Sandia's broad national security mission has supported novel optoelectronics and integrated photonics R&D and technology transfer for over 30 years. Examples of this history, current capabilities, and potential future directions will be discussed.

Sandia National Laboratories is leveraging the extensive CMOS, MEMS, compound semiconductor, and nanotechnology fabrication and test resources at Sandia National Laboratories to explore new science and technology in photonic crystals, plasmonics, metamaterials, and silicon photonics.

Beginning in the mid-1990s, Sandia National Laboratories began its migration to Silicon-on-Insulator (SOI) wafers to develop a radiation-hardened semiconductor process for sub-0.5mum geometries. Successfully radiation hardening SOI technologies enabled an in-house processing familiarity that exceeded our expectations by opening opportunities to improve other technologies. Rather than rely on a single SOI technology, we have developed families of SOI processes using SOI wafers specifically tailored for each of a number of diverse applications. From this SOI expertise, we have designed, developed, and fabricated a number of novel devices that exploit a variety of mechanical, electrical, and optical phenomena, including atomic-physics based devices. We present a high-level description of our SOI process technologies using product examples. Of particular note are a novel accelerometer, RF MEMS microresonators and contacting switches, integrated optics (low-loss Si waveguides, the smallest and lowest power micro-ring modulators and thermo-optic phase modulators/switches), and ion traps for quantum computing (along with other atomic physics device examples).

Three-dimensional (3D) nano-structures are vital for emerging technologies such as photonics, sensors, fuel cells, catalyst supports, and data storage. The Proximity-field nanoPatteming(1) method generates complex 3D nanostructures using a single exposure through an elastomeric "phase mask" patterned in x, y, and z, and a single development cycle. We developed a model that predicts the phase mask required to generate a specific desired nanostructure. We have compared this inverse model with experimental 3D structures to test the validity of the simulation. We have transferred the PnP fabrication process to a class-10 commercial cleamoom and scaled-up the processed area to >2000mm(2), tested photopolymer additives designed to reduce resist shrinkage, incorporated atomic layer deposition (ALD) to coat the 3D patterned resist with metals/metal-oxides improve structure robustness, and generated quasi-crystal patterned 3D nanostructures.

A MEMS bulk wave acoustic bandgap has been designed and experimentally verified. The acoustic bandgaps are realized by including tungsten (W) scatterers in a SiO2 matrix. Wide frequency ranges where acoustic waves are forbidden to exist are formed due to the large density and acoustic impedance mismatch between W and SiO2. The acoustic bandgap structures are fabricated in a 7-mask process that features integrated aluminum nitride piezoelectric couplers. Acoustic bandgaps in a square lattice have been measured at 33 and 67 MHz with up to 35 dB of acoustic rejection and bandwidths exceeding 35% of the midgap.

The LIGA microfabrication technique offers a unique method for fabricating 3-dimensional photonic lattices based on the Iowa State "logpile" structure. These structures represent the [111] orientation of the [100] logpile structures previously demonstrated by Sandia National Laboratories. The novelty to this approach is the single step process that does not require any alignment. The mask and substrate are fixed to one another and exposed twice from different angles using a synchrotron light source. The first exposure patterns the resist at an angle of 45 degrees normal to the substrate with a rotation of 8 degrees. The second exposure requires a 180 degree rotation about the normal of the mask and substrate. The resulting pattern is a vertically oriented logpile pattern that is rotated slightly off axis. The exposed PMMA is developed in a single step to produce an inverse lattice structure. This mold is filled with electroplated gold and stripped away to create a usable gold photonic crystal. Tilted logpiles demonstrate band characteristics very similar to those observed from [100] logpiles. Reflectivity tests show a band edge around 5 μm and compare well with numerical simulations.

We have designed, fabricated, and tested large sheets of photonic bandgap (PBG) material that have a "cubic array of cubes" structure. Structures with bandgaps in two wavebands have been fabricated: the thermal IR (8-12 mu m) and the visible/near IR (0.6-2.5 mu m). A thermal-IR PBG can modify the emission properties of structures for temperature control. Visible/near-IR PBGs can be used in photonic circuits and can improve illumination efficiency.

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 cm 2 . 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

We describe a new optoelectronic switching system demonstration that implements part of the distribution fabric for a large asynchronous transfer mode (ATM) switch. The system uses a single optoelectronic VLSI modulator-based switching chip with more than 4000 optical input-outputs. The optical system images the input fibers from a two-dimensional fiber bundle onto this chip. A new optomechanical design allows the system to be mounted in a standard electronic equipment frame. A large section of the switch was operated as a 208-Mbits/s time-multiplexed space switch, which can serve as part of an ATM switch by use of an appropriate out-of-band controller. A larger section with 896 input light beams and 256 output beams was operated at 160 Mbits/s as a slowly reconfigurable space switch.

This paper presents a system capable of static and dynamic simulationsof heterogeneous opto-electronic systems. It is capable ofmodeling Gaussian optical signal propagation with mechanicaltolerancing at the system level. We present results which demonstratethe system's ability to predict the effects of various componentparameters, such as detector geometry, and system levelparameters, such as alignment tolerances, on system performance.

We describe an optoelectronic switching system demonstration that implements part of the distribution fabric for a large ATM switch. The system uses a single optoelectronic VLSI modulator-based switching chip with more than 4000 optical I/O. The optical system images the input fibers from a two dimensional fiber bundle onto this chip. The optomechanical design allows the system to be mounted in a standard electronic equipment frame. A large section of the switch was operated as a 208 Mb/s time multiplexed space switch, which can serve as part of an ATM switch using the appropriate out-of-band controller. A larger section with 896 input light beams and 256 output beams was operated at 160 Mb/s as a slowly reconfigurable space switch. In this presentation, we will give an overview of the demonstration system, including the motivation, architecture, switching chip, optical system, input lasers, fiber bundle array, opto-mechanics, control software, and experimental results.

This talk will review several optical design and system packaging approaches explored in the past and currently under investigation in demonstration systems. To make the jump to a commodity-level smart pixel platform, new components and approaches will be needed and examples of potential useful techniques will be surveyed.

In the past few years, the demand for telecommunications services beyond voice telephony has skyrocketed. For the growth of these services to continue at this rate, cost effective means of transporting and switching large amounts of information must be found. Although fiber optic transmission has significantly reduced the cost of transmission, switching high bandwidth signals remains expensive. While all electronic switching systems are certainly possible for these high bandwidth systems, considerable effort has been expended to reduce the cost of fiber optic connections between frames or racks of equipment separated by several meters. As an example, one can envision fiber-optic data links connecting the line units that receive and transmit data from the outside world with an electronic switching fabric. Optical data links, ODLs, can perform the optical to electrical conversions. Several of these optical data links can be electrically connected with electronic switching chips on a printed circuit board. As the demand for bandwidth increases, several hundred to several thousand optical fibers might be incident on the switching fabric. Discrete optical data links and parallel data links with up to 32 fibers per data link remain an expensive solution to transporting this information due to their per-link cost, physical size, and power dissipation. Power dissipation on the switching chips is high because of the need for electronic drivers for the high speed electrical interconnections between the switching chips and the data links. By integrating the O/E conversions directly onto the switching chips, lower cost and higher density systems can be built. In this paper, we describe preliminary results of an experimental optoelectronic switching network based on this lower cost solution. The network is designed to be part of an asynchronous transfer mode (ATM) network based on the Growable Packet Architecture. The switching chip consists of GaAs/AlGaAs multiple quantum well modulators and detectors flip- chip bonded to silicon VLSI circuitry. The optical system images the inputs from a two dimensional fiber bundle onto the switching chip, provides optical fan-out of the signals from the fibers to the switching chip, and images the outputs from the chip onto the fiber bundle.

Details are presented of the design, fabrication, and use of a hybrid lens employed to interconnect two-dimensional arrays of optical transceivers. The hybrid lens consists of a custom-designed, 42-mm focal length, ƒ/5 compound lens followed by an array of afocal telescope compound microlenses.

Smart pixel optoelectronic device arrays enable the interconnection and communication advantages of optics to complement the processing power of electronics in computing and switching applications. GaAs multiquantum well (MQW) FET-SEED smart pixels have been used in a 32 input, 16 output multistage switching fabric prototype1 using 5 stages of (2,1,1) node arrays2 (16 nodes/stage), as shown in Fig. 1(a). Optimization of the initial system experiment has increased the fabric's bit rate from 50 Mb/s to 155 Mb/s per channel. As shown in Fig. 2, these FET-SEED systems incorporate smart pixels using GaAs MQW modulators and detectors, computer generated holograms, 2-D fiber bundles, external cavity semiconductor lasers, high resolution bulk and microoptics, and custom optical bench optomechanics.

Within the past 15 years there has been significant progress in the development of two-dimensional arrays of optical and optoelectronic devices. This progress has, in turn, led to the construction of several free-space digital optical system demonstrators. The first was an optical master-slave flip-flop using Hughes liquid-crystal light valves as optical logic gates and computer-generated holograms as the gate-to-gate interconnects. This was demonstrated at USC in 1984. Since then there have been numerous demonstrations of free-space digital optical systems including a simple optical computing system (1990) and five switching fabrics designated System/sub 1/ (1988), System/sub 2/ (1989), System/sub 3/ (1990), System/sub 4/ (1991) and System/sub 5/ (1993). The main focus of this paper will be to describe the five switching fabric demonstrators constructed by AT&T in Naperville, IL. The paper will begin with an overview of the SEED technology which was the device platform used by the demonstrators. This will be followed by a discussion of the architecture, optics, and optomechanics developed for each of the five demonstrators. >

The interconnection problems present in many high-performance digital systems may be alleviated through the use of surface normal optical interconnections using optoelectronic smart pixels. We present recent results of high-speed operation of a five-stage experimental free-space switching network using embedded control techniques for network control. The smart pixels consist of buffered GaAs FET logic with MQW SEED detectors and modulators. The system also incorporates external cavity lasers, bulk, micro, and diffractive optics, two-dimensional fiber bundles, and novel optomechanics. At 155 Mb/s, 77 of the 80 total pixels in the system and 31 of the 32 input fibers were functional. Two of the network paths have carried digital video at 105 Mb/s for over four months without readjustment. Error rate measurements on these paths have shown a short-term BER of 10/sup -10/.< >

Several different shuffle-equivalent interconnection topologies that can be used within the optical link stages of photonic-switching networks are studied. These schemes include the two shuffle, the two banyan, and the segmented two shuffle, which can be used to interconnect two-input, two-output switching nodes. The schemes also include the four shuffle and the four banyan, which can be used to interconnect four-input, four-output switching nodes. (Note: The segmented two shuffle and the four banyan are novel interconnection topologies that were developed to satisfy some of the constraints of free-space digital optics). It is shown that each of these interconnection topologies can be implemented by the use of relatively simple imaging optics that contain space-invariant computer-generated binaryphase gratings. The effects of node type and interconnection topology on the laser power requirements and the optical component complexity within the resulting systems are also studied. The general class of networks nown as extended generalized shuffle networks is used as a baseline for the analysis. It is shown that (2, 1, 1) nodes and (2, 2, 2) nodes connected by two-banyan interconnections can produce power-efficient and cost-effective systems. The results should help identify the architectural trade-offs that exist when a node type and an interconnection topology are selected for implementation within a switching system based on free-space digital optics.

The design, construction, and operational testing of a five-stage, fully interconnected 32 × 16 switching fabric by the use of smart-pixel (2, 1, 1) switching nodes are described. The arrays of switching nodes use monolithically integrated GaAs field-effect transistors, multiple-quantum-well p-i-n detectors, and self-electro-optic-device modulators. Each switching node incorporates 25 field-effect transistors and 17 p-i-n diodes to realize two differential optical receivers, the 2 × 1 node switching logic, a single-bit node control memory, and one differential optical transmitter. The five stages of node arrays are interconnected to form a two-dimensional banyan network by the use of Fourier-plane computer-generated holograms. System input and output are made by two-dimensional fiber-bundle matrices, and the system optical hardware design incorporates frequency-stabilized lasers, pupil-division beam combination, and a hybrid micro-macro lens for fiber-bundle imaging. Optomechanical packaging of the system ut lizes modular kinematic component positioning and active thermal control to enable simple rapid assembly. Two preliminary operational experiments are completed. In the first experiment, five stages are operated at 50 Mbits/s with 15 active inputs and outputs. The second experiment attempts to operate two stages of second-generation node arrays at 155 Mbits/s, with eight of the 15 active nodes functioning correctly along the straight switch-routing paths.

A 5 stage, fully interconnected 32/spl times/16 switching network using smart pixel 2/spl times/1 switching nodes is demonstrated. The system was designed to operate with 150 Mbps data rates.< >