Photonic MEMS interferometers are proving to be strong candidates for compact miniaturized spectrometers. In this work, a 2 mm x 2 mm MEMS-based Michelson interferometer, composed of a thin beam splitter, one fixed mirror, and one moving mirror, is designed and analyzed using Fourier optics propagation techniques and partial coherent source excitation. The model takes into consideration light divergence effects and beam truncation due to the limited dimensions of the device mirrors and beam splitter. The elementary source model is used to represent a partially coherent light source that is typically used in infrared spectroscopy applications. Flat micromirrors are compared to curved ones to explore the possible performance enhancements of the interferometer yielding an improvement of more than two times in the device optical throughput, which typically limits the performance of MEMS devices when dealing with light bulbs sources.
A compact imaging Köhler homogenizer with adjustable flattop size was implemented for a DLP engine. It is composed of pulsed UV LED, collimator aspheric lens, double-sided micro-lens array (MLA) with 34×15 micro-lenses and 0.8mmx1.76mm pitch size, and condenser lens. The homogenizer is dedicated for DMD chip of size 1920×1080 pixels (4K resolution) for 3D printer application. The produced flattop at the DMD has 98% measured uniformity and 85% optical efficiency. The calculated Fresnel number was greater than 60, indicating that our MLA has low diffraction effects. A low-cost RTIR prism was proposed using a wedge and a right-angle prism. Compared to conventional RTIR, the structure characterized by low cost and simplicity in assembly.
Gas sensors are crucial instruments for different industries and air quality monitoring. Micro-electro-mechanical system MEMS technology was proved as a solution for reducing the cost and size of spectrometers. Building gas cells with same technology enables the whole integration of the whole sensor. We present an HWG, as an example for integarted gas cell, which is fabricated on the silicon wafer using the MEMS technology. The HWG length is 2 cm long. The insertion loss of the HWG was measured. Carbon dioxide from exhaling and butane were measured using the HWG in conjunction with the MEMS based spectrometer. This proves the applicability of such HWG for portable gas sensors.
Air pollution is used to refer to the release of pollutants into the air, where these pollutants are harmful to the human health and our planet. The main source of these pollutants comes from energy production and consumption that release Volatile Organic Compounds (VOCs) such as BTEX and Aldehydes group. Real time monitoring of these VOCs in factories, stations, homes and in the street is important for analysis of the pollution sources fingerprint and for alerting, when exceeding the harmful limits. In this work we report the use of a MEMS FTIR spectrometer in the mid-infrared for this purpose. The spectrometer works in the wavelength range of 1.6 μm - 4.9 μm with a resolution down to 33 cm-1. This covers the absorption spectrum of water vapour, BTEX, Aldehydes and CO2 around 2.65 μm, 3.27 μm, 3.6 μm and 4.3 μm, respectively. The spectra of Toluene with different concentrations are measured, using a multipass gas cell with a physical length of 50 cm and an optical path length of 20 m, showing excellent sensor linearity. The minimum concentration measured is 350 ppb limited by the interference of the side lobes of the strong absorption of water vapour, which can be overcome in the future by humidity compensation. The SNR is measured and found to be 5000:1, corresponding to a detection limit of about 90 ppb. The achieved results open the door for a compact and low-cost solution targeting air pollution monitoring.
We have studied polluting gases in tobacco smoke by investigating the phenomenon of capturing and photocatalysis effects of ZnO nanowire array (NWA). Capturing and photocatalysis reactions were continuously tracked by FTIR spectroscopy. The presence of ZnO improves the capture rate at room temperature, while the photocatalytic reactions can lead to a further reduction of the pollutants. MEMS-FTIR spectrometer operating in the Mid-Infra-Red appeared as a very promising tool for the online monitoring of air purification process.
Multimode fibers are used extensively in many applications including optical illumination, sensing, imaging, and spectroscopy. Recently many optical MEMS applications reported the use of MM fiber for delivery of the optical beam to the MOEMS component to make use of its high throughput and thus higher power carrying capacity. In such applications, the spatial distribution and the spatial coherence of the output beam from the MM fiber affects greatly the performance especially if the beam is launched into an optical interferometer. In this work, we present a new model for the MM fiber output, in which the output beam is considered as a quasi-homogeneous shell source decomposed to its coherent elementary functions. Experimental results are obtained for multimode fibers with core/cladding dimensions of 62.5/125 μm, 200/220 μm and 400/440 μm and for different excitation conditions. The model shows very good agreement with the measured intensity distribution at different propagation distances.
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