Fiber optics is well established today due to the high capacity and speed, unrivaled flexibility and quality of service. However, state of the art optical elements and components are hardly scalable in terms of cost and size required to achieve competitive port density and cost per bit. Next-generation high-speed coherent optical communication systems targeting a data rate of 100-Gb/s and beyond goes along with innovations in component and subsystem areas. Consequently, by leveraging the advanced silicon micro and nano-fabrication technologies, significant progress in developing CMOS platform-based silicon photonic devices has been made all over the world. These achievements include the demonstration of high-speed IQ modulators, which are important building blocks in coherent optical communication systems. In this paper, we demonstrate silicon photonic QPSK modulator based on a metal-oxide-semiconductor (MOS) capacitor structure, address different modulator configuration structures and report our progress and research associated with highspeed advanced optical modulation in silicon photonics
Development of a silicon-based on-chip light source could be facilitated by the incorporation of nanocrystalline silicon
(<i>nc</i>-Si) into a multislot waveguide structure, using erbium embedded in silicon oxide as a luminescence source. The
multislot waveguide confines TM polarized light in the oxide (low-index) layers, thus reducing the loss caused by
interaction with free carriers in the <i>nc</i>-Si layers. Here we demonstrate a lateral electrical injection scheme using a p-i-n
junction embedded into the multislot, allowing much more efficient charge injection than alternative vertical injection
approaches which have been limited by the highly insulating oxide layers. By exploiting the difference in the mode
profiles of TE and TM light, we were able to gauge the injection of free carriers as a function of applied voltage, by
measuring the polarization-dependent optical loss for light transmitted through the multislot waveguide. Experimental
measurements are well-predicted by numerical computations using both FDTD and the transfer matrix method.
Although switching techniques based on charge injection in silicon have progressed greatly in recent years, switching
energies are still above 10 fJ/bit, which is considered the threshold for practical implementation in on-chip optical
interconnects. This is due primarily to silicon's relatively weak electro-optic response, as well as the large physical
extent of existing switching geometries, both of which increase the energy required to achieve switching. By using a
resonant approach in which the optical mode is spatially tightly confined, however, the volume of active material is
decreased, resulting in reduced switching energy. In this paper we report on the use of a thin MOS capacitor to inject
charge into a resonator based on a photonic crystal microcavity. By injecting charge only into the volume in which the
optical mode is localized, switching energy can be reduced below 1 fJ/bit. The index shift available (Δn ~ 0.001) allows
the use of a relatively low-Q resonator (Q ~ 550), enabling high optical bandwidth of 100 Gbps with a device footprint
below 25 μm<sup>2</sup>.
We report the development and characterization of 2-D photonic crystal (PC) microcavity devices on silicon on
insulator. The transmission of light through a 2-D PC microcavity near resonance can be switched on and off by
modulating the refractive index of the PC. Because silicon has poor electro-optical properties, it is advantageous to insert
electro-optic materials inside the air holes. In this work, we report the design, fabrication, and characterization of such
hybrid PC microcavity switches using liquid crystals as the electro-optic material. In addition, we demonstrate an
electrode geometry that eliminates electric field screening by the more conducting silicon host, and thus enables
A slip ring is a rotary electrical interface, collector, swivel or joint. It is a component
or architecture that can perform continuous data transfer between a rotary and
stationary structure. A few of the numerous approaches for transferring data include
contact and non-contact methods which use wires, radio waves, optical fibers and
even liquid as the transfer media. However, they all suffer inherent drawbacks in
durability, reliability, stability, electromagnetic interference and speed. The system
introduced in this paper alleviates many of these issues by employing a wireless
through the air optical solution.
Silicon-based 2-D photonic bandgap (PBG) structures have an unmatched potential for integration with well-established microelectronic devices and circuits. They can allow for compact optical devices with enhanced functionality and performance. While a number of passive PBG silicon-based devices have already been demonstrated, electrical tuning of their properties has yet to be implemented. PBG tuning can be achieved by replacing the air inside the device with active optical material, for example liquid crystals (LCs) or an electro-optic polymer. The two main requirements necessary for tuning in PBG structures are (i) the electric field of the control signal should be present inside the active optical material to modify its properties, and (ii) the energy of the optical mode of interest should be distributed inside the active material. While the latter condition can be satisfied by proper optical design, the former requirement is difficult to satisfy due to external electric field screening by the conductive silicon walls. In this work, an analysis of this effect is conducted and guidelines to overcome screening and thus allow for switching are suggested. Further, by using LCs as an active optical material, electric field switching in 2-D silicon-based PBG structures is demonstrated for the first time. Results of this work can lead to the development of silicon-based switches, active routers and filters for future optical interconnects.
We have been developing a decentralised architecture for data fusion for several years. In this architecture, sensing nodes, each with their own processing, are networked together. Previously, we have researched fully connected networks, tree-connected networks, and networks with loops, and have developed a range of theoretical and empirical results for dynamic networks. Here we report the results obtained from building and demonstrating a decentralised data fusion system in which the nodes are connected via an ad hoc network. Several vision based tracking nodes are linked via a wireless LAN. We use UDP to establish local routing tables within the network whenever a node joins, and TCP/IP to provide point to point communications within the network. We show that the resulting data fusion system is modular, scalable and fault tolerant. In particular, we demonstrate robustness to nodes joining and leaving the network, either by choice or as a result of link drop-out. In addition to experimental results from the project, we present some thoughts on how the technology could be applied to large scale, heterogeneous sensor networks.
Previously, we have developed techniques for Simultaneous Localization and Map Building based on the augmented state Kalman filter. Here we report the results of experiments conducted over multiple vehicles each equipped with a laser range finder for sensing the external environment, and a laser tracking system to provide highly accurate ground truth. The goal is simultaneously to build a map of an unknown environment and to use that map to navigate a vehicle that otherwise would have no way of knowing its location, and to distribute this process over several vehicles. We have constructed an on-line, distributed implementation to demonstrate the principle. In this paper we describe the system architecture, the nature of the experimental set up, and the results obtained. These are compared with the estimated ground truth. We show that distributed SLAM has a clear advantage in the sense that it offers a potential super-linear speed-up over single vehicle SLAM. In particular, we explore the time taken to achieve a given quality of map, and consider the repeatability and accuracy of the method. Finally, we discuss some practical implementation issues.
We have developed techniques for Simultaneous Localization and Map Building based on the augmented state Kalman filter, and demonstrated this in real time using laboratory robots. Here we report the results of experiments conducted out doors in an unstructured, unknown, representative environment, using a van equipped with a laser range finder for sensing the external environment, and GPS to provide an estimate of ground truth. The goal is simultaneously to build a map of an unknown environment and to use that map to navigate a vehicle that otherwise would have no way of knowing its location. In this paper we describe the system architecture, the nature of the experimental set up, and the results obtained. These are compared with the estimated ground truth. We show that SLAM is both feasible and useful in real environments. In particular, we explore its repeatability and accuracy, and discuss some practical implementation issues. Finally, we look at the way forward for a real implementation on ground and air vehicles operating in very demanding, harsh environments.