Showing papers by "Lynford L. Goddard published in 2015"

Grating integrated single mode microring laser

Abstract: Microring and microdisk lasers are potential candidates for small footprint, low threshold in-plane integrated lasers; however, they exhibit multimode lasing spectra and bistability. Here, we theoretically propose and experimentally demonstrate a novel approach for achieving single mode lasing in microring lasers. Our approach is based on increasing the radiation loss of all but one of the resonant modes of microring resonators by integrating second order gratings on the microrings’ waveguide. We present single mode operation of electrically pumped semiconductor microring lasers whose lasing modes are lithographically selected via the second order grating. We also show that adding the grating does not increase the lasing threshold current significantly.

Monolithically integrated self-rolled-up microtube-based vertical coupler for three-dimensional photonic integration

Abstract: We demonstrate a self-rolled-up microtube-based vertical photonic coupler monolithically integrated on top of a ridge waveguide to achieve three-dimensional (3D) photonic integration. The fabrication process is fully compatible with standard planar silicon processing technology. Strong light coupling between the vertical coupler and the ridge waveguide was observed experimentally, which may provide an alternative route for 3D heterogeneous photonic integration. The highest extinction ratio observed in the transmission spectrum passing through the ridge waveguide was 23 dB.

Measuring the Nonuniform Evaporation Dynamics of Sprayed Sessile Microdroplets with Quantitative Phase Imaging.

Abstract: We demonstrate real-time quantitative phase imaging as a new optical approach for measuring the evaporation dynamics of sessile microdroplets. Quantitative phase images of various droplets were captured during evaporation. The images enabled us to generate time-resolved three-dimensional topographic profiles of droplet shape with nanometer accuracy and, without any assumptions about droplet geometry, to directly measure important physical parameters that characterize surface wetting processes. Specifically, the time-dependent variation of the droplet height, volume, contact radius, contact angle distribution along the droplet's perimeter, and mass flux density for two different surface preparations are reported. The studies clearly demonstrate three phases of evaporation reported previously: pinned, depinned, and drying modes; the studies also reveal instances of partial pinning. Finally, the apparatus is employed to investigate the cooperative evaporation of the sprayed droplets. We observe and explain the neighbor-induced reduction in evaporation rate, that is, as compared to predictions for isolated droplets. In the future, the new experimental methods should stimulate the exploration of colloidal particle dynamics on the gas-liquid-solid interface.

9nm node wafer defect inspection using three-dimensional scanning, a 405nm diode laser, and a broadband source

Abstract: We recently built a 405nm laser based optical interferometry system for 9nm node patterned wafer defect inspection. Defects with volumes smaller than 15nm by 90nm by 35nm have been detected. The success of defect detection relied on accurate mechanical scanning of the wafer and custom engineered image denoising post-processing. To further improve the detection sensitivity, we designed a higher precision XYZ scanning stage and replaced the laser source with an incoherent LED to remove the speckle noise. With these system modifications, we successfully detected both defects and surface contamination particles in bright-field imaging mode. Recently, we have upgraded this system for interferometric defect inspection.

Semiconductor defect metrology using laser-based quantitative phase imaging

Abstract: A highly sensitive laser-based quantitative phase imaging tool, using an epi-illumination diffraction phase microscope, has been developed for silicon wafer defect inspection. The first system used a 532 nm solid-state laser and detected 20 nm by 100 nm by 110 nm defects in a 22 nm node patterned silicon wafer. The second system, using a 405 nm diode laser, is more sensitive and has enabled detection of 15 nm by 90 nm by 35 nm defects in a 9 nm node densely patterned silicon wafer. In addition to imaging, wafer scanning and image-post processing are also crucial for defect detection.

Hydrogen Detection Using a Single Palladium Nano-Aperture on a Fiber Tip

Abstract: This chapter discusses the development of fiber optic hydrogen sensors. A motivation for these sensors is given followed by an explanation of the underlying physics of the palladium-hydrogen system. Research results and the strengths and weaknesses of several different fiber optic hydrogen sensor types are discussed. Specifically, the Pd fiber mirror, tapered fiber, Fabry–Perot interferometer, Fiber Bragg grating, and long period grating sensor architectures are reviewed. Next, a new sensor topology that uses a nano-aperture patterned onto the tip of a Pd coated fiber is presented. The nano-aperture enhances sensitivity because it not only confines light tightly to the Pd surface, but it also creates a Fabry–Perot resonant structure. Thus, the power shifts in transmission and reflection due to hydrogen induced optical and mechanical changes to the Pd film are amplified. Finally, some conclusions and suggestions for future work are given.

Halo-free quantitative phase imaging with partially coherent light

Abstract: We provide a quantitative model for image formation in common-path QPI systems under partially coherent illumination. Our model is capable of explaining the phase reduction phenomenon and halo effect in phase measurements. We further show how to fix these phenomena with a novel iterative post-processing algorithm. Halo-free and correct phase images of nanopillars and live cells are used to demonstrate the validity of our method.

Quantitative phase imaging with programmable illumination

Abstract: Even with the recent rapid advances in the field of microscopy, non-laser light sources used for light microscopy have not been developing significantly. Most current optical microscopy systems use halogen bulbs as their light sources to provide a white-light illumination. Due to the confined shapes and finite filament size of the bulbs, little room is available for modification in the light source, which prevents further advances in microscopy. By contrast, commercial projectors provide a high power output that is comparable to the halogen lamps while allowing for great flexibility in patterning the illumination. In addition to their high brightness, the illumination can be patterned to have arbitrary spatial and spectral distributions. Therefore, commercial projectors can be adopted as a flexible light source to an optical microscope by careful alignment to the existing optical path. In this study, we employed a commercial projector source to a quantitative phase imaging system called spatial light interference microscopy (SLIM), which is an outside module for an existing phase contrast (PC) microscope. By replacing the ring illumination of PC with a ring-shaped pattern projected onto the condenser plane, we were able to recover the same result as the original SLIM. Furthermore, the ring illumination is replaced with multiple dots aligned along the same ring to minimize the overlap between the scattered and unscattered fields. This new method minimizes the halo artifact of the imaging system, which allows for a halo-free high-resolution quantitative phase microscopy system.

A Zeroth-Order Modification of Coupled Mode Theory for Waveguide Gratings

Abstract: This letter demonstrates the importance of selecting the correct unperturbed structure for coupled mode theory calculations of waveguide gratings. Neglecting the spatial dependence of the average value of the perturbation can cause considerable inaccuracies in the analysis of many common structures. Here, we show the improvement that can be achieved by including this zeroth-order modification and how to choose the proper unperturbed structure through several practical device examples.

Demonstration of the first monolithically integrated self-rolled-up tube based vertical photonic coupler

Abstract: We demonstrated the first monolithically integrated self-rolled-up SiN x tube based vertical photonic coupler on top of a planar ridge waveguide. The coupling efficiency between the elements is >10 times higher than similar non-integrated device.

Quantitative phase-shifting DIC using programmable spatial light modulators

Abstract: A quantitative phase-shifting Differential Interference Contrast (DIC) system is built using a programmable spatial light modulator (SLM). Our system offers halo-free phase gradient images with low illumination coherence and very good axial sectioning. Results are presented for standard polystyrene micro-beads and live cells.

White-light interferometric microscopy for wafer defect inspection

Abstract: White-light imaging systems are free of laser-speckle. Thus, they offer high sensitivity for optical defect metrology, especially when used with interferometry based quantitative phase imaging. This can be a potential solution for wafer inspection beyond the 9 nm node. Recently, we built a white-light epi-illumination diffraction phase microscopy (epi-wDPM) for wafer defect inspection. The system is also equipped with an XYZ scanning stage and real-time processing. Preliminary results have demonstrated detection of 15 nm by 90 nm in a 9 nm node densely patterned wafer with bright-field imaging. Currently, we are implementing phase imaging with epi-wDPM for additional sensitivity.

Microfluidic device fabrication utilizing virtual masks and photochemical etching

Abstract: We demonstrate using virtual masks to perform photochemical etching to facilitate microfluidic device fabrication. Applications of this cost-efficient alternative to conventional fabrication methods are expansive in many fields such as medical diagnostics.

Phase correction in low coherence diffraction phase microscopy using the optical transfer function

Abstract: In this work, we experimentally determine the transfer function of our recently reported epi-illumination white light diffraction phase microscopy (epi-wDPM) system The transfer function identifies how the low frequencies below k0NAcon are modified due to the limited spatial coherence and how the high frequencies above k0NAobj are affected due to the limited objective numerical aperture Using this transfer function, we perform deconvolution to remove the halo and obtain proper quantitative phase measurements without the need for excessive spatial filtering The wDPM and epi-wDPM systems are now capable of obtaining halo-free images with proper topography at much higher speeds

Fabrication of gray-scale semiconductor structures with dynamic digital projection photochemical etching

Abstract: Digital projection photochemical etching is a novel single-step process for fabricating customized gray-scale semiconductor structures. Several features including a variable height pyramid array are fabricated, demonstrating the resolution, range, accuracy, and dynamics of the technique.

Vertically Tapered Adiabatic Waveguide Mode Converters Fabricated with Digital Projection Photochemical Etching

Abstract: We combine conventional planar semiconductor processing with gray-scale topography created by digital projection photochemical etching to fabricate adiabatic waveguide mode converters. Applications include efficient coupling to fiber or between planes of multi-layer photonic integrated circuits.

Monolithically integrated self-rolled-up tube based vertical coupler with planar waveguide - a new 3D photonic integration scheme

Abstract: Self-rolled-up SiNx tube based vertical photonic couplers are monolithically integrated on top of planar ridge waveguides in various configurations. The coupling efficiency between the elements is >10 times higher than similar non-integrated device.

In-situ measurements of nanoscale phenomena using diffraction phase microscopy

Abstract: In this work, we present recent results on several novel applications including optically monitoring the dissolution of biodegradable materials proposed for use in biological electronic implants, the self-assembly of microtubes during semiconductor etching, and the expansion and deformation of palladium structures for use in hydrogen sensing applications. The measurements are done using diffraction phase microscopy (DPM), a quantitative phase imaging (QPI) technique, which uses the phase of the imaging field to reconstruct a map of the sample’s surface. It combines off-axis and common-path geometries allowing for single-shot, high-speed dynamics with sub-nanometer noise levels.