What is E/FSO Laser Communication System ?
FSO is free space optics provides point-point broadband communications using Laser Light as the transmission medium. FSO is a state of art data communication method which is based on a very old communication solution. Ancient Chinese developed a protection system against the Mongol tribes, building watchtowers within the line of site to other towers. And as soon as the towers saw some hostile sign on the horizon they use they shield to reflect the sun to the remote towers. In this way the area could be prepared against the attack in a very short period of time. In the ancient times for this communication use the mirror as a transmitter and the sunlight was the light source, and the receiver was the remote guard’s eye. This basic signalling method was developed later into up communication device which used „line coding”. This allowed the guards to tell the number of enemy, or the direction they are coming from. Current FSO systems use a laser-diode as a light source, and a receptor diode (photo diode) to receive the signals coming from the laser diode from the transmitter side. But the basic elements are still the same: line of site between the communication nodes, and individual line coding. It is all about performance. FSO offers FSO systems with the highest power budget available on the market.
How is E/FSO System Works ?
The principle used in free space laser transmission is very similar to the one is used for fibre optic transmission. The difference is while fibre optic devices use electronics and optics optimized for transmission to the air. Also one can observe to the similarity in the transmission properties. No galvanic contact, no ground-loops, no need for surge protection, noise immunity, long distances, high bandwidth. What makes it unique – and difficult to design – is that it does not require any transmission medium like fibre or copper, but it has to cope with the dynamically changing parameters. For instance while the attenuation of an optical fibre is constant, the attenuation of the atmosphere between the laser units can change dramatically (depending on the weather conditions). The laser-heads are usually placed on top of building, where the clean line of site is guaranteed and the beam cannot be interrupted. In the head the incoming signal is amplified, encoded, and then drives the laser- diode. The transmitter optics assures the proper beam shape and controls the beam divergence. The receive optics perceives and directs the transmitter signal to the photo diode. The diode converts it back into electrical, than it is decoded, amplified and converted. There are several things that can influence the quality of transmission. We can classify those factors into three main groups. System conditions – transmitting power, transmitter’s wavelength, beam divergence, receiver optics diameter, receiver sensitivity, parameters of optical system and casing. These parameters determine the system’s characteristic at a certain distance and are controlled by system design and factory set up. Weather conditions – molecular absorption, particle scattering and turbulence. These elements have great effect on the operational conditions of the system. We do not have very much influence on them; proper product selection can eliminate the undesirable effects. Environmental conditions – building movements, direct sunlight, refractive surfaces. These are also key factors related to the installation sites and can be controlled by appropriate site survey and system installation.
Most typically the FSO Next product are is used to interconnect LAN-s. The system is protocol transparent, thus other applications also can be taken into consideration. Appropriate interface converters are needed and system bandwidth must be matched for that. Here we collected some circumstances, where the deployment of the FSO is the most adequate as a cost effective solution.