Optical fiber evaluation method and system
First Claim
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1. A method for evaluating properties of an optical fiber, comprising the steps of:
- making incident a first signal light in the form of modulated light from a first light source upon an optical fiber to be measured;
propagating a second signal light from a second light source in said optical fiber to be measured in the direction opposite to that of the first signal light;
controlling the frequency of at least one of said first and second light sources;
setting the frequency difference Δ
f between said first signal light and said second signal light at a predetermined value;
producing an optical nonlinear interaction between said first signal light and said second signal light;
detecting said second signal light after it undergoes said optical nonlinear interaction;
determining the time dependent signal power W of the detected second signal light; and
evaluating the properties of said optical fiber to be measured on the basis of said time dependent signal power W,wherein said optical nonlinear interaction is Brillouin light amplification, andwherein the loss α
(dB/km) of a given section <
a, b>
of said optical fiber is evaluated from the equation
space="preserve" listing-type="equation">α
=1000×
10 log.sub.10 (W.sub.a /W.sub.b)/(vt.sub.ab /2) (dB/km), where v represents the velocity of light in said optical fiber (m/s), Wa and Wb represent the detected time-dependent signal power of said second signal light at the respective ends a and b of said section of said optical fiber to be measured, and tab represents the time required for the first or second signal light to go back and forth between said section <
a, b>
.
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Abstract
Use is made of a non linear interaction between a first modulated signal light from a first light source and a second signal light from a second light source which propagate in an optical fiber to be examined in opposite directions, i.e., so-called Brillouin light amplification, to analyze the signal waveform of the second signal light, which is influenced by the action of such light amplification.
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Citations
15 Claims
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1. A method for evaluating properties of an optical fiber, comprising the steps of:
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making incident a first signal light in the form of modulated light from a first light source upon an optical fiber to be measured; propagating a second signal light from a second light source in said optical fiber to be measured in the direction opposite to that of the first signal light; controlling the frequency of at least one of said first and second light sources; setting the frequency difference Δ
f between said first signal light and said second signal light at a predetermined value;producing an optical nonlinear interaction between said first signal light and said second signal light; detecting said second signal light after it undergoes said optical nonlinear interaction; determining the time dependent signal power W of the detected second signal light; and evaluating the properties of said optical fiber to be measured on the basis of said time dependent signal power W, wherein said optical nonlinear interaction is Brillouin light amplification, and wherein the loss α
(dB/km) of a given section <
a, b>
of said optical fiber is evaluated from the equation
space="preserve" listing-type="equation">α
=1000×
10 log.sub.10 (W.sub.a /W.sub.b)/(vt.sub.ab /2) (dB/km),where v represents the velocity of light in said optical fiber (m/s), Wa and Wb represent the detected time-dependent signal power of said second signal light at the respective ends a and b of said section of said optical fiber to be measured, and tab represents the time required for the first or second signal light to go back and forth between said section <
a, b>
. - View Dependent Claims (2, 3, 4, 5)
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6. A method for evaluating properties of an optical fiber, comprising the steps of:
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making incident a first signal light in the form of modulated light from a first light source upon an optical fiber to be measured; propagating a second signal light from a second light source in said optical fiber to be measured in the direction opposite to that of the first signal light; controlling the frequency of at least one of said first and second light source; setting the frequency difference Δ
f between said first signal light and said second signal light at a predetermined value;producing an optical nonlinear interaction between said first signal light and said second signal light; detecting said second signal light after it undergoes said optical nonlinear interaction; determining the time dependent signal power W of the detected second signal light; and evaluating the properties of said optical fiber to be measured on the basis of said time dependent signal power W, wherein said optical nonlinear interaction is Brillouin light amplification, and wherein said step of evaluating the properties of said optical fiber includes evaluation of the relative refractive index difference distribution, temperature distribution, or stress distribution in said optical fiber to be measured from the frequency difference Δ
f (where Δ
f=fB, the Brillouin frequency shift) that makes the amplitude of said time dependent signal power W maximum. - View Dependent Claims (7, 8)
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9. A system for evaluating properties of an optical fiber, comprising:
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a first light source means for emitting a first signal light in the form of modulated light; a second light source means for emitting a second signal light; an optical frequency controlling device means for controlling the optical frequency difference between said first signal light and said second signal light; means for launching said second signal light into an end of said optical fiber to be measured; an optical multi-demultiplexing means for launching said first signal light onto the other end of said optical fiber to be measured, and for extracting said second signal light at the other end of said optical fiber; .[.an optical frequency filter which receives light from said multi-demultiplexing means and passes said second signal light but not said first signal light;
.].a photo detecting means for convening .[.the light passed by said optical frequency filter.]. .Iadd.said second signal light extracted by said multi-demultiplexing .Iaddend.into an electric signal; and a signal processing means for processing and analyzing the time dependent waveform of said electric signal from said photo detecting means, wherein at least one of said first light source means and said second light source means is an optical frequency variable type longitudinal single mode oscillation laser, and wherein the optical frequency difference between said first signal light and said second signal light is equal to or approximately equal to the Brillouin frequency shift of said optical fiber to be measured. - View Dependent Claims (10, 11, 12, 13, 14, 15)
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Specification