JP5428630B2 - Light reflection measuring device and light reflection measuring method - Google Patents

Description

  The present invention relates to a light reflection measurement device and a light reflection measurement method for measuring a reflectance distribution in an optical line.

  In an optical communication system that performs optical communication using an optical fiber line, it is important to detect failures such as breakage of the optical fiber line and increase in transmission loss. In particular, in a subscriber optical communication system that has become widespread in recent years, when a failure occurs in an optical fiber line or a subscriber terminal, it is required to quickly identify and repair the failure location.

  Therefore, in an optical communication system, a light reflection measurement device is provided as a device for monitoring an optical line in order to detect such a failure. The light reflection measuring device uses optical reflectometry technology, and based on the reflected light (Fresnel reflected light and Rayleigh scattered light) generated when the monitoring light propagates through an optical line such as an optical fiber line, The reflectance distribution in the optical line is obtained, and the location of the failure in the optical line is detected. Such a light reflection measuring apparatus is required to measure the reflectance distribution with high spatial resolution.

  Optical time domain reflectometry (OTDR) technology that measures the reflectance distribution based on the temporal change of the intensity of the reflected light generated when pulsed monitoring light propagates through the optical line. It has been known. Further, as another optical reflectometry technique, an optical coherence domain reflectometry technique (OCDR: Optical Coherence Domain Reflectometry) is also known (see Patent Document 1 and Non-Patent Document 1).

  In OCDR, the optical frequency is modulated to generate monitoring light having a comb-like optical wave coherence function, and the reflected light generated when the monitoring light propagates through the optical line is input, and a part of the monitoring light is The reference light taken out by branching is also input, and the reflectance at a specific position in the optical line is determined by utilizing the fact that the magnitude of interference between the reflected light and the reference light depends on the delay time difference between the two lights. taking measurement. Further, in the OCDR, the reflectance distribution in the optical line is obtained by changing the position where the reflectance is measured, for example, by changing the interval of the optical frequency modulation in the monitoring light.

  The light wave coherence function is a function obtained by normalizing the autocorrelation function of the electric field V (t) of light, which is a function having time t as a variable, with the light intensity, and normalizing the Fourier transform of the optical power spectrum with the light intensity. It is. When the light of the electric field V (t) is branched into two and the delay time difference between the two branched lights is τ, the size of the interference fringes of these two branched lights is the light wave coherence function of the light. Represented by the real part of Further, the absolute value of the lightwave coherence function is called coherence and represents the magnitude of interference.

The monitoring light used in the OCDR has a modulated optical frequency and has a comb-like light wave coherence function. As a specific example, the optical frequencies are sequentially set to f ₀ , f ₀ + f _s , f ₀ −f _s , f ₀ + 2f _s , f ₀ −2f _s , f ₀ + 3f _s , f ₀ −3f _s ,.・ ・ The modulated light is used as monitoring light. Alternatively, light whose optical frequency is modulated in a sinusoidal shape with the modulation frequency f _s is used as the monitoring light. The optical coherence function of the monitoring light whose optical frequency is modulated in this way has a peak (coherence peak) having a shape similar to the delta function shape when f _s τ is an integer. That is, these monitoring lights have a comb-like lightwave coherence function. As f _s changes, the position of the coherence peak also changes.

The comb-like lightwave coherence function has a plurality of coherence peaks arranged at intervals (1 / f _s ). As one of the coherence peaks exists in the section to be measured in the optical line, a gate having a time width shorter than the coherence peak arrangement interval (1 / f _s ) is applied to the monitoring light, and a pulse of the monitoring light is generated. Cut out.

Japanese Patent Laid-Open No. 10-148596

Kazuo Hotate, et al., Journal of Lightwave Technology, Vol.24, No.7, pp.2541-2557 (2006).

  In order to obtain high spatial resolution with OTDR, it is necessary to narrow the pulse width of the monitoring light. Also, if the pulse width of the monitoring light is reduced, the signal-to-noise ratio (SNR) of the measurement due to the decrease in the energy of the monitoring light is reduced. Therefore, in order to compensate for this decrease in SNR, It is necessary to increase the power. However, when the power of the monitoring light is increased, non-linear optical phenomena such as stimulated Brillouin scattering appear in the optical line, which may cause a decrease in measurement performance and interference with communication signals. Therefore, in OTDR, the spatial resolution is limited to a few meters.

  On the other hand, it is known that OCDR can obtain a higher spatial resolution than OTDR, and can measure, for example, a reflection point several kilometers away with a spatial resolution of several centimeters. However, OCDR requires frequency modulation and phase modulation in the light wave region, and the performance required for the light source is very severe.

  The present invention has been made to solve the above problems, and provides a light reflection measurement device and a light reflection measurement method capable of easily measuring the reflectance distribution in an optical line with high spatial resolution. Objective.

  The light reflection measurement device according to the present invention is a light reflection measurement device that measures a reflectance distribution in an optical line, and (1) a signal source that outputs a modulation signal having a delta function peak in an autocorrelation function; (2) a light source that outputs light whose intensity is modulated according to the modulation signal output from the signal source, and (3) the reflected light generated when the light output from the light source propagates through the optical path and receives the reflected light. A light receiving unit that outputs a detection signal having a value corresponding to the intensity, and (4) a delay unit that delays the modulation signal output from the signal source and outputs the modulation signal, and the delay amount is variable. 5) an arithmetic unit that outputs an electrical signal representing a temporal average value of the product of the detection signal output from the light receiving unit and the modulation signal output from the delay unit; and (6) controlling the delay amount in the delay unit. , The reaction in the optical line based on the electrical signal output from the arithmetic unit And a control unit for obtaining an emissivity distribution.

  The light reflection measurement method according to the present invention is a light reflection measurement method for measuring a reflectance distribution in an optical line, and outputs a modulation signal having a peak of a delta function in an autocorrelation function from a signal source. The light whose intensity is modulated in accordance with the modulation signal output from the light source is output from the light source, and the reflected light generated when the light output from the light source propagates through the optical path is received by the light receiving unit, and the light corresponding to the reflected light intensity A detection signal output from the light receiving unit by outputting a value detection signal from the light receiving unit, delaying the modulation signal output from the signal source by the delay unit having a variable delay amount, and outputting the modulation signal An electric signal representing a temporal average value of the product of the modulation signal output from the delay unit is output from the arithmetic unit, the amount of delay in the delay unit is controlled, and a light beam is generated based on the electric signal output from the arithmetic unit. Anti-road And obtaining the percentage distribution.

  In the light reflection measuring apparatus according to the present invention or the light reflection measuring method according to the present invention, it is preferable that the signal source outputs a modulation signal generated based on the M-sequence code.

  In the light reflection measuring apparatus or the light reflection measuring method according to the present invention, (a) the first section of the optical line based on the detection signal output from the light receiving unit when pulsed light is output from the light source. It is preferable to obtain the reflectance distribution in the second section included in the first section of the optical line on the basis of the electrical signal output from (b) the calculation unit.

  Further, in the light reflection measuring apparatus or the light reflection measuring method according to the present invention, (a) the delay amount in the delay unit is scanned in the first unit time, and based on the electric signal output from the calculation unit. The reflectance distribution in the first section of the optical line is obtained, (b) the delay amount in the delay unit is scanned in the second unit time shorter than the first unit time, and based on the electrical signal output from the calculation unit, It is also preferable to obtain the reflectance distribution in the second section included in the first section of the optical line.

  According to the present invention, the reflectance distribution in the optical line can be easily measured with high spatial resolution.

It is a figure which shows the structure of the light reflection measuring device 1 which concerns on this embodiment. It is a figure which shows the structural example of the calculating part 60 contained in the light reflection measuring device 1 which concerns on this embodiment. PN signal m ₆ generated by the M sequence code of six _stages, and shows the autocorrelation function of the pseudo-random number signal m _6. It is a figure explaining the aspect of the reflectance distribution measurement by the light reflection measuring device 1 or the light reflection measuring method which concerns on this embodiment.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted.

  FIG. 1 is a diagram illustrating a configuration of a light reflection measuring apparatus 1 according to the present embodiment. The light reflection measuring device 1 shown in this figure is a device for measuring a reflectance distribution in an optical line (for example, an optical fiber line) 2, and includes a signal source 10, a light source 20, an optical circulator 30, a light receiving unit 40, a delay unit. 50, the calculating part 60, and the control part 70 are provided.

  The signal source 10 outputs a modulated signal m (t) having a peak in which the autocorrelation function is a delta function to the light source 20. Further, the signal source 10 outputs the modulation signal m (t−nτ) delayed by the time nτ to the modulation signal m (t) to the delay unit 50. τ is the pulse width of the light output from the light source 20. n is a natural number. The signal source 10 preferably outputs a modulated signal m (t) generated based on the M-sequence code.

  The light source 20 outputs light, which has been intensity-modulated according to the modulation signal m (t) output from the signal source 10, to the optical circulator 30. The light source 20 preferably includes a laser diode. The optical circulator 30 outputs the light output from the light source 20 and arrives at the optical line 2, and receives the reflected light generated when the light propagates through the optical line 2, and inputs the reflected light to the light receiving unit 40. Output. The light receiving unit 40 receives light (reflected light generated when the light output from the light source 20 propagates through the optical line 2) that has arrived from the optical circulator 30, and a detection signal having a value corresponding to the intensity of the reflected light. I (t) is output to the calculation unit 60. The light receiving unit 40 preferably includes a photodiode.

  The delay unit 50 gives a delay to the modulation signal m (t−nτ) output from the signal source 10, and outputs the modulation signal m (t−nτ−Δτ) to the calculation unit 60. The delay amount Δτ in the delay unit 50 is variable. The delay amount in the delay unit 50 is preferably scanned in a unit time of 100 ps or less, and more preferably in a unit time of 10 ps or less. As the delay unit 50, for example, a product CDX-ATI011 of Candox Systems Inc. is preferably used. The variable range of the delay amount of this product is 1 ns, and the resolution of the delay amount is 0.5 ps.

  The arithmetic unit 60 receives the detection signal I (t) output from the light receiving unit 40 and also receives the modulation signal m (t−nτ−Δτ) output from the delay unit 50. Then, the calculation unit 60 outputs to the control unit 70 an electric signal V that represents a temporal average value of the product of the detection signal I (t) and the modulation signal m (t−nτ−Δτ). The arithmetic unit 60 may perform processing digitally or may perform analog processing. The control unit 70 controls the delay amount in the delay unit 50, obtains the reflectance distribution in the optical line 2 based on the electrical signal output from the computing unit 60, and displays the obtained reflectance distribution.

  In this embodiment, both the signal source 10 and the delay unit 50 add a delay to the modulation signal supplied to the calculation unit 60 with respect to the modulation signal m supplied to the light source 20. In this case, for example, by increasing the delay amount provided by the signal source 10 and reducing the delay amount provided by the delay unit 50, coarse and fine adjustments of the delay amount can be realized.

  FIG. 2 is a diagram illustrating a configuration example of the calculation unit 60 included in the light reflection measurement apparatus 1 according to the present embodiment. The arithmetic unit 60 shown in this figure obtains an electric signal V representing the temporal average value of the product of the detection signal I (t) and the modulation signal m (t−nτ−Δτ) by analog processing. The arithmetic unit 6 includes a resistor 61, a resistor 62, an NMOS transistor 63, a PMOS transistor 64, an amplifier 65, an amplifier 66, a low-pass filter 67, a low-pass filter 68, and a differential amplifier 69.

  The input end of the amplifier 65 is connected to the light receiving unit 40 via the resistor 61 and is also connected to the source terminal of the transistor 63. The input end of the amplifier 66 is connected to the light receiving unit 40 via the resistor 62 and is also connected to the source terminal of the transistor 64. The drain terminals of the transistors 63 and 64 are grounded. The gate terminals of the transistors 63 and 64 are connected to the delay unit 50.

  The low pass filter 67 receives a signal output from the output terminal of the amplifier 65 and selectively outputs a low frequency component of the input signal to the differential amplifier 69. The low pass filter 68 receives a signal output from the output terminal of the amplifier 66 and selectively outputs a low frequency component of the input signal to the differential amplifier 69. The differential amplifier 69 inputs low-frequency component signals output from the low-pass filters 67 and 68, and outputs a signal V corresponding to the difference between these input signals.

  The arithmetic unit 60 having such a configuration inputs the detection signal I (t) output from the light receiving unit 40 to the resistors 61 and 62 and also modulates the modulation signal m (t−nτ− output from the delay unit 50. By inputting [Delta] [tau] to the gate terminals of the transistors 63 and 64, an electric signal V representing the temporal average value of the product of the detection signal I (t) and the modulation signal m (t-n [tau]-[Delta] [tau]) is output. Can do.

  Next, the modulation signal m output from the signal source 10, the delay amount given to the modulation signal by the signal source 10 or the delay unit 50, the electric signal V output from the calculation unit 60, and the light reflection measurement by the control unit 70. This control will be described in detail.

The photoelectric field E _f (t, x) of the forward propagating light that is output from the optical circulator 30 of the light reflection measuring device 1 and propagates through the optical line 2 is expressed by Expression (1). Here, j is an imaginary unit. t is a variable representing time. x is a variable representing a position. A is the amplitude of the carrier wave. ω is an angular frequency. k is the wave number. v _g is the group velocity. n (ωt−kx) is intensity noise. Θ (ωt−kx) is phase noise.

The photoelectric field E _b of the backward propagating light generated by the reflection (Fresnel reflection and Rayleigh scattering) at the position x ′ on the optical line 2 is expressed by Expression (2). Therefore, the detection signal I (t) output from the light receiving unit 40 is expressed by Expression (3). Here, r is an amplitude coupling coefficient at the time of coupling from forward propagating light to backward propagating light at the position x ′. Η is the light receiving sensitivity of the light receiving unit 40.

  Assuming a sufficiently long measurement time T and noting that the modulation signal m (t) is a real function, the electric signal V output from the calculation unit 60 is expressed by Expression (4). Here, m * m is an autocorrelation function of the modulation signal m (t). As can be seen from this equation, since the autocorrelation function m * m of the modulation signal m (t) has a delta function peak, the electrical signal V output from the calculation unit 60 is a ray corresponding to the peak position. The reflectance r at the position x ′ on the road 2 is expressed.

  In order to obtain the light reflection position x ′ in the optical line 2 with high spatial resolution, it is necessary to use a modulation signal m (t) such that the autocorrelation function m * m converges to a Dirac delta function at an appropriate limit. . Furthermore, it is preferable that light is continuously output from the light source 20 over the measurement time T, and the modulation signal supplied to the calculation unit 60 is from time 0 to time T with respect to the modulation signal m supplied to the light source 20. It is preferable that a delay of up to is added.

Such a modulation signal m can be generated from an M-sequence (maximum-length sequences) code. In the following, the pseudo random number signal m _N generated by changing 0 of the N-stage M-sequence code to −1 is used as the modulation signal m. Properties of M-sequence pseudo-random number signal _{m N} of N stages is represented by the formula (5) to (10).

Here, T is a code length (formula (11)). τ is the pulse width. Δτ is a delay time shorter than the pulse width τ (formula (12)). p, q, and q ′ are positive integers different from each other, and the combination can be uniquely determined for each M sequence. Further, b _τ is a function of the period τ expressed by the equation (13).

3 (a) is a diagram showing the pseudo-random number signal m ₆ generated by the M-sequence code of six stages. 3 (b) is a diagram showing an autocorrelation function of the pseudo-random number signal m _6. As shown in this figure, the autocorrelation function of the pseudo random number signal m _N generated by the N-stage M-sequence code has a delta function-like peak.

Assuming P reflection points {x _p } on the optical line 2, the photoelectric field E _b of the backscattered light is expressed as shown in Expression (14). Here, r _p is an amplitude coupling coefficient at the time of coupling from forward propagating light to backward propagating light at the position x _p . Further, for the sake of simplicity, it is assumed that the intensity noise n of the carrier wave can be ignored.

From this equation (14), the detection signal I (t) output from the light receiving unit 40 is expressed as equation (15). Where δ _pq is the Kronecker delta. Δτ _pq is the overlapping time of the backward propagating light pulses generated at the position x _p and the position x _q, respectively. ξ _pq and ζ _pq represent the apparent reflection positions due to the interference of the backward propagating light generated at the positions x _p and x _q and the property of the equation (7).

In Expression (7), the combination of p, q, and q ′ is different for each M series, so that the true reflection point and the apparent reflection point can be distinguished by changing the M series and measuring a plurality of times. Θ _pq is defined by equation (16).

Here, when _{obtaining the} electric signal V output from the calculation unit 60 based on the detection signal I (t) and the modulation signal m expressed by the equation (15), the parameter X _pq is defined by the equation (17). , Parameter Y _pq is defined by equation (18).

When p = q, the value of θ _{pq in} the equation (16) is 0, and therefore the diagonal components X _pp and Y _pp of the parameters X _pq and Y _pq are expressed by the equations (19) and (20). Thus, the value is independent of the phase noise θ.

On the other hand, the off-diagonal component of the parameters X _pq and Y _pq depends on the phase noise θ. Here, a very small amount ε that satisfies the equation (21) is assumed. The minute amount ε can be arbitrarily reduced by appropriate frequency modulation in the light wave region. In particular, when the light source 20 includes a semiconductor laser diode, the phase of the output light diffuses in a random walk, and therefore the expression (21) is established without intention.

When the number of repetitions of the pseudo random number signal m _N and cos θ _pq as the modulation signals are greatly different from each other, the autocorrelation function has a good value of 0. Conversely, when the number of repetitions of the pseudo random number signal m _N and cos θ _pq as modulation signals is close to each other, the maximum value of the autocorrelation function can be insignificant, but the probability is very small. Therefore, in most cases, Expression (22) and Expression (23) hold for the off-diagonal component of the parameters X _pq and Y _pq .

From the above, the diagonal component of the parameters X _pq and Y _pq becomes dominant. Therefore, for the electric signal V output from the calculation unit 60 based on the detection signal I (t) and the modulation signal m expressed by the equation (15), the equation (24) is established in most cases.

  As can be seen from this equation, the electric signal V output from the calculation unit 60 represents the reflectance r at a position on the optical line 2 corresponding to the peak position of the autocorrelation function m * m of the modulation signal m (t). By scanning the peak position of the autocorrelation function m * m, the reflectance distribution in a certain range of the optical line 2 is represented. Further, in order to scan the peak position of the autocorrelation function m * m, the delay time given to the modulation signal given to the arithmetic unit 60 may be scanned with respect to the modulation signal m given to the light source 20.

  The light reflection measurement method according to the present embodiment is a method of measuring the reflectance distribution in the optical line 2 using the light reflection measurement device 1 described above. In the light reflection measurement method according to the present embodiment, a modulation signal m (t) whose autocorrelation function has a delta function peak is output from the signal source 10 and intensity modulation is performed according to the modulation signal m output from the signal source 10. The emitted light is output from the light source 20. The light output from the light source 20 propagates through the optical line 2 through the optical circulator 30.

  The reflected light generated when the light output from the light source 20 propagates through the optical line 2 is received by the light receiving unit 40 through the optical circulator 30, and the detection signal I (t) having a value corresponding to the reflected light intensity is generated. Output from the light receiving unit 40. Also, a modulation signal m (t−nτ−Δτ) to which a delay is given is output from the delay unit 50 having a variable delay amount. An electric signal V representing a temporal average value of a product of the detection signal I (t) output from the light receiving unit 40 and the modulation signal m (t−nτ−Δτ) output from the delay unit 50 from the arithmetic unit 60. Is output. Then, the amount of delay in the delay unit 50 is controlled by the control unit 70, and the reflectance distribution in the optical line 2 is obtained based on the electric signal V output from the calculation unit 60.

  The light reflection measurement technique according to this embodiment is the same as OTDR and OCDR in that it belongs to the light reflectometry technique. Further, a part of the configuration of the light reflection measuring apparatus 1 according to the present embodiment is common to the configuration of the OTDR apparatus. That is, pulse light is output from the light source 20, the pulse light is propagated to the optical line 2, reflected light generated in the optical line 2 is received by the light receiving unit 40, and a detection signal is output from the light receiving unit 40. For example, OTDR measurement is possible based on this detection signal. Hereinafter, such an operation is referred to as an OTDR mode.

  Further, in the light reflection measurement technique according to the present embodiment, the optical line obtained based on the electric signal V output from the calculation unit 60 depending on the amount of delay given to the modulation signal by the signal source 10 or the delay unit 50. The spatial resolution of the two light reflectance distributions is different. For example, the amount of delay given by the signal source 10 can be scanned in a first unit time (for example, pulse width τ unit), and light reflection measurement on the optical line 2 can be performed with a relatively low spatial resolution. Further, the delay amount provided by the fine-tuning delay unit 50 is scanned in a second unit time (for example, a unit time less than the pulse width τ) shorter than the first unit time, and the light in the optical line 2 is relatively high in spatial resolution. Reflection measurement can be performed. Hereinafter, the former low-resolution measurement operation is referred to as a first measurement mode, and the latter high-resolution measurement operation is referred to as a second measurement mode.

FIG. 4 is a diagram for explaining an aspect of reflectance distribution measurement by the light reflection measurement apparatus 1 or the light reflection measurement method according to the present embodiment. The aspect of reflectance distribution measurement combining the OTDT mode, the first measurement mode, and the second measurement mode will be described with reference to FIG. Here, the length of the optical fiber used as the optical path 2 and 20 km, and the group velocity of the pulse light in the optical fiber v _g a 2 × 10 8 ^{m /} s.

  First, the reflectance distribution of the optical line 2 is measured in the OTDR mode (FIG. 4A). At this time, since the measurement time per one pulsed light output is 0.2 ms, an overview of the reflectance distribution of the entire length of the optical line 2 can be obtained in about 1 second even assuming 10 repeated measurements. If the pulse width is 1 μs, the reflectance distribution measurement spatial resolution is 400 m.

  Next, a section to be measured in detail is selected from the sections of the optical line 2 measured in the OTDR mode, and the reflectance distribution of the selected section is measured in the first measurement mode. If the pulse width τ is 1 ns and the delay amount is scanned in a unit time of the pulse width τ, the spatial resolution of the reflectance distribution measurement is 40 cm. Since the period of the autocorrelation function may be 20 km or more, the M sequence may be 17 stages. The 17-stage M series corresponds to a length of 26 km. For example, assuming 10 cycles per point, the reflectance distribution in a section (3000 points) having a length of 1200 m is measured in several seconds.

  Finally, a section to be measured in more detail is selected from the sections of the optical line 2 measured in the first measurement mode, and the reflectance distribution of the selected section is measured in the second measurement mode. The modulation signal in the second measurement mode is the same as the modulation signal in the first measurement mode. If the delay amount given by the delay unit 50 is scanned at a unit time of 10 ps, the spatial resolution of the reflectance distribution measurement is 4 mm. If it takes about 1 second to set up, the reflectance distribution in a section (300 points) with a length of 120 cm is measured in about 5 minutes.

  As described above, in the light reflection measurement device 1 or the light reflection measurement method according to the present embodiment, the reflectance distribution in the optical line 2 can be measured with a higher spatial resolution as compared with the OTDR. Further, in the light reflection measuring apparatus 1 or the light reflection measuring method according to the present embodiment, frequency modulation or phase modulation in the light wave region such as OCDR is unnecessary, and phase noise of light output from the light source 20 is rather large. Since it is preferable, a normal laser diode can be used as the light source 20, and therefore, the reflectance distribution in the optical line 2 can be easily measured.

  Regarding the spatial resolution of the reflectance distribution measurement by the light reflection measurement technique according to the present embodiment, the signal source 10 that outputs a 1 Gbps 17-stage M-sequence pseudorandom signal as the modulation signal m is used, and the resolution is 10 ps with respect to the modulation signal. In principle, the optical line 2 having a maximum length of 26 km can be monitored with a spatial resolution of 4 mm.

  Even when the reflectance distribution measurement mode described with reference to FIG. 4 is implemented, the light reflection measurement device 1 according to the present embodiment can be used as an OTDR device. And cost increase can be suppressed.

  DESCRIPTION OF SYMBOLS 1 ... Light reflection measuring device, 2 ... Optical line, 10 ... Signal source, 20 ... Light source, 30 ... Optical circulator, 40 ... Light-receiving part, 50 ... Delay part, 60 ... Calculation part, 70 ... Control part.

Claims (6)

A light reflection measurement device for measuring a reflectance distribution in an optical line,
A signal source for outputting a modulated signal having an autocorrelation function having a delta function peak;
A light source that outputs light whose intensity is modulated in accordance with a modulation signal output from the signal source;
A light receiving unit that receives reflected light generated when the light output from the light source propagates through the optical line and outputs a detection signal having a value corresponding to the intensity of the reflected light;
A delay unit that delays the modulation signal output from the signal source and outputs the modulation signal, and the delay amount is variable;
An arithmetic unit that outputs an electrical signal representing a temporal average value of a product of the detection signal output from the light receiving unit and the modulation signal output from the delay unit;
A control unit for controlling a delay amount in the delay unit and obtaining a reflectance distribution in the optical line based on an electric signal output from the arithmetic unit;
Bei to give a,
The control unit is
Based on a detection signal output from the light receiving unit when pulsed light is output from the light source, obtain an OTDR measurement result in the first section of the optical line,
Based on the electrical signal output from the arithmetic unit, to determine the reflectance distribution in the second section included in the first section of the optical line,
A light reflection measuring apparatus characterized by that. A light reflection measurement device for measuring a reflectance distribution in an optical line,
A signal source for outputting a modulated signal having an autocorrelation function having a delta function peak;
A light source that outputs light whose intensity is modulated in accordance with a modulation signal output from the signal source;
A light receiving unit that receives reflected light generated when the light output from the light source propagates through the optical line and outputs a detection signal having a value corresponding to the intensity of the reflected light;
A delay unit that delays the modulation signal output from the signal source and outputs the modulation signal, and the delay amount is variable;
An arithmetic unit that outputs an electrical signal representing a temporal average value of a product of the detection signal output from the light receiving unit and the modulation signal output from the delay unit;
A control unit for controlling a delay amount in the delay unit and obtaining a reflectance distribution in the optical line based on an electric signal output from the arithmetic unit;
Bei to give a,
The control unit is
The delay amount in the delay unit is scanned in a first unit time, and based on the electrical signal output from the calculation unit, the reflectance distribution in the first section of the optical line is obtained,
A second interval included in the first interval of the optical line based on an electrical signal output from the arithmetic unit by scanning a delay amount in the delay portion in a second unit time shorter than the first unit time. Find the reflectance distribution at
A light reflection measuring apparatus characterized by that. Outputting a modulated signal generated by the signal source based on an M-sequence code;
The light reflection measuring apparatus according to claim 1 or 2 . A light reflection measurement method for measuring a reflectance distribution in an optical line,
A modulated signal having a peak whose autocorrelation function is a delta function is output from the signal source,
The light that has been intensity-modulated according to the modulation signal output from the signal source is output from the light source,
The reflected light generated when the light output from the light source propagates through the optical line is received by the light receiving unit, and a detection signal having a value corresponding to the reflected light intensity is output from the light receiving unit,
A delay unit having a variable delay amount delays the modulation signal output from the signal source to output the modulation signal,
An electric signal representing a temporal average value of a product of the detection signal output from the light receiving unit and the modulation signal output from the delay unit is output from the arithmetic unit,
Based on a detection signal output from the light receiving unit when pulsed light is output from the light source, obtain an OTDR measurement result in the first section of the optical line,
And it controls the delay amount in the delay unit based on the electric signal output from said arithmetic unit calculates the reflectance distribution in the second section included in the first section of the optical line,
A light reflection measurement method characterized by that. A light reflection measurement method for measuring a reflectance distribution in an optical line,
A modulated signal having a peak whose autocorrelation function is a delta function is output from the signal source,
The light that has been intensity-modulated according to the modulation signal output from the signal source is output from the light source,
The reflected light generated when the light output from the light source propagates through the optical line is received by the light receiving unit, and a detection signal having a value corresponding to the reflected light intensity is output from the light receiving unit,
A delay unit having a variable delay amount delays the modulation signal output from the signal source to output the modulation signal,
An electric signal representing a temporal average value of a product of the detection signal output from the light receiving unit and the modulation signal output from the delay unit is output from the arithmetic unit,
The delay amount in the delay unit by scanning in a first unit time, based on the electric signal output from said arithmetic unit calculates a reflectance distribution in the first section of the optical line,
A second interval included in the first interval of the optical line based on an electrical signal output from the arithmetic unit by scanning a delay amount in the delay portion in a second unit time shorter than the first unit time. Find the reflectance distribution at
A light reflection measurement method characterized by that. Outputting a modulation signal generated based on the M-sequence code from a signal source;
The light reflection measurement method according to claim 4 or 5 , wherein

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