AVS1997 Session EM-MoM: Technology Challenges for Optical Communications

Monday, October 20, 1997 8:20 AM in Room C1/2

Monday Morning

Start	Invited?	Item
8:20 AM	Invited	EM-MoM-1 New Trends in Lightwave Communications T. Li (AT&T Labs-Research) Telecommunications industries worldwide are undergoing fundamental changes brought about by deregulation, competition, and the availability of potent new technologies in photonics and electronics. Network planners and service providers now have a choice of technologies and architectures for building new local access networks and upgrading the capacity of embedded terrestrial long-distance infrastructures. A new generation of undersea-cable transmission systems has also been developed and is being deployed for transoceanic applications. Not only do these new, revolutionary systems provide vastly increased transmission capacity at an affordable incremental cost, they also offer enhanced operational flexibility and network reliability. In the future, optical networking may be implemented for managing the large volume of traffic expected from the growth of Internet and broadband services. The enabling technologies for these revolutionary systems include: high-power semiconductor lasers, fiber optical amplifiers, integrated photonic devices, guided-wave components, and wavelength-multiplexing (WDM) techniques. The traditional (single-channel) transmission paradigm that capacity upgrades must be accompanied by higher channel bit rates has been overturned by the amplified WDM (multi-channel) systems currently being installed by long-distance carriers. Much like parallel processing in computers, WDM operation at lower bit rates with existing electronics allows large but graceful growth in transmission capacity in the embedded network, without having to develop costly higher-speed electronics and to compensate for fiber dispersion. The lower first cost and the potential savings in operating cost are two cardinal considerations that favor amplified WDM systems. On the research front, WDM system experiments with aggregate transmission capacities in the terabit-per-second range have been demonstrated over long distances. Large-scale experimental projects are also underway to explore the potential of WDM technology for high-capacity optical networking. These present and future revolutionary system solutions will meet the demand of envisioned Internet and broadband services for many years to come, and thus make lightwave communications the principal component of the global information infrastructure.
9:00 AM	Invited	EM-MoM-3 Novel Optoelectronic Devices using Wafer Bonding J. Bowers, N. Margalit, Unknown Hawkins (University of California, Santa Barbara); B. Levine (Lucent Technologies); A. Black, P. Abraham, E. Hu (University of California, Santa Barbara) Lattice matching of thick epitaxial films is required to avoid threading dislocations in the epitaxial layers. However, by growing to films on dissimilar substrates and fusing them together, materials with different lattice constants can be combined without threading dislocations, but with excellent optical and electrical properties. Examples to be discussed include vertical cavity lasers, avalanche photodiodes and LEDs. Integration of lasers and photodetectors on silicon substrates is important for optoelectronic integration. In many of these cases, record device performance has been demonstrated because the lattice matching requirement was removed. The fusing conditions strongly affect the properties of the interface, and obtaining a low forward voltage is difficult. SIMS analysis indicates significant levels of carbon and oxygen at the interface. Forward voltage measurements on InGaAs/Si PIN diodes indicate that fusing in hydrogen at 650 C produces I-V curves with low leakage current and ideality factors close to unity with exponential behavior. Other fusing conditions typically produce higher leakage currents and a forward characteristic showing evidence of a thin barrier. In summary, fusing wafers together can be used to solve inherent device limitations, to combine wafers together with different orientations, to introduce structure within a device and to allow optoelectronic integration. The process conditions strongly affect the device performance.
9:40 AM	Invited	EM-MoM-5 III-V Technology, Materials and Processing for Photonic Integration I. Mito (NEC Corporation) Photonic integration circuits (PICs) consisted of lasers, detectors, optical modulators, optical waveguides and so on, are the key devices to satisfy the expanding demand on high speed and large band of optical communications. Although the technology for discrete optical devices have been matured, the photonic integration technology has been under the way of development. The most difficult problem is how to connect physically the optical core layers composing the PICs. Each component should consist of the optical core layer with different bandgap energy, that is in large contrast to Si ICs. We have been engaged in new technology development for PICs, that is narrow-stripe-area metal-organic vapor phase epitaxy (NSA MOVPE). 1-1.5 micron wide optical waveguides of InGaAsP multi-quantum well (MQW) layers clad in InP were directly grown on the mask patterned InP substrates. The bandgap energy of the MQW layer was possible to be controlled by changing the mask patterns. The features of the bandgap energy control along the waveguide direction as well as the direct waveguide formation have greatly facilitated to develop PICs such as electro-absorption modulator integrated lasers, wavelength tunable semiconductor lasers, multi-wavelength lasers, and so on. Those PICs are expected to exploit photonic networks as well as the cost reduction of optical modules by removing the troublesome optical packaging procedure between several optical chips and fibers.
10:20 AM	Invited	EM-MoM-7 Fibers for the 21st Century: Materials Challenges J.B. MacChesney (Bell Laboratories, Lucent Technologies) Glass intended for the transmission medium of optical communications must exhibit maximum transparency and minimum dispersion. After some initial threshing-about with multicomponent glasses, the world settled on fused silica as the material of choice. Over the next two decades efforts concentrated on optimizing both performance and economy. More recently, spurred by development of an Erbium doped fiber amplifier, attention has turned to glass as an active medium. Now, ultraviolet irradiation and poling are being explored to develop nonlinear phenomena resulting in photosensitivity and other active and passive components such as filters, multiplayers and routers. Thus, from the simplest glass arise an amazing array of properties generated by chemically and physically induced defects in the glass network.
11:00 AM	Invited	EM-MoM-9 Optical Communication Technology Challenges for Polymeric Integrated Optic Waveguide Circuitry B.L. Booth (DuPont Photopolymer and Electronic Materials) The primary facilitator for the communication and information revolution is optical communication technology because of its high data rate capability delivered cost effectively. In addition to the continued installation of optical fiber networks the escalating demand requires cost effective mass deployment of optical interconnection circuits, components and connectors. To meet the challenging performance, cost and manufacturing requirements of the communication industry polymeric waveguide optical interconnection technology is becoming increasingly important and is considered by many as the candidate technology of choice. This paper addresses and relates the market driven technological demands relative to polymeric system requirements. Significant industry issues and challenges and their current state of resolution will be elaborated on regarding materials, waveguide formation, packaging, connectivity, operational performance, environment, lifetime, installation process compatibility, and cost effective manufacturability. For descriptive purposes emphasis will be on DuPont's Polyguide* polymeric waveguide system for which these polymer material and system issues have been and continue to be extensively addressed to insure commercial viability. Alternative polymeric systems will also be described where ever appropriate to further elucidate material and system needs and issues relative to the communication technology challenge.
11:40 AM		EM-MoM-11 Optical Demultiplexer Devices for Communication Systems using Wavelength Division Multiplexing M. Spector (Bell Laboratories, Lucent Technologies) With the explosion of optical communication applications, the need for increased capacity of the existing system fibers has become a critical factor. An efficient way to achieve a higher transmission capacity is by Wavelength Division Multiplexing (WDM), whereby channels with several different wavelengths can be combined, transmitted long distance with optical amplification, and demultiplexed. A critical device for this operation is the Optical Demultiplexer Unit (ODU). This ODU uses three main technologies: Silicon Optical bench, Thin Films and Fiber Gratings. In this presentation, the different technologies are described, according to the required device performance. The silicon optical bench, which combines a novel waveguide design with mature silicon processing, is widely used as a low cost ODU, although their are still important materials issues related to the inherent temperature dependence and high insertion loss. Thin film interference filters can achieve temperature independence and have a relatively low insertion loss. But the required high thickness uniformity is difficult to achieve and the assembly is still a challenge for large volume manufacturing. Fiber gratings have a very low insertion loss, as the grating is directly written in the fiber core, and can also be made temperature independent. However, the implementation as a demultiplexer is complicated by the need for other components such as circulators and passive combiners. Furthermore, the nature of the defects created in the fibers by the UV irradiation used to write the grating is not well characterized nor understood. Comparative performances and materials requirements will be discussed.