Stanley H. Kravitz

Highly accurate etching of ridge‐waveguide directional couplers using in situ reflectance monitoring and periodic multilayers

A novel periodic multilayer structure has been used in conjunction with in situ reflectance monitoring to give ±10 nm endpoint detection during reactive‐ion‐beam etching. The method has been used to fabricate ridge‐waveguide directional couplers in GaAs/AlGaAs having coupling lengths within 100 μm of the desired 650 μm value. The added loss due to coupling length error was only 0.3 dB per guide. The method is directly applicable to photonic integrated circuits employing complex optical routing of waveguides, directional couplers and y‐junctions where total height of the waveguide plays a key role in performance of the circuit.

Waveguide-to-fiber coupling using a second-order grating and an anamorphic binary optic

Historically, obtaining efficient coupling from single-mode waveguides in high performance GaAs modulator devices to single-mode fiber has been difficult. The reasons are; (1) the large modal mismatch between the elliptical waveguide output and the gaussian profile of the optical fiber; and (2) the large NA difference (0.9 for the waveguide in one direction) and 0.16 for fiber. Despite this difficulty, there exists a need for packaging devices with multiple fiber outputs, that have been gang-aligned, efficiently coupled, and hermetically sealed. (The latter item will be very important in automotive or aerospace applications.) Instead of trying to have fiber penetrate the package wall, the SNL approach to efficient coupling and hermeticity has been to allow light to penetrate the package wall. This has been accomplished by sending out the light normal to the waveguides and collecting it with a binary optic that focuses it on to a fiber outside the package. The optical design of this system requires that the beam be nearly collimated as it leaves the surface of the device. To accomplish this, a second-order grating was etched into a 200 /spl mu/m long section of an adiabatically expanded single-mode waveguide.<<ETX>>

A passive micromachined device for alignment of arrays of single-mode fibers for manufacturable photonic packaging

Summary form only given. This work provides a method of passive mechanical alignment of an array of single mode fibers to an array of binary optics. The technique employs the use of a micro-machined metal spring, that captures a vertical, pre-positioned fiber, moves it into accurate alignment, and holds it for attachment.

Digital optical phase control in ridge-waveguide phase modulators

The authors report a digital optical phase modulation concept based on depletion-edge-translation p-n junction GaAs/AlGaAs ridge-waveguide modulators. Digital modulation is achieved by integrating in series several discrete waveguide modulators with lengths related by successive factors of two. To illustrate the concept, the authors fabricated and demonstrated a three-bit digital phase modulator with 45 degrees resolution. This structure represents the first photonic integrated circuit that performs direct digital-electronic to analog-optical conversion.<<ETX>>

Phased-array antenna control by a monolithic photonic integrated circuit

An optical based RF beam steering system is proposed for phased-array antenna systems. The system, COMPASS (Coherent Optical Monolithic Phased Array Steering System), is based on optical heterodyning employed to produce microwave phase shifting. At the heart of the system is a monolithic Photonic Integrated Circuit (PIC) constructed entirely of passive components. Microwave power and control signal distribution to the antenna is accomplished by optical fiber, thus separating the PIC and its control functions from the antenna. This approach promises to reduce size, weight, and complexity of future phased-array antenna systems.

Fabrication and characterization of large-area 3D photonic crystals

Full bandgap (3D) photonic crystal materials offer a means to precisely engineer the electromagnetic reflection, transmission, and emission properties of surfaces over wide angular and spectral ranges. However, very few 3D photonic crystals have been successfully demonstrated with areas larger than 1 cm2. Large sheets of photonic bandgap (PBG) structures would be useful, for example, as hot or cold mirrors for passively controlling the temperature of satellites. For example, an omni-directional 3D PBG structure emitting only at wavelengths shorter than 8 microns radiates only 7% of what a black body would at 200degK while radiating more than 40% at 400degK. 3D PBG materials may also find application in thermophotovoltaic energy generation and scavenging, as well as in wide field of view spectral filtering. Sandia National Laboratory is investigating a variety of methods for the design, fabrication, and characterization of PBG materials, and three methods are being pursued to fabricate large areas of PBG material. These methods typically fabricate a mold and then fill it with metal to provide a high refractive index contrast, enabling a full 3D bandgap to be formed. The most mature scheme uses silicon MEMS lithographic fabrication means to create a mold which if filled by a novel tungsten deposition method. A second method uses LIGA to create a mold in PMMA, which is filled by electro-deposition of gold, copper, or other materials. A third approach uses nano-imprinting to define the mold, which is filled using evaporative deposition or atomic layer deposition of metals or other materials. Details of the design and fabrication processes and experimental measurements of the structures are presented at the conference

Quartz Channel Fabrication for Electrokinetically Driven Separations

For well resolved electrokinetic separation, we utilize crystalline quartz to micromachine a uniformly packed separation channel. Packing features are posts 5 micrometers on a side with 3 micrometers spacing and etched 42 micrometers deep. In addition to anisotropic wet etch characteristics for micromachining, quartz properties are compatible with chemical solutions, electrokinetic high voltage operation, and stationary phase film deposition. To seal these channels, we employ a room temperature silicon-oxynitride deposition to form a membrane, that is subsequently coated for mechanical stability. Using this technique, particulate issues and global warp, that make large area wafer bonding methods difficult, are avoided, and a room temperature process, in contrast to high temperature bonding techniques, accommodate preprocessing of metal films for electrical interconnect. After sealing channels, a number of macro- assembly steps are required to attach a micro-optical detection system and fluid interconnects.

Mass-producible microscopic computer-generated holograms: microtags

We have developed a method for encoding phase and amplitude in microscopic computer-generated holograms (microtags) for security applications. An 8 x 8 cell phase-only and an 8 x 8 cell phase-and-amplitude microtag design has been exposed in photoresist by the extreme-ultraviolet (13.4-nm) lithography tool developed at Sandia National Laboratories. Each microtag measures 80 microm x 160 microm and contains features that are 0.2 microm wide. Fraunhofer zone diffraction patterns can be obtained from fabricated microtags without any intervening optics and compare favorably with predicted diffraction patterns.

Microtags with 150-nm line gratings fabricated by use of extreme-ultraviolet lithography

The microtag concept is an anticounterfeiting and security measure. Microtags are computer-generated holograms (CGHs) consisting of 150-nm lines arranged to form 300-nm-period gratings. The microtags that we describe were designed for readout at 442nm . The smallest microtag measures 56micromx80 microm when viewed at normal incidence. The CGH design process uses a modified iterative Fourier-transform algorithm to create either phase-only or phase-and-amplitude microtags. We also report on a simple and compact readout system for recording the diffraction pattern formed by a microtag. The measured diffraction patterns agree very well with predictions.

Integrated optic distributed Bragg reflector Fabry-Perot modulator for microwave applications

An integrated optic Fabry-Perot modulator is considered. The device, fabricated on III-V materials, uses distributed Bragg reflectors as mirrors. The greatest technical challenge in the realization of this device was the fabrication of the gratings with nanometer feature sizes. First order gratings 0.09 /spl mu/m in width and of 0.8 /spl mu/m in depth were written on a 2 /spl mu/m wide rib waveguide and successfully etched. The design, fabrication, and performance of the device is discussed.<<ETX>>