FIELD: physics.
SUBSTANCE: on a section of a transmission line on the near end of a fibre-optic transmission line, a sequence of optical probing pulses is transmitted into the optical fibre, where duration of said pulses is greater than propagation time on the length of beats. The inverse Rayleigh process signal reaching the near end from the optical fibre is transmitted to the input of an optical radiation polarisation analyser, on whose output optical radiation power of the same polarisation is received. The backscattering characteristic is measured. The alternating component of this characteristic is selected and then broken into elementary sections and length of beats on each elementary section is defined as half the period of the alternating component of the characteristic. Duration of the probing pulse T0 is periodically varied linearly with given interval from 
to . The average value of duration of the probing pulses 
is selected based on the conditions νg->>LB and νg·<<L, and boundaries for measuring duration of the probing pulse from the conditions 2·νg-ΔT<<
>>LB and 2·νg
·ΔT≥(3…5)·LB, where vg is group velocity, LB is length of beats, L is length of the line, is average duration of the probing pulse. The backscattering characteristic for each value of duration of the probing pulse is measured and stored several times. The average value of the backscattering characteristic is determined on the interval for measuring duration of the probing pulse for each reference point of the length of the line 
(х). The mean-square deviation of values of the alternating component of the backscattering characteristic is calculated on the interval for measuring duration of the probing pulse for each reference point of the length of the line,
. The characteristic σp(x) is broken into elementary sections and the average length of the beats 
is determined on each of the elementary sections as half its period of oscillation, after which distribution of the lengths of beats is determined on the elementary section using the formula:
, where 
is average value (х) on the elementary section.
EFFECT: possibility of estimating such characteristics as linear channel as correlation length, polarisation modal dispersion and reduced error in measuring length of beats.
1 dwg
