EQUIPMENT AND METHODS FOR EVALUATING THE CHARACTERISTICS OF SPATIAL MULTIPLEX OPTICAL TRANSMISSION LINES
A backscattered light intensity measurement unit is presented that acquires a combination of backscattered light intensities of individual transmittable spatial channels of an optical fiber obtained when test light, for the respective transmittable spatial channels of the optical fiber, is incident on the optical fiber, and a transfer matrix calculation unit that calculates a transfer matrix for each section of the optical fiber in order from a side closer to an incident end of the test light, in which characteristics in a section of the optical fiber are evaluated by using the transfer matrix.
1 . An apparatus comprising:
a backscattered light intensity measurement unit that acquires a combination of backscattered light intensities of individual transmittable spatial channels of an optical fiber obtained when test light, for the individual transmittable spatial channels of the optical fiber, is incident on the optical fiber; and
a transfer matrix calculation unit that calculates a transfer matrix for each section of the optical fiber in order from a side closer to an incident end of the test light, wherein
characteristics in a section of the optical fiber are evaluated by using the transfer matrix.
2 . The apparatus according to claim 1 , wherein
the backscattered light intensity measurement unit measures, as a function P out (z) of a distance z, a matrix of a backscattered light intensity obtained using light incident on a j-th spatial channel, for transmission through the optical fiber by using spatial multiplexing, and detected from an i-th spatial channel, as an (i,j) component, and
the transfer matrix calculation unit
obtains T(z k-1 , z k ) (where k is a natural number) satisfying Equation (C1) for each case of k=1 to b by using the P out (z), and
calculates a transfer matrix T(z a , z b ) in a section z a ≤z<z b (where a and b are non-negative integers) by using Equation (C2).
[Math. C 1]
P out ( z k )= T ( z 0 ,z 1 ) . . . T ( z k-2 ,z k-1 ) T ( z k-1 ,z k ) P out ( z 0 ) T ( z k-1 ,z k ) T ( z k-2 ,z k-1 ) . . . T ( z 0 ,z 1 ) (C1)
[Math. C 2]
T ( z a ,z b )= T ( z b-1 ,z b ) T ( z b-2 ,z b-1 ) . . . T ( z a+1 ,z a+2 ) T ( z a ,z a+1 ) (C2)
3 . The apparatus according to claim 2 , wherein
the transfer matrix calculation unit
calculates a square error of the right side with respect to the left side of Equation (C1) as a function c(η 1,1 , . . . , η i,j , . . . , η M,M ) having matrix components η 1,1 , . . . , η i,j , . . . , and η M,M (where η i,j is the (i,j) component of T(z k-1 , z k )) of T(z k-1 , z k ) as variables, and
gives initial values to η 1,1 , . . . , η i,j , . . . , and η M,M changes values of η 1,1 , . . . , η i,j , . . . , and η M,M in a reverse direction of a gradient of c(η 1,1 , . . . , η i,j , . . . , η M,M ), and calculates the T(z a , z b ) by using η 1,1 , . . . , η i,j , . . . , and η M,M when a value of c(η 1,1 , . . . , η i,j , . . . , η M,M converges.
4 . The apparatus according to claim 2 , wherein
the transfer matrix calculation unit
calculates a difference between the left side and the right side of Equation (C1) as a function f(η 1,1 , . . . , η i,j , . . . , η M,M ) having matrix components η 1,1 , . . . , η i,j , . . . , and η M,M (where η i,j is the (i,j) component of T(z k-1 , z k )) of T(z k-1 , z k ) as variables,
gives initial values to η 1,1 , . . . , η i,j , . . . , and η M,M , changes values of η 1,1 , . . . , η i,j , . . . , and η M,M to approach an η 1,1 coordinate . . . , an η i,j coordinate, . . . , and an η M,M coordinate of intersections of a tangent of f(η 1,1 , . . . , η i,j , . . . , η M,M ) and an η 1,1 axis, β, an η i,j axis . . . , and an η M,M axis, respectively, and
calculates the T(z a , z b ) by using η 1,1 , . . . , η i,j , . . . , and η M,M when a value of f(η 1,1 , . . . , η i,j , . . . , η M,M ) converges.
5 . The apparatus according to claim 2 , further comprising:
a crosstalk calculation unit that calculates crosstalk in the section z a ≤z<z b by using a non-diagonal component of the T(z a , z b ).
6 . The apparatus according to claim 2 , further comprising:
an optical loss calculation unit that calculates an optical loss in the section z a ≤z<z b by using a diagonal component of the T(z a , z b ).
7 . A method comprising the following sequence of steps:
a backscattered light intensity distribution measurement step of acquiring a combination of backscattered light intensities of individual transmittable spatial channels of an optical fiber obtained when test light, for the individual transmittable spatial channels of the optical fiber, is incident on the optical fiber;
a transfer matrix calculation step of calculating a transfer matrix for each section of the optical fiber in order from a side closer to an incident end of the test light; and
an evaluation step of evaluating characteristics in a section of the optical fiber by using the transfer matrix.