Colleen Mary Fitzpatrick

Integrated-optic lossless beamsplitters

Erbium-doped thin-film waveguides are promising as loss-compensating devices for various photonic integrated circuits. We have addressed major challenges in the development of lossless splitters based on the Er-doped glass films: the requirement of high Er concentrations, the fabrication of quality waveguides, and the development of suitable architectures for beamsplitting and for signal and pump combining and separating, and the limitations of maximum-obtainable gain of Er-doped thin-film amplifiers. Based on these results, we have successfully developed integrated-optic, lossless splitters. The fabricated devices clearly demonstrate lossless transmission of an optical signal at 1.54 (mu) m wavelength through a 1x2 splitter and an Er-doped amplifier that are monolithically integrated on the same substrate.

Bacteriorhodopsin-based single and dual wavelength holographic interferometry for monitoring crystal growth

Bacteriorhodopsin-based holographic interferometry is a new technique with which high-resolution interferograms can be recorded at one or more wavelengths in real time. The erasable nature of bacteriorhodopsin (bR), its panchromatic response to light, and the fact that recording is done on the molecular level allow for the formation of fringe patterns combining the high resolution of conventional silver halide recording materials with the real-time properties of CCD cameras. In this context, we have used bR to image changes in the crystal environment at single and dual wavelengths, using a real-time sequencing architecture whereby successive exposures of a bR thin film are overlapped to produce a continuous stream of interferometric images. This allows realtime data buffering and immediate, on-line observation of results. In this paper, we present real-time single and dual wavelength interferograms of growing KAl(SO4)2 and melting sugar crystals recorded on bR thin films. The interferograms were produced with a shuttered cw argon or a pulsed Nd:YAG write laser, and a helium-neon read laser, and show contrast more than adequate for the given application. The results of this effort clearly demonstrate the real-time recording capabilities of bR thin films.

New integrated optics architecture including onboard sensing elements

As fiber optics transformed the telecommunications industry, integrated optics is enabling dramatic advances in the speed of optical networks. This new technology is also leading to compact optical sensors for physics, chemistry and biology. Ideally, an integrated optics sensor would be self-contained, with the light source, detectors, and other electronic elements incorporated on the same integrated optics platform as the optical waveguides themselves. However, many challenges remain in the fabrication of fully integrated optoelectronic sensors. In this paper, we present innovative approaches in integrated optics packaging technology we have developed for fabricating integrated optics sensors for navigation, guidance, and combustion microdiagnostics. As an example, we will focus on the development of the RB-3, a three-axis rotation sensor we developed under funding from the U.S. Army Yuma Proving Ground. Besides innovations in optical layout, our design approach presents new possibilities as well as challenges for photonic integrated,incorporating active detection elements directly onboard the integrated optics chip (IOC) platform. Eliminating the fiber pigtails which would normally carry the optical output to an external detection scheme not only adds ruggedness to the sensor, it also allows a reduction in size and mass. With this configuration, the incorporation of the IOC into a larger system only requires electrical inputs and output to the IOC, eliminating all but the input fiber pigtail from the light source. In describing the on-board detectors system, we include a description of the chemical dry etching and micropositioning techniques we have developed, as well as the wirebonding schemes we used to interface the detectors with external electronics. We also briefly discuss the engineering of the sensor package and the external housing. We finally give a summary of some of the challenges that remain to the practical implementation of fully integrated optics sensors which include onboard light sources and other electronic components.

Integrated optics rotation sensor (IORS) for dual use in military and commercial applications

In this paper, we present our design of an integrated optics rotation sensor (IORS). Based on rugged glass-on-silicon technology, this gyro represents a versatile, low cost approach to high tech commercialization. The IORS is suited for a number of applications, including robotics, navigation, and guidance, and as an automotive safety device. In terms of compactness and ease of use, the IORS presents an improved approach to rotation sensing over other gyro technologies. In this paper, we present the basic operation of the gyro, along with a brief explanation of its use as an automotive yaw sensor.

Bacteriorhodopsin‐based two wavelength interferometry (BTI) for the real time monitoring of crystal growth

The real time crystal monitoring technique described in this paper has high commercial potential particularly in the medical industry. The fundamental knowledge of the dynamics of protein crystal growth would lead to higher quality pharmaceuticals through more accurate process control. But the application of bacteriorhodopsin‐based imaging does not stop with crystal growth monitoring. Many other applications could benefit from bacteriorhodopsin‐based interferometric instrumentation, as there currently exists no convenient way of making real time measurements of this kind even at a single wavelength. Conventional silver halide materials are too time consuming and awkward, while other materials, such as thermoplastic slides require high voltage and are very slow to recycle. In addition, photorefractive crystals have never been shown to be practical in terms of cost and flexibility. Monitoring flame spread, shearographic and holographic nondestructive testing, aero‐optic holography, and high speed modal anal...

Nonintrusive fiber optic diagnostic for monitoring spacecraft contamination

Contamination of spacecraft surfaces by deposition and ablation can potentially limit the performance and lifetime of solar panels, optical systems and microsatellite structural elements. However, instrumentation for on-orbit contamination assessment is limited by payload requirements and the experiments which can be conducted are limited by spacecraft geometry and mission lifetime. We present the design of a fiber optics evanescent wave sensor capable of real time detection of the contamination of spacecraft surfaces during flight. While other evanescent wave detection schemes rely on special coatings to selectively and reversibly absorb a target analyte, in the present context, such coatings would themselves be considered undesirable forms of contamination, and are therefore prohibited. The sensor described here is capable of detecting contamination by direct exposure of the evanescent wave to the environment through the use of a reduced-cladding fiber. The sensor can measure contamination from foreign substances, and ablation from the impact of space debris or ion thruster exhaust. In this paper, we briefly discuss the major forms of contamination. We describe the operating principles of the fiber optic evanescent wave sensor we have constructed for monitoring these forms of contamination, and provide preliminary results indicating sensor performance characteristics. We demonstrate the feasibility of the sensor for detecting the deposition of a variety of substances, and for observing the effects of ablation from thruster exhaust. In all cases, we make a qualitative comparison between sensor performance and theory.

MICRODIAGNOSTICS USING INTEGRATED OPTICS

Optical diagnostic techniques can complement existing performance characterization methods for microthrusters under development for microsatellite technology. We present a design for a miniature nonintrusive optical diagnostic sensor to measure the flow characteristics of water-based microthrusters. Our design uses silica waveguide-based integrated optic sensors, which can be constructed as an integral part of microthruster walls, providing real-time, in-situ measurements, during tests and in flight. Based on available thruster characteristics and performance estimates supplied by the Air Force Research Laboratory at Edwards Air Force Base, together with calculations of the scattering and obscuration properties of the exhaust particles with plausible sizes and concentrations, we analyze acceptable sensor geometries, and examine feasible ranges of operation.

Comparison of pulsed versus cw behavior of the diffraction efficiency of bacteriorhodopsin thin films

The feasibility of using the organic nonlinear photopolymer bacteriorhodopsin in holographic interferometry has been of growing interest in recent years because of its real time properties and its relatively high diffraction efficiency. In this paper, a comprehensive analysis of the behavior of bacteriorhodopsin thin films under both CW and pulsed conditions will be presented. Because bR is an erasable material, a simultaneous read-write geometry was used for these experiments, and data taken as a function of both read and write parameters. In the CW case, the dynamic behavior of the diffraction efficiency has been characterized in the initial growth region, to obtain sensitivity curves, and in the decay region, to obtain the behavior of the M-state lifetime. In the pulsed experiments, the behavior of the material was observed in the growth region, to study the reciprocity behavior of the material. From the data, a comparison between the behavior of the diffraction efficiency was made for pulsed and CW illumination, in terms of diffraction efficiency, sensitivity, and the time-dependent M- state population.

Bacteriorhodopsin-based single- and dual-wavelength interferometry for monitoring crystal growth

Bacteriorhodopsin-based interferometry is a new technique with which high resolution interferograms can be recorded at one or more wavelengths in real time. The erasable nature of bacteriorhodopsin, its panchromatic response to light, and the fact that recording is done on the molecular level, allow for the formation of fringe patterns combining the high resolution of conventional silver halide recording materials with the real time properties of CCD cameras. In this context, we have used bacteriorhodopsin to image changes in the crystal environment at single and dual wavelengths, using a real time sequencing architecture whereby successive exposures of a bR thin film are overlapped to produce a continuous stream of interferometric images. This allows real-time data buffering and immediate, on-line observation of results. In this paper, we present real time single and dual wavelength interferograms of growing KAl(SO4)2 and melting sugar crystals recorded on bacteriorhodopsin thin films. The interferograms were produced with a shuttered cw argon or a pulsed Nd:YAG write laser, and a helium neon read laser, and show enhanced contrast and resolution. The results of this effort clearly demonstrate the superior, real time recording capabilities of bacteriorhodopsin thin films.

Integrated Optics Rotation Sensor (IORS)

The Integrated Optics Rotation SEnsor (IORS) is a rugged, lightweight, and low cost gyro instrument which is currently being sponsored by the Defense Advanced Research Projects Agency under funding from Small Business Innovative Research/Technology Reinvestment Program. It uses glass-on- silicon optical waveguide technology. The design of the IORS is quite simple, and can potentially be adapted to a number of military and commercial applications, including yaw rate sensing for an anti-skid safety device in automobiles, rotation rate sensing for robotics, weapon aiming,and guidance of smart munitions. The basic design is presented, along with preliminary performance specifications for an IORS prototype. The characteristics of the IORS is also compared to other gyros in terms of performance, size, weight, and price.