Akinetic Tuneable Optical Sources with Applications

Optical Coherence Tomography (OCT) is a modern, non-invasive imaging technique in biomedical research and medical diagnostics. It was initially developed for clinical applications in ophthalmology, providing high-resolution, cross-sectional images of the retina, retinal nerve fibre layer and the optic nerve head. Today, OCT is used for in vivo imaging of almost every type of tissue and it also branched out in fields outside medicine, like industrial or pharmaceutical applications. OCT is a continuously improving imaging technique, benefiting from the development of advanced optical components and broadband optical sources. The objective of the work presented in the thesis was the development of both short and, respectively, long cavity akinetic optical devices, employing several types of dispersive optical fibre components in the cavity, like chirped fibre Bragg gratings, single mode or dispersion compensating fibre, and actively radio-frequency tuned semiconductor optical amplifiers, used as gain media. The use of external modulators, like Fabry-Perot assemblies, rotating mirrors and other mechanical devices is therefore completely eliminated, while versatility is added in the control of the coherence length, output bandwidth, repetition rate and power. The short cavity source was developed in the 1060 nm region, the output power and bandwidth showing a slow decay with the increase of repetition rate up to 250 kHz. Without any booster, the power achieved was 2 mW at 100 kHz. A novel dual-mode-locking mechanism was developed in order to tune an akinetic swept source based on dispersive cavities at a repetition rate close to, but different from the inverse of the cavity roundtrip. Several optical source configurations emitting in the 1060 nm or 1550 nm wavelength region were developed, characterised and tested in OCT applications. For the 1550 nm swept source employing a Faraday Rotating Mirror in a dispersive cavity, sweeping rates in the range of MHz were achieved, from 782 kHz to up to 5 times this value, with proportional decrease in the tuning bandwidth. Linewidths smaller than 60 pm and output powers exceeding 10 mW were measured. OCT topographic imaging was demonstrated. The thesis ends with a proposed broadband investigation of microresonators written in silica glass employing akinetic optical sources at 1550 nm. The work presented in this thesis resulted in several peer reviewed papers, one patent application and several conference presentations, listed after the final conclusions

1996 Laboratory directed research and development annual report

This report summarizes progress from the Laboratory Directed Research and Development (LDRD) program during fiscal year 1996. In addition to a programmatic and financial overview, the report includes progress reports from 259 individual R&D projects in seventeen categories. The general areas of research include: engineered processes and materials; computational and information sciences; microelectronics and photonics; engineering sciences; pulsed power; advanced manufacturing technologies; biomedical engineering; energy and environmental science and technology; advanced information technologies; counterproliferation; advanced transportation; national security technology; electronics technologies; idea exploration and exploitation; production; and science at the interfaces - engineering with atoms

Design and Development of an Optical Chip Interferometer For High Precision On-Line Surface Measurement

Advances in manufacturing and with the demand of achieving faster throughput at a lower cost in any industrial setting have put forward the need for embedded metrology. Embedded metrology is the provision of metrology on the manufacturing platform, enabling measurement without the removal of the workpiece. Providing closer integration of metrology upon the manufacturing platform will improve material processing and reliability of manufacture for high added value products in ultra-high-precision engineering. Currently, almost all available metrology instrumentation is either too bulky, slow, destructive in terms of damaging the surfaces with a contacting stylus or is carried out off-line. One technology that holds promise for improving the current state-of-the-art in the online measurement of surfaces is hybrid photonic integration. This technique provides for the integration of individual optoelectronic components onto silicon daughter boards which are then incorporated on a silica motherboard containing waveguides to produce a complete photonic circuit. This thesis presents first of its kind a novel chip interferometer sensor based on hybrid integration technology for online surface and dimensional metrology applications. The complete metrology sensor system is structured into two parts; hybrid photonic chip and optical probe. The hybrid photonic chip interferometer is based on a silica-on-silicon etched integrated-optic motherboard containing waveguide structures and evanescent couplers. Upon the motherboard, electro-optic components such as photodiodes and a semiconductor gain block are mounted and bonded to provide the required functionality. Optical probe is a separate entity attached to the integrated optic module which serves as optical stylus for surface scanning in two measurement modes a) A single-point for measuring distance and thus form/surface topography through movement of the device or workpiece, b) Profiling (lateral scanning where assessment of 2D surface parameters may be determined in a single shot. Wavelength scanning and phase shifting inteferometry implemented for the retrival of phase information eventually providing the surface height measurement. The signal analysis methodology for the two measurement modes is described as well as a theoretical and experimental appraisal of the metrology capabilities in terms of range and resolution. The incremetal development of various hybrid photonic modules such as wavelength encoder unit, signal detection unit etc. of the chip interferometer are presented. Initial measurement results from various componets of metrology sensor and the surface measurement results in two measurement modes validate the applicability of the described sensor system as a potential metrology tool for online surface measurement applications

Applications of programmable MEMS micromirrors in laser systems

The use of optical microelectromechanical systems (MEMS) as enabling devices has been shown widely over the last decades, creating miniaturisation possibilities and added functionality for photonic systems. In the work presented in this thesis angular vertical offset comb-drive (AVC) actuated scanning micromirrors, and their use as intracavity active Q-switch elements in solid-state laser systems, are investigated. The AVC scanning micromirrors are created through a multi-user fabrication process, with theoretical and experimental investigations undertaken on the influence of the AVC initial conditions on the scanning micromirror dynamic resonant tilt movement behaviour. A novel actuator geometry is presented to experimentally investigate this influence, allowing a continuous variation of the initial AVC comb-offset angle through an integrated electrothermal actuator. The experimentally observed changes of the resonant movement with varying initial AVC offset are compared with an analytical model, simulating this varying resonant movement behaviour. In the second part of this work AVC scanning micromirrors are implemented as active intra-cavity Q-switch elements of a Nd:YAG solid-state laser system. The feasibility of achieving pulsed laser outputs with pulse durations limited by the laser cavity and not the MEMS Q-switch is shown, combined with a novel theoretical model for the Q-switch behaviour of the laser when using a bi-directional intra-cavity scanning micromirror. A detailed experimental investigation of the pulsed laser output behaviour for varying laser cavity geometries is presented, also discussing the influence of thin film coatings deposited on the mirror surfaces for further laser output power scaling. The MEMS Q-switch system is furthermore expanded using a micromirror array to create a novel Q-switched laser system with multiple individual controllable output beams using a common solid-state gain medium. Experimental results showing the simultaneous generation of two laser outputs are presented, with cavity limited pulse durations and excellent laser beam quality.The use of optical microelectromechanical systems (MEMS) as enabling devices has been shown widely over the last decades, creating miniaturisation possibilities and added functionality for photonic systems. In the work presented in this thesis angular vertical offset comb-drive (AVC) actuated scanning micromirrors, and their use as intracavity active Q-switch elements in solid-state laser systems, are investigated. The AVC scanning micromirrors are created through a multi-user fabrication process, with theoretical and experimental investigations undertaken on the influence of the AVC initial conditions on the scanning micromirror dynamic resonant tilt movement behaviour. A novel actuator geometry is presented to experimentally investigate this influence, allowing a continuous variation of the initial AVC comb-offset angle through an integrated electrothermal actuator. The experimentally observed changes of the resonant movement with varying initial AVC offset are compared with an analytical model, simulating this varying resonant movement behaviour. In the second part of this work AVC scanning micromirrors are implemented as active intra-cavity Q-switch elements of a Nd:YAG solid-state laser system. The feasibility of achieving pulsed laser outputs with pulse durations limited by the laser cavity and not the MEMS Q-switch is shown, combined with a novel theoretical model for the Q-switch behaviour of the laser when using a bi-directional intra-cavity scanning micromirror. A detailed experimental investigation of the pulsed laser output behaviour for varying laser cavity geometries is presented, also discussing the influence of thin film coatings deposited on the mirror surfaces for further laser output power scaling. The MEMS Q-switch system is furthermore expanded using a micromirror array to create a novel Q-switched laser system with multiple individual controllable output beams using a common solid-state gain medium. Experimental results showing the simultaneous generation of two laser outputs are presented, with cavity limited pulse durations and excellent laser beam quality

Integrated Circuits/Microchips

With the world marching inexorably towards the fourth industrial revolution (IR 4.0), one is now embracing lives with artificial intelligence (AI), the Internet of Things (IoTs), virtual reality (VR) and 5G technology. Wherever we are, whatever we are doing, there are electronic devices that we rely indispensably on. While some of these technologies, such as those fueled with smart, autonomous systems, are seemingly precocious; others have existed for quite a while. These devices range from simple home appliances, entertainment media to complex aeronautical instruments. Clearly, the daily lives of mankind today are interwoven seamlessly with electronics. Surprising as it may seem, the cornerstone that empowers these electronic devices is nothing more than a mere diminutive semiconductor cube block. More colloquially referred to as the Very-Large-Scale-Integration (VLSI) chip or an integrated circuit (IC) chip or simply a microchip, this semiconductor cube block, approximately the size of a grain of rice, is composed of millions to billions of transistors. The transistors are interconnected in such a way that allows electrical circuitries for certain applications to be realized. Some of these chips serve specific permanent applications and are known as Application Specific Integrated Circuits (ASICS); while, others are computing processors which could be programmed for diverse applications. The computer processor, together with its supporting hardware and user interfaces, is known as an embedded system.In this book, a variety of topics related to microchips are extensively illustrated. The topics encompass the physics of the microchip device, as well as its design methods and applications

Membrane-Based Broadband Semiconductor Light Sources for Optical Coherence Tomography

Optical coherence tomography (OCT) has experienced tremendous progress over the last three decades and has nowadays become a standard optical imaging modality in the field of biomedicine. High-resolution, multi-dimensional imaging including information about depth is provided in real-time for clinical in-vivo applications even while the field is rapidly growing pushed by continuous technological advance. The scope of the thesis is to advance OCT technology along two main avenues: i) more versatile membrane-based sources for visible wavelength range; ii) development of polarization sensitive OCT (PS-OCT) as an advanced technique providing information of birefringence. For the first path several membrane external-cavity surface-emitting lasers (MECSELs) were demonstrated targeting operation at difficult wavelength ranges, i.e., the red and near-infrared spectral range, and broad-band tuning, an essential feature for OCT. Main results including tunable emission were successfully demonstrated yet full scale implementation into OCT set-ups would require more advanced engineering to stabilize the operation for wavelength tuning. Broad-emitting MECSEL structures were presented based on novel design structures, including the incorporation of quantum dots in the gain region, as well as using two different quantum well types in the same active region. Also, the characterization of a novel design criterion to mitigate undesired spectral effects inherent in MECSELs is presented. For the PS-OCT the impact of changes in temperature of a setup was characterized using a technique to obtain depth information from a measured set of interference fringes using reference signals with known distances. This approach has never been carried out for fiber-based polarization-sensitive systems, which are known to be highly sensitive to dispersion changes. This study can contribute to further development of this approach to image birefringence. In addition to this, a novel approach is proposed to demonstrate super-luminescence operation based on the membrane emitting platform. As in the case of MECSEL, this allows to surpass the limitations of carrier injection that edge emitting laser devices are facing when operating at short wavelength ranges

Optoelectronics – Devices and Applications

Optoelectronics - Devices and Applications is the second part of an edited anthology on the multifaced areas of optoelectronics by a selected group of authors including promising novices to experts in the field. Photonics and optoelectronics are making an impact multiple times as the semiconductor revolution made on the quality of our life. In telecommunication, entertainment devices, computational techniques, clean energy harvesting, medical instrumentation, materials and device characterization and scores of other areas of R&D the science of optics and electronics get coupled by fine technology advances to make incredibly large strides. The technology of light has advanced to a stage where disciplines sans boundaries are finding it indispensable. New design concepts are fast emerging and being tested and applications developed in an unimaginable pace and speed. The wide spectrum of topics related to optoelectronics and photonics presented here is sure to make this collection of essays extremely useful to students and other stake holders in the field such as researchers and device designers