Fiber optic chip for fully-guided Raman iterrogation of molecular adsorbates.

Planar fiber-optic chips (FOC) take advantage of the evanescent field effects of side-polished fibers, exhibiting usefulness in fluorescence, absorbance, electrochemical investigations, and as presented here Raman spectroscopy. The fabrication of the FOC utilizes a side-polishing process of a multi-mode optical fiber. The fiber core is exposed creating a D-shape when viewed laterally. The cylindrical fiber is mounted in a V-groove of a Si-wafer and side-polished, creating a platform for easier analyte handling with greater control over surface chemistry. A longer path length when compared with end-tip fiber probes results in a larger cross section of analyte signal. This work presents decoupled investigations of excitation and collection of Raman scattering using the FOC, for bulk media and thin films. Realization of a fully in-line system would alleviate the need for alignment of cumbersome bench-top optics, further increasing the utility of this device by allowing for interrogation of remote, hostile environments

Optical sensing of microbial life on surfaces

The label-free detection of microbial cells attached to a surface is an active field of research. The field is driven by the need to understand and control the growth of biofilms in a number of applications, including basic research in natural environments, industrial facilities, and clinical devices, to name a few. Despite significant progress in the ability to monitor the growth of biofilms and related living cells, the sensitivity and selectivity of such sensors are still a challenge. We believe that among the many different technologies available for monitoring biofilm growth, optical techniques are the most promising, as they afford direct imaging and offer high sensitivity and specificity. Furthermore, as each technique offers different insights into the biofilm growth mechanism, our analysis allows us to provide an overview of the biological processes at play. In addition, we use a set of key parameters to compare state-of-the-art techniques in the field, including a critical assessment of each method, to identify the most promising types of sensors. We highlight the challenges that need to be overcome to improve the characteristics of current biofilm sensor technologies and indicate where further developments are required. In addition, we provide guidelines for selecting a suitable sensor for detecting microbial cells on a surface

Microscale Infrared Technologies for Spectral Filtering and Wireless Neural Dust

Pivotal technologies, such as optical computing, autonomous vehicles, and biomedical implantables, motivate microscale infrared (IR) components. Hyperspectral imagers (HSI), for example, require compact and narrowband filters to obtain high-spatial and -spectral resolution images. HSIs acquire continuous spectra at each pixel, enabling non-destructive analyses by resolving IR scattering/absorption signatures. Toward this end, dielectric subwavelength gratings (SWG) are intriguing filter candidates since they are low-loss, have no moving parts, and exhibit narrow spectral features. Wireless neural implantables are another apropos microscale IR technology. Wireless IR data and power transfer disposes of infection-prone percutaneous wires by leveraging the IR transparency window in biological tissue. This dissertation contains two related topics. The first details SWG IR filters, and the second studies progress toward wireless neural motes. This work extends the capabilities of SWG IR filters. Following a theoretical overview, mid-wave infrared (MWIR, 3-7 um) transmittance filters are experimentally demonstrated using the zero-contrast grating scheme. Via a facile silicon fabrication process, we realize narrowband polarization-dependent and polarization-independent MWIR transmittance filters with some of the highest Q observed in MWIR SWGs. An empirical study confirms the relationship between filter performance and grating size, an important trade-off for HSIs. We then demonstrate GaAs SWG filters for monolithic integration with active optoelectronic devices. The GaAs SWGs perform comparably to their silicon counterparts. To enable narrowband filtering at normal incidence, we investigate symmetry-breaking in geometrically asymmetric gratings. The presented SWG geometries access quasi-bound states in the continuum (BIC). Studies in Fano resonance and diffraction efficiency symmetry provide physical insight. Asymmetric 1D and 2D SWGs furnish polarization-dependent and -independent filtering, respectively. We experimentally demonstrate normal incidence long-wave IR (LWIR, 7-12 um) transmittance filtering in asymmetric SWGs and confirm symmetry-breaking implications. A reduced-symmetry hexagonal pattern presents an early design for truly polarization-independent quasi-BIC coupling in SWGs. Advancements in implantable neural devices promise great leaps in brain mapping and therapeutic intervention. To meet this challenge, we investigated a wireless neural mote system using near-infrared (NIR, 800 nm – 3 um) photovoltaics and LEDs to wirelessly harvest power and transmit data. The neural recorders consist of three subsystems: an epitaxial GaAs-based optoelectronic chip, a Si CMOS IC, and a carbon fiber probe. Though this work encompasses the efforts of many, this dissertation outlines contributions in a few critical areas. To overcome low-flux LED emission, we devise an optical setup with ≈0.1% photon detection efficiency. Monte Carlo techniques model NIR scattering in biological tissue. Another steep challenge is the heterogeneous integration of the three material systems in a compact (200x170x150 um^3) package. To relay data and power between the GaAs and CMOS chips, through-wafer vias are critical. Using a novel selective copper plating technique, we demonstrate through-wafer GaAs vias with <2 Ohm series resistance. Additionally, conductive blind vias are presented for carbon fiber probe insertion. A self-aligned parylene etch mask permits sub-kOhm connection to a buried metal contact while maintaining GOhm substrate isolation. Both via structures meet the requirements of being low-resistance, insulated from the substrate, and amendable to thinned wafer processing. Finally, we demonstrate extensive processing on thinned chips and advances toward full heterogeneous integration via flip-chip alignment and solder bump bonding.PHDElectrical and Computer EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/169986/1/barrowm_1.pd

MEMS Technology for Biomedical Imaging Applications

Biomedical imaging is the key technique and process to create informative images of the human body or other organic structures for clinical purposes or medical science. Micro-electro-mechanical systems (MEMS) technology has demonstrated enormous potential in biomedical imaging applications due to its outstanding advantages of, for instance, miniaturization, high speed, higher resolution, and convenience of batch fabrication. There are many advancements and breakthroughs developing in the academic community, and there are a few challenges raised accordingly upon the designs, structures, fabrication, integration, and applications of MEMS for all kinds of biomedical imaging. This Special Issue aims to collate and showcase research papers, short commutations, perspectives, and insightful review articles from esteemed colleagues that demonstrate: (1) original works on the topic of MEMS components or devices based on various kinds of mechanisms for biomedical imaging; and (2) new developments and potentials of applying MEMS technology of any kind in biomedical imaging. The objective of this special session is to provide insightful information regarding the technological advancements for the researchers in the community

High Sensitivity Optical Fiber Interferometric Sensors

Optical fiber interferometers have been widely employed and investigated for monitoring the changes in both physical and chemical parameters, with the advantages of compact size, light weight, immunity to electromagnetic interference, high sensitivity, capability to work in harsh environments and remote operation capabilities. Among the different kinds of fiber sensors based on interferometry, singlemode-multimode-singlemode (SMS) structures has attracted considerable interest due to their inherent advantages of high sensitivity, ease of fabrication and interconnection to other fiber systems and low cost. However, the challenge is that the sensitivity of the traditional SMS based fiber structure is not sufficient in some cases, for example in bio-chemical applications, where detection of a very small variation in a bio-chemicals’ concentration is required. There is thus a need to investigate how to modify or enhance an SMS structure to achieve ultrahigh sensitivity. This thesis presents research and its applications concerning approaches to improve the sensitivity and detection accuracy of a traditional SMS fiber structure based sensor. The key achievements of this thesis include: Traditional SMS fiber structure for breathing state monitoring A bend SMS structure is investigated as a breathing sensor by attaching it to a thin plastic film in an oxygen mask. Breath rate can be monitored using this sensor by detecting power variations due to the macro bending applied to the SMS section during each inhalation and exhalation cycles. Different types of breathing conditions including regular and irregular breath patterns can be distinguished. The proposed sensor is capable of working in a strong electromagnetic field and radioactive environment. Tapered small core singlemode fiber (SCSMF) for the detection of refractive index (RI), ammonia, and volatile organic compounds (VOCs) A modified SMS structure based on a tapered SCSMF is proposed and investigated with significantly improved RI sensitivity. It is found that the sample with a smaller waist diameter gives higher sensitivity. In the experiment, a maximum sensitivity of 19212.5 nm/RIU (RI unit) in the RI range from 1.4304 to 1.4320 has been demonstrated when the waist diameter of the SCSMF is tapered down to 12.5 μm. The best corresponding theoretical resolution of the proposed sensor is 5.025 × 10-7 RIU which is over 10 times higher than that of many previous reported optical fiber based RI sensors. The proposed structure is capable of monitoring relative humidity level change even without coating of the fiber sensor’s surface with a layer of hygroscopic material. A silica sol-gel based coating has been used as a sensitive material to ammonia for the first time, by applying it to the surface of the tapered SCSMF for the detection of ammonia in water. The proposed sensor shows an ultra-high sensitivity of 2.47 nm/ppm with short response and recovery time of less than 2 and 5 minutes respectively. The corresponding theoretical detection limit of ammonia in water is calculated to be 4 ppb, which is 3 orders of magnitude improvement compared to the previous reported interferometry based ammonia sensor. In addition, the sensor has good performance in terms of repeatability of measurement and selectivity for sensing ammonia compared to that of other common ions and organic molecules in water. VOCs sensors are also demonstrated by coating a mixture of sol-gel silica and Nile red on the surface of two different types of tapered fiber sensors (tapered SCSMF) and a microfiber coupler (MFC)). The MFC based sensor shows better sensitivities to ethanol and methanol than that based on a tapered SCSMF due to its smaller waist diameter. The detectable gas concentration changes of the MFC based sensor are calculated to be ~77 ppb and ~281 ppb for ethanol and methanol respectively which are over one order of magnitude improvement than many other reports. The sensors also show fast response times of less than 5 minutes and recovery times varied from 7 to 12 minutes. Simultaneous measurement of ethanol and methanol is achieved by utilizing two different coating recipes. Hollow core fiber (HCF) structure for high temperature and twist sensing. A modified SMS structure with much improved spectral quality factor (Q) is investigated both theoretically and experimentally. The modified structure is based on a HCF. It is found that periodic transmission dips with high spectral extinction ratio and high Q factor are excited because of the multiple beam interferences introduced by the cladding of the HCF. The HCF structure can be used as a high sensitivity (up to 33.4 pm/°C) temperature sensor in a wide working temperature range (from room temperature to 1000 °C). By coating a thin layer of silver (~ 6.7 nm) on one side of the HCF surface, a twist sensor with a maximum sensitivity of 0.717 dB/°has been achieved, which is the highest twist sensitivity reported for intensity modulation based fiber sensors, with excellent measurement repeatability. Further theoretical and experimental investigation attributes this high twist sensitivity to the polarization dependent reflection coefficient at the outer HCF surface associated with the partial silver coating