02-10-2010, 11:40 AM
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INTRODUCTION
freespace optics
INTRODUCTION
Communication, as it has always been relied and simply depended upon speed. The faster the means! The more popular, the more effective the communication is! Presently in the twenty-first century wireless networking is gaining because of speed and ease of deployment and relatively high network robustness. Modern era of optical communication originated with the invention of LASER in 1958 and fabrication of low-loss optical fiber in 1970.
When we hear of optical communications we all think of optical fibers, what I have for u today is AN OPTICAL COMMUNICATION SYSTEM WITHOUT FIBERS or in other words WIRE FREE OPTICS. Free space optics or FSO –Although it only recently and rather suddenly sprang in to public awareness, free space optics is not a new idea. It has roots that 90 back over 30 years-to the era before fiber optic cable became the preferred transport medium for high speed communication. FSO technology has been revived to offer high band width last mile connectivity for today’s converged network requirements.
Mention optical communication and most people think of fiber optics. But light travels through air for a lot less money. So it is hardly a surprise that clever entrepreneurs and technologists are borrowing many of the devices and techniques developed for fiber-optic systems and applying them to what some call fiber-free optical communication. Although it only recently, and rather suddenly, sprang into public awareness, free-space optics is not a new idea. It has roots that go back over 30 years--to the era before fiber-optic cable became the preferred transport medium for high-speed communication. In those days, the notion that FSO systems could provide high-speed connectivity over short distances seemed futuristic, to say the least. But research done at that time has made possible today's free-space optical systems, which can carry full-duplex (simultaneous bidirectional) data at gigabit-per-second rates over metropolitan distances of a few city blocks to a few kilometers. FSO first appeared in the 60's, for military applications. At the end of 80's, it appeared as a commercial option but technological restrictions prevented it from success. Low reach transmission, low capacity, severe alignment problems as well as vulnerability to weather interferences were the major drawbacks at that time. The optical communication without wire, however, evolved! Today, FSO systems guarantee 2.5 Gb/s taxes with carrier class availability. Metropolitan, access and LAN networks are reaping the benefits. FSO success can be measured by its market numbers: forecasts predict it will reach a USS 2.5 billion market by 2006.
The use of free space optics is particularly interesting when we perceive that the majority of customers does not possess access to fibers as well as fiber installation is expensive and demands long time. Moreover, right-of-way costs, difficulties in obtaining government licenses for new fiber installation etc. are further problems that have turned FSO into the option of choice for short reach applications.
FSO uses lasers, or light pulses, to send packetized data in the terahertz (THz) spectrum range. Air, ot fiber, is the transport medium. This means that urban businesses needing fast data and Internet access have a significantly lower-cost option.
An FSO system for local loop access comprises several laser terminals, each one residing at a network node to create a single, point-to-point link; an optical mesh architecture; or a star topology, which is usually point-to-multipoint. These laser terminals, or nodes, are installed on top of customers' rooftops or inside a window to complete the last-mile connection. Signals are beamed to and from hubs or central nodes throughout a city or urban area. Each node requires a Line-Of-Sight (LOS) view of the hub.
Free space optics (FSO) has been used for more than a decade as a short/medium distance point-to-point (building-to-building) connectivity solution in campus enterprise LAN markets. The license free nature of this technology combined with its high-speed bandwidth capabilities, comparable to optical fiber, allow network administrators to interconnect LAN segments at real networking speeds (e.g. 100 Mbps or 1000 Mbps) without the hastle of digging to install optical fiber. Since digging to install fiber is typically a very expensive and time-consuming process, the value proposition of using FSO can be very appealing. Only recently has the carrier market started to look into FSO technology as an alternative network connectivity solution. However, when considering the carrier market, the requirements in terms of component reliability and overall weather related system availability are much more stringent than system requirements in the enterprise market. This paper addresses some of the issues that are most important in the design of an overall carrier system architecture. Briefly described are the basic physics of transmission at various short and long infrared wavelengths and their overall impact on the system design. This is followed by an overview of basic transmitter and detector technologies. When selecting suitable components, reliability and commercial availability of those components should play an important factor. Eye safety is another factor that has to be taken into consideration in a carrier class system design. Finally, the page link budget will determine the overall system availability under various weather conditions. This aspect is discussed near the close of this document.
When we hear of optical communications we all think of optical fibers, what I have for u today is AN OPTICAL COMMUNICATION SYSTEM WITHOUT FIBERS or in other words WIRE FREE OPTICS. Free space optics or FSO –Although it only recently and rather suddenly sprang in to public awareness, free space optics is not a new idea. It has roots that 90 back over 30 years-to the era before fiber optic cable became the preferred transport medium for high speed communication. FSO technology has been revived to offer high band width last mile connectivity for today’s converged network requirements.
Mention optical communication and most people think of fiber optics. But light travels through air for a lot less money. So it is hardly a surprise that clever entrepreneurs and technologists are borrowing many of the devices and techniques developed for fiber-optic systems and applying them to what some call fiber-free optical communication. Although it only recently, and rather suddenly, sprang into public awareness, free-space optics is not a new idea. It has roots that go back over 30 years--to the era before fiber-optic cable became the preferred transport medium for high-speed communication. In those days, the notion that FSO systems could provide high-speed connectivity over short distances seemed futuristic, to say the least. But research done at that time has made possible today's free-space optical systems, which can carry full-duplex (simultaneous bidirectional) data at gigabit-per-second rates over metropolitan distances of a few city blocks to a few kilometers. FSO first appeared in the 60's, for military applications. At the end of 80's, it appeared as a commercial option but technological restrictions prevented it from success. Low reach transmission, low capacity, severe alignment problems as well as vulnerability to weather interferences were the major drawbacks at that time. The optical communication without wire, however, evolved! Today, FSO systems guarantee 2.5 Gb/s taxes with carrier class availability. Metropolitan, access and LAN networks are reaping the benefits. FSO success can be measured by its market numbers: forecasts predict it will reach a USS 2.5 billion market by 2006.
The use of free space optics is particularly interesting when we perceive that the majority of customers does not possess access to fibers as well as fiber installation is expensive and demands long time. Moreover, right-of-way costs, difficulties in obtaining government licenses for new fiber installation etc. are further problems that have turned FSO into the option of choice for short reach applications.
FSO uses lasers, or light pulses, to send packetized data in the terahertz (THz) spectrum range. Air, ot fiber, is the transport medium. This means that urban businesses needing fast data and Internet access have a significantly lower-cost option.
An FSO system for local loop access comprises several laser terminals, each one residing at a network node to create a single, point-to-point link; an optical mesh architecture; or a star topology, which is usually point-to-multipoint. These laser terminals, or nodes, are installed on top of customers' rooftops or inside a window to complete the last-mile connection. Signals are beamed to and from hubs or central nodes throughout a city or urban area. Each node requires a Line-Of-Sight (LOS) view of the hub.
Free space optics (FSO) has been used for more than a decade as a short/medium distance point-to-point (building-to-building) connectivity solution in campus enterprise LAN markets. The license free nature of this technology combined with its high-speed bandwidth capabilities, comparable to optical fiber, allow network administrators to interconnect LAN segments at real networking speeds (e.g. 100 Mbps or 1000 Mbps) without the hastle of digging to install optical fiber. Since digging to install fiber is typically a very expensive and time-consuming process, the value proposition of using FSO can be very appealing. Only recently has the carrier market started to look into FSO technology as an alternative network connectivity solution. However, when considering the carrier market, the requirements in terms of component reliability and overall weather related system availability are much more stringent than system requirements in the enterprise market. This paper addresses some of the issues that are most important in the design of an overall carrier system architecture. Briefly described are the basic physics of transmission at various short and long infrared wavelengths and their overall impact on the system design. This is followed by an overview of basic transmitter and detector technologies. When selecting suitable components, reliability and commercial availability of those components should play an important factor. Eye safety is another factor that has to be taken into consideration in a carrier class system design. Finally, the page link budget will determine the overall system availability under various weather conditions. This aspect is discussed near the close of this document.
