Physical quantity measuring method using Brillouin optical fiber sensor

A physical quantity measuring method using a Brillouin optical fiber sensor comprising:

• a step S1000 of setting an optical fiber 100 on a predetermined structure as a sensing structure;
• a step S2000 of selecting a pair of first and second pulse lights having different pulse widths;
• a step S3000 of sequentially transmitting the first and second pulse lights through the optical fiber 100 to obtain Brillouin gain spectra;
• a step S4000 of comparing the Brillouin gain spectra with each other to obtain a normal spectrum;
• a step S5000 of determining a Brillouin frequency having a peak value from the normal spectrum;
• and
• a step S6000 of multiplying the Brillouin frequency by a conversion factor of a physical quantity to be measured resulting in a measurement of the physical quantity wherein the measurement is outputted as a signal;
• wherein the normal spectrum is obtained using the following equation,
• NBGS
• ⁡
• (
• x
• ,
• v
• )
• =
• I
• (
• 2
• )
• ⁡
• (
• x
• ,
• v
• )
• I
• (
• 1
• )
• ⁡
• (
• x
• ,
• v
• )
• =
• exp
• ⁡
• [
• ∫
• x
• +
• Δ
• ⁢
• ⁢
• z
• 1
• x
• +
• Δ
• ⁢
• ⁢
• z
• 2
• ⁢
• g
• ⁡
• (
• z
• ′
• ,
• v
• )
• ⁢
• Δ
• ⁢
• ⁢
• I
• pu
• ⁡
• (
• z
• ′
• ,
• v
• )
• ⁢
• ⁢
• ⅆ
• z
• ′
• ]
• wherein NBGS(x,v) represents the normalized Brillouin gain spectrum, which means back scattering lights accumulated in the portion corresponding to Δz2−Δz1, I(1)(x,v) denotes the first Brillouin gain spectrum, I(2)(x,v) represents the second Brillouin gain spectrum, x means the position where each back scattering light starts, g(z′,v) represents a Brillouin gain factor, and ΔIpu(z′,v) denotes the intensity of each pulse light.