresentada uma análise da perda média de propagação com base medições realizadas e a comparação com as previsões fornecidas para os mesmos percursos pela implementação do modelo do ITU-R. A caracterização em banda larga do canal é realizada pela modelagem estatística do perfil de retardos de multipercurso do canal. Finalmente é apresentado a modelagem do canal como uma linha densa de retardos e a modelagem estatística dos parâmetros do canal com base nos resultados experimentais. / [en] This work aims to obtain through a field measurement the characterization of the propagation channel for Digital TV using single frequency networks (SFN) and to develop models for simulating the performance of broadcasting services. The evaluation of the performance of individual networks by means of measurements has significant drawbacks: high cost, considerable time demand and is not always possible to apply field measurement results in the performance evaluation of commercial receivers. In this case, laboratory simulations using models conditioned by the radio channel properties may be the answer to this problem. These models can be used in different simulations making possible not only the performance evaluation but also the analysis and design of equipment and communication systems suitable for a particular SFN channel characteristic. This text presents the measurement campaigns carried out, including the description of regions and measurement settings, measurement techniques and data processing used. In sequence, is presented an analysis of the average path loss based on the performed measurements and its comparison with the predicted path loss provided by the ITU-R recommended model. The broadband channel characterization is carried out by the statistical modeling of the channel multipath power delay profile. Finally, the modeling of the channel as a tapped delay line and the statistical description of the channel dispersion parameters based on experimental results are presented.

L’objectif général de ce projet de thèse est le développement industriel de source lasers accordables de haute cohérence à base de technologies III-V dans les gammes spectrales 0.95-1.1µm, et 2-2.5µm. Ce travail est le fruit d'un partenariat entre les laboratoires IES et C2N, avec la société INNOPTICS spécialisée dans l'intégration de composant opto-électronique.Il s'agit ici de tirer profit des nombreux avantages des composants VeCSELs (Vertical external Cavity Surface Emitting Laser) pour atteindre une combinaison des performances cohérence - puissance - accordabilité - compacité, inaccessible avec les technologies laser commerciales d'aujourd'hui. Pour atteindre cet objectif le travail est scindé en deux grandes parties :- L'étude physique de la dynamique non linéaire d'un laser VECSEL en régime continu et en présence de dispersion de phase. Nous montrons l'existence d'une dynamique déterministe du champ laser qui donne naissance à un régime multimode longitudinal non stationnaire régulier ou à un régime mono-fréquence stable. Ce résultat permet alors la conception de source de haute cohérence à forte puissance sans élément intracavité sélectif en longueur d'ondes.- Le développement de nouvelles sources monofréquences compact largement accordables bas bruit avec une largeur de raie étroite. Cette partie comporte l’étude physique des composants, depuis l’optimisation du milieu à gain jusqu'à l'émission laser en terme de cohérence spatiale et temporelle, ainsi qu'un travail sur l'environnement du laser (mécanique et thermique optimisée pour la stabilité de la fréquence laser). / The main goal of this thesis is the industrial development of highly coherent tunable laser sources based on III-V technologies in the 0.95-1.1μm and 2-2.5μm spectral ranges.This work is the result of a partnership between the IES and C2N laboratory together with the company INNOPTICS, specialized in the packaging of optoelectronics devices.We take advantage of the Vertical External Cavity Surface Emitting Laser (VECSEL) technology to achieve a combination of coherence - power -tunability -compactness, overcoming the performances of today's commercial laser technologies. To achieve this goal the work is divided into two main parts:- The physical study of the non-linear dynamics of a VECSEL laser in continuous wave operation and in the presence of cavity phase dispersion. We show the existence of a deterministic dynamics of the laser field that gives rise to a regular non-stationary longitudinal multimode regime or a stable single-frequency regime. This result then makes it possible to design a source of high coherence with high power without any intracavity wavelength selective element.- The development of new low noise compact single frequency sources with a narrow linewidth. This part involves the physical study of the components, from optimization of the gain medium to the laser emission in terms of spatial and temporal coherence, as well as a work on the environment of the laser (optimization of the thermal mechanical properties of the packaging for the stability of the laser frequency).

This thesis investigates the major errors and processes affecting the performance of a viable, standalone point positioning technique known as single frequency Precise Point Positioning (PPP). The PPP processing utilises both single frequency code and carrier phase GPS observables. The mathematical model implemented is known as the code and quasi-phase combination. Effective measures to improve the quality of the positioning solutions are assessed and proposed. The a priori observations sigma (or standard deviation) ratio in the sequential least squares adjustment model plays a significant role in determining the accuracy and precision of the estimated solutions, as well as the solutions convergence time. An

<p>Wireless Sensor Network is an emerging technology that has applicationsin Wireless Actuators, remote controlling, distribution of softwareupdates and distribution of parameters to sensor nodes. This projectwork basically covers the concept of macro-diversity. This is a situationin which several transmitters are used for transferring the same signal (inmulti-hop sensor networks) to check the increase in connected nodes orin network coverage. Transmitter macro-diversity increases the receivedsignal strength and thus increases the signal-to-noise ratio which resultsin a lower outage probability. To accomplish this task three differentstrategies have been simulated using thirteen different cases. Broadcastingis used when forming SFN of size one (strategy one) and uni-castingis used for forming SFNs of size two (strategy two) and size three (strategythree).In this project reference material has been gathered frombooks, journals and web sources; and MATLAB has been used as thesimulation tool in which codes are written in the M programming language.The algorithm works firstly by discovering all the nodes that areconnected directly with the Base Station through multi-hoping, afterwhich the second algorithm is applied to check how many more nodescan be reached by forming SFNs. A gain of up to 79% was observedusing strategy one and strategy two and up to 83% in strategy three.The results shows that strategy one (Forming SFNs using BroadcastingTechnique) is the best as more nodes can be reached (for different cases)than for the other two strategies (forming SFNs using uni-casting technique).</p>

In this dissertation I report the development of high power pulsed fiber laser systems. These systems utilize phosphate glass fiber for active elements, instead of the industry-standard silica fiber. Because the phosphate glass allows for much higher doping of rare-earth ions than silica fibers, much shorter phosphate fibers can be used to achieve the same gain as longer silica fibers.This single-frequency laser technology was used to develop an all-fiber actively Q-switched fiber lasers. A short cavity is used to create large spacing between longitudinal modes. Using this method, we demonstrated the first all-fiber Q-switched fiber laser in the 1 micron region.In addition to creating high peak powers with Q-switched lasers, created even higher powers using fiber amplifier systems. High power fiber lasers typically produce spectral broadening through the nonlinear effects of stimulated Raman scattering, stimulated Brullion scattering, and self-phase modulation. The thresholds for these nonlinearities scale inversely with intensity and length. Thus, we used a short phosphate fiber gain stage to reduce the length, and a large core fiber final stage to reduce intensity. In this way we were able to generate high peak power pulses while avoiding visible nonlinearities, and keeping a narrow bandwidth.The immediate goal of developing these high power fiber laser systems was to generate narrowband terahertz radiation. Two different wavelengths were combined into the final amplifier stage at orthogonal polarizations. These were collimated and directed into a GaSe crystal, which has a very high figure of merit for THz generation. The two wavelengths combined in the crystal through the process of nonlinear difference frequency generation. This produced a narrowband beam of THz pulses, at higher powers than previous narrowband THz pulses produced by eyesafe fiber lasers.

Wireless Sensor Network is an emerging technology that has applicationsin Wireless Actuators, remote controlling, distribution of softwareupdates and distribution of parameters to sensor nodes. This projectwork basically covers the concept of macro-diversity. This is a situationin which several transmitters are used for transferring the same signal (inmulti-hop sensor networks) to check the increase in connected nodes orin network coverage. Transmitter macro-diversity increases the receivedsignal strength and thus increases the signal-to-noise ratio which resultsin a lower outage probability. To accomplish this task three differentstrategies have been simulated using thirteen different cases. Broadcastingis used when forming SFN of size one (strategy one) and uni-castingis used for forming SFNs of size two (strategy two) and size three (strategythree).In this project reference material has been gathered frombooks, journals and web sources; and MATLAB has been used as thesimulation tool in which codes are written in the M programming language.The algorithm works firstly by discovering all the nodes that areconnected directly with the Base Station through multi-hoping, afterwhich the second algorithm is applied to check how many more nodescan be reached by forming SFNs. A gain of up to 79% was observedusing strategy one and strategy two and up to 83% in strategy three.The results shows that strategy one (Forming SFNs using BroadcastingTechnique) is the best as more nodes can be reached (for different cases)than for the other two strategies (forming SFNs using uni-casting technique).