Links FAQ
Free-Space Optics
Free Space Optics (FSO) is a telecommunication technology that uses light propagating in free space to transmit data between two points. The technology is useful where the physical connection of the transmit and receive locations is difficult, for example in cities where the laying of fibre optic cables is expensive. Free Space Optics is also used to communicate between space-craft, since outside of the atmosphere there is little to distort the signal. The optical links usually use infrared laser light, although low-data-rate communication over short distances is possible using LEDs. IrDA is a very simple form of free-space optical communications. Distances up to the order of 10 km are possible, but the distance and data rate of connection is highly dependent on atmospheric conditions.
Applications
Typically scenarios for use are:
- LAN-to-LAN connections on campuses at Fast Ethernet or Gigabit Ethernet speeds
- LAN-to-LAN connections in a city. example, Metropolitan area network
- To cross a road or other barriers
- Speedy service delivery of high bandwidth access to fiber networks
- Converged Voice-Data-Connection
- Temporary network installation (for events or other purposes)
- Re-establish high speed connection quickly (Disaster Recovery)
- As an alternative or upgrade addon to existing wireless technologies
- As a safety addon for important fiber connections (redundancy)
- For communications between spacecraft, including elements of a satellite constellation
- For interstellar communication
The lightbeam can be very narrow, which makes FSO hard to intercept, improving security. FSO provides vastly improved EMI behavior using light instead of microwaves.
History
The reflected sun has been used for communications for thousands of years (heliograph). Alexander Graham Bell developed a light based free space communication system (the photophone).
Beginning with laser developments in the 1960s, the first serious trials started to develop "Lightphones". Military organizations especially were interested and forced some developments. During the boom period of optical fiber installation civil FSO technology lay dormant, but in military and space laboratories the development didn't really stop. Some features of FSO technology were important for the military and again became important for civil use.
Technology disadvantages and behaviour
When used in a vacuum, for example for inter-space craft communication, FSO may provide similar performance to that of fibre-optic systems. However, for terrestrial applications, the principle limiting factors are:
- beam dispersion
- atmospheric absorption
- rain (lower attenuation)
- fog (10..~100dB/km attenuation)
- snow (lower attenuation)
- scintillation (lower attenuation)
- Background light
- Shadowing
- Pointing stability in wind
- Pollution / smog
- If the sun goes exactly behind the transmitter, it can swamp the signal
These factors cause an attenuated receiver signal and lead to higher bit error rates (BER). To overcome these issues, vendors found some solutions, like multibeam or multipath architectures, which use more than one sender and more than one receiver. Some state-of-the-art devices also have larger fade margin (extra power, reserved for rain, smog, fog). To keep an eye-safe environment, good FSO systems have a limited laser power density and support laser classes 1 or 1M. Atmospheric and fog attenuation, which are exponential in nature, limit practical range of FSO devices to several kilometres.
Advantages and Challenges
Main Advantages are:
- Quick link setup
- License free operation
- High transmission security
- High bit rates
- Low bit error rate
- No Fresnel zone necessary
- Low snow and rain impact
- Full duplex transmission
- Protocol transparency
- No interference
- Great EMI behavior
- In some devices, the beam can be visible, faciliating aiming and detection of failures.
Compared to a microwave link, the advantages are that it can support higher bit rates (under good conditions), that its dispersion is lower, and that it is license free in all jurisdictions [citation needed].
Benefits of DAB
Current AM and FM terrestrial broadcast technology is well established, compatible, and cheap to manufacture. Benefits for DAB over and above analogue systems are as follows:
See also
- Applications of atomic line filters in laser tracking and communication
- Free-space loss
- IrDA
- Laser safety
- Mie scattering
- Millimeter Wave
- Optical telegraph for the early history of optical communication, including semaphore
- Optical window
- Radio window
- Rayleigh scattering
- RONJA Free space optics device with free sources
- Smoke signals
Free Space Optic Information Sites
Harvard Broadband Communications Laboratory: Free-Space Optical Communications
Technology Explanation Sites
Further Information
- NyeTec Lyd - Professional Broadcast and Telecommunications Products & Solutions
- Case studies
- Broadcast applications
- FSO Primer
- FSO Technology
- FSO Guide
- FSO Comparisons
- FSO Laser Guide
- FSO Glossary
- FSO FAQ
- FSO Tech FAQ
- FSO Metro App
- FSO Industry Links
- Wi-MAN website
- Wireless Excellence website
- New CableFree website
- LaserHop website
Information on Cablefree solutions
CableFree Solutions is a leading designer and manufacturer of Free Space Optical (FSO) and Broadband Radio links for point-to-point and point-to-multipoint wireless connections. CableFree offers a complete range of line-of-sight wireless laser and radio systems for data networking, service providers, broadcast and CCTV. Free Space Optics, or FSO, offers high-performance and cost-effective alternatives to existing microwave, leased-line and fibre-optic options. CableFree's FSO systems use state-of-the-art infrared laser technology to link sites with bandwidth upgradeable from E1/T1 to Gigabit Ethernet and beyond. CableFree Broadband Radios offer complimentary technology high speed links up to 200Mbps capacity in licensed or unlicensed bands with distances up to 40km and beyond
The CableFree advantage - CableFree's FSO offers customers major benefits:
- Entry-level and Carrier Class products
- Automatic Transmit Power Control (ATPC)
- Plug-upgradeable network interfaces
- Integrated Voice & Data and 4xE1/T1 multiplexers
- Optional Indoor Unit (IDU)
- Comprehensive Software Management Suite
- Single and Multi-laser systems
- Stable proven wide-beam optics
- All products Class 1M eye-safe
- Cost-competitive against any quality product
CableFree's customers use FSO to connect wherever line-of-sight exists and traditional access solutions are not appropriate. Providing high-speed and rapid deployment wireless links, FSO overcomes limitations of traditional radio wireless networks. Compared to broadband ADSL VDSL and cable modem solutions, CableFree offers a quantum leap in capacity offering Gigabits of capacity compared to a few megabits.
CableFree's FSO (Free Space Optics) is used in last-mile carrier applications, and backhaul in PCS, GSM, EDGE, GPRS and 3G wireless networks. Rapid deployment, high capacity, license-free operation and low cost of ownership are all tangible benefits of FSO for Service Providers.
Metropolitan Area Networks (MAN) benefit from CableFree's Free Space Optics where customers can extend existing infrastructure or entirely bypass local-loop connections. Mesh, Ring and Star network topologies are used to provide high availability solutions
Free space optical (FSO) systems offers a flexible networking solution that delivers on the promise of broadband. Only free space optics or Free Space Optics (FSO) provides the essential combination of qualities required to bring the traffic to the optical fibre backbone with virtually unlimited bandwidth, low cost, ease and speed of deployment. Freedom from licensing and regulation translates into ease, speed and low cost of deployment. Since Free Space Optics (FSO) optical wireless transceivers can transmit and receive through windows, it is possible to mount Free Space Optics (FSO) systems inside buildings, reducing the need to compete for roof space, simplifying wiring and cabling, and permitting the equipment to operate in a very favourable environment. The only essential for Free Space Optics (FSO) is line of sight between the two ends of the link.
Free Space Optics (FSO) summary:
CableFree's FSO is ideal to use anywhere there is Clear Line-of-sight, where high bandwidth wireless connections are required, for Local Area Network and Wide Area Network applications, for telecom, enterprise, broadcast, military and security wireless applications. FSO does not suffer interference from other transmitters, does not require licenses and offers inherently-secure wireless connectivity.
To find out more, please visit: www.cablefree.com
Copyright 1998 CableFree Solutions Limited. All Rights Reserved
For more information please get in touch
terry@nyetec.com +44 2380 269113
Definition of Terms from Wikipedia, the free encyclopaedia.
The above articles are licensed under the GNU Free Documentation License.