Method and system for inspecting a fibered optical path
A method and system for inspecting polarization in a fibered optical path. The method being executed by a computer-implemented system comprising a controller and at least one detector communicatively coupled to the controller, the computer-implemented system being operatively connected to the fibered optical path, including: causing a laser to emit at least one optical pulse into the fibered optical path; detecting a plurality of reflected optical signals from the fibered optical path; determining a plurality of experimental correlation values based on the plurality of reflected optical signals and a reference signal function; and in response to a given experimental correlation value of the plurality of experimental correlation values being less than a threshold, identifying a mechanical disturbance caused by birefringence in the fibered optical path, the mechanical disturbance being located at a location of the plurality of locations corresponding to the given experimental correlation value.
1 . A method for inspecting polarization in a fibered optical path, the method being executed by a computer-implemented system comprising a controller and at least one detector communicatively coupled to the controller, the computer-implemented system being operatively connected to the fibered optical path, the method comprising:
causing a laser to emit at least one optical pulse into the fibered optical path;
detecting a plurality of reflected optical signals from the fibered optical path, the plurality of reflected optical signals having been reflected from a corresponding plurality of locations along the fibered optical path;
determining a plurality of experimental correlation values based on the plurality of reflected optical signals and a reference signal function, the plurality of reflected optical signals and the reference signal function being of a same polarization;
determining a reference correlation function for the fibered optical path being in an unperturbed state;
determining a difference between the plurality of experimental correlation values and the reference correlation function; and
in response to a given experimental correlation value of the plurality of experimental correlation values being less than a threshold, identifying a mechanical disturbance caused by birefringence in the fibered optical path, the mechanical disturbance being located at a location of the plurality of locations corresponding to the given experimental correlation value,
the given experimental correlation value being below the threshold when the difference between the plurality of experimental correlation values and the reference correlation function is greater than a predetermined deviation value,
wherein determining the reference correlation function comprises calculating a theoretical correlation function C, the correlation at a given location z k being determined by:
C
(
z
k
)
≈
∑
i
=
0
N
exp
(
-
4
α
(
z
k
+
i
Δ
z
)
)
∑
i
=
0
N
exp
(
-
4
α
(
z
k
+
i
Δ
z
)
)
∑
i
=
0
N
exp
(
-
4
α
(
z
k
+
i
Δ
z
)
)
+
N
P
n
,
where:
α is a fiber loss coefficient of the fibered optical path,
P n is a normalized noise power level, and
N is a number of steps over a correlation window length.
2 . The method of claim 1 , further comprising, prior to determining the plurality of experimental correlation values, determining the reference signal function.
3 . The method of claim 2 , wherein determining the reference signal function comprises determining an average signal function with the fibered optical path being in an unperturbed state.
4 . The method of claim 3 , wherein determining the average signal value comprises:
causing the laser to emit a plurality of control optical pulses into the fibered optical path;
for each pulse of the plurality of control optical pulses, detecting a plurality of control reflected optical signals from the fibered optical path; and
calculating the average signal value function averaging the plurality of control reflected optical signals over the plurality of control optical pulses.
5 . A method for inspecting polarization in a fibered optical path, the method being executed by a computer-implemented system comprising a controller and at least one detector communicatively coupled to the controller, the computer-implemented system being operatively connected to the fibered optical path, the method comprising:
causing a laser to emit at least one optical pulse into the fibered optical path;
detecting a plurality of reflected optical signals from the fibered optical path, the plurality of reflected optical signals having been reflected from a corresponding plurality of locations along the fibered optical path;
determining a plurality of experimental correlation values based on the plurality of reflected optical signals and a reference signal function, the plurality of reflected optical signals and the reference signal function being of a same polarization;
determining a reference correlation function for the fibered optical path being in an unperturbed state;
determining a difference between the plurality of experimental correlation values and the reference correlation function; and
in response to a given experimental correlation value of the plurality of experimental correlation values being less than a threshold, identifying a mechanical disturbance caused by birefringence in the fibered optical path, the mechanical disturbance being located at a location of the plurality of locations corresponding to the given experimental correlation value, the given experimental correlation value being below the threshold when the difference between the plurality of experimental correlation values and the reference correlation function is greater than a predetermined deviation value,
wherein determining the plurality of experimental correlation values comprising calculating an experimental correlation value C i , the correlation at a given location z k being determined by:
C
i
(
z
k
)
≈
〈
S
(
z
k
:
z
k
+
L
)
R
i
(
z
k
:
z
k
+
L
)
〉
〈
S
(
z
k
:
z
k
+
L
)
2
〉
〈
R
i
(
z
k
:
z
k
+
L
)
2
〉
,
where:
L is a correlation window length,
R i (z k :z k +L) is the plurality of reflected optical signals over the correlation window length,
S(z k :z k +L) is the reference signal function over the correlation window length, and
f is an expectation operation over a function f.
6 . The method of claim 1 , wherein the given experimental correlation value being less than the threshold is caused by a change in state of polarization induced by the mechanical disturbance.
7 . A system for inspecting in a fibered optical path, the system comprising:
a controller;
a laser communicatively coupled to the controller, the laser being configured for operatively coupling to the fibered optical path; and
at least one detector communicatively coupled to the controller, the at least one detector being configured to receive signals from the fibered optical path;
the controller being configured to:
cause the laser to emit at least one optical pulse into the fibered optical path;
detect a plurality of reflected optical signals from the fibered optical path, the plurality of reflected optical signals having been reflected from a corresponding plurality of locations along the fibered optical path;
determine a plurality of experimental correlation values based on the plurality of reflected optical signals and a reference signal function;
determine a reference correlation function for the fibered optical path being in an unperturbed state;
determining a difference between the plurality of experimental correlation values and the reference correlation function; and
in response to a given experimental correlation value of the plurality of experimental correlation values being less than a threshold, identify a mechanical disturbance caused by birefringence in the fibered optical path, the mechanical disturbance being located at a location of the plurality of locations corresponding to the given experimental correlation value,
the given experimental correlation value being below the threshold when the difference between the plurality of experimental correlation values and the reference correlation function is greater than a predetermined deviation value,
the controller being further configured to determine the reference correlation function by calculating a theoretical correlation function C, the correlation at a given location z k being determined by:
C
(
z
k
)
≈
∑
i
=
0
N
exp
(
-
4
α
(
z
k
+
i
Δ
z
)
)
∑
i
=
0
N
exp
(
-
4
α
(
z
k
+
i
Δ
z
)
)
∑
i
=
0
N
exp
(
-
4
α
(
z
k
+
i
Δ
z
)
)
+
N
P
n
,
where:
α is a fiber loss coefficient of the fibered optical path,
P n is a normalized noise power level, and
N is a number of steps over a correlation window length.
8 . The method of claim 5 , further comprising, prior to determining the plurality of experimental correlation values, determining the reference signal function.
9 . The method of claim 8 , wherein determining the reference signal function comprises determining an average signal function with the fibered optical path being in an unperturbed state.
10 . The method of claim 9 , wherein determining the average signal value comprises:
causing the laser to emit a plurality of control optical pulses into the fibered optical path;
for each pulse of the plurality of control optical pulses, detecting a plurality of control reflected optical signals from the fibered optical path; and
calculating the average signal value function averaging the plurality of control reflected optical signals over the plurality of control optical pulses.
11 . The method of claim 5 , wherein the given experimental correlation value being less than the threshold is caused by a change in state of polarization induced by the mechanical disturbance.