1,786 research outputs found

    Tunable MEMS VCSEL on Silicon substrate

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    We present design, fabrication and characterization of a MEMS VCSEL which utilizes a silicon-on-insulator wafer for the microelectromechanical system and encapsulates the MEMS by direct InP wafer bonding, which improves the protection and control of the tuning element. This procedure enables a more robust fabrication, a larger free spectral range and facilitates bidirectional tuning of the MEMS element. The MEMS VCSEL device uses a high contrast grating mirror on a MEMS stage as the bottom mirror, a wafer bonded InP with quantum wells for amplification and a deposited dielectric DBR as the top mirror. A 40 nm tuning range and a mechanical resonance frequency in excess of 2 MHz are demonstrated

    Fabrication and characterisation of tellurite planar waveguides

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    Tellurite glasses, which contain Tellurium dioxide as the main component, have some remarkable optical properties which are well recognised and exploited in the bulk optics and fibre fields. They include a high acousto-optic figure of merit, wide mid infrared transparency, the highest optical nonlinearity amongst oxides, and excellent rare earth hosting, etc. Despite these attractive properties, until now, no one has succeeded in fabricating low loss planar waveguides in these materials. This work develops high quality optical planar waveguides in Tellurium dioxide for the first time. The project investigates the materials science for optical Tellurium dioxide films and discovers an appropriate waveguide fabrication method. The thin films have been fabricated by reactive radio frequency magnetron sputtering using a Tellurium target in an oxygen and argon atmosphere. Propagation losses at 1550nm in the planar films are 0.1dB/cm or lower in stoichiometric composition. The properties of films have been also found to be stable with thermal annealing up to 300 degree Celsius. Plasma etching of tellurite glasses has been systematically studied. High quality etching of Tellurium dioxide and chalcogenide glass films has been demonstrated with a Methane/Hydrogen/Argon gas mixture. As a result, a fabrication recipe which produces low loss (0.1dB/cm) planar waveguides has been discovered. The nonlinear coefficient of the sputtered TeO2 has been characterised by self-phase modulation (SPM) experiments and the second order nonlinear coefficient has been measured to be around 25 times that of silica. Significant signal conversion, -4dB, has achieved with large bandwidth of 30nm in the four-wave mixing (FWM) experiment pumped at 1550nm in a slightly normal dispersion waveguide. Erbium doped Tellurium oxide thin films have also been fabricated by co-sputtering of Erbium and Tellurium targets into an Oxygen and Argon atmosphere. The obtained films have been found to have good properties for Erbium doped waveguide amplifiers. The Erbium concentration can be controlled within the range of interest with Erbium/Tellurium ratios ranging from 0.1% to 3% or more. The 1.5 micrometre photoluminescence properties of the films are excellent with effective bandwidth of more that 60nm and intrinsic lifetime of order of 3ms. Despite the fact that there was OH contamination in the films, single mode Erbium doped waveguide amplifiers with high internal gain have been successfully obtained. The 1480nm pumped amplifier achieved internal gain from below 1520nm to beyond 1600nm. The peak gain of 2.8dB/cm and 40nm 3dB gain bandwidth have been accomplished. These results are a major stepping stone towards ""system-on-chip"" optical applications for telecom and mid infrared optics given the multifunctional nature of tellurite materials. -- provided by Candidate

    Surface micromachined MEMS variable capacitor with two-cavity for energy harvesting

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    In this research, a novel MEMS variable capacitor with two capacitive cavities for energy harvesting was developed that use the wasted energy associated with undesirable mechanical vibrations to power microelectronic sensors and actuators widely found in structures and systems surrounding us. The harvested power, though very small, can have a profound effect on the usage of microsensors. First, the self-powered sensors will no longer require regular battery maintenance. Second, the self-powered chip is a liberating technology. On a circuit board, it can simplify the connection. On a commercial jet, the sensors can greatly simplify cabling. The design, fabrication, modeling and complete set of characterization of MEMS variable capacitors with two-cavity are presented in details in this thesis. The MEMS variable capacitors are unique in its two-cavity design and use of electroplated nickel as the main structural material. The device consists of 2x2 mm² movable capacitive proof mass plates with a thickness of 30 [mu]m suspended between two fixed electrodes forming two vertical capacitors. When the capacitance increases for one cavity, it decreases for the other. This allows using both up and down directions to generate energy. The suspended movable plates are supported by four serpentine springs with a thickness of 3-5 [mu]m that are attached to the address lines on a silicon substrate only at the anchors' points which is made of electroplated nickel. The serpentine suspension beams are made with a width, thickness and total length (four serpentine turns) of 15 [mu]m, 5 [mu]m and 1485 [mu]m. Five gold stoppers with height of 2-4 [mu]m were electroplated on the fixed plates to prevent snap-down of the movable plates by overwhelming electrostatic force. SiO2 and Si3N4 thin layers were patterned on the fixed plates to insulate the stoppers and enhance the dielectric property of capacitive cavities. The MEMS variable capacitor with two-cavity has been designed and modeled using MEMS CAD tool and COMSOL Multi-PhysIncludes bibliographical references (pages 108-118)

    Fabrication and Testing of a Micro-scalable pH Sensor for Implanted Biomedical Use

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    Biosensors have recently moved into the arena of implantable devices. This incredible capability,to continuously monitor physiological parameters in-situ, allows for earlier and fundamentallymore accurate measurements. As pH is one of the most important biological factors, implantabledevices to measure pH are of great interest. Unfortunately, current pH sensors exhibit signal driftand require regular recalibration. Since this is impractical for implanted devices, much work isneeded in order to extend the working life of the pH sensor. The present work implemented threetechniques for fabricating a pH sensor based on an iridium oxide sensing layer that are compatiblewith micro-fabrication techniques and implantable devices. They are the oxidation of pure iridium,reactive sputtering of iridium in an oxygen environment, and anodic electrodeposition of iridiumoxide. The response of the sensors based on these indicating layers to tests in buer solution revealeda high degree of linearity. Slopes of the response were in agreement with those found in theliterature. Life tests were performed to characterize the signal drift over 20 hours of continuoususe. The established processes for fabricating the pH sensors provide a vehicle for further investigationinto techniques for extending life, specifically, by using microfluidic devices. Preliminarytests were done to show that interruption of the electrochemical circuit slows signal drift. This canbe accomplished in microscale devices using a microfluidic switching mechanism proposed here

    Advanced dispersive mirrors for ultrashort laser pulses from the near-UV to the mid-IR spectral range

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    Advanced Focused Beam-Induced Processing for Nanoscale Synthesis and 2D Materials Device Architectures

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    Nanofabrication has come to prominence over recent years due to miniaturization of electronic devices as well as interesting physical phenomena that arise in material systems at the nanoscale. Particle beam induced processing enables additive as well as subtractive nanoprocessing techniques. Focused beam induced processing facilitates direct-write processing, thus making it a common technique for fabrication and synthesis on the nanoscale and is typically carried out with charged particles such as electrons or ion species, each of which offer distinct capabilities. This dissertation addresses several challenges which currently plague the focused beam-induced processing community and explores novel applications.Chapter I explores laser based purification strategies for electron beam induced deposition. This addresses the challenge of material purity, which currently limits broader application of the nanofabrication technique. Chapter II covers advanced helium ion beam induced processing using a Gas Field Ionization source. This chapter explores novel applications for the helium ion beam as well as the mitigation of helium-induced subsurface damage, which currently prevents ubiquitous adoption of the helium ion microscope as a nanofabrication tool. Chapter III studies defect introduction in 2D materials under helium ion irradiation, which proves to be an ideal nanoprocessing application for the helium ion beam
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