Proof-of-concept demonstration of free-form optics enhanced confocal Raman spectroscopy in combination with optofluidic lab-on-chip

Raman spectroscopy is a powerful optical and non-destructive technique and a well-known method for analysis purposes, especially to determine the molecular fingerprint of substances. Traditionally, such analyses are done in a specialized lab, with considerable requirements in terms of equipment, time and manual sampling of substances of interest. In this paper we take a step from bulky Raman spectroscopy laboratory analyses towards lab-on-chip (LOC) analyses. We present an optofluidic lab-on-chip for confocal Raman spectroscopy, which can be used for the analysis of liquids. The confocal detection suppresses the unwanted background from the polymer material out of which the chip is fabricated. We design the free-form optical reflector using non-sequential ray-tracing combined with a mathematical code to simulate the Raman scattering behavior of the substance under test. We prototype the device in Polymethyl methacrylate (PMMA) by means of ultraprecision diamond tooling. In a proof-of-concept demonstration, we first show the confocal behavior of our Raman lab-on-chip system by measuring the Raman spectrum of ethanol. In a next step, we compare the Raman spectra measured in our lab-on-chip with spectra measured with a commercial Raman spectrometer. Finally, to calibrate the system we perform Raman measurements on urea solutions with different concentrations. We achieve a detection limit that corresponds to a noise equivalent concentration of 20mM. Apart from strongly reducing the background perturbations, our confocal Raman spectroscopy system has other advantages as well. The reflector design is robust from a mechanical point of view and has the potential for mass-manufacturing using hot embossing or injection molding

Fabrication-tolerant four-channel wavelength-division-multiplexing filter based on collectively tuned Si microrings

We demonstrate a robust, compact and low-loss four-channel wavelength-division multiplexing (WDM) filter based on cascaded double-ring resonators (2RR) in silicon. The flat-top channel response obtained by the second-order filter design is exploited to compensate for the detrimental effects of local fabrication variations and their associated phase errors on the ring-based filter response. Full wafer-scale characterization of a cascaded, four-channel 2RR filter with channel spacing of 300 GHz shows an average worst-case insertion loss below 1.5 dB and an average worst-case crosstalk below -18 dB across the wafer, representing a substantial improvement over a first-order based ring (1RR) design. The robust 2RR filter design enables the use of a simple collective thermal tuning mechanism to compensate for global fabrication variations as well as for global temperature fluctuations of the WDM filter, the WDM laser source, or both. Highly uniform collective heating is demonstrated using integrated doped silicon heaters. The compact filter footprint of less than 50 x 50 mu m(2) per channel enables straightforward scaling of the WDM channel count to 8 channels and beyond. Such low-loss collectively tuned ring-based WDM filters can prove beneficial in scaling the bandwidth density of chip-level silicon optical interconnects

Laser teeth bleaching: evaluation of eventual side effects on enamel and the pulp and the efficiency in vitro and in vivo.

Light and heat increase the reactivity of hydrogen peroxide. There is no evidence that light activation (power bleaching with high-intensity light) results in a more effective bleaching with a longer lasting effect with high concentrated hydrogen peroxide bleaching gels. Laser light differs from conventional light as it requires a laser-target interaction. The interaction takes place in the first instance in the bleaching gel. The second interaction has to be induced in the tooth, more specifically in the dentine. There is evidence that interaction exists with the bleaching gel: photothermal, photocatalytical, and photochemical interactions are described. The reactivity of the gel is increased by adding photocatalyst of photosensitizers. Direct and effective photobleaching, that is, a direct interaction with the colour molecules in the dentine, however, is only possible with the argon (488 and 415 nm) and KTP laser (532 nm). A number of risks have been described such as heat generation. Nd:YAG and especially high power diode lasers present a risk with intrapulpal temperature elevation up to 22°C. Hypersensitivity is regularly encountered, being it of temporary occurrence except for a number of diode wavelengths and the Nd:YAG. The tooth surface remains intact after laser bleaching. At present, KTP laser is the most efficient dental bleaching wavelength.Peer Reviewe

Insight in the chemistry of laser-activated dental bleaching.

The use of optical radiation for the activation of bleaching products has not yet been completely elucidated. Laser light is suggested to enhance the oxidizing effect of hydrogen peroxide. Different methods of enhancing hydrogen peroxide based bleaching are possible. They can be classified into six groups: alkaline pH environment, thermal enhancement and photothermal effect, photooxidation effect and direct photobleaching, photolysis effect and photodissociation, Fenton reaction and photocatalysis, and photodynamic effect.Peer Reviewe

Design and Characterisation of RF-MEMS Components

Design and characterisation of RF MEMS devices Miniaturisation of IC technologies has enabled the performance of electronic systems to progress by leaps and bounds over the past couple of decades. The ability to create ever smaller electrical components in astoundingly massive amounts has inspired researchers to extend IC manufacturing techniques towards the fabrication of miniature devices with mechanical functionality. This effort has resulted in a large variety of microelectromechanical systems (MEMS) or microsystems that are used for sensing pressure, acceleration, angular rate, the presence of chemical or biological substances, as well as for actuating optical or electrical switches, microfluidic pumps and valves, micromirror arrays and a host of other micromachines. Applications of microsystems in RF circuits are usually gathered under the acronym RF MEMS, which are the main topic of this dissertation. The first chapter of this text briefly introduces the origins of microfabrication and gives a topical review of RF MEMS devices that have been developed to date. As electrostatic actuation is commonly used in many microsystems for RF as well as for other applications, the second chapter deals with mechanical modelling of electrostatic actuators. Several aspects of the operation of electrostatic actuators are investigated: spring constants, CV characteristics, influence of stress and stress gradient. Experimental characterisation results are presented and compared with modelling results. In the third chapter, the influence of environmental changes on the performance of electrostatic actuators is investigated. The influence of temperature changes is studied, as well as the impact of ambient pressure on the damping and switching time of parallel-plate actuators. Measured damping properties are used for hermeticity evaluation of wafer-level packaging. In addition, the influence of mechanical shock impulses is analysed and empirically verified. Chapter four covers the RF properties of the devices that are modelled and characterised in the previous chapters. The performance of capacitive series and shunt switches is measured and component models are fitted onto the measured results. The performance of the devices is then optimised by combining series and shunt switches, and by integrating additional inductance in the suspension beams of the devices. Finally, the devices are combined into an antenna switch module featuring 6 RF input ports and a common antenna port.status: publishe

Device and method for the measurement of anchor shear strength in MEMS devices

This paper presents a test structure, designed for measuring the shear strength of anchors in MEMS devices. It consists of an in-plane comb drive actuator, operating in its lateral mode, which pushes a tip against test anchors of various sizes. Mechanical failure of the anchors is observed electrically by monitoring the resistance across the anchor.status: publishe