Flory-Huggins Photonic Sensors

openThis Thesis focuses on the design of a simple optical method for the determination of molecular diffusion coefficients and for the quali-quantitative assessment of the diffusing species in polymer photonic sensors and in commercial polymer thin films used in packaging. This project arose to overcome the lack of methodologies related to the detection of hazardous vapor molecules both in air and in goods packaging. To tackle this task, this Thesis proposes simple optical spectroscopy coupled to photonic crystal sensors (called Flory-Huggins Photonic Sensors, FHPSs) and commercial polymer thin films to retrieve quali-quantitative information of polluted air and molecular diffusion coefficient in the polymers themselves. This is achieved studying the kinetics of optical variations in the diffraction and/or interference pattern of the sensors, which are opportunely designed to interact with the analyte species. In the first Chapters, after discussing the problematics related to the monitoring of vapor analytes and to the determination of diffusion coefficients, this Thesis explains the working principle of the FHPSs, and the optical set-up designed to the purpose. Then, commodity polymers FHPSs are used as proof of principle to create a receipt for the design of sensors suitable for any class of chemical compounds. This system also shows colorimetric response with sensitivity and lower detection limit approaching the part per million and label free selectivity to the tested analytes. Moreover, the study of the kinetics of the spectral response allow to evaluate the diffusion coefficients of the analytes within the photonic structure. The method is then tested for the detection of various pollutants. The possibility to use unstructured commercial films to the same purposes in also discussed and demonstrated. These results promise to simplify detection of volatile pollutants in atmosphere and a new simple tool to asses diffusion of hazardous molecules in packaging systems. The possibility to assess the colorimetric response of the FHPSs even by the naked eye, together with the capability to monitor diffusive processes in polymer packaging film directly on the shelf, promises also safety devices and continuous assessment of goods.openXXXII CICLO - SCIENZE E TECNOLOGIE DELLA CHIMICA E DEI MATERIALI - Scienze e tecnologie chimicheLova, Paol

Integrated sensors for process monitoring and health monitoring in microsystems

This thesis presents the development of integrated sensors for health monitoring in Microsystems, which is an emerging method for early diagnostics of status or “health” of electronic systems and devices under operation based on embedded tests. Thin film meander temperature sensors have been designed with a minimum footprint of 240 m × 250 m. A microsensor array has been used successfully for accurate temperature monitoring of laser assisted polymer bonding for MEMS packaging. Using a frame-shaped beam, the temperature at centre of bottom substrate was obtained to be ~50 ºC lower than that obtained using a top-hat beam. This is highly beneficial for packaging of temperature sensitive MEMS devices. Polymer based surface acoustic wave humidity sensors were designed and successfully fabricated on 128° cut lithium niobate substrates. Based on reflection signals, a sensitivity of 0.26 dB/RH% was achieved between 8.6 %RH and 90.6 %RH. Fabricated piezoresistive pressure sensors have also been hybrid integrated and electrically contacted using a wire bonding method. Integrated sensors based on both LiNbO3 and ZnO/Si substrates are proposed. Integrated sensors were successfully fabricated on a LiNbO3 substrate with a footprint of 13 mm × 12 mm, having multi monitoring functions for simultaneous temperature, measurement of humidity and pressure in the health monitoring applications

Glassy Materials Based Microdevices

Microtechnology has changed our world since the last century, when silicon microelectronics revolutionized sensor, control and communication areas, with applications extending from domotics to automotive, and from security to biomedicine. The present century, however, is also seeing an accelerating pace of innovation in glassy materials; as an example, glass-ceramics, which successfully combine the properties of an amorphous matrix with those of micro- or nano-crystals, offer a very high flexibility of design to chemists, physicists and engineers, who can conceive and implement advanced microdevices. In a very similar way, the synthesis of glassy polymers in a very wide range of chemical structures offers unprecedented potential of applications. The contemporary availability of microfabrication technologies, such as direct laser writing or 3D printing, which add to the most common processes (deposition, lithography and etching), facilitates the development of novel or advanced microdevices based on glassy materials. Biochemical and biomedical sensors, especially with the lab-on-a-chip target, are one of the most evident proofs of the success of this material platform. Other applications have also emerged in environment, food, and chemical industries. The present Special Issue of Micromachines aims at reviewing the current state-of-the-art and presenting perspectives of further development. Contributions related to the technologies, glassy materials, design and fabrication processes, characterization, and, eventually, applications are welcome

Engineering the optical properties of luminescent solar concentrators at the molecular scale

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2012.Cataloged from PDF version of thesis.Includes bibliographical references (p. 121-128).Luminescent Solar Concentrators (LSCs) concentrate solar radiation onto photovoltaic (PV) cells using an inexpensive collector plate to absorb incoming photons and waveguide fluorescently re-emitted photons to PVs at the edge. This thesis addresses the two main energy loss mechanisms in LSCs, namely transport losses and trapping losses. We used phycobilisomes, a biological light-harvesting complex, as dyes in the LSC collector to circumvent transport losses caused by photon re-absorption. The selfassembled structure of phycobilisomes couples numerous donor chromophores to a handful of acceptor chromophores through an internal F6rster energy pathway that isolates the absorption and emission spectra. We established that energy transfer within intact phycobilisomes reduces LSC self-absorption losses by approximately (48±5)% by comparing intact and partly decoupled phycobilisome complexes. To reduce trapping losses in LSCs, we leveraged the anisotropic emission pattern of dichroic dye molecules. We aligned their dipole moments normal to the face of the waveguide by embedding them in a liquid crystal host. Vertical dye alignment increased the fraction of the power emitted below the critical angle of the waveguide, thereby raising the trapping efficiency to 81% from 66% for LSCs with unaligned dyes. The enhanced trapping efficiency was preserved for geometric gains up to 30, and an external diffuser can enhance absorption in LSCs with vertically-aligned dyes. This thesis also explores an energy harvesting strategy for portable electronics based on LSCs with dye molecules that are aligned in-plane. The purely absorptive polarizers used to enhance contrast ratios in displays can be replaced with two linearly polarized luminescent concentrators (LSCs) that channel the energy of absorbed photons to PVs at the edge of the display. We coupled up to 40% of incoming photons to the edge of a prototype LSC that also achieved a polarization selection ratio of 3. Finaly, we investigated the contribution of self-absorption and optical waveguiding to triplet exciton transport in crystalline tetracene (Tc) and rubrene (Rb). A timeresolved imaging technique that maps the triplet distribution showed that optical waveguiding dominates over diffusion and can transport energy several micrometers at the high excitation rates commonly used to probe the exciton diffusion constants in organic materials.by Carlijn Lucinde Mulder.Ph.D

Sample extraction and injection with a microscale preconcentrator.

This report details the development of a microfabricated preconcentrator that functions as a fully integrated chemical extractor-injector for a microscale gas chromatograph (GC). The device enables parts-per-billion detection and quantitative analysis of volatile organic compounds (VOCs) in indoor air with size and power advantages over macro-scale systems. The 44 mm{sup 3} preconcentrator extracts VOCs using highly adsorptive, granular forms of graphitized carbon black and carbon molecular sieves. The micron-sized silicon cavities have integrated heating and temperature sensing allowing low power, yet rapid heating to thermally desorb the collected VOCs (GC injection). The keys to device construction are a new adsorbent-solvent filling technique and solvent-tolerant wafer-level silicon-gold eutectic bonding technology. The product is the first granular adsorbent preconcentrator integrated at the wafer level. Other advantages include exhaustive VOC extraction and injection peak widths an order of magnitude narrower than predecessor prototypes. A mass transfer model, the first for any microscale preconcentrator, is developed to describe both adsorption and desorption behaviors. The physically intuitive model uses implicit and explicit finite differences to numerically solve the required partial differential equations. The model is applied to the adsorption and desorption of decane at various concentrations to extract Langmuir adsorption isotherm parameters from effluent curve measurements where properties are unknown a priori

The feasibility of micromachined dynamic resonant beam coriolis true mass flow meter

The technological advances of micro-electro-mechanical systems (MEMS) in the past two decades have been remarkable for innovations in microfluidic systems as well as automotive applications such as pressure sensors and accelerometers. MEMS flow sensing has emerged as a field of interest in microfluidics, with a variety of sensing methods being miniaturized, such as thermal anemometry, ultrasonic sensing and flow measurement based on the Coriolis effect. Coriolis sensing is particularly attractive since, unlike most other methods which provide volumetric flow information, Coriolis sensing is capable of providing a direct, true mass flow measurement. Because of this advantage, Coriolis flow sensing has engendered strong interest in developing miniature device designs, fabrication techniques, and sensitive Coriolis detection methods. Research and development efforts have been undertaken both in academia and industry to make inexpensive, highly sensitive, reliable, and appropriately packaged Coriolis solutions. One research focus has been on detection and read-out methods for Coriolis-induced signals. Piezoresistive, optical and capacitive methods have all been tried. This dissertation introduces the resonant beam as a detecting method for Coriolis mass flow sensing. Because resonant beams measure frequency changes, they can be highly sensitive, much more so than the previously tried methods. Resonant beams have been successfully demonstrated in MEMS pressure sensors and accelerometers. This work extends their application to Coriolis mass flow devices

Femtosecond Laser Micromachining of Advanced Fiber Optic Sensors and Devices

Research and development in photonic micro/nano structures functioned as sensors and devices have experienced significant growth in recent years, fueled by their broad applications in the fields of physical, chemical and biological quantities. Compared with conventional sensors with bulky assemblies, recent process in femtosecond (fs) laser three-dimensional (3D) micro- and even nano-scale micromachining technique has been proven an effective and flexible way for one-step fabrication of assembly-free micro devices and structures in various transparent materials, such as fused silica and single crystal sapphire materials. When used for fabrication, fs laser has many unique characteristics, such as negligible cracks, minimal heat-affected-zone, low recast, high precision, and the capability of embedded 3D fabrication, compared with conventional long pulse lasers. The merits of this advanced manufacturing technique enable the unique opportunity to fabricate integrated sensors with improved robustness, enriched functionality, enhanced intelligence, and unprecedented performance. Recently, fiber optic sensors have been widely used for energy, defense, environmental, biomedical and industry sensing applications. In addition to the well-known advantages of miniaturized in size, high sensitivity, simple to fabricate, immunity to electromagnetic interference (EMI) and resistance to corrosion, all-optical fiber sensors are becoming more and more desirable when designed with characteristics of assembly free and operation in the reflection configuration. In particular, all-optical fiber sensor is a good candidate to address the monitoring needs within extreme environment conditions, such as high temperature, high pressure, toxic/corrosive/erosive atmosphere, and large strain/stress. In addition, assembly-free, advanced fiber optic sensors and devices are also needed in optofluidic systems for chemical/biomedical sensing applications and polarization manipulation in optical systems. Different fs laser micromachining techniques were investigated for different purposes, such as fs laser direct ablating, fs laser irradiation with chemical etching (FLICE) and laser induced stresses. A series of high performance assembly-free, all-optical fiber sensor probes operated in a reflection configuration were proposed and fabricated. Meanwhile, several significant sensing measurements (e.g., high temperature, high pressure, refractive index variation, and molecule identification) of the proposed sensors were demonstrated in this dissertation as well. In addition to the probe based fiber optic sensors, stress induced birefringence was also created in the commercial optical fibers using fs laser induced stresses technique, resulting in several advanced polarization dependent devices, including a fiber inline quarter waveplate and a fiber inline polarizer based on the long period fiber grating (LPFG) structure

Optical pulse processing towards Tb/s high-speed photonic systems

Due to the continued growth of high-bandwidth services provided by the internet, there is a requirement to operate individual line rates in excess of 100 Gb/s in next generation optical communications systems. Thus, to implement these high-speed optical networks all-optical processing techniques are necessary for pulse shaping and pulse routing. Two sub-systems (pulse generation and wavelength conversion), which exploit optical processing techniques are explored within this thesis. Future systems will require high-quality pulse sources and this thesis develops the pulse generation technique of gain switching to provide simple and cost efficient pulse sources. The poor pulse quality typically associated with gain switching is enhanced by developing all-optical methods. The main attribute of the first pulse generation scheme presented is its wavelength tunability over 50 nm. The novelty of the second scheme lies in the ability to design a grating which has a nonlinear chirp profile exactly opposite to the gain-switched pulses. This grating used in conjunction with the gain-switched laser generates transform limited pulses suitable for 80 Gb/s systems. Furthermore the use of a vertical microcavity-based saturable absorber to suppress detrimental temporal pulse pedestals of a pulse source is investigated. Next generation networks will require routing of data in the optical domain, which can be accomplished by high-speed all-optical wavelength converters. A semiconductor optical amplifier (SOA) is an ideal device to carry out wavelength conversion. In this thesis pulses following propagation through an SOA are experimentally characterised to examine the temporal and spectral dynamics due to the nonlinear response of the SOA. High-speed wavelength conversion is presented using SOA-based shifted filtering. For the first time 80 Gb/s error-free performance was obtained using cross phase modulation in conjunction with blue spectral shifted filtering. In addition an important attribute of this work experimentally examines the temporal profile and phase of the SOA-based shifted filtering wavelength converted signals. Thus the contribution and effect of ultrafast carrier dynamics associated with SOAs is presented