John P. Barber

Integrated ARROW waveguides with hollow cores.

We report the design, fabrication, and demonstration of antiresonant reflecting optical (ARROW) waveguides with hollow cores. We describe the design principles to achieve low waveguide loss in both transverse and lateral directions. A novel fabrication process using silicon dioxide and silicon nitride layers as well as sacrificial polyimide core layers was developed. Optical characterization of 3.5mum thick waveguides with air cores was carried out. We demonstrate single-mode propagation through these hollow ARROW waveguides with propagation loss as low as 6.5cm-1 and mode cross sections down to 6.7mum2. Applications of these waveguides to sensing and quantum communication are discussed.

Integrated optical waveguides with liquid cores

We report the design, fabrication, and demonstration of single-mode integrated optical waveguides with liquid cores. The principle of the device is based on antiresonant reflecting optical (ARROW) waveguides with hollow cores. We describe design principles for waveguide loss optimization down to 0.1∕cm. Using a fabrication process based on conventional silicon microfabrication and sacrificial core layers, waveguides of varying widths and lengths with volumes covering the pico- to nanoliter range were fabricated. We observe confined mode propagation, measure waveguide losses of 2.4∕cm, and demonstrate that the waveguides possess tailorable wavelength selectivity. The potential for highly integrated, sensitive devices based on these properties of the ARROW waveguides is discussed.

Single-molecule detection sensitivity using planar integrated optics on a chip

We present a fully planar integrated optical approach to single-molecule detection based on microfabricated planar networks of intersecting solid and liquid-core waveguides. We study fluorescence from dye molecules in liquid-core antiresonant reflecting optical waveguides, and demonstrate subpicoliter excitation volumes, parallel excitation through multiple pump waveguides, and single-molecule detection sensitivity. Integrated silicon photonics combined with single-molecule detection in solution create a compact, robust, and sensitive platform that has applications in numerous fields ranging from atomic physics to the life sciences.

Hollow-core waveguides and 2-D waveguide arrays for integrated optics of gases and liquids

We present integrated antiresonant reflecting optical (ARROW) structures with hollow cores as a new paradigm for integrated optics with gases and liquids. ARROW waveguides with micrometer-sized hollow cores allow for single-mode propagation in low-index nonsolid core materials where conventional index guiding is impossible. Fabrication methods and considerations are described, and measurements of the core-size dependence of the waveguide loss are presented. We analyze the dependence of waveguide loss in hollow-core ARROW waveguides on polarization, shape, and wavelength. We propose two-dimensional hybrid device geometries using solid and nonsolid core ARROWs and show that they can form the basis of integrated fluorescence and Raman sensors. We derive the design principles for simultaneous low-loss propagation in both waveguides and efficient cross-coupling between waveguides.

Integrated hollow waveguides with arch-shaped cores

An optical waveguide is described that has a hollow arch-shaped core. Optical confinement for this structure is based on the antiresonant reflecting optical waveguide principle. The waveguides are built on a silicon substrate using a sacrificial etch technique with reflowed photoresist serving as the sacrificial material and producing the cores arch shape. Investigations of fabrication parameters are reported that allow for predicting a final arch-shaped geometry based on initial photoresist width and thickness. Optical mode guiding is demonstrated in an arch-shaped waveguide with a liquid core.

Waveguide loss optimization in hollow-core ARROW waveguides

We discuss optimization of the optical properties of hollow-core antiresonant reflecting optical waveguides (ARROWs). We demonstrate significant reduction of waveguide loss to 2.6/cm for a 10.4microm(2) mode area after adding an initial etching step of the substrate material. The effect of differences in confinement layer thickness is quantified and an optimized design is presented. The polarization dependence of the waveguide loss is measured and the implications for applications are discussed.

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.

Optical characterization of arch-shaped ARROW waveguides with liquid cores.

We present the characterization of the optical properties of integrated antiresonant reflecting optical (ARROW) waveguides with arch-shaped liquid cores. Optical mode shapes and coupling, waveguide loss, and polarization dependence are investigated. Waveguide loss as low as 0.26/cm with near-single-mode coupling and mode areas as small as 4.5microm2 are demonstrated. A detailed comparison to ARROW waveguides with rectangular cores is presented, and shows that arch-shaped cores are superior for many applications.

Highly efficient fluorescence detection in picoliter volume liquid-core waveguides

We report loss improvement and fluorescence detection in integrated antiresonant reflecting optical waveguides with liquid cores. The minimum waveguide loss is reduced to 0.33∕cm by compensating for thickness variations in the fabrication process. We demonstrate fluorescence detection from as few as 490molecules in a 57pl core using these optimized waveguides. We measure angular fluorescence collection factors as high as 15% per facet in good agreement with theory. This demonstrates the potential of integrated hollow-core waveguides as optical sensors for single-molecule spectroscopy.

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.