Optical device loss measurement apparatus, and optical device loss measurement method
An optical test system capable of accurately measuring a loss of each mode at each position of an optical fiber which propagates a plurality of modes is provided. An optical fiber loss measuring apparatus for measuring using an OTDR technique includes a crosstalk suppressing light input unit that inputs light of a different mode different from the predetermined mode, the different mode causing crosstalk to the probe light, to the target optical fiber to be measured through the near end as crosstalk suppressing light at a second frequency obtained by giving a frequency that is equivalent to a Brillouin frequency shift of the predetermined mode to a first frequency, a light separating unit that removes light of the second frequency from light that is output from the target optical fiber to be measured through the near end to separate light of the first frequency, and a propagation mode loss measuring unit that measures an intensity of the separated light to measure a loss of each propagation mode at each position of the target optical fiber to be measured.
1. An optical fiber loss measuring apparatus that measures losses of a plurality of propagation modes at a plurality of positions of a target optical fiber to be measured which propagates a plurality of modes by inputting light, as probe light, having a first frequency of a predetermined mode of the plurality of modes to the target optical fiber to be measured through a near end of the target optical fiber to be measured and measuring an intensity of backward scattered light generated at each position of the plurality of positions of the target optical fiber to be measured using an Optical Time Domain Reflectometry (OTDR) technique, the optical fiber loss measuring apparatus comprising:
a crosstalk suppressing light input unit configured to input light of a different mode of the plurality of modes different from the predetermined mode, the different mode causing crosstalk to the probe light, to the target optical fiber to be measured through the near end as crosstalk suppressing light at a second frequency obtained by giving a frequency that is equivalent to a Brillouin frequency shift of the predetermined mode to the first frequency;
a light separating unit configured to remove light of the second frequency from light that is output from the target optical fiber to be measured through the near end to separate light of the first frequency; and
a propagation mode loss measuring unit configured to measure an intensity of the light that is separated to measure a loss of each propagation mode of the plurality of propagation modes at each position of the plurality of positions of the target optical fiber to be measured.
2. The optical fiber loss measuring apparatus according to claim 1 , wherein the light separating unit includes an optical bandpass filter that passes only light of the first frequency.
3. The optical fiber loss measuring apparatus according to claim 1 , wherein the light separating unit includes a coherent detection unit configured to perform coherent detection on light that is output from the optical fiber through the near end using light of the first frequency as local light to separate only light of the first frequency.
4. The optical fiber loss measuring apparatus according to claim 1 , wherein the crosstalk suppressing light input unit is configured to set the second frequency to a frequency which minimizes an output intensity of light in the different mode which is a mode of the plurality of modes identical to a mode of the crosstalk suppressing light.
5. An optical fiber loss measuring method that measures losses of a plurality of propagation modes at a plurality of positions of a target optical fiber to be measured which propagates a plurality of modes by inputting light, as probe light, having a first frequency of a predetermined mode of the plurality of modes to the target optical fiber to be measured through a near end of the target optical fiber to be measured and measuring an intensity of backward scattered light generated at each position of the plurality of positions of the target optical fiber to be measured using an Optical Time Domain Reflectometry (OTDR) technique, the optical fiber loss measuring method comprising the steps of:
inputting the probe light to the target optical fiber to be measured through the near end and light of a different mode of the plurality of modes different from the predetermined mode, the different mode causing crosstalk to the probe light, to the target optical fiber to be measured through the near end as crosstalk suppressing light at a second frequency obtained by giving a frequency that is equivalent to a Brillouin frequency shift of the predetermined mode to the first frequency;
removing light of the second frequency from light that is output from the target optical fiber to be measured through the near end to separate light of the first frequency; and
measuring an intensity of the light that is separated to measure a loss of each propagation mode of the plurality of propagation modes at each position of the plurality of positions of the target optical fiber to be measured.
6. The optical fiber loss measuring method according to claim 5 , wherein the removing step includes separating only light of the first frequency through an optical bandpass filter that passes only light of the first frequency.
7. The optical fiber loss measuring method according to claim 5 , wherein the removing step includes performing coherent detection on light that is output from the optical fiber through the near end using light of the first frequency as local light to separate only light of the first frequency.
8. The optical fiber loss measuring method according to claim 5 , wherein the inputting step includes setting the second frequency to a frequency which minimizes an output intensity of light in the different mode which is a mode of the plurality of modes identical to a mode of the crosstalk suppressing light.