Semiconductor Nanolasers

Recent progress in the field of semiconductor nanolasers is discussed. New designs have emerged that eliminate the need for a conventional Fabry-Perot cavity, bringing down the physical dimensions of the lasers below the diffraction limit. Semiconductor nanolasers are critical components for nanophotonics and offer possible integration with Si nanoelectronics

A nanophotonic laser on a graph

Conventional nano-photonic schemes minimise multiple scattering to realise a miniaturised version of beam-splitters, interferometers and optical cavities for light propagation and lasing. Here instead, we introduce a nanophotonic network built from multiple paths and interference, to control and enhance light-matter interaction via light localisation. The network is built from a mesh of subwavelength waveguides, and can sustain localised modes and mirror-less light trapping stemming from interference over hundreds of nodes. With optical gain, these modes can easily lase, reaching $\sim$100 pm linewidths. We introduce a graph solution to the Maxwell's equation which describes light on the network, and predicts lasing action. In this framework, the network optical modes can be designed via the network connectivity and topology, and lasing can be tailored and enhanced by the network shape. Nanophotonic networks pave the way for new laser device architectures, which can be used for sensitive biosensing and on-chip optical information processing

Design and Characterisation of III-V Semiconductor Nanowire Lasers

The development of small, power-efficient lasers underpins many of the technologies that we utilise today. Semiconductor nanowires are promising for miniaturising lasers to even smaller dimensions. III-V semiconductors, such as Gallium Arsenide (GaAs) and Indium Phosphide (InP), are the most widely used materials for optoelectronic devices and so the development of nanowire lasers based on these materials is expected to have technologically significant outcomes. This PhD dissertation presents a comprehensive study of the design of III-V semiconductor nanowire lasers, with bulk and quantum confined active regions. Based on the design, various III-V semiconductor nanowire lasers are demonstrated, namely, GaAs nanowire lasers, GaAs/AlGaAs multi-quantum well (MQW) nanowire lasers and InP nanowire lasers. These nanowire lasers are shown to operate at room temperature, have low thresholds, and lase from different transverse modes. The structural and optoelectronic quality of nanowire lasers are characterised via electron microscopy and photoluminescence spectroscopic techniques. Lasing is characterised in all these devices by optical pumping. The lasing characteristics are analysed by rate equation modelling and the lasing mode(s) in these devices is characterised by threshold gain modelling, polarisation measurements and Fourier plane imaging. Firstly, GaAs nanowire lasers that operate at room temperature are demonstrated. This is achieved by determining the optimal nanowire diameter to reduce threshold gain and by passivating nanowires to improve their quantum efficiency (QE). High-quality surface passivated GaAs nanowires of suitable diameters are grown. The growth procedure is tailored to improve both QE and structural uniformity of nanowires. Room-temperature lasing is demonstrated from individual nanowires and lasing is characterised to be from TM01 mode by threshold gain modelling. To lower threshold even further, nanowire lasers with GaAs/AlGaAs coaxial multi-quantum well (MQW) gain regions are investigated. The TE01 mode, due to its polarisation and excellent overlap with the gain region, is predicted to lase in these nanowire heterostructures. Through gain/loss calculations, important design criteria, such as the optimal well thickness to minimise the threshold carrier density and the optimal number of QWs to minimise the threshold fluence are determined. Based on the design, MQW nanowire heterostructures containing eight uniform coaxial GaAs/AlGaAs MQWs are grown. Room-temperature lasing is demonstrated from individual nanowires at a threshold fluence that is two times lower compared to the bulk GaAs nanowire lasers. Lasing is also verified to be from TE01 mode by polarisation measurements. Lastly, a mode characterisation technique based on imaging the polarisation dependent far-field emission pattern of nanowire lasers is presented. To demonstrate this technique, InP nanowire lasers are used, because of their excellent structural characteristics. The InP nanowire lasers are designed to lase from different guided modes by varying the nanowire diameter. The experimentally obtained polarisation dependent far-field profiles match very well with numerical simulations and enable unambiguous identification of the lasing mode(s) in nanowire lasers. Overall, this thesis presents extensive modelling of nanowire lasers, which is supported by experimental results. The modelling will provide a useful reference for developing novel nanoscale lasers and improving the performance of current nanowire lasers

A RARE CASE OF INVASIVE PAPILLARY CARCINOMA OF BREAST

Papillary carcinoma of the breast is extremely rare variety of carcinoma breast with a mere incidence of only 0.5% of all recently diagnosed cases of breast cancer. We present a case of 63 years old postmenopausal female who came to surgical outpatient department with complaints of a slowly increasing mass in the left breast of 1 month duration which was painless. A Left-sided modified radical mastectomy was performed with an absolutely normal post operative period. The final histopathology report was suggestive of invasive papillary carcinoma. We report this case as it is rarely diagnosed. KEYWORDS: Invasive papillary carcinoma; Modified radical mastectomy; Carcinoma breast

Manipulation Planning Among Movable Obstacles Using Physics-Based Adaptive Motion Primitives

Robot manipulation in cluttered scenes often requires contact-rich interactions with objects. It can be more economical to interact via non-prehensile actions, for example, push through other objects to get to the desired grasp pose, instead of deliberate prehensile rearrangement of the scene. For each object in a scene, depending on its properties, the robot may or may not be allowed to make contact with, tilt, or topple it. To ensure that these constraints are satisfied during non-prehensile interactions, a planner can query a physics-based simulator to evaluate the complex multi-body interactions caused by robot actions. Unfortunately, it is infeasible to query the simulator for thousands of actions that need to be evaluated in a typical planning problem as each simulation is time-consuming. In this work, we show that (i) manipulation tasks (specifically pick-and-place style tasks from a tabletop or a refrigerator) can often be solved by restricting robot-object interactions to adaptive motion primitives in a plan, (ii) these actions can be incorporated as subgoals within a multi-heuristic search framework, and (iii) limiting interactions to these actions can help reduce the time spent querying the simulator during planning by up to 40x in comparison to baseline algorithms. Our algorithm is evaluated in simulation and in the real-world on a PR2 robot using PyBullet as our physics-based simulator. Supplementary video: \url{https://youtu.be/ABQc7JbeJPM}.Comment: Under review for the IEEE Robotics and Automation Letters (RA-L) journal with conference presentation option at the 2021 International Conference on Robotics and Automation (ICRA). This work has been submitted to the IEEE for possible publication. Copyright may be transferred without notice, after which this version may no longer be accessibl

A RARE CASE OF INVASIVE PAPILLARY CARCINOMA OF BREAST

Papillary carcinoma of the breast is extremely rare variety of carcinoma breast with a mere incidence of only 0.5% of all recently diagnosed cases of breast cancer. We present a case of 63 years old postmenopausal female who came to surgical outpatient department with complaints of a slowly increasing mass in the left breast of 1 month duration which was painless. A Left-sided modified radical mastectomy was performed with an absolutely normal post operative period. The final histopathology report was suggestive of invasive papillary carcinoma. We report this case as it is rarely diagnosed. KEYWORDS: Invasive papillary carcinoma; Modified radical mastectomy; Carcinoma breast

Biocompatible polymer and protein microspheres with inverse photonic glass structure for random micro-biolasers

This research was funded by Vietnam National Foundation for Science and Technology Development (NAFOSTED) under grant number 103.03-2017.318 and the the EPSRC Standard Grant EP/T027258/1.The miniaturization of random lasers to the micrometer scale is challenging but fundamental for the integration of lasers with photonic integrated circuits and biological tissues. Herein, it is demonstrated that random lasers with a diameter from 30 to 160 μm can be achieved by using a simple emulsion process and selective chemical etching. These tiny random laser sources are made of either dye-doped polyvinyl alcohol (PVA) or bovine serum albumin (BSA) and they are in the form of microporous spheres with monodisperse pores of 1.28 μm in diameter. Clear lasing action is observed when the microporous spheres are optically excited with powers larger than the lasing threshold, which is 154 μJ mm−2 for a 75 μm diameter PVA microporous sphere. The lasing wavelength redshifts 10 nm when the PVA microsphere diameter increases from 34 to 160 μm. For BSA microspheres, the lasing threshold is around 55 μJ mm−2 for a 70 μm diameter sphere and 104 μJ mm−2 for a 35 μm diameter sphere. The simple fabrication process reported allows for detail studies of morphology and size, important for fundamental studies of light–matter interaction in complex media, and applications in photonic integrated circuits, photonic barcoding, and optical biosensing.Publisher PDFPeer reviewe