The purpose of this thesis is to develop ring resonators with simple processes and integration. We used loop mirror as a reflector in the semiconductor lasers. In the material, a 1.55£gm symmetric quantum well InGaAsP epi-layer is used to fabricate the lasers. In device design, we designed four kinds of semiconductor lasers by using loop mirror and cleaved facet. The curvature radiuses are 160 and 260£gm that are presented to investigate bending loss and material loss. In the input/output we had an inclined 7 degree to avoid interference. We also designed another two semiconductor lasers by using ring resonator and cleaved facet. Applying the resonance characteristic of ring resonator can achieve wavelength selection and filtering. In fabrication process, we developed new etching technique. The ICP-RIE dry etching and wet etching method were used in the process. Fist we etched half of the total depth by ICP-RIE dry etching. And then the multi-step technique was used to approach the expecting depth. Beside, we had extra deep wet etching process in MMI. Finally, we used the etching solution HBr:HCl:H2O2:H2O =5:4:1:70 to smooth the sidewall and reduce the scattering loss. In device characteristic, we obtained differential quantum efficiency of 20£gW/mA for the 1000£gm straight waveguide laser. We can not observe laser characteristics for the loop mirror laser, partly because of the high loss in bending section.

We present design and fabrication of ring cavity semiconductor lasers and single ring filter with simple fabrication processes. A 1.55-£gm symmetric quantum well InGaAlAs epi-layer wafer is used to fabricate the lasers. In device design, we apply loop mirror to obtain reflection instead of cleaved facet and take 1x2, and 2x2 Multi-Mode Interference (MMI) with different splitting ratio(50%:50%¡F15%:85%) as a coupler. Then we combine MMI couplers with ring cavities to control the output of specific wavelength. Therefore we can obtain filter and lasers with the property of wavelength selection. We also design two kinds of special waveguides to achieve low reflectivity. One is a tapered spiral waveguide tail. The other waveguide is expanded in a curve and then cut off at the Brewster¡¦s angle. In loop mirror, two curvature radius(260,160£gm) were introduced to study bending loss and material loss. In single ring filter, we design two kinds of resonator lengths(1479,1385£gm) and the corresponding Free Spectrum Range (FSR) are 63.4, 67.75GHz, respectively. In fabrication, owing to the unstable dry etch condition for InGaAlAs, we adopted multi-step etch technology. In the part of curved waveguide, we also use this method to make deep-etching to increase the difference of refractive index between waveguide and the outside part. Finally, we use the etch solution (HBr:HCl:H2O2:H2O=5:4:1:70) to smooth the sidewall of the waveguide, and to reduce scattering loss of the device.

The purpose of this research is to present design and fabrication of resonant loop-mirror Fabry-Perot lasers. Single filter has simple fabrication processes and good potential for intergration. A 1.55-£gm symmetric quantum well InGaAlAs epi-layer wafer is used to fabricate the laser. In device design, we apply loop mirror to obtain reflection instead of cleaved facet and take 1x2, 2x2 Multi-Mode Interference (MMI) with different splitting ratio (50%:50%¡F15%:85%) as a coupler. Then we combine MMI couplers with ring cavities to reflect specific wavelength at particular position. Therefore we can obtain semiconductor laser with property of wavelength-selection filter. In this design of the mask, we add a mask of deep-etch around MMI in order to decrease the loss of higher mode inside MMI. In the part of devices design, we apply multi-step technology for wet etch to obtain necessary depth. Finally, we use the etch solution (HBr¡GHCl¡GH2O2¡GH2O¡×5¡G4¡G1¡G70) to smooth the sidewall of the waveguide, and to reduce scattering loss of the device. In the part of planarization, we can adhere dummy wafers to surround the main sample and extend the total area. If we can fill the gap flat, the problem of high edge by spinning will be solved. However, we were not able to fill the gap.

Self-adaptivity, characterized by the ability to dynamically adjust behavior at runtime, is a growing trend in the evolution of modern embedded systems. While self-adaptive systems tend to be flexible and autonomous, self-adaptivity may inevitably complicate software design, test and analysis. A strategy for taming the growing software complexity of self-adaptive systems is to partition system behaviors into different operational modes specified at design time. Such a multi-mode system can change behavior by switching between modes at runtime under certain circumstances. Multi-mode systems can benefit from a complementary approach to the software development of complex systems: Component-Based Software Engineering (CBSE), which fosters reuse of independently developed software components. However, the state-of-the-art component-based development of multi-mode systems does not take full advantage of CBSE, as reuse of modes at component level is barely addressed. Modes are often treated as system properties, while mode switches are handled by a global mode manager. This centralized mode management entails global information of all components, whereas the global information may be inaccessible in component-based systems. Another potential problem is that a single mode manager does not scale well, particularly at design time,  for a large number of components and modes.   In this thesis we propose a distributed solution to the component-based development of multi-mode systems, aiming for a more efficient and scalable mode management. Our goal is to fully incorporate modes in software component reuse, supporting reuse of multi-mode components, i.e., components able to run in multiple modes. We have developed a generic framework, the Mode-Switch Logic (MSL), which not only supports reuse of multi-mode components but also provides runtime mechanisms for handling mode switch. MSL includes three fundamental elements: (1) a mode-aware component model with the formal specification of reusable multi-mode software components; (2) a mode mapping mechanism for the seamless composition of multi-mode components; and (3) a mode-switch runtime mechanism which is executed by each component in isolation from its functional execution and coordinates the mode switches of different components without the need of global mode information. The mode-switch runtime mechanism has been verified by model checking in conjunction with mathematical proofs. We also provide a mode-switch timing analysis for the runtime mechanism to respect real-time requirements.   MSL is dedicated to the mode aspect of a system irrespective of component execution semantics, thus independent of the choice of component models. We have integrated MSL in the ProCom component model with the extension of support for reuse of multi-mode components and distributed mode-switch handling. Although the distributed mode-switch handling of MSL is more flexible and scalable than the conventional centralized approach, when components are deployed on a single hardware platform and global mode information is available, centralized mode-switch handling is more efficient in terms of runtime overhead and mode-switch time. Hence, MSL is supplemented with a mode transformation technique to enhance runtime mode-switch efficiency by converting the distributed mechanism to a centralized mechanism. MSL together with the mode transformation technique has been implemented in a prototype tool where one can build multi-mode systems by reusing multi-mode components. The applicability of MSL is demonstrated in two proof-of-concept case studies. / ARROWS - Design Techniques for Adaptive Embedded Systems

In this dissertation, the combined optical link, where the baseband digital signal and wireless signal are transmitted simultaneously over a multi-mode fiber (MMF) using an VCSEL and received through a photoreceiver and a feed forward equalizer (FFE). For this hybrid optical link, a new type of combiner is developed using the multi-layer organic (MLO) process. For the overall link simulation, a rate-equation-based VCSEL model is developed with circuit components. This model describes the high-speed modulation characteristic as well as the thermal effect on the L-I (light vs. bias current) characteristic. Additionally, The FFE is developed to further extend a MMF distance by compensating differential modal delay (DMD) in MMF. Two different implementation approaches are taken for the FFE by passive LC ladder based delay line and active inductance peaking delay line structure. To overcome the voltage headroom limitation of the conventional Gilbert cell architecture, modified Gilbert cell is presented and implemented as a multiplier cell for both FFEs. The FFEs are fully integrated on a single chip and fabricated by a standard 0.18 ?m CMOS process. The developed FFE successfully rebuild the distorted signal form the MMF at 10 Gbps data rate.

This paper presents design and fabrication of ring cavity semiconductor lasers and optical filters with simple fabrication process. A 1.55

International Telemetering Conference Proceedings / October 17-20, 1994 / Town & Country Hotel and Conference Center, San Diego, California / With the increased concerns for reducing cost and improving reliability in today's telemetry systems, many users are employing simulation and automation to guarantee reliable telemetry systems operation. This places an increased demand on the remote capabilities of the equipment used in the telemetry system. Furthermore, emphasis has been placed on the ability to decrease the space and power consumption of the telemetry system to facilitate transportability of the a single telemetry system to multiple sites. Finally, today's telemetry systems demand that all equipment provide multiple functions to provide the maximum performance for the lowest system cost.

Thesis ((PhD)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: This dissertation proposes a multi-mode antenna element excited through a multiconductor feed. It is shown that each of the orthogonal transverse electromagnetic modes supported by the antenna feed results in a unique radiated far-field pattern that collectively allow for nearhemispherical field-of-view coverage. Three multi-mode antenna designs are presented: a dual-mode antenna, integrating a single linearly polarised dipole antenna with a co-located monopole, as well as two quad-mode antenna designs integrating two dual-polarised dipole elements with a co-located monopole element. The dual-mode antenna is excited through a balanced transmission line feed supporting both differential- and common-mode signals that, respectively, result in typical dipole-over-ground and monopole radiated far-field patterns. The quad-mode antennas are each fed through a quadraxial transmission line allowing for excitation through four orthogonal transverse electromagnetic port modes. To characterise the multi-mode response of the multi-mode antennas, generalised transformations are derived by which the multi-mode S-parameters and radiated far-fields can be calculated from the S-parameters and far-fields corresponding to single-ended excitations. These transformations are implemented to validate the response of a dual-mode and quad-mode antenna design through measurements. An equivalent network representation for active multi-mode antennas is presented, including generalised transformations relating the multi-mode signal and noise response of the low-noise amplifiers to the two-port S-parameters and noise parameters of the low-noise amplifiers. Through the use of classical beamforming algorithms, the performance of an active dual-mode and quadmode antenna is presented. In the case of the active dual-mode antenna, it is shown that through the added use of common-mode signals, a variation in sensitivity of less than 50% is achieved in the E-plane. Similarly, the additional excitation modes supported by the active quad-mode antenna is shown to result in a significant improvement in the polarimetric capabilities over the field-of-view coverage. / AFRIKAANSE OPSOMMING: Hierdie proefskrif stel ’n multimodale antenna element voor wat deur ’n multi-geleier transmissielyn gevoer word. Dit word gewys dat elk van die ortogonale transversale elektromagnetiese opwekkingsmodusse wat deur die antenna voer ondersteun word, ’n unieke vêrveld stralingspatroon skep, wat gesamentlik lei tot ’n hemisferiese gesigsveld. Drie multimodale antenna ontwerpe word voorgestel: ’n dubbelmodale antenna, waarin ’n enkel lineêrgepolariseerde dipool antenna en monopool mede-geleë word, asook twee viermodale antenna ontwerpe waarin twee dubbelgepolariseerde dipool elemente geïntegreer word met medegeleë monopool antenna elemente. Die dubbelmodale antenna word gevoer deur ’n gebalanseerde transmissielyn wat beide differensiële- en gemene-modus seine ondersteun, waar elk onderskeidelik dipool-oor-aardvlak en monopool stralingspatrone voortbring. Die viermodale antennas word elk gevoer deur vier-as transmissielyne wat vier ortogonale transversale elektromagnetiese opwekkingsmodusse ondersteun. Om die multimodale gedrag van die drie multimodale antennas te karakteriseer, word veralgemeende transformasies afgelei waardeur die multimodale strooiingsparameters asook die vêrveld stralingspatrone vanaf enkelpoort strooiingsparameters en vêrvelde bereken word. Hierdie transformasies word toegepas om die gedrag van ’n dubbel- en viermodale antenna ontwerp te karakteriseer deur metings. Ekwivalente netwerkvoorstellings vir aktiewe multimodale antennas word voorgestel, insluitend veralgemeende transformasies om die multimodale sein asook ruis gedrag van die lae-ruis versterkers betreklik te maak tot die tweepoort strooiingsparameters en ruisparameters van die laeruis versterkers. Deur gebruik te maak van klasieke bundelvormingsalgoritmes, word die gedrag van aktiewe dubbelmodale en viermodale antennas voorgestel. Vir die aktiewe dubbelmodale antenna word daar aangedui dat die gesamentlike gebruik van differensiële- en gemene-modus seine, ’n variasie in sensitiwiteit onder 50% tot gevolg het in die E-vlak. Soortgelyk word daar aangedui dat die addisionele opwekkingsmodusse wat deur die aktiewe viermodale antenna ondersteun word, tot ’n beduidende verbetering in die polarisasievermoë oor die gesigsveld lei.

A measurement of the primordial B-mode polarisation of the Cosmic Microwave Background would provide direct evidence of inflation in the early universe. The extremely weak nature of the B-mode signal necessitates an instrument with a high sensitivity and precise control over systematic effects. Multi-mode antenna feed horns offer higher sensitivity than their single-mode counterparts, however their behaviour is much more complex. The Short Wavelength Instrument for the Polarisation Explorer (SWIPE) onboard the Large Scale Polarisation Explorer (LSPE) is one instrument planning to implement multi-mode feed horns. SWIPE will attempt to detect the primordial B-mode at large angular scales, measuring the sky in three bands at 140, 220 and 240 GHz. A single on-axis High-Density PolyEthylene (HDPE) lens and polarisation-splitting wire grid combine to focus the radiation from the sky onto two focal planes of multi-mode horns feeding bolometric detectors. A large diameter rotating metal-mesh half-wave plate allows both polarisations to be measured by the same pixel, therefore bypassing many detector systematics. Simulations are performed to predict the sky beam for two key pixels: closest to and furthest from the centre of the focal plane. For the 140 GHz channel the cross-polarisation is predicted, and the optimum location at which to place the telescope’s focus behind the horn aperture to maximise gain and optimise beam shape is investigated. A measurement of the multi-mode horn is performed using a room-temperature bolometer. An investigation is also conducted to assess to what extent the same measurements can be performed using a coherent measurement system such as a vector network analyser. A working coherent measurement technique is devised, however it is limited to horns carrying only the first 3 modes.

Charging technology is becoming more and more important since rechargeable batteries are commonly used in many applications than ever before. To facilitate various charging profiles, a battery charger with multi-mode is proposed. The charger is composed of an innovative reflex charging circuit and a controllable half-bridge converter with pulse-width-modulation. This multi-mode charger provides not only four basic functions of constant voltage (CV), constant current (CC), pulsed current (PS) and reflex charging (RX), but also the multi-stage charging with hybrid charging modes. The desired charging profile can easily be accomplished by adjusting the controllable parameters of the charger. In order to simplify the control circuit, a digital signal processor (DSP) with the associated sensors and interface circuits are used as the control kernel. By continuously monitoring the charging current and battery voltage, the charging modes can be adapted to the charging strategy. An experimental charging circuit is built and tested. The experiments in this dissertation are carried out on lead-acid batteries, Experimental results show that the charger is able to execute the charging functions of various tentative charging strategies with hybrid charging modes.