A study of beam wander and scintillation loss factors has been carried out in several locations at distances from 200 m to 1300 m. Three different types of transmitters (LED, SH laser and VCSEL) were investigated and compared for their susceptibility to atmospheric turbulence under similar conditions.

The San Diego LaserNet is a research platform for studying the effects of weather and scintillation on a computer network that utilizes free-space laser communication (lasercom). The geometry of the present and future configurations of the LaserNet is described. The research goals for the LaserNet are discussed. Atmospheric attenuation from weather like fog and rain, and scintillation can introduce bit and burst errors at the physical layer for networks using lasercom. One of the primary research goals of the LaserNet is to better understand and characterize these burst errors. The effects of these errors at the physical layer on the performance of the higher layers of the Open Systems Interconnect protocol stack are discussed. Data is presented that show how total network throughput at the application layer is affected by increasing the bit error rate (BER) of a lasercom physical layer. Models of lasercom availability in different BER scenarios are shown. Future work will involve correlating measurements of real-time visibility (as well as other meteorological data) to lasercom availability to produce more accurate lasercom availability curves.

This paper presents the design of a prototype terrestrial lasercom terminal for operation in the 1.55 micrometers wavelength range. The design is based on a multibeam-multipath technology which allows multiple laser beams to be transmitted from various spatially separated optics, and optical signals to be received by using multiple large aperture lenses. The goal of this project is to experimentally study performance parameters of shorter distance terrestrial laser links in the 1.5 micrometers wavelength range which use an optical array approach to increase system performance and reliability.

A VideoBeam^TM portable laser communicator has been developed which provides full duplex communication links consisting of high quality analog video and stereo audio. The 3.2-pound unit resembles a binocular-type form factor and has an operational range of over two miles (clear air) with excellent jam-resistance and low probability of interception characteristics. The VideoBeam^TM unit is ideally suited for numerous military scenarios, surveillance/espionage, industrial precious mineral exploration, and campus video teleconferencing applications.

We describe a terrestrial free-space optical data link operating at 2.5 Gb/s using currently available 1.5 micrometers telecommunications electro-optic transmission components. The 2.4 km free-space optical data-link is characterized by bit-error-rate system performance. The optical link utilizes a 1.5 micrometers DFB laser device which is directly modulated and operating within the erbium amplification band.

In this paper we address the problem of measuring the performance of optical wireless communication links limited by atmospheric turbulence. Because atmospheric turbulence occurs on a short time scale but depends on meteorological parameters, complete link characterization would require measurement over several days with a 10 ms or less time resolution. We discuss two techniques to characterize the performance of optical wireless communication links. The first technique consists in the measurement versus time of OWC system bit error rate. The second technique consists in the statistical characterization of the optical channel. Finally, we analyze some of the experimental data and compare them to measured C²_n.

Wireless infrared communication systems are attracting interest for high-data-rate, wireless, in-building local area networks. We investigate the use of mobility tracking and prediction for mobile users in such systems. One promising approach to achieving high data rates in such systems is to use narrowband optical systems to improve the signal-to-noise ratio. However, the angle dependency of such systems requires either tunable systems or adaptive arrays. The latency in such adaptation, if unmitigated, may cause the bit-error rate for mobile users to exceed acceptable levels, which in turn increases delay and reduces throughput. Mobility tracking and prediction can help by anticipating the required change in the adaptation parameter such as peak transmission wavelength or the angle of receiver axis. In this paper, we developed a set of terminal mobility model and movement observation model that closely represent indoor movement behavior and channel fading characteristics. Based on the established model, an extended Kalman filtering algorithm is developed which achieves efficient location tracking, shadow fading estimation and prediction of the peak-transmission wavelength of infrared radiation. Simulation results demonstrate the feasibility and efficiency of this algorithm in line of sight configurations and prove that with efficient trajectory tracking, location and fade transparent communication channels can be built to support high data rate transmission and improve overall QoS for wireless infrared LANs.

This paper presents a study of digital pulse interval modulation (DPIM) as a candidate modulation scheme for optical wireless communications. DPIM code characteristics are discussed and the theoretical error probability performance of DPIM is analyzed in terms of the packet error rate. Performance comparisons are made with the more established techniques of on-off keying and pulse position modulation (PPM). We show that, for a simple threshold detector based receiver, DPIM can out perform PPM in terms of bandwidth efficiency and power efficiency, by taking advantage of its inherent variable symbol duration. Practical results are given for an experimental system in the form of eye diagrams. The use of a coding scheme with a non-uniform symbol duration does have implications for system design, which are discussed in the paper.

In this communication we consider the use of coding techniques to improve the performance of infrared wireless communication systems. We perform a review of the most common modulation methods used in such systems, and present the expressions for the probability of symbol error and channel capacity. We review the most common coding techniques and address the use of trellis code modulation, to improve the performance of uncoded PPM. To augment the alphabet size of PPM, we propose an hybrid modulation scheme called APPM, and derive the best codes for 2 X 2-APPM. The results show that non-negligible gains can be obtained with convolutional codes of moderate complexity.

The performance of optical wireless transmission systems is mainly impaired by the shot noise induced by ambient light, interference produced by artificial light sources, transmitted optical power limitations due to high path losses and channel bandwidth limitations due to inter-symbol interference produced by the multipath dispersion of the optical signal. The contribution of these factors to the performance evaluation of infrared links have only been addressed independently and the combined effect of these channel impairments was not presented yet. The work presented in this paper extends the previous analysis by taking into account the combined effects of both optical noise (shot noise and interference) and channel impulse response. A simulation package was used to determine the indoor optical channel impulse response due to the propagation losses and multipath dispersion under various room geometries and emitter/receiver parameters. The contribution of the interference produced by incandescent and fluorescent lamps was done through the utilization of analytical models. The penalty introduced by these channel characteristics was quantified considering the modulation schemes usually considered for optical wireless communication systems: 2-, 4- and 16-PPM (pulse position modulation) at bit rates from 1 to 10 Mbps.

A process to estimate LMDS (Local Multipoint Distribution Service) equipment costs is provided for deployment planning purposes. Crucial LMDS network design parameters are reviewed. The composite effects of the LMDS cell propagation are investigated by taking into account the rainfall level, size of the area, business density, antenna height, and foliage. A composite multiplier is derived for a few example cities. The derivation needs to be verified with field measurements.

Millimeter wave systems in the 30 - 47, 95 - 100, and 140 GHz regions are found attractive for satellite communications on the basis of expected cost per information bit. Loss comparisons with optical systems may be found with Chu and Hogg's analysis. Chan's economic comparison of millimeter wave and optical systems implies that 10 micron systems may be competitive for cloud thickness less than 300 meters.

A two-point bending technique has been used not only to measure the breaking stress of optical fiber but also to predict its static and dynamic fatigue. The present theory of this test is based on elastica theory of rod. However, within the limits of elastica theory the tensile and shear stresses cannot be determined. In this paper we study dynamic and static problems for optical fiber in the two- point bending test on the base of geometrically exact theory in which rod can suffer flexure, extension, and shear. We obtain the governing partial differential equations taking into account the fact that the lateral motion of the fiber is restrained by the presence of flat parallel plates. We develop the computational methods for solving the initial and equilibrium free-boundary nonlinear planar problems. We derive the formulas for predicting of the tensile strength from strength in the bending and calculate one example.

Great efforts have been made on the research and development of resonant cavity enhanced photodetectors since the structure was proposed by Katsumi Kishino and M. Selim Unlu in 1991. Based on all these works, a new analysis method, considering the effect of the refractive index differences between different layers of the structure on the characteristics of the device with matrix simulation, is presented in this paper. With such an analytical way, we can analyze the effects of the dielectric stacks, which forming the mirrors, on the response of the photodetector directly. And the standing wave effects of the detector's responses can be accurately calculated. In comparison with the former method established by Katsumi Kishino and M. Selim Unlu, our analysis leads to little difference in calculated maximum quantum efficiency but an obvious one in calculated optical response spectrum, for small inter-layer refractive index differences (< +/- 0.6). Whereas for large inter-layer refractive index differences, remarkable differences in both aspects of the above mentioned characteristics are resulted. Our analysis shows better agreement with experiments.