Experimental demonstration of RGB LED-based optical camera communications

Red, green, and blue (RGB) light-emitting diodes (LEDs) are widely used in everyday illumination, particularly where color-changing lighting is required. On the other hand, digital cameras with color filter arrays over image sensors have been also extensively integrated in smart devices. Therefore, optical camera communications (OCC) using RGB LEDs and color cameras is a promising candidate for cost-effective parallel visible light communications (VLC). In this paper, a single RGB LED-based OCC system utilizing a combination of undersampled phase-shift on off keying (UPSOOK), wavelength-division multiplexing (WDM), and multiple-input multiple-output (MIMO) techniques is designed, which offers higher space efficiency (3 bits/Hz/LED), long-distance, and nonflickering VLC data transmission. A proof-of-concept test bed is developed to assess the bit-error-rate performance of the proposed OCC system. The experimental results show that the proposed system using a single commercially available RGB LED and a standard 50-frame/s camera is able to achieve a data rate of 150 bits/s over a range of up to 60 m

GaN/AlN Multiple Quantum Wells and Nitride-Based Waveguide Structures for Ultrafast All-Optical Switch Utilizing Intersubband Transition

Intersubband transition （ISBT） in multiple quantum wells （MQW） has drawn much attention for ultrafast optoelectronic devices owing to its wide wavelength-tunability and extremely fast energy relaxation process. Recently, the extension of ISBT wavelength to near-infrared wavelength, especially 1.55 μm, is of particular interest because such wavelength is vital for the development of ultrafast photonic devices for silica-fiber-based optical-communication networks. Among various materials proposed for intersubband transition at 1.55 μm, GaN/AlN MQW structures are promising due to their large conduction band offset of approximately 2 eV. Furthermore, the large electron effective mass and the large LO phonon energy in nitrides make their intersubband relaxation extremely fast in the order of sub-picoseconds. This makes intersubband transition in nitrides immensely interesting for the development of ultrafast photonic devices operating at a bit rate higher than 1 Tb/s.//The intersubband transition at 1.55 μm and shorter wavelengths have been achieved by molecular beam epitaxy （MBE） with the shortest wavelength of 1.08 μm. On the other hand, growth by metalorganic vapor phase epitaxy （MOVPE） has not yielded satisfactory results as the shortest ISBT wavelength reported is merely 2.4 μm. The demonstration of 1.55-μm ISBT by MOVPE, however, is still attractive since much better crystalline quality for device fabrication can be achieved. Moreover, MOVPE also has another advantage over MBE in industrial point of view. Indeed, the ultrafast optical switching utilizing intersubband transition has been demonstrated by MBE-grown GaN ridge waveguide structure with a bit rate higher than 1 Tb/s. However, such device requires optical-pulse switching energy higher than 10pJ/μm2 to utilize the saturable intersubband absorption, which is still too large for the applications in conventional optical communication networks. Reduction of the switching energy is therefore another important issue for the intersubband transition devices. In order to reduce the switching energy, not only the waveguide fabrication process, but also the epitaxial growth technique and the device structure have to be improved.//In this dissertation, the GaN/AlN multiple quantum wells and nitride-based waveguide structures are studied and fabricated for the applications of ultrafast all-optical switch utilizing intersubband transition. The ultrafast intersubband transition device is realized by using AlN waveguide structure with GaN/AlN quantum wells. This AlN-waveguide-based intersubband transition device can operate in the optical communication wavelength range, covering 1.3 μm, the shortest wavelength ever demonstrated for the intersubband transition devices.//In order to perform epitaxial growth of such structure with high quality, MOVPE is more preferable than MBE because the AlN layer can be grown with much better quality by the MOVPE. However, since the MOVPE growth of GaN/AlN MQW for the 1.55-μm ISBT is very difficult, the AlN waveguide structure was fabricated with a combination of both MOVPE and MBE growth techniques: MOVPE growth for AlN buffer layer and MBE re-growth for GaN/AlN multiple quantum wells. With this combination, the high quality waveguide with intersubband absorption in a wavelength range of 1.3-1.55 μm is achieved.//In addition to the improvement in the epitaxial growth technique, this dissertation also discusses on the problems in growing the waveguide structure of both MOVPE and MBE. Moreover, the design and fabrication of nitride-based waveguide structures are studied in details to improve the waveguide quality. The high-optical-confinement waveguide structures are proposed and successfully fabricated for the first time thanks to the successful demonstration of epitaxial growth and the improvement of fabrication process. Additionally, a new waveguide characterization method using the supercontinuum light source is also proposed and demonstrated. With this new characterization method, not only are the direct measurements of intersubband absorption in waveguides realized, but the problems in waveguide quality of the MBE-grown waveguide are also revealed. This provides very useful information for the improvement of fabrication process, especially the epitaxial growth process. The achievements in each area of epitaxial growth, waveguide fabrication process, and characterization, have made contributions to the improvement of waveguide characteristic, leading to the successful demonstration of the first AlN-waveguide-based intersubband transition devices with high performance.報告番号: 甲21171 ; 学位授与年月日: 2006-03-23 ; 学位の種別: 課程博士 ; 学位の種類: 博士(工学) ; 学位記番号: 博工第6261号 ; 研究科・専攻: 工学系研究科電子工学専

An Implementation Approach and Performance Analysis of Image Sensor Based Multilateral Indoor Localization and Navigation System

Optical camera communication (OCC) exhibits considerable importance nowadays in various indoor camera based services such as smart home and robot-based automation. An android smart phone camera that is mounted on a mobile robot (MR) offers a uniform communication distance when the camera remains at the same level that can reduce the communication error rate. Indoor mobile robot navigation (MRN) is considered to be a promising OCC application in which the white light emitting diodes (LEDs) and an MR camera are used as transmitters and receiver respectively. Positioning is a key issue in MRN systems in terms of accuracy, data rate, and distance. We propose an indoor navigation and positioning combined algorithm and further evaluate its performance. An android application is developed to support data acquisition from multiple simultaneous transmitter links. Experimentally, we received data from four links which are required to ensure a higher positioning accuracy

Experimental characterization of CMOS photonic devices

Current electrical interconnects in super-computers and high-performance processors present a bottleneck in terms of bandwidth and power consumption. A migration to the optical domain in order to cope with the connectivity between units (e.g. CPUs and memory) is needed to overcome these issues. Zero-change CMOS photonic devices represent a very attractive solution to the design of optical on-chip links. This approach makes use of up-to-date CMOS process, having enormous benefits regarding integration with state-of-the-art electronics. Designing and characterizing zero-change CMOS photonic devices is key for the future of optical interconnects. This thesis presents the characterization both theoretical and experimental of a Silicon-Germanium ring resonator modulator. It represents the first ever depletion modulator up to the date using SiGe as an active material. Moreover, it shows the best wavelength shift reported so far for zero-change CMOS modulators, enhancing the shift of a pure Silicon device. The demonstration of this device begins a new era of optical modulator designs using silicon-germanium to enhance modulation efficiency, and therefore reduce power consumption.Las interconexiones eléctricas de supercomputadores y de microprocesadores de alto rendimiento representan actualmente un bottleneck en cuanto a ancho de banda y potencia consumida se refiere. Se necesita una migración hacia el dominio óptico, para realizar la conectividad entre las diferentes unidades (por ejemplo CPU y memoria), con tal de superar estas limitaciones. Los dispositivos fabricados con la tecnología zero-change CMOS representan una solución muy atractiva para el diseño de links ópticos dentro de un chip. Esta técnica utiliza procesos CMOS actuales, beneficiándose así enormemente de la fácil integración con dispositivos electrónicos actuales. Diseñar y caracterizar dispositivos trabajando con zero-change CMOS es clave para el futuro de las interconexiones ópticas. Esta tesis presenta la caracterización tanto teórica como experimental de un modulador tipo ring resonator de Silicon-Germanium. Es el primer modulador de depletion utilizando SiGe como un material activo. Además, este dispositivo muestra el desplazamiento en longitud de onda más grande publicado hasta la fecha, comparándolo con otros moduladores zero-change CMOS, mejorando el desplazamiento de dispositivos de puro silicio. La demostración de este dispositivo comienza una nueva era de diseños de moduladores ópticos que utilizaran silicon-germanium para mejorar la eficiencia de modulación, y por lo tanto reducir el consumo de potencia.Les interconnexions elèctriques de super-computadors i microprocessadors de alt rendiment representen actualment un coll d'ampolla en quant a ample de banda i potència consumida. Es necessita una migració cap al domini òptic, per realitzar la connectivitat entre les diferents unitats (per exemple entre la CPU i la memòria), per tal de superar aquests problemes. Els dispositius fabricats sota zero-change CMOS technology representen una solució molt atractiva al disseny de links òptics dins d'un xip. Aquesta tècnica utilitza processos CMOS actuals, tenint enormes beneficis en quant a la integració amb dispositius electrònics actuals. Dissenyar i caracteritzar dispositius treballant amb zero-change CMOS és clau pel futur de les interconnexions òptiques del futur. Aquesta tesi presenta la caracterització tant teòrica com experimental d'un modulador ring resonator de Silicon-Germanium. Representa el primer modulador de depletion usant SiGe con un material actiu. A més a més, aquest dispositiu mostra el desplaçament en longitud d'ona més gran publicat fins ara en qualsevol dispositiu zero-change CMOS, millorant el desplaçament de dispositius de pur silici. La demostració d'aquest dispositiu comença una nova era de dissenys de moduladors òptics que utilitzaran silicon-germanium per millorar l'eficiència de modulació i per tant per reduir el consum de potència