soliton mode of link
loss in a fiber
distortion of a digital signal
optical telecom systems
A.H. Sultanov, I.L. Vinogradova, A.A. Kashbiev
The high requirement of telecommunication systems for a passband results that the bit speeds on a highway quickly have grown up to 40 GB/s. But effective operation of such high-speed optical fiber transfers lines (FTL), and furthermore the further increase of bit speed, encounters essential distortion from the party chromatic dispersion (CD) in fiber line (FL). The traditional methods of dispersion indemnification, based on serial inclusion of segments FL with dispersion factors of various marks, application locally of included devices detaining certain spectral components, thus leveling phase speeds of their distribution, appear insufficiently effective. It also justifies use of a solitons mode transfer (ST), working with a chirp linear signal. The application ST allows to lower dispersion influence because of use specifity interaction of such signal with a material FL.
The analysis of indemnification CD existing means with attraction a chirping information signal is executed. Is shown, that the devices of electronic dispersion indemnification (EDC - electrical dispersion compensate), used on the central equipment, do not represent interest from the point of construction completely view of optical telecommunication systems. Optical means based on application of compensating optical fibers inserts with opposite is familiar of dispersion factor, allow slightly to lower influence CD, but do not provide all-round use of a signal resources. Besides, effective utilization compensating optical fibers on high bit speed needs large addition of length FTL.
For overcoming the specified lack it is offered to use erbiem doped optical fiber EDFA and together with them - and nonlinear optical fiber in entrance and in subsequent linear coupling. Thus pump for located on a line EDFA to make distance from nearest unit of connection on FTL, transferring pump radiation together with an information signal. It will allow to keep completely optical principle with КСП, i.e. to not use electrical components in a zone FTL. Besides - to strengthen positive influence of nonlinear refraction effect: in addition to influence on the part of coupling nonlinear fibers in addition there will be a phase cross-phase modulation (XPM) between pump radiation and information signal also causing positive chirp.
The mathematical model of a pulse dynamics is developed for three characteristic sites:
- In optical fiber of forming coupling, having high importance of nonlinear refraction;
- In optical fiber of a transfer line having negative meaning CD; and
- In optical fiber of restoring coupling.
In a basis of mathematical model the method of complex amplitude of an optical pulse modeling with use of the nonlinear Shredinger equation is incorporated. For the entry condition was accepted a supergaussov pulse containing initial symmetric chirp of fronts. The integration of the equations was carried out numerically with use of a software package Synplify 8.1.
Is established, that distance between restoring coupling should decrease in process of their distance from the transmitter. The initial level of pump capacity needs to be chosen within the limits of 70 mW. To limit efficiency of a method application increased noise level on FTL can. Nevertheless, the method can be of interest for organization of high-speed transfer (40 GB/s and above on the channel) with impossibility to use the concentrated equalizers CD, which can bring of interference distortion.