Micro-LED arrays for spatio-temporally correlated multi-mode operation

Micro-LEDs are the basis of attractive new forms of high brightness and high resolution displays. We discuss how broader conceptions and convergences with lighting, communications, imaging and sensing are emerging from this rapidly developing technology

On Small Satellites for Oceanography: A Survey

The recent explosive growth of small satellite operations driven primarily from an academic or pedagogical need, has demonstrated the viability of commercial-off-the-shelf technologies in space. They have also leveraged and shown the need for development of compatible sensors primarily aimed for Earth observation tasks including monitoring terrestrial domains, communications and engineering tests. However, one domain that these platforms have not yet made substantial inroads into, is in the ocean sciences. Remote sensing has long been within the repertoire of tools for oceanographers to study dynamic large scale physical phenomena, such as gyres and fronts, bio-geochemical process transport, primary productivity and process studies in the coastal ocean. We argue that the time has come for micro and nano satellites (with mass smaller than 100 kg and 2 to 3 year development times) designed, built, tested and flown by academic departments, for coordinated observations with robotic assets in situ. We do so primarily by surveying SmallSat missions oriented towards ocean observations in the recent past, and in doing so, we update the current knowledge about what is feasible in the rapidly evolving field of platforms and sensors for this domain. We conclude by proposing a set of candidate ocean observing missions with an emphasis on radar-based observations, with a focus on Synthetic Aperture Radar.Comment: 63 pages, 4 figures, 8 table

Event-based Vision: A Survey

Event cameras are bio-inspired sensors that differ from conventional frame cameras: Instead of capturing images at a fixed rate, they asynchronously measure per-pixel brightness changes, and output a stream of events that encode the time, location and sign of the brightness changes. Event cameras offer attractive properties compared to traditional cameras: high temporal resolution (in the order of microseconds), very high dynamic range (140 dB vs. 60 dB), low power consumption, and high pixel bandwidth (on the order of kHz) resulting in reduced motion blur. Hence, event cameras have a large potential for robotics and computer vision in challenging scenarios for traditional cameras, such as low-latency, high speed, and high dynamic range. However, novel methods are required to process the unconventional output of these sensors in order to unlock their potential. This paper provides a comprehensive overview of the emerging field of event-based vision, with a focus on the applications and the algorithms developed to unlock the outstanding properties of event cameras. We present event cameras from their working principle, the actual sensors that are available and the tasks that they have been used for, from low-level vision (feature detection and tracking, optic flow, etc.) to high-level vision (reconstruction, segmentation, recognition). We also discuss the techniques developed to process events, including learning-based techniques, as well as specialized processors for these novel sensors, such as spiking neural networks. Additionally, we highlight the challenges that remain to be tackled and the opportunities that lie ahead in the search for a more efficient, bio-inspired way for machines to perceive and interact with the world

Development and implementation of monolithic GaN uLED arrays for multifunctional optical systems

Monolithic LED arrays comprising micron-sized pixels are rapidly maturing as a technology due to their high efficiency and modulation rates. When coupled with complementary metal-oxide semiconductor (CMOS) electronics, which offer high level spatiotemporal control, such devices are capable of communications based applications along with the ability to provide structured illumination based functionality. This novel 'smart display' technology opens up a range of potential new applications. This thesis describes the full development of such micro-LED arrays from initial design and fabrication through to implementation. By manipulating their fabrication process, highly customised devices can be created to accommodate the needs of a specialised setup or application scenarios. An example of this is the creation of n-contact devices and modifying the epitaxial structure of the array to allow for individually addressable pixels to better suit specific driving electronics. Devices such as these were developed and characterised. When compared to existing state-of-the art alternatives, these devices are shown to be either comparable with or to exceed them in terms of modulation rate and optical power output. In addition to modifying LED epitaxy to create novel applications, arrays of LEDs can also be implemented to create imaging systems capable of 3D imaging using only a single camera. This setup along with the steps taken to optimise the process is also detailed. Furthermore it includes the incorporation of a 3-dimensional tracking system, which can be used simultaneously with 3D imaging. Along with new technologies introduced by micro-LED arrays, they can also be used to improve existing technologies and even add additional functionality to them. This thesis documents the development of a maskless photolithography setup wherein the optical emission pattern of the micro-LEDs is controllable through CMOS drivers to implement a direct writing tool and replace the quartz masks, typically used in photolithography. The setup is shown to be capable of producing highly uniform photolithography defined structures of controllable width across a 16 x 16 grid where each coordinate is individually addressable. By synchronising the LED array's emission pattern with a motorised XYZ stage, continuous customisable directly written structures can be developed. Along with the photocuring components of the setup, an additional LED array was incorporated allowing for additional functionality through structured illumination. This comes in the form of the recognition, tracking and automated alignment to non-standardised alignment markers on a micrometre scale. Photocuring was performed whilst aligned to these markers while simultaneously tracking these markers to ensure the quality of fabricated structures.Monolithic LED arrays comprising micron-sized pixels are rapidly maturing as a technology due to their high efficiency and modulation rates. When coupled with complementary metal-oxide semiconductor (CMOS) electronics, which offer high level spatiotemporal control, such devices are capable of communications based applications along with the ability to provide structured illumination based functionality. This novel 'smart display' technology opens up a range of potential new applications. This thesis describes the full development of such micro-LED arrays from initial design and fabrication through to implementation. By manipulating their fabrication process, highly customised devices can be created to accommodate the needs of a specialised setup or application scenarios. An example of this is the creation of n-contact devices and modifying the epitaxial structure of the array to allow for individually addressable pixels to better suit specific driving electronics. Devices such as these were developed and characterised. When compared to existing state-of-the art alternatives, these devices are shown to be either comparable with or to exceed them in terms of modulation rate and optical power output. In addition to modifying LED epitaxy to create novel applications, arrays of LEDs can also be implemented to create imaging systems capable of 3D imaging using only a single camera. This setup along with the steps taken to optimise the process is also detailed. Furthermore it includes the incorporation of a 3-dimensional tracking system, which can be used simultaneously with 3D imaging. Along with new technologies introduced by micro-LED arrays, they can also be used to improve existing technologies and even add additional functionality to them. This thesis documents the development of a maskless photolithography setup wherein the optical emission pattern of the micro-LEDs is controllable through CMOS drivers to implement a direct writing tool and replace the quartz masks, typically used in photolithography. The setup is shown to be capable of producing highly uniform photolithography defined structures of controllable width across a 16 x 16 grid where each coordinate is individually addressable. By synchronising the LED array's emission pattern with a motorised XYZ stage, continuous customisable directly written structures can be developed. Along with the photocuring components of the setup, an additional LED array was incorporated allowing for additional functionality through structured illumination. This comes in the form of the recognition, tracking and automated alignment to non-standardised alignment markers on a micrometre scale. Photocuring was performed whilst aligned to these markers while simultaneously tracking these markers to ensure the quality of fabricated structures

Design and Realization of Fully-digital Microwave and Mm-wave Multi-beam Arrays with FPGA/RF-SOC Signal Processing

There has been a constant increase in data-traffic and device-connections in mobile wireless communications, which led the fifth generation (5G) implementations to exploit mm-wave bands at 24/28 GHz. The next-generation wireless access point (6G and beyond) will need to adopt large-scale transceiver arrays with a combination of multi-input-multi-output (MIMO) theory and fully digital multi-beam beamforming. The resulting high gain array factors will overcome the high path losses at mm-wave bands, and the simultaneous multi-beams will exploit the multi-directional channels due to multi-path effects and improve the signal-to-noise ratio. Such access points will be based on electronic systems which heavily depend on the integration of RF electronics with digital signal processing performed in Field programmable gate arrays (FPGA)/ RF-system-on-chip (SoC). This dissertation is directed towards the investigation and realization of fully-digital phased arrays that can produce wideband simultaneous multi-beams with FPGA or RF-SoC digital back-ends. The first proposed approach is a spatial bandpass (SBP) IIR filter-based beamformer, and is based on the concepts of space-time network resonance. A 2.4 GHz, 16-element array receiver, has been built for real-time experimental verification of this approach. The second and third approaches are respectively based on Discrete Fourier Transform (DFT) theory, and a lens plus focal planar array theory. Lens based approach is essentially an analog model of DFT. These two approaches are verified for a 28 GHz 800 MHz mm-wave implementation with RF-SoC as the digital back-end. It has been shown that for all proposed multibeam beamformer implementations, the measured beams are well aligned with those of the simulated. The proposed approaches differ in terms of their architectures, hardware complexity and costs, which will be discussed as this dissertation opens up. This dissertation also presents an application of multi-beam approaches for RF directional sensing applications to explore white spaces within the spatio-temporal spectral regions. A real-time directional sensing system is proposed to capture the white spaces within the 2.4 GHz Wi-Fi band. Further, this dissertation investigates the effect of electro-magnetic (EM) mutual coupling in antenna arrays on the real-time performance of fully-digital transceivers. Different algorithms are proposed to uncouple the mutual coupling in digital domain. The first one is based on finding the MC transfer function from the measured S-parameters of the antenna array and employing it in a Frost FIR filter in the beamforming backend. The second proposed method uses fast algorithms to realize the inverse of mutual coupling matrix via tridiagonal Toeplitz matrices having sparse factors. A 5.8 GHz 32-element array and 1-7 GHz 7-element tightly coupled dipole array (TCDA) have been employed to demonstrate the proof-of-concept of these algorithms

Roadmap on spatiotemporal light fields

Spatiotemporal sculpturing of light pulse with ultimately sophisticated structures represents the holy grail of the human everlasting pursue of ultrafast information transmission and processing as well as ultra-intense energy concentration and extraction. It also holds the key to unlock new extraordinary fundamental physical effects. Traditionally, spatiotemporal light pulses are always treated as spatiotemporally separable wave packet as solution of the Maxwell's equations. In the past decade, however, more generalized forms of spatiotemporally nonseparable solution started to emerge with growing importance for their striking physical effects. This roadmap intends to highlight the recent advances in the creation and control of increasingly complex spatiotemporally sculptured pulses, from spatiotemporally separable to complex nonseparable states, with diverse geometric and topological structures, presenting a bird's eye viewpoint on the zoology of spatiotemporal light fields and the outlook of future trends and open challenges.Comment: This is the version of the article before peer review or editing, as submitted by an author to Journal of Optics. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from i

Frequency conversion in nonlinear optical waveguides : from classical to quantum applications

This thesis encompasses a broad area of physics including linear and nonlinear optics, photonics and quantum physics. It combines the phenomena of nonlinearoptical frequency conversion with waveguiding and coupling, taking advantage of new opportunities presented by advances in fabrication technologies of micro- and nano-waveguides. In this dissertation an in-depth analysis of quantum and classical properties of light traveling in nonlinear optical waveguides, directional couplers and waveguide arrays is performed. The concepts of spatial and temporal dispersion, waveguiding in structures with subwavelength dimensions and nonlinear interactions between different frequencies of light are studied both theoretically and experimentally. Some sections of this thesis include development and implementation of novel physical ideas, while other sections are focused on comprehensive experimental and numerical analysis of advanced theoretical concepts. The results presented in this dissertation demonstrate new physical phenomena with potential applications in the areas of telecommunications and quantum information. The research performed in this thesis opens opportunities for frequency conversion with world-leading power efficiency, including operation with ultrashort pulses for a variety of wavelengths to suit a wide range of perspective application requirements. It also shows an approach for simple and energy efficient spatio-temporal optical signal control, which can find applications in next generation telecommunications networks. Furthermore, the results obtained in this dissertation demonstrate the possibility for flexible shaping of quantum statistics of photons generated in photonic waveguiding structures through spontaneous frequency conversion, contributing to the development of integrated quantum circuits. The new methods of frequency conversion in micro- and nano-scale waveguides and optical circuits have potential to advance the performance, energy efficiency, and security of future optical communication networks and computing systems

Thermography of semiconductor lasers

Halbleiterlaser stellen mit über 70% Wirkungsgrad einzigartig effiziente Lichtquellen dar. Dennoch ist ihre zuverlässige Nutzung, insbesondere im Bereich hoher Leistungsdichten, von thermischen Limitierungen geprägt. Einen grundlegenden Beitrag zu deren physikalischen Verständnis leistet die Analyse der thermischen Eigenschaften und Degradationsprozesse solcher Bauelemente. In dieser Arbeit wird hierzu die Thermographie als innovative Analysemethode untersucht. Das Plancksche Strahlungsgesetz erlaubt die radiometrische Ermittlung der Temperatur. Die wichtige physikalische Kenngröße Emissivität wird in dieser Arbeit für Halbleiter und Halbleiterlaserstrukturen spektral gemessen und auf fundamentale physikalische Eigenschaften zurückgeführt. Auf dieser Grundlage werden methodische Aspekte der Thermographie diskutiert, welche durch den thermischen Hintergrund und die teilweise Transparenz der Halbleitermaterialien geprägt sind. Die daraus folgenden analytischen Fähigkeiten erlauben unter anderem die orts- und zeitaufgelöste Bestimmung der thermischen Eigenschaften von komplexen Hochleistungslasern unterschiedlichster Bauart. Darüber hinaus ermöglicht die Kenntnis der beteiligten thermischen Zeitkonstanten die Extraktion von lokalen Überhöhungen in der Infrarotemission, deren Zusammenhang zur Degradation der Bauelemente untersucht wird. Eine grundsätzliche Begrenzung der Ausgangsleistung ist durch einen abrupten Degradationsprozess gegeben, welcher maßgeblich durch eine Reabsorption der Laserstrahlung an der Frontfacette verursacht wird. Mithilfe einer kombinierten Thermographie-Nahfeld-Messung wird dieser Prozess orts- und zeitaufgelöst analysiert. Die Erweiterung des Messfensters zu kürzeren Wellenlängen hin erlaubt die Detektion strahlender Übergänge unter Einbeziehung von Defektzentren welche als strahlende Signaturen von graduellen Degradationsprozessen aufzufassen sind.Semiconductor lasers are unequaled efficient light sources, reaching efficiencies of more than 70%. Nevertheless, thermal limits govern their reliable application, in particular in the field of high power densities. The analysis of thermal properties and degradation processes in such devices contributes essentially to the understanding of these limits. This work exploits thermography as an innovative analytical technique for such purpose. Planck''s law allows for a radiometric detection of temperatures. In this work, the important physical parameter emissivity is measured spectrally resolved for both semiconductors and semiconductor laser structures and is related to fundamental physical properties. Based on that, methodological aspects are discussed, which are affected on the one hand by the omnipresent thermal radiation and on the other hand by the partial transparency of the semiconductor materials. The resulting analytical capacities allow, for instance, for the determination of the thermal properties of complex high-power lasers of a wide range of different designs in a spatio-temporally resolved fashion. Furthermore, does the knowledge of the involved thermal time constants allow for an extraction of localized peaks of the infrared emission that is analyzed for its relationship with device degradation. The output power of high-power devices is fundamentally limited by the catastrophic optical damage, an abrupt degradation process that is induced significantly by reabsorption of laser radiation at the front facet. This process is analyzed spatio-temporally resolved with help of a combined thermography and optical near-field technique. Extending the detection range down to shorter wavelengths allows for imaging of radiative transitions that are related to defect centers, which are interpreted as radiative signatures of gradual device degradation processes