12 Terrestrial 1550 nm WDM free-space optical communication systems have been demonstrated to provide a viable means to transport data, voice and video channels for point-to-point applications without the use of optical fiber. Key features of free-space optical transmission systems are their ability to utilize present day telecommunication components such as: laser diode transmitters, high-power optical amplifiers operating within the 1550 nm optical transmission window and high-sensitivity optical receivers designed for multi-Giga- bit data rates. In this paper, we report on details of the world's first field test, demonstrating real time video transmission of eight uncompressed standard-definition (SD) video channels operating at an aggregate data rate of 1.485 Gb/s over a 0.89 km terrestrial free-space link. This data link was used in support of the 2000 Olympic games held recently in Sydney, Australia. Results from this eight- channel SD terrestrial free-space laser communications systems are presented. The transmission system operated error-free continuously from September 14, 2000 until October 1, 2000, twenty-four hours a day, throughout the coverage of the games. Modeling results predict that free- space SD video transmission systems can be designed and operated over significant link distances under nominal visibility conditions.

12 We demonstrate record error-free transmission of a single 160 Gb/s RZ data channel at 1550 nm over 200 meters of free space. This represents the largest data bandwidth transmitted over this distance, without the use of optical fibers.

12 The requirement to send ever increasing amounts of tactical military information between sensor aircraft and information processing facilities for command and control purposes has begun to reach the physical limits of present RF data links, even when data compression is employed. Use of laser data links is under consideration by the United States Air Force and Directorate. This technology development program is being conducted in two phases.

12 There is currently a misconception among designers and users of free space laser communication (lasercom) equipment that 1550 nm light suffers from less atmospheric attenuation than 785 or 850 nm light in all weather conditions. This misconception is based upon a published equation for atmospheric attenuation as a function of wavelength, which is used frequently in the free-space lasercom literature. In hazy weather (visibility > 2 km), the prediction of less atmospheric attenuation at 1550 nm is most likely true. However, in foggy weather (visibility < 500 m), it appears that the attenuation of laser light is independent of wavelength, ie. 785 nm, 850 nm, and 1550 nm are all attenuated equally by fog. This same wavelength independence is also observed in snow and rain. This observation is based on an extensive literature search, and from full Mie scattering calculations. A modification to the published equation describing the atmospheric attenuation of laser power, which more accurately describes the effects of fog, is offered. This observation of wavelength-independent attenuation in fog is important, because fog, heavy snow, and extreme rain are the only types of weather that are likely to disrupt short (< 500 m) lasercom links. Short lasercom links will be necessary to meet the high availability requirements of the telecommunications industry.

12 We present performance results from a trial of an OC-48 optical wireless link spanning 1.2 km in New York City. The measured laser communication link performance parameters include: link availability, SONET Errors, received optical power, visibility, scintillation characteristics, and alignment effects associated with transmission through a glass window. These were supplemented by concurrent measurements from a MET station to correlate performance with meteorological conditions.

12 Recently, free space optical communication systems have been discussed as solutions to provide high-speed local loop connectivity in metropolitan area network environments. Free space optical technology is capable of providing much higher bandwidth than any other competing wireless connectivity options such as classical RF or microwave systems. A widespread concern regarding free space optical systems is related to its capability to provide the high availability figures commonly envisioned by network service providers. Wireless microwave systems tend to have high availability figures, but at the expense of the ability to operate at higher data rates. LightPointe suggests an integrated network solution that combines the benefits of both technologies.

12 This paper describes a promising optical wireless broadband technology that will provide low cost broadband services to the local access `last mile' market. This paper examines the application, advantages and limitations of utilizing Free Space Optical Communications (FSOC) systems for broadband access markets. The service markets that would fully utilize FSOC technologies include metropolitan areas, BLECs (multi- tenant dwellings/business apartments), campuses, industrial parks and `pole-to-hole' neighborhood deployments. This paper will identify weather dependent link availability as being the primary consideration in defining and selecting suitable locations for FSOC-based systems. Link availability in turn determines link range, type of service, and the need for transmission diversity. This paper will describe the implications of telecom `five nines' last-mile access availability and its effect on the transparent integration of FSOC technologies into the existing fiber optic networks. This paper will also describe propagation losses and link budget requirements for broadband FSOC-based local service. During adverse weather conditions, stand-alone, FSOC-based optical wireless links typically offer path lengths of less than 200 meters while still meeting the `five nines' availability criteria. This paper will also consider `availability limited' services. These services may prove to be attractive to customers who are willing to accept broadband service on an `as available basis'. The use of availability-enhancing transmission diversity and the use of intelligent `roof-top' routing and optical wireless cross connects between buildings will also be discussed.

12 This paper addresses the hardware and operational requirements for broadband metro and local services using line of sight wireless Free Space Optical Communication (FSOC) optical links. The primary considerations for successful optical wireless service provisions include link availability, type of service and integration into existing fiber optic networks. A comprehensive link analysis for broadband access services is presented. This paper addresses FSOC critical atmospheric transmission impairments and describes one possible FSOC/network fiber optic interface and routing scenario. This paper will also detail methods to restor FSOC service links that have failed due to atmospheric impairments. This paper will detail the use of secondary radio (mm wave or ISM band radio) link architectures to provide critical transmission back-up for data, emergency and voice call services. An FSOC back-up link for existing millimeter-wave radio local services is also discussed. A co-operative network of FSOC links is discussed for achieving availability requirements for metro and local distribution services. This paper also describes one possible rooftop routing scenario using optical cross- connect architectures located at each node of the local FSOC access network. Rooftop routing will utilize the technology flexibility and system redundancy described above to provide high `five nines' metro service availability. This paper will also describe a proposed FSOC test installation to study link architectures, performance of such links, and vendor product interface and evaluation.

12 A large scale Lunar teleoperation project has been proposed consisting of a small fleet of ten Lunar roving vehicles, each with a compliment of fifty remotely steerable stereoscopic camera heads. Earth-bound users gain access through the Internet with a hierarchy of participation, ranging from vehicle driver, to active viewer, to passive viewer. Earth uplink to the Moon consist of vehicle piloting and camera head positioning commands, and are of relatively low bandwidth. The Moon-to-Earth downlink, however, must have sufficient bandwidth to handle 500 simultaneous stereoscopic video feeds. An optical communication link is described, first as a free space link between the Moon and Low Earth Orbiting satellites, and second, with atmospheric effects for ground-based reception. Link budget and aperture/power tradeoffs for various baseline designs are considered. Technical challenges of operating in a Lunar environment are described.

12 In this work we present a novel optical lens that can be designed to provide any specified angular sensitivity to a receiver, illuminating the sensitive area almost isotropically. This lens, which has been designed in the framework of nonimaging optics, consists in a single dielectric piece that encapsulates the receiver (as conventional epoxy packages of photodiodes), whose interface with air is an aspheric refractive surface. Several trial products have been manufactured with different angular sensitivities (linear response, cos^-1(theta) and cos^-2(theta) ). The experimental results have shown that the trial devices have the specified angular sensitivity with +/- 5% accuracy.

12 Maintaining high bandwidth indoor optical wireless channels under a wide range of operating conditions usually requires relatively complex transceiver components. Integrating optical, optoelectronic and optical components using techniques that are suitable for mass manufacture is an important step in the development of these systems. This paper describes work to develop low cost integrated tracking transmitter and receiver components for use in a cellular indoor optical wireless network. A seven channel demonstrator operating at 155 Mb/s is under construction, using arrays of Resonant Cavity LEDs, PIN detectors, Silicon CMOS driver circuits and associated optics. Development of components, design methodology and initial results are detailed.

12 In the design of infrared wireless networks, it is often assumed that the noise from the detector and preamplifier is much lower than that from ambient light sources and hence can be ignored in performance analysis calculations. However, in cellular tracked networks, where the fields of view are narrow, the contribution of the noise from the ambient light sources is greatly reduced and the detector and preamplifier noise become a dominant noise source. An optical system and preamplifier model is used to predict the performance of a single channel indoor wireless link operating in this regime. Simulations predict a single 10 mW source can provide 1 Gbit/s wireless coverage over a cell 0.4 m in diameter at a distance of 2 m from the source. Further, overall link performance is found to be relatively insensitive to photodetector capacitance.

12 A 155 Mb/s CMOS LED driver for low-cost optical wireless links is presented. The driver is realized in a 0.7 micrometers commodity mixed-signal CMOS process from Alcatel Microelectronics. The driver employs switching transistors which drive a current mirror to generate modulation current. The circuit also contains a controllable quiescent current source. The transmitter driver incorporates two novel features: adjustable current peaking and adjustable charge extraction. These functions are implemented with the use of original timing generators. Simulations indicate that the design achieves output rise times and fall times of less than 2 ns. Other design parameters were selected to suit the requirements of the InP resonant cavity LED that was developed for this application.

12 This paper presents the design and implementation of a CMOS 310 Mb/s receiver for use in a multi-channel 155 Mb/s Manchester-coded optical wireless link. The receiver consists of a pre-amplifier followed by a post amplifier circuit. The pre-amplifier is a three stage transimpedance amplifier with an NMOS load at the output of each stage to control gain and stability. To allow the sensitivity of the performance to key parameters to be visualized a nomograph technique was developed. The contours of the nomograph show how DC bias, dominant pole frequency and the gain of each stage vary with transistor dimensions. This allows the designer to select transistor sizes for a given bit rate and for stable operation. The design has been optimized to achieve -30 dBm sensitivity at a BER of 10^-9.

12 In this paper, we present a study of dual header-pulse interval modulation (DH-PIM) scheme for optical wireless communications. System theory and code properties of DH-PIM are discussed and expressions for the power spectral density, slow and packet error rates and optical power requirements are presented. The problem of baseline wander is also studied. The performance of DH-PIM is compared with other modulation schemes such as on-off keying (OOK), pulse position modulation (PPM), differential pulse position modulation and digital pulse interval modulation. We show that, DH-PIM offers higher bit rate and has a built-in frame synchronization capability. For a simple threshold detector receiver, it offers improved error performance compared with OOK, but marginally inferior performance compared with PPM. The optimum system performance in terms of optical power and bandwidth requirements is achieved at bit resolution of 5.

12 A hybrid pulse interval modulation--code-division multiple- access (PIM-CDMA) is proposed for optical wireless communication systems. It offers higher transmission rate compared with the hybrid pulse position modulation (PPM)-- CDMA due to its non-fixed frame structure. Strict optical orthogonal code is used as a signature sequence located at the start each frame. Expressions for bit error rate are given for both PPM-CDMA and PIM-CDMA schemes, assuming that the dominant noise and interference are due to the self- interference and optical multiple access interference. The numerical results are compared with both PPM-CDMA and OOK- CDMA, and it shows that the proposed scheme is a viable scheme for optical wireless communications.

12 Currently, higher and higher transmission speeds are being pursuit for wireless LANs. The present investigation deals with one of the most prospective candidates for high-speed in-house wireless communications, namely, Multi-Spot Diffusing Configuration (MSDC). Since it uses optical medium for data transmission, it possesses inherent potential for achieving very high capacity level. Channel characteristics in MSDC are simulated and the causes for channel distortion are analyzed. Then, conditions for creation of a virtually ideal channel are derived. It is shown that the 3 dB-channel bandwidth can be extended up to frequencies beyond 2 GHz. The large bandwidth comes at the cost of poor power efficiency. In order to compensate for this, a novel receiver optical front-end design is proposed and its performance is analyzed. Taking advantage of unique properties of holographic optical elements, conventional optical front-end consisting of a concentrator and a filter, is replaced by a single holographic curved mirror. Utilization of such a holographic optical element improves the signal-to-shot noise ratio by up to 18.5 dB.

12 Pollution-free transportation in the new millennium will be provided by the recharging of a vehicle's non-polluting on- board energy storage unit (batteries, flywheel, ultracapacitors, etc.) as the vehicle travels unrestricted down the roadway. The backbone of this new transportation system will be wireless power transmission using laser or microwave energy technology to replenish the energy storage unit on these non-polluting vehicles while maintaining an all-important communication link for safety, security, data transmission, etc. The proposed system allows the same freedom of movement currently enjoyed by Americans with the internal combustion engine powered automobile. The all- electric vehicle transportation system has the same power, maneuverability and range capability provided by today's vehicles. The many laser-based tracking and communication challenges proposed by this new system along with vehicle configurations for energy conversion in this non-polluting transportation system will be discussed. The main concern during system operation, safety, will be addressed with specific design considerations.

12 A free-space laser link closes an otherwise all-fiber SONET ring, demonstrating for the first time the feasibility of using wireless optics as a back-up to fiber in an application demanding the highest levels of statistical availability and sub-50-ms protection-restoral times. This experiment demonstrates that protocol-transparent wireless optical links can be readily internetworked with industry- standard fiber-based protection protocols to achieve SONET restoral times in the event of a fiber cut. By using the wireless optics as a back-up to fiber rather than as the primary link, end-users are normally protected from the unavoidable burst errors and outages that can arise on a wireless optical link in the event of anomalously poor atmospheric visibility or unanticipated line-of-sight obstructions. While an all-fiber SONET ring operating over physically diverse paths is generally preferred, hybrid fiber/air rings operating over physically-diverse paths (fiber as one path and air as the other) will easily meet or exceed existing Bellcore availability standards for SONET rings. The hybrid part-fiber, part-air ring advantageously protects customers from fiber cuts (a.k.a. `backhoe fade') and may be preferable to over service via either an unprotected fiber spur or over a `collapsed' fiber ring made up of fiber segments sharing a common conduit. The experiment is performed at an OC-12 (622 Mbps) data rate in a point-to-consecutive point configuration which demonstrates the use of a relay site to work-around a line- of-sight obstruction.