Urban optical wireless communication (UOWC) is rapidly gaining popularity as an effective means of transferring data at high rates over short distances The UOWC terminal includes an optical transmitter and a receiver positioned, for example, on high-rise buildings separated by several hundred meters Light beams propagating through the atmosphere carry the information from the transmitter to the receiver UOWC boasts many advantages over its rivals Notably, UOWC facilitates rapidly deployable, lightweight, high-capacity communication without licensing fees and tariffs However, UOWC still faces many challenges, including how to improve communication performance in adverse weather conditions or during building sway We present and evaluate some of the exciting new research approaches that have been suggested to deal with these issues, including optimization of telescope gain, new technologies for pointing systems, and solutions at the network level

Urban optical wireless communication networks: the main challenges and possible solutions

The intensive investment in optical microelectromechanical systems (MEMS) in the last decade has led to many successful components that satisfy the requirements of lightwave communication networks. In this paper, we review the current state of the art of MEMS devices and subsystems for lightwave communication applications. Depending on the design, these components can either be broadband (wavelength independent) or wavelength selective. Broadband devices include optical switches, crossconnects, optical attenuators, and data modulators, while wavelength-selective components encompass wavelength add/drop multiplexers, wavelength-selective switches and crossconnects, spectral equalizers, dispersion compensators, spectrometers, and tunable lasers. Integration of MEMS and planar lightwave circuits, microresonators, and photonic crystals could lead to further reduction in size and cost

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Optical MEMS for Lightwave Communication

Wireless Optical Communication Systems addresses the problem of designing efficient signaling and provides a link between the areas of communication theory and modem design for amplitude constrained linear optical intensity channel. Topics include historical perspective, channel impairments, amplitude constraints and the characteristics of popular optoelectronic components. A variety of wireless optical channel topologies are presented along with a survey and analysis of present day signalling techniques employed for these channels. The author provides a unifying framework for signalling design which allows the channel constraints to be represented geometrically and permits the use of modem design principles from electrical channels. Modulation schemes are designed using the formalism of lattice codes and a design process for signalling sets is specified. The use of multiple-input/multiple-output (MIMO) wireless optical channels to improve the spectral efficiency of links is explored. The basic spatio-temporal modem design problem is specified and a spatial multiplexing gain is quantified. New spatial discrete multitone modulation is proposed and the unique features are discussed. Based on measurements on an experimental prototype, a channel model is formulated and a realizable spatio-temporal coding scheme is simulated to quantify performance gains. This volume is organized for professional and academic readers engaged in modem design for wireless optical intensity channels. Significant background material is presented on both the properties as well as on fundamental communications principles. Wireless Optical Communication Systems can be used by physicists and experimentalists as an introduction to signalling design as well as communication systems designers.

Wireless Optical Communication Systems

Progress in 2D photonic crystal Fano resonance photonics

Thanks to advanced semiconductor microfabrication technology, chip-scale integration and miniaturization of lab-on-a-chip components, silicon-based optical biosensors have made significant progress for the purpose of point-of-care diagnosis In this review, we provide an overview of the state-of-the-art in evanescent field biosensing technologies including interferometer, microcavity, photonic crystal, and Bragg grating waveguide-based sensors Their sensing mechanisms and sensor performances, as well as real biomarkers for label-free detection, are exhibited and compared We also review the development of chip-level integration for lab-on-a-chip photonic sensing platforms, which consist of the optical sensing device, flow delivery system, optical input and readout equipment At last, some advanced system-level complementary metal-oxide semiconductor (CMOS) chip packaging examples are presented, indicating the commercialization potential for the low cost, high yield, portable biosensing platform leveraging CMOS processes

Silicon Photonic Biosensors Using Label-Free Detection.

Free-space optical interconnects can provide high bandwidth with no physical contact, but suffer from poor tolerances to misalignment. In order to obtain high misalignment tolerances, we propose the use of an active alignment scheme in conjunction with an optimized optical design. The active alignment scheme uses a redundant set of optical links and the active selection of the best link. The optical design maximizes the alignment tolerances between the two boards to /spl plusmn/1 mm of lateral and /spl plusmn/1/spl deg/ of angular misalignment for a target data rate of 1.25 Gb/s.

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Free-space optical link with spatial redundancy for misalignment tolerance

We present a novel air-bridge subwavelength grating reflector with very high reflectivity be used as a top mirror in a VCSEL structure. We explain the design method, model the structure using both RCWA and FDTD, and predict the characteristics of a Fabry-Perot structure built with this reflector. We describe the fabrication of the suspended grating.

High reflectivity air-bridge subwavelength grating reflector and Fabry-Perot cavity in AlGaAs/GaAs

We demonstrate a Finite-Difference Time-Domain (FDTD) phase methodology to estimate resonant wavelengths in Fabry-Perot (FP) cavity structures. We validate the phase method in a conventional Vertical-Cavity Surface-Emitting Laser (VCSEL) structure using a transfer-matrix method, and compare results with a FDTD reflectance method. We extend this approach to a Sub-Wavelength Grating (SWG) and a Photonic Crystal (Phc) slab, either of which may replace one of the Distributed Bragg Reflectors (DBRs) in the VCSEL, and predict resonant conditions with varying lithographic parameters. Finally, we compare the resonant tunabilities of three different VCSEL structures, taking quality factors into account.

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DBR, Sub-wavelength grating, and Photonic crystal slab Fabry-Perot cavity design using phase analysis by FDTD.

An integrated etched multilayer grating-based wavelength multiplexer/demultiplexer is disclosed wherein an etched multilayer grating structure is monolithically integrated within the optical waveguide stack of the multiplexer/demultiplexer to reflectively diffract an input optical beam. The multilayer grating structure is generally comprised of a series of etched diffractive elements and an etched multilayer reflector, the combined optical response of which providing the desired multiplexing/demultiplexing effect. The etched structures are generally comprised of shallow etch structures in a top surface of the multiplexer/demultiplexer waveguide stack. Monolithically integrated input and output ridge waveguides may also be provided, optionally fabricated in a same etching step as the etched multilayer grating.

Integrated etched multilayer grating based wavelength demultiplexer

An electro-optic switching device, namely an optical phased array (OPA) or a reprogrammable optical phased array (ROPA), that can accommodate high switching speeds, reduced losses and increased efficiency while being adapted to operate at various wavelengths using suitably low activation voltages is presented. The ROPA designs presented herein are generally comprised of an electro-optic (EO) crystal electrically mounted to a high-voltage CMOS chip activated to apply an array of activation voltages across the crystal and induce a refractive index profile therein, such profile adaptable to selectively control and manipulate an optical beam interacting with the device.

Eric Bisaillon

Papers

Free-space optical link with spatial redundancy for misalignment tolerance

High reflectivity air-bridge subwavelength grating reflector and Fabry-Perot cavity in AlGaAs/GaAs

DBR, Sub-wavelength grating, and Photonic crystal slab Fabry-Perot cavity design using phase analysis by FDTD.

Integrated etched multilayer grating based wavelength demultiplexer

High speed reprogrammable electro-optical switching device