No abstract

No abstract

No abstract

A significant challenge for free-space optical (FSO) links is the restrictive alignment requirements, especially when the transceivers are moving. For moderate distances and rapid unpredictable motion, the receiver's field of view and the positioning system's dynamics become factors. We explore the use of adaptive transmitter power and beam divergence to improve the likelihood of maintaining a mobile FSO link by using Gaussian beam propagation theory and link budgets. We calculate the allowable misalignment between the transceivers' optical axes as a function of power, divergence, and transceiver distance. The maximum allowable error is independent of the distance, except when the field of view is a limiting factor. Certain combinations of divergence and power, while suboptimal for one distance, provide a relaxed misalignment limit for many distances. Based on the calculations, we make initial suggestions for system design.

No abstract

No abstract

No abstract

Optical fiber offers many advantages over coaxial cable for the transmission of radio frequency ͑rf͒ signals in antenna-remoting applications, as well as cellular networks and cable television ͑CATV͒ signal distribution networks. Optical fiber shows significantly less loss, can support signals demanding much higher bandwidth, is immune to electromagnetic interference ͑EMI͒, and enables considerable size and weight savings when compared to coaxial cable. Free-space optics ͑FSO͒ communications is a technology that uses modulated optical beams to transmit information line of sight through the atmosphere. FSO can be deployed faster and cheaper when compared with optical fiber. Recently, FSO has been investigated by the telecommunications industry and research centers to transport digital signals for civilian "last mile" applications and military applications. We demonstrate the successful transport of modulated rf analog signals over an FSO link and compare key performance measures against a fiber optic link configured in an identical manner. Results of measurements of optical power, transmission response, reflection response, group delay that defines phase distortion, carrier-to-noise ratio ͑CNR͒, and dynamic range that defines nonlinear distortion are presented. Results from this comparative study indicate that FSO for rf applications is a suitable replacement for fiber optic transmission links over short distances.