JP5478087B2 - Optical frequency domain reflection measurement method and apparatus - Google Patents

Description

  The present invention relates to an optical frequency domain reflection measurement method capable of measuring reflected light and backscattered light with high spatial resolution in an optical component or an optical transmission line, and a measurement apparatus using this method.

  As a technique capable of measuring reflected light and backscattered light from an optical component or an optical transmission line with high spatial resolution, an optical frequency domain reflection measurement method using coherent light as shown in Non-Patent Document 1 (C -OFDR). In the optical frequency domain reflection measurement method, frequency-swept coherent light is incident on the measurement object, and the reflected and backscattered light from the measurement object and the reference light branched in advance are coherently detected, and the obtained measurement beat signal Is a technique for obtaining the reflected light and backscattered light intensity at an arbitrary position in the measurement object and identifying the loss distribution and the failure point of the measurement object.

  Further, as shown in Non-Patent Document 2, by monitoring the coherence characteristics of the light source using a reference interferometer and correcting the measurement beat signal, the phase fluctuation of the light source (light source phase) is also obtained in a region exceeding the laser coherence length. It is said that a highly accurate measurement result can be obtained by compensating the spread of the reflection spectrum due to noise.

W. Eickhoff and R. Ulrich, Applied physics Letters, vol. 39, no 9, pp. 693-695, 1981 X.Fan 、 Y.Koshikiya and F.Ito, Optics Letters, vol.32.no.22, pp.3227-3229,2007 “Small Soundproof Box”, [online], [searched on November 28, 2008], Internet <URL: https://www.soundenvironment.jp/soundproof-box.htm> “Sound insulation sheet”, [online], [searched on November 28, 2008], Internet <URL: https://www.nittobo.co.jp/kw/juuken/syaon.html>

  However, in existing technologies, disturbances such as sound, vibration, and temperature change are added to the reference interferometer, and phase fluctuations (phase noise due to disturbances) different from the light source phase noise are superimposed, and such disturbances are superimposed. The monitor beat signal has a problem that the measurement beat signal cannot be corrected correctly.

  In particular, when the delay length used in the reference interferometer is long, the section subjected to the disturbance becomes long, so that the phase noise due to the disturbance becomes large. As a result, the measurement beat signal cannot be sufficiently corrected, the reflection spectrum is widened, and high-accuracy measurement is impossible. As described above, the effect of the correction by the reference interferometer becomes small due to the influence of the disturbance. Therefore, the phase fluctuation due to the disturbance is a great obstacle when the optical frequency domain reflection measurement method (OFDR) is applied to an object with a long measurement distance. It was.

In order to solve the above-mentioned problem, the present invention divides the output light from a light source that sweeps the optical frequency with respect to time and enters the reference interferometer and the measurement interferometer, respectively. Is obtained by detecting the monitor beat signal between the output light from the light and the light obtained by delaying the output light with a delay fiber, and the measurement interferometer makes the output light from the light source and the output light incident on the measurement object An optical frequency domain reflection measurement method (OFDR) that detects a measurement beat signal of backscattered light and reflected light, corrects the measurement beat signal based on the monitor beat signal, and measures a reflectance in a light wave propagation direction in a measurement target. in), characterized by applying soundproofing measures delay fiber of the reference interferometer for applying suppress the light wave phase fluctuation due to sound a disturbance delay fiber of the reference interferometer is subjected To.

The optical frequency domain reflectometry apparatus of the present invention includes a light source that sweeps an optical frequency with respect to time, light that is output from the light source, and light that has been incident and delayed by a delay fiber. A reference interferometer for detecting a monitor beat signal, and measurement of backscattered light and reflected light obtained by making the output light from the light source incident and making the incident output light and the output light incident on the measurement object A measurement interferometer that detects a beat signal, a sampling unit that receives and samples the monitor beat signal and the measurement beat signal, a measurement beat signal sampled by the sampling unit is corrected based on the monitor beat signal, and is measured an analysis unit that measures the reflectance of light wave propagation direction in a subject, provided the delay fiber of the reference interferometer, light waves of the phase swing due to sound a disturbance It is characterized in that it comprises a soundproof mechanism for suppressing the technique.

  The optical frequency domain reflection measurement method of the present invention can suppress phase fluctuations of light waves due to disturbances such as light wave phase fluctuations caused by sound, for example, which is received by the delay fiber of the reference interferometer, and is an object with a long measurement distance. However, high-resolution measurement can be performed.

It is a structure explanatory view showing an optical frequency domain reflection measuring apparatus according to an embodiment of the present invention. It is a figure which shows the spectrum of the reflective point measured with the optical frequency domain reflection measuring method which concerns on embodiment of this invention, (a) is a case where the delay fiber of a reference interferometer is not put in a soundproof box, (b) is reference interference. This is when the total delay fiber is placed in a soundproof box.

Hereinafter, embodiments of the present invention will be described in detail.
In FIG. 1, 11 is a frequency sweep light source, 12, 18, 21, 22, and 23 are optical directional couplers, 13 is a measurement interferometer, 14 is a measurement object, 15 is a reference interferometer, 16 is a sampling unit, and 17 is Analysis unit, 19 is a delay fiber, 20 is a soundproofing mechanism, 24 and 26 are optical receivers, 25 and 27 are sampling devices, 28 is a clock generator, 29 is an arithmetic processing unit, 30 is output light, 31 is measurement light, 32 is monitoring light, 33 is signal light, and 34 is local light.

  As shown in FIG. 1, the optical frequency domain reflectometry apparatus according to the embodiment of the present invention uses an optical directional coupler 12 to output light 30 output from a frequency sweep light source 11 that sweeps the optical frequency with respect to time. One is incident on the measurement interferometer 13 and the measurement object 14 as the measurement light 31, and the other is incident on the reference interferometer 15 as the monitoring light 32 for monitoring the coherence characteristics of the output light 30.

  The reference interferometer 15 includes optical directional couplers 18 and 21 and a delay fiber 19, and a monitor beat signal between the incident monitoring light 32 (output light 30) and the light obtained by delaying the monitoring light 32 by the delay fiber 19. Is detected. The delay fiber 19 of the reference interferometer 15 is provided with a mechanism for suppressing the phase fluctuation of the light wave due to the disturbance, for example, a soundproof mechanism 20 for suppressing the phase fluctuation of the light wave caused by the sound acting as a disturbance.

  The measurement interferometer 13 includes optical directional couplers 22 and 23, and is obtained by causing the signal light 33 (output light 30, measurement light 31) and the measurement light 31 (output light 30) to enter the measurement object 14. The measurement beat signal with the local light 34 of the scattered light and the reflected light is detected.

  The monitor beat signal detected by the reference interferometer 15 is received by the optical receiver 24 of the sampling unit 16 and sampled by the sampling device 25. The measurement beat signal detected by the measurement interferometer 13 is received by the optical receiver 26 of the sampling unit 16 and sampled by the sampling device 27. Clock pulses are input from the clock generator 28 of the analysis unit 17 to the sampling devices 25 and 27.

  The monitor beat signal sampled by the sampling device 25 and the measurement beat signal sampled by the sampling device 27 are input to the arithmetic processing device 29 of the analysis unit 17, and the arithmetic processing device 29 monitors the measurement beat signal sampled by the arithmetic processing. Correction is performed based on the coherence characteristics of the beat signal, the intensity distribution of the reflected light and the backscattered light at the measurement object 14 is obtained, and the reflectance in the light wave propagation direction at the measurement object 14 is measured.

  The sampling device 25 samples the monitor beat signal input from the optical receiver 24 and records the sampling data Xn in an internal memory or the like. The arithmetic processing unit 29 calculates a continuous function X (t) when obtaining the phase of the sampling data Xn. On the other hand, the sampling device 27 samples the measurement beat signal input from the optical receiver 26 at the same interval, and records the sampling data Yn in an internal memory or the like.

Further, the arithmetic processing unit 29 uses the function X (t) received from the sampling unit 25 and the data Yn received from the sampling unit 27 to perform data processing including sampling processing and FFT (fast Fourier transform) processing. Repeat N times. The data FFT _N obtained in this way is recorded. The arithmetic processing unit 29 calculates the measurement result using the data FFT ₁ , FFT ₂ ,..., FFT _N.

  As described above, the reference interferometer 15 for monitoring the coherence characteristic of the light source 11 is provided, and the measurement result in the measurement interferometer 13 is corrected based on the result of the monitor. The reference interferometer 15 generates a monitor beat signal of the output light of the light source 11 by self-delayed homodyne detection, generates a reference signal of the beat signal, and samples the beat signal of the measurement interferometer 13 based on the generated reference signal. The obtained number sequence is subjected to FFT processing to obtain a measurement result.

  That is, the output light from the frequency swept light source 11 that sweeps the optical frequency with respect to time is split into two beams and incident on the reference interferometer 15 and the measurement interferometer 13, respectively. The reference interferometer 15 outputs the light from the light source 11. A monitor beat signal between the light and the light obtained by delaying the output light with a delay fiber is detected, and the measurement interferometer 13 obtains the output light from the light source 11 and the output light incident on the measurement object 14. An optical frequency domain reflection measurement method for detecting a measurement beat signal of backscattered light and reflected light, correcting the measurement beat signal based on the monitor beat signal, and measuring the reflectance in the light wave propagation direction in the measurement target 14 ( In the OFDR), a measure for suppressing phase fluctuation of the light wave due to the disturbance received by the delay fiber 19 of the reference interferometer 15, for example, a soundproof measure is taken. That.

  As the soundproofing mechanism 20 in the delay fiber 19 of the reference interferometer 15, for example, a small soundproof box as shown in Non-Patent Document 3 or a highly airtight box with a soundproof sheet as shown in Non-Patent Document 4 is attached. This can be realized by installing the reference interferometer 15 in the above.

  Further, since the light wave is most affected by the disturbance when propagating through the delay fiber 19 having an extremely long optical path length in the measuring apparatus, the range to be sound-insulated must be at least the delay fiber 19 used in the reference interferometer 15. I must. Therefore, if the delay fiber 19 is inside the soundproof mechanism 20, the same effect can be obtained even if the range accommodated in the soundproof mechanism 20 extends to the entire apparatus. However, no sound source should be present inside the soundproof mechanism 20.

  FIG. 2 shows a case where the measurement beat signal is corrected using the monitor beat signal obtained when the delay fiber (5 km) 19 of the reference interferometer 15 is housed in a wooden soundproof box with a sound insulation sheet attached inside (b) ) And the result of OFDR measurement (waveform in the vicinity of the 40 km point) obtained when the measurement beat signal is corrected using the monitor beat signal obtained when the delay fiber 19 is not accommodated in the soundproof box. ing.

  The measurement object 14 was a single-mode fiber having a length of 40 km, and the far end was an open end of an AdPC polished SC connector. By accommodating the reference interferometer 15 in the soundproof box, the full width at half maximum, which is the spectral resolution at the reflection point, is narrowed from 110 cm to 10 cm, and it can be seen that the resolution is improved. In this way, by applying the soundproofing mechanism 20 to the reference interferometer 15, the phase fluctuation of the light wave due to sound can be suppressed, and a monitor beat signal that accurately monitors the coherent characteristics of the frequency sweep light source 11 can be obtained. Can be corrected correctly.

  The above describes the case where the disturbance applied to the reference interferometer 15 is sound. However, even when the temperature change and vibration act on the reference interferometer 15 as disturbances and cause phase fluctuations of the light wave, the temperature adjustment mechanism and the anti-vibration respectively. It is obvious that the light source coherent characteristic can be accurately monitored by applying the vibration mechanism to the reference interferometer 15, and the resolution can be improved.

  As described above, since the light source coherency characteristic obtained by the reference interferometer is correctly monitored by using the optical frequency domain reflection measurement method according to the embodiment of the present invention, the maximum beat signal measured by the reference interferometer can be maximized. A correction effect is obtained, and it becomes possible to provide a highly accurate optical frequency domain reflection measurement method over a long distance by suppressing the spread of the reflection spectrum.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. Further, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, you may combine suitably the component covering different embodiment.

  DESCRIPTION OF SYMBOLS 11 ... Frequency sweep light source, 12, 18, 21, 22, 23 ... Optical directional coupler, 13 ... Measurement interferometer, 14 ... Measurement object, 15 ... Reference interferometer, 16 ... Sampling part, 17 ... Analysis part, 19 DESCRIPTION OF SYMBOLS ... Delay fiber, 20 ... Soundproofing mechanism, 24, 26 ... Optical receiver, 25, 27 ... Sampling device, 28 ... Clock generator, 29 ... Arithmetic processing device, 30 ... Output light, 31 ... Measurement light, 32 ... Monitoring light 33 ... Signal light, 34 ... Local light emission.

Claims (2)

The output light from the light source that sweeps the optical frequency with respect to time is bifurcated and is incident on the reference interferometer and the measurement interferometer, respectively. In the reference interferometer, the output light from the light source and the output light are transmitted through a delay fiber. A monitor beat signal with delayed light is detected, and in the measurement interferometer, a measurement beat signal of output light from the light source and backscattered light and reflected light obtained by making the output light incident on a measurement object is detected. In the optical frequency domain reflection measurement method for detecting and correcting the measurement beat signal based on the monitor beat signal, and measuring the reflectance in the light wave propagation direction in the measurement target,
Optical frequency domain reflectometry method characterized by applying soundproofing measures delay fiber of the reference interferometer for applying suppress the light wave phase fluctuation due to sound a disturbance delay fiber of the reference interferometer is subjected. A light source that sweeps the optical frequency over time;
A reference interferometer for detecting a monitor beat signal of the output light from the light source and the incident output light and the light obtained by delaying the output light with a delay fiber;
A measurement interferometer for detecting a measurement beat signal of backscattered light and reflected light obtained by making the output light from the light source incident and making the incident output light and output light incident on a measurement object;
A sampling unit that receives and samples the monitor beat signal and the measurement beat signal;
An analysis unit that corrects the measurement beat signal sampled by the sampling unit based on the monitor beat signal, and measures the reflectance in the light wave propagation direction in the measurement target;
An optical frequency domain reflection measurement apparatus comprising: a soundproofing mechanism for suppressing phase fluctuation of a light wave caused by a disturbance sound , provided in a delay fiber of the reference interferometer.

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