Mehmet E. Solmaz

Vertically integrated As2S3 ring resonator on LiNbO3

Titanium-diffused lithium niobate (Ti:LiNbO(3)) waveguides are widely used in current fiber optic networks because of their high-speed, electro-optic modulation, and low-loss integration with standard single-mode fibers. However, they cannot achieve small ring resonators owing to their lack of a high core-to-cladding index contrast. To overcome this challenge, we vertically integrate an emerging chalcogenide glass waveguide technology on well-established Ti:LiNbO(3) waveguides. We present, to our knowledge, the first arsenic trisulfide (As(2)S(3)) race-track ring resonator with a 290.8 microm bend radius in an all-pass filter configuration, integrated on a Ti:LiNbO(3) waveguide. Vertical coupling is achieved using a unique taper design. Experimental results are shown for 10.6% coupling, 2.08 dB roundtrip loss, and a 25.4 GHz free-spectral range.

Poly (methyl vinyl ether-co-maleic acid) – Pectin based hydrogel-forming systems: Gel, film, and microneedles

Graphical abstract Figure. No caption available. ABSTRACT Cross‐linking of natural and synthetic polymers is widely explored to achieve the desired material properties (mechanical strength, drug loading capacity, swelling and erosion rates). However, the potential of polymers produced by crosslinking poly (methyl vinyl ether‐co‐maleic acid) (PMVE/MA) and pectin (PE) in pharmaceutics is mainly unexplored so far. We have investigated the effect of various esterification conditions and pectin content on the physicochemical properties. Materials have been characterized by fourier transform infrared, differential scanning calorimetry and scanning electron microscopy. In addition, swelling and bioadhesive features of PMVE/MA‐PE hydrogel systems were investigated. A band shift for the carbonyl group from 1706 to 1776 cm−1, and glass transition (Tg) increased from 55.4 ± 0.9 °C to 119.5 ± 0.3 °C confirmed the formation of esterification reaction within the cross‐linked films. Cross‐linked PMVE/MA:PE films with a ratio of 5 demonstrated a superior mass increase when compared to 2.5, 3.125, 3.75, 6.25, and 7.5 ratios of the same hydrogel film. Formulations containing PMVE/MA and pectin with a ratio of 3.75 showed superior bioadhesive features. For the first time, we engineered three‐dimensional printing based swell‐able microneedle arrays made out of cross‐linked PMVE/MA‐PE. Microneedle arrays height and aspect ratio were ranged from 702.5 ± 11.9 &mgr;m to 726 ± 23.3 &mgr;m and 3.12 ± 0.20 to 3.29 ± 0.21, respectively. Cross‐linked PMVE/MA‐PE Microneedle arrays (10‐2, 24 h) indicated the least height loss, 22.33 ± 4.15%, during axial compression test; whilst, transverse failure of cross‐linked PMVE/MA‐PE Microneedle arrays was varied from 0.15 ± 0.05 to 0.25 ± 0.04 N/needle. In conclusion, we obtained a novel cross‐linked polymer system with promising features of drug delivery and bio‐analytical applications.

CO2 laser polishing of microfluidic channels fabricated by femtosecond laser assisted carving

In this study, we investigate the effects of CO2 laser polishing on microscopic structures fabricated by femtosecond laser assisted carving (FLAC). FLAC is the peripheral laser irradiation of 2.5D structures suitable for low repetition rate lasers and is first used to define the microwell structures in fused silica followed by chemical etching. Subsequently, the bottom surface of patterned microwells is irradiated with a pulsed CO2 laser. The surfaces were characterized using an atomic force microscope (AFM) and scanning electron microscope (SEM) in terms of roughness and high quality optical imaging before and after the CO2 laser treatment. The AFM measurements show that the surface roughness improves more than threefold after CO2 laser polishing, which promises good channel quality for applications that require optical imaging. In order to demonstrate the ability of this method to produce low surface roughness systems, we have fabricated a microfluidic channel. The channel is filled with polystyrene bead-laden fluid and imaged with transmission mode microscopy. The high quality optical images prove CO2 laser processing as a practical method to reduce the surface roughness of microfluidic channels fabricated by femtosecond laser irradiation. We further compared the traditional and laser-based glass micromachining approaches, which includes FLAC followed by the CO2 polishing technique.

Smartphone-based detection of dyes in water for environmental sustainability

We report the applicability of an ultra-low cost, field-deployable, plastic fiber based smartphone spectrometer system to study dye adsorption from water. A custom cradle using the smartphones built-in flash and camera was designed for visible absorbance spectroscopy without any need for external electrical components. We firstly investigated the performance of the smartphone spectrometer for methylene blue (MB) absorbance in water with a detection limit of 0.5 ppm, and compared it to that of a commercial spectrometer. We elaborated on the contribution of image formats to the calibration of the standard absorbance curve. We then studied the catalytic activity of electrospun polyacrylonitrile (PAN)/zeolite composite nanofibers by analyzing MB adsorption as a function of time. The results obtained in the proposed compact, cost-effective and high-performance platform can help transform measurement science for sustainable water management.

Smartphone-based colorimetric detection via machine learning

We report the application of machine learning to smartphone-based colorimetric detection of pH values. The strip images were used as the training set for Least Squares-Support Vector Machine (LS-SVM) classifier algorithms that were able to successfully classify the distinct pH values. The difference in the obtained image formats was found not to significantly affect the performance of the proposed machine learning approach. Moreover, the influence of the illumination conditions on the perceived color of pH strips was investigated and further experiments were conducted to study the effect of color change on the learning model. Non-integer pH levels are identified as their nearest integer pH values, whereas the test results for integer pH levels using JPEG, RAW and RAW-corrected image formats captured under different lighting conditions lead to perfect classification accuracy, sensitivity and specificity, which proves that colorimetric detection using machine learning based systems is able to adapt to various experimental conditions and is a great candidate for smartphone-based sensing in paper-based colorimetric assays.

Femtosecond laser fabrication of fiber based optofluidic platform for flow cytometry applications

Miniaturized optofluidic platforms play an important role in bio-analysis, detection and diagnostic applications. The advantages of such miniaturized devices are extremely low sample requirement, low cost development and rapid analysis capabilities. Fused silica is advantageous for optofluidic systems due to properties such as being chemically inert, mechanically stable, and optically transparent to a wide spectrum of light. As a three dimensional manufacturing method, femtosecond laser scanning followed by chemical etching shows great potential to fabricate glass based optofluidic chips. In this study, we demonstrate fabrication of all-fiber based, optofluidic flow cytometer in fused silica glass by femtosecond laser machining. 3D particle focusing was achieved through a straightforward planar chip design with two separately fabricated fused silica glass slides thermally bonded together. Bioparticles in a fluid stream encounter with optical interrogation region specifically designed to allocate 405nm single mode fiber laser source and two multi-mode collection fibers for forward scattering (FSC) and side scattering (SSC) signals detection. Detected signal data collected with oscilloscope and post processed with MATLAB script file. We were able to count number of events over 4000events/sec, and achieve size distribution for 5.95μm monodisperse polystyrene beads using FSC and SSC signals. Our platform shows promise for optical and fluidic miniaturization of flow cytometry systems.

Sheathless Microflow Cytometry Using Viscoelastic Fluids

Microflow cytometry is a powerful technique for characterization of particles suspended in a solution. In this work, we present a microflow cytometer based on viscoelastic focusing. 3D single-line focusing of microparticles was achieved in a straight capillary using viscoelastic focusing which alleviated the need for sheath flow or any other actuation mechanism. Optical detection was performed by fiber coupled light source and photodetectors. Using this system, we present the detection of microparticles suspended in three different viscoelastic solutions. The rheological properties of the solutions were measured and used to assess the focusing performance both analytically and numerically. The results were verified experimentally, and it has been shown that polyethlyene oxide (PEO) and hyaluronic acid (HA) based sheathless microflow cytometer demonstrates similar performance to state-of-the art flow cytometers. The sheathless microflow cytometer was shown to present 780 particles/s throughput and 5.8% CV for the forward scatter signal for HA-based focusing. The presented system is composed of a single capillary to accommodate the fluid and optical fibers to couple the light to the fluid of interest. Thanks to its simplicity, the system has the potential to widen the applicability of microflow cytometers.

Perfectly absorbing ultra thin interference coatings for hydrogen sensing.

Here we numerically demonstrate a straightforward method for optical detection of hydrogen gas by means of absorption reduction and colorimetric indication. A perfectly absorbing metal-insulator-metal (MIM) thin film interference structure is constructed using a silver metal back reflector, silicon dioxide insulator, and palladium as the upper metal layer and hydrogen catalyst. The thickness of silicon dioxide allows the maximizing of the electric field intensity at the Air/SiO2 interface at the quarter wavelengths and enabling perfect absorption with the help of highly absorptive palladium thin film (∼7 nm). While the exposure of the MIM structure to H2 moderately increases reflection, the relative intensity contrast due to formation of metal hydride is extensive. By modifying the insulator film thickness and hence the spectral absorption, the color is tuned and eye-visible results are obtained.

Boundless-Range Optical Phase Shifters and Sideband Reduction

A boundless-range phase shifter is demonstrated at 10GHz using a dual parallel electro-optic modulator. Sideband and carrier rejections over 30dB are achieved using a coherent optical spectrum analyzer to verify the operation.

Single-Image-Referenced Colorimetric Water Quality Detection Using a Smartphone

In this paper, we present a smartphone platform for colorimetric water quality detection based on the use of built-in camera for capturing a single-use reference image. A custom-developed app processes this image for training and creates a reference model to be used later in real experimental conditions to calculate the concentration of the unknown solution. This platform has been tested on four different water quality colorimetric assays with various concentration levels, and results show that the presented platform provides approximately 100% accuracy for colorimetric assays with noticeable color difference. This portable, cost-effective, and user-friendly platform is promising for application in water quality monitoring.