Donald B. Conkey

Fabrication of hollow waveguides with sacrificial aluminum cores

We have developed a process to fabricate dielectric waveguide structures with long hollow cores formed by etching a sacrificial core material. The process is compatible with other planar silicon fabrication techniques. Using aluminum as the sacrificial material, we have investigated fabrication limits and design parameters that determine mechanical integrity of the waveguides. Internal pressure due to the production of gaseous compounds during the core removal process was identified as the yield-limiting factor. A mechanical model based on finite element analysis and confirmed by experiment, predicts ultimate pressures sustainable by these structures. Waveguides less than 10 /spl mu/m wide with 2-/spl mu/m-thick coatings should sustain 50 MPa of internal pressure. Low-loss guided-mode propagation in optical waveguides based on these hollow cores is demonstrated.

Planar thin film device for capillary electrophoresis

Hollow tubular microfluidic channels were fabricated on quartz substrates using sacrificial layer, planar micromachining processes. The channels were created using a bottom-up fabrication technique, namely patterning a photoresist/aluminum sacrificial layer and depositing SiO(2) over the substrate. The photoresist/aluminum layer was removed by etching first with HCl/HNO(3), followed by etching in Nano-Strip, a more stable form of piranha (H(2)SO(4)/H(2)O(2)) stripper. Rapid separation of fluorescently labeled amino acids was performed on a device made with these channels. The fabrication process presented here provides unique control over channel composition and geometry. Future work should allow the fabrication of highly complex and precise devices with integrated analytical capabilities essential for the development of micro-total analysis systems.

Structural models and design rules for on-chip micro-channels with sacrificial cores

This paper provides a structural analysis of hollow silicon dioxide micro-channels that have applications in microfluidics and photonics. A specific fabrication method is highlighted that uses aluminum as a sacrificial material. Possible causes of failures that occur during fabrication are investigated, and internal pressure produced during the fabrication process is identified as the most likely failure mechanism. Three models are developed for the fabricated micro-channels. Models based on elementary beam theory and energy methods verify a nonlinear finite element model. Design parameters in the finite element model are varied to investigate which have the greatest effect on structural strength and ultimate failure. Experimental results are used with the model to estimate the pressure at failure. Finally, based on the model and experimental results, a rule is developed for the design of the hollow micro-channels described in the paper: maintain the width-to-thickness ratio below 35.

Towards integration of quantum interference in alkali atoms on a chip

We discuss a new integrated approach to realizing optical quantum interference effects such as electromagnetically induced transparency (EIT), slow light, and highly efficient nonlinear processes on a semiconductor chip. An ensemble of alkali atoms represents one of the canonical systems that exhibit slow light and related phenomena. At the same time, it would be desirable to build slow-light and related devices on a semiconductor platform in order to move to practical applications. We review progress towards combining the large magnitude of quantum interference effects in alkali vapors with the convenience of integrated optics in the form of hollow-core antiresonant reflecting optical waveguides (ARROWs). We discuss the benefits and challenges of this integrated approach with special emphasis on nonlinear optics. We present strategies to optimize the optical waveguides and discuss the current status of building rubidium-filled optical waveguides on a chip. Recent results on optimization of waveguide loss and transfer of rubidium atoms through hollow microchannels on a chip are presented.

Hollow waveguides on planar substrates with selectable geometry cores

We report the fabrication of hollow waveguide structures with various core geometries. These structures are suitable for low-loss anti-resonant reflecting (ARROW) and photonic crystal waveguides, and integration with microfluidic systems.

Rubidium spectroscopy on a chip

We review the current status of integrating optical quantum interference effects such as electromagnetically induced transparency (EIT), slow light, and highly efficient nonlinear processes on a semiconductor chip. A necessary prerequisite for combining effects such as slow light and related phenomena with the convenience of integrated optics is the development of integrated alkali vapor cells. Here, we describe the development of integrated rubidium cells based on hollow-core antiresonant reflecting optical waveguides (ARROWs). Hollow-core waveguides were fabricated on a silicon platform using conventional microfabrication and filled with rubidium vapor using different methods. Rubidium absorption through the waveguides was successfully observed which opens the way to integrated atomic and molecular on a chip. The realization of quantum coherence effects requires additional surface treatment of the waveguide walls, and the effects of the surface coating on the waveguide properties are presented.

Microfabrication of integrated atomic vapor cells

The integration of hollow anti-resonant reflecting optical waveguides (ARROWs) with vapor cells on silicon chips provides a compact platform for a number of optical applications, including the study of quantum coherence effects such as electromagnetically induced transparency and single-photon nonlinearities, as well as frequency stabilization standards. The use of hollow waveguides allows for light propagation in low index (vapor) media with compact mode areas. ARROWs make particularly attractive waveguides for this purpose because they can be interfaced with solid core waveguides, microfabricated on a planar substrate, and are effectively single mode. ARROW fabrication utilizes an acidremoved sacrificial core surrounded by alternating plasma deposited dielectric layers, which act as Fabry-Perot reflectors. A demonstration platform consisting of solid and hollow core waveguides integrated with rubidium vapor cells has been constructed. Rubidium was used because it is of particular interest for studying quantum coherence effects. Liquefied rubidium was transferred from a bulk supply into an on-chip vapor cell in an anaerobic atmosphere glovebox. Optical absorption measurements confirmed the presence of rubidium vapor within the hollow waveguide platform. Coherence dephasing in the small dimensions of the ARROW (quantum coherence effect) can be addressed by adding a buffer gas and passivation coatings to the ARROW walls.

Integrated Semiconductor Chips for EIT

We review fabrication and characterization of monolithically integrated rubidium vapor cells on a chip. Mode areas of 9 mum2 and optical densities in excess of 2 are demonstrated - ideal for EIT-based nonlinear optics.

Saturation Absorption Spectroscopy in an Integrated Rubidium Vapor Cell

We demonstrate integrated rubidium vapor cells using hollow-core ARROW waveguides on a silicon chip. Optical mode areas of 8.8 square microns are promising for nonlinear optical applications. Saturation spectroscopy on the Rb-D2 line is demonstrated.