AVS2001 Session PH-ThA: Photonic Materials: Applications and Processing

Thursday, November 1, 2001 2:00 PM in Room 120

Thursday Afternoon

Start	Invited?	Item
2:00 PM	Invited	PH-ThA-1 Recent Progress on Silica-based Planar Lightwave Circuits for Photonic Networks S. Mino (NTT, Japan) The increasing demand for Internet traffic is the motivation for a large-capacity and flexible network. Photonic networks utilizing wavelength division multiplexing (WDM) are expected to meet these requirements. Silica-glass-based planar lightwave circuit (PLC) technologies provide various optical devices for such photonic networks. This paper reviews silica-based PLC devices including arrayed-waveguide gratings (AWG), thermo-optic switches (TOSW), and hybrid-integrated PLC devices with optical semiconductor devices. A PLC is an optical integrated circuit that employs silica glass, which is a stable optical fiber material. Thus the PLC has characteristics that include low-loss, compactness, low-cost, suitability for mass-production, and good reliability. The AWG multiplexer is a key component in dense optical WDM networks, since it is capable of multi/demultiplexing N optical signals of different wavelengths. This is because the multiplexer employs the same system as a grating-based spectrometer. We recently reported a 400-ch AWG multiplexer, which is the largest number of channels yet achieved. An optical switch is required to eliminate the bottleneck in conventional electronic switching systems and the PLC-TOSW is a promising candidate because of its excellent characteristics and reliability. We have already reported 16x16 and 1 x 32 TOSW modules. We can construct a larger-scale photonic switching system with more than 100 ports using these modules. Furthermore we developed hybrid-integration technologies in which optical semiconductor devices can be assembled on a PLC substrate. Using hybrid integration, we can realize a high-speed wavelength channel selector and an optical transceiver for optical access systems.
2:40 PM		PH-ThA-3 Silica Deep Etching with Vertical and Smooth Sidewall and Reduced RIE Lag D.Y. Choi, J.H. Lee, D.S. Kim, S.T. Jung (Samsung Electronics, Korea) Silica waveguides are very important for use in Planar Lightwave Circuits(PLC) because of its low loss and inherent compatibility with silica optical fibers. Deep silica etching(>30um) is necessary when silica PLC is used as a platform to integrate with active devices(LD, PD, SOA, etc.). To lower propagation loss, polarization dependent loss(PDL), and reflectance at waveguide end facet(junction between waveguide and active device), vertical and smooth sidewalls are required. In this work the profile and sidewall roughness of etched waveguides were investigated. Vertical profile was obtained when etching mask was thickened and polymer deposition on sidewall was promoted. But sidewall roughness was increased as deposited polymer thickened. When the clamp in the plasma chamber was changed from alumina to silicon, vertical and smooth sidewall was obtained. RIE lag(Aspect ratio Dependent Etching) becomes important in deep silica etching. We investigated the extent of RIE lag as a function of aspect ratio of trench structures, etching depth, bias power, and pressure. RIE lag increased irrespective of etching depth as aspect ratio increased. When process pressure was high and Si clamp was used, nearly RIE lag-free trench was etched.
3:00 PM		PH-ThA-4 Development of Integrated Multifunctional Optical Sensors based on III-Nitrides Grown on Si D. Starikov, J.-W. Um, C. Boney, A. Bensaoula (University of Houston) An approach to integrating III-Nitrides-based optoelectronic diode structures into multifunctional optical sensors working in the absorption, scattering, or fluorescence mode is described. The proposed concept is evaluated using an optical sensor prototype assembled from discrete III-Nitrides- and Si-based components coupled to a sapphire window. Testing of this prototype proved the applicability of a wide-range silicon photodetector and UV/blue LEDs in multifunctional optical sensors, and the feasibility of the back-side illumination with a lateral setup of the components. Absorption of light was measured in aquatic polyethylene glycol solutions placed between the sapphire window and a mirror attached in front of it. Observable signals were measured for dilutions ranging from 1000-35000 ppm with a linear dependence for concentrations up to 5000 ppm. The internal reflection from the sapphire window, resulted in a low signal-to-noise ratio, since our prototype did not have any antireflection coating. Scattering measurements were performed using slurries of alumina powder in water at particle concentrations from 6x105 to 4x1012 cm-3. The highest sensitivity and dynamic range is achieved for particle sizes of 0.3-5 mm. The photoresponse dependence is linear for very small (0.05 mm) and very large (15 and 20 mm) particles. Fluorescence measurements of Fluoresceinâ„¢ dye and Chlorophyll in ethanol solutions ranging in concentration from 0.029 to 58 ppm show a more than 6 times wider dynamic range and 5000 times higher sensitivity to the concentration variation than either absorption or scattering measurements. In addition fluorescence shows sensitivity to the pH of the solution. The above results are currently utilized in device modeling, simulation and development of integrated GaN-InGaN multifunctional sensors on Si and sapphire. The talk will present the latest results on the growth, processing, and characterization of these sensors.
4:00 PM		PH-ThA-7 Application of Photosensitive Methylsilsesquiazane(MSZ) to Lithographic Fabrication of Three Dimensional Periodic Structures T. Matsuura, A. Yamada, J. Murota (Tohoku University, Japan) \|> We have proposed a novel lithographic process for fabricating three dimensional periodic structures.¹ The essence of the process is that multiple layers of photoresist are coated on the wafer with each layer being exposed with a different pattern without development, and finally after all the photoresist layers are exposed they are developed from upper ones. In this paper, we have applied photosensitive methylsilsesquiazane (MSZ) to enhance the potential of the process. MSZ was spin-coated on the Si wafer, pre-baked at 90°C, and exposed to UV light with a lines-&-spaces mask. Then, the wafer was kept in a moisture case. MSZ contains Si-N bonds, which are converted to alkaline-soluble Si-O bonds after UV-generated photoacid and hydrolysis. Without development of the MSZ at this time, 20nm-thick aluminum is vacuum-evaporated, and then the second photosensitive MSZ was coated. Here, the aluminum layer suppresses mixing of the MSZ layers during coating and penetration of the light to the first layer during exposing the second layer with a different pattern. After these coating and pre-patterning processes are repeated for desired times, the wafers were dipped in a standard developer (TMAH) for MSZ. The areas of the thin aluminum layers wetted by TMAH are also etched, and a periodically stacked structure is formed. When the wafer is cured at 400°C in O₂, the remaining MSZ is converted directly to methylsilsesquioxane (MSQ) containing stable Si-O-Si networks. As remarkable merits, the present process is simple, easy, and fast, and it possesses intentional-defect-introduction-ability and compatibility with microlithography technology. ¹ Matsuura et.al, SSDM 2000, p.542.
4:20 PM	Invited	PH-ThA-8 Microphotonics: The Next Platform for the Information Age L.C. Kimerling (Massachusetts Institute of Technology) A rebuilding of the world’s information infrastructure is taking place to give instantaneous availability of data, voice and video. This revolution of the Information Age is being gated more by the introduction of new materials and components, than by the design of systems, software and networks. The key frontier is the large scale integration and manufacturing of photonic components to enable the distribution of high bit rate optical streams to the individual information appliance. It is now one-half century since the advent of solid state electronics with the invention of the transistor. Through unparalleled gains in functionality at relatively constant cost, integrated circuits have enabled telecommunications, computation and manufacturing to move to the leading edge of societal change. This revolution has been conducted with "the turn of a single knob": the shrinking of device dimensions. During the last two decades a new "killer technology" has emerged in the telecommunications field. This photonic technology uses optical fibers for interconnection, and has delivered an exponential increase with time of information carrying capacity to the industry. A single optical fiber, with several hundred gigabits/second of capacity, is limited by electronic processing at each circuit node. To avoid this problem direct optical connections are required. To provide full functionality, optical components must be integrated at densities compatible with microelectronic integration. This microphotonics platform represents not only a solution to information access, but it can also solve key problems relating to reliability and complexity that threaten to end the advance of the silicon integrated circuit technology. The Information Age was ushered into existence by Microelectronics. The future will depend on the networking of communications and databases for universal accessibility. This new Age of Connectivity will require a mating of microelectronic and fiber optic technology through integrated of Microphotonic functionality.