ARROW based optofluidic sensors are fabricated by out collaborators from BYU. Silicon wafers with the fabricated photonic devices are first inspected via optical microscope for defects and debris. Next, dimensions of the device are measured and confirmed using microscope images (for width or length measurements) and profilometer (Filmetrics, for 3D measurements). Some times ellipsometric measurements are done on test thin films to confirm the refractive index of core or cladding of the waveguides. Wafer metrology helps us to make wafer maps to filter out good devices that would be suitable for optical characterization. These preliminary inspections also sometimes give information regarding which part of the fabrication steps certain defects arise.

Chips are diced for further characterization. SEM images are taken to get more accurate measurements of the waveguide dimensions. FIB millings are done when needed to investigate parts of the devices that are not accessible other wise, Ex: "solid core-liquid core" waveguide intersections. These measurements help to build more accurate simulation models to better understand optical properties of the devices and to get reasons for device out puts deviating from the designed values. (I am not an expert in SEM, these were taken with the help of Dr.Tom at our facility.

Optical characterization starts with mode image analysis of single-mode and multi-mode solid core waveguides. FWHM, confinement factor, SNR (Peak-valley ratio) and the position of the modes tells the quality of the waveguides. Correlations between the self imaging of the single mode in the MMI waveguide is studied and optimizations to the waveguide dimensions are made. Top down fluorescent images of the MMI patterns in the dye filled liquid core waveguide when excited by the MMI waveguide with a tunable laser (NKT) are also analysed to study self imaging of the modes. Through-put or transmission measurements (percentage of light transmitted via SC to LC to SC) are also done to quantify coupling efficiency at the SC-LC intersections. Some of the Matlab and C# program used for image analysis and automation can be found here.

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