The basic theory of optical signals in optical fiber transmission
It’s a new technology that using lightwavetransmission of Television signals and data in the late 20thcentury. And its emergence makes the world’s IT industry have a rapid development,now Optica transmission technology is developing fast which is beyond people’simagine pace, its speed improved for 100 times compared with it 10 years ago,another 100 times will be gained in the future. With the continuous developmentof fiber optic transmission technology, in optical domain, it can be applied inmultiplexing, demultiplexing, routing, stwiching, the network can takeadvantage of the huge fiber bandwidth resourses, increase network capacity andto achieve “ transparent” transmission of a variety of business..
Optical transmission system is made up of Opticaltransmission, Optical receiver, Optic fiber cables and other components.
The Optical transmission technology is in the shape of the opticalsignal transmission between sender and recipient.The work for optical transmission television signal is toprocess among optical transmitter, optic fiber cables and optical receiver: Theoptical transmitter in the center room to transform the input RF televisionsignals into optical signals, by the electrical / optical converter(Electric-Optical Transducer, E / O) to complete, and transformation into theoptical signal received by the optical fiber transmission orientation device(opticalreceiver) to receive the optical receiver to transform the opticalsignal obtained from the fiber to restore into electrical signals.Therefore, the rationale of the optical transmission signal is the wholeprocess of electricity / light and optical / electrical conversion, also knownas the optical link.Now light transmission is using light intensity modulation.Such as the so-called coherent light of laser light device issued by aphase-coherent, so take the luminous intensity of the overall changemodulation, which uses the output optical power corresponding to the electrical/ optical converter input signal current changes linearly with changesinfeatures.
In the optical / electrical converter (Optical-Electric Transducer, the O/ E), the output is proportional to the input optical signal intensity of thecurrent, the output current waveform of the optical / electrical converter andtherefore the electrical / optical converter input current waveform similar,reaching the purpose of signal transmission. So, how do optic fiber cablesorient the optical signal? The fiber optic cable system is a cylindrical fiber,by fiber cylinder and a cladding composed of quartz glass material. Claddingplays a role in the light tightly enclosed in the fiber to protect the core,and enhance the strength of the fiber itself, while the function of fiber is totransfer optical signal.Although the core and the cladding ofquartz glass materials from production, but in the production of both dopedcomposition, resulting in a refractive index of different sizes (1.463 ~ 1.467core cladding1.45 to 1.46) and, of course, related to the different materialsused. When the laser emission of the light source into the core, the incidentlight to the cladding interface, as long as the angle of incidence greater thanthe critical angle, will produce total internal reflection within the core, theleakage light does not reach all parts of the cladding, so that togetherintothe optical signal within the core will be uninterrupted spread untiloriented optical receiver. The procedure is the theory that optical signal tranfers in optical fiber cable.