JP2019078637A - OTDR device - Google Patents

Abstract

To expand a dynamic range in one session of measurement trace and shorten a measurement time for the whole in measuring the loss distribution of an optical fiber by OTDR.SOLUTION: An OTDR device 301 pertaining to the present invention applies a test light pulse to an optical fiber 50 under test, coherently receives back-scattered light generated in the optical fiber 50 under test and measures the loss distribution of the optical fiber 50 under test. The OTDR device comprises: an optical modulator 13 for IQ-modulating each test light pulse with an inputted IQ modulating signal sequence; and signal processing means 18 for performing computation to derive the loss distribution of the optical fiber 50 under test relative to the distance from a received signal that is coherently received using the IQ modulating signal sequence.SELECTED DRAWING: Figure 1

Description

  The present disclosure relates to an OTDR apparatus that evaluates the loss distribution of an optical fiber that is a transmission medium of an optical signal in the optical communication system field and tests the position of a break point.

  In optical fiber communication systems, optical time domain reflectometers (OTDRs) (eg, for loss testing during installation of optical fiber cables, investigation of failure points, and reevaluation during upgrade of system capacity) Loss distribution measurement using Non-Patent Document 1 is indispensable.

  The OTDR's dynamic range is an important parameter that determines the measurable length and measurement reliability of the measured optical fiber (Fiber Under Test, FUT), and many techniques for extending the dynamic range have been proposed. There is. As the simplest method, the dynamic range can be increased by broadening the pulse width of the test light, but this leads to a decrease in spatial resolution. Coherent OTDR (Coherent ODTR, C-OTDR) improves the reception sensitivity by coherent detection and increases the dynamic range as compared with direct detection OTDR (see, for example, Non-Patent Documents 2, 3 and 4).

  On the other hand, 13 dB of dynamic range improvement by frequency division multiplexing OTDR (FDM-OTDR) using test light pulses of 200 frequency channels has been reported (see, for example, Non-Patent Document 5). Also, by using a test light pulse encoded by a specific code such as Golay code (see, for example, Non-patent documents 6 and 7) or Simplex code (see, for example, Non-patent document 8) The coding gain and dynamic range can be increased.

  The most commonly used dynamic range extension method is to repeat OTDR measurements and average the data obtained. In this case, if the number of measurements is Nmeas, the dynamic range is improved by (Nmeas) ^ (1/2).

M. K. Barnoski and S. M. Jensen, “Fiber waveguides: A novel technique for investigating attenuation characteristics”, Appl. Opt. 15 (9), 2112-2115 (1976). P. Healey and D. J. Malyon, “OTDR in single-mode fiber at 1.5 μm using heterodyne detection”, Electron. Lett. 18 (20), 862-863 (1982). Y. Koyamada, and H. Nakamoto, "High performance single mode OTDR using coherent detection and fiber amplifiers", Electron. Lett. 26 (9), 573-575 (1990). H. Izumita, Y. Koyamada, S. Furukawa, and I. Sankawa, “The performance limit of coherent OTDR enhanced with optical fiber amplifiers due to optical nonlinear phenomena”, J. Lightw Technol. 12 (7), 1230-1238 (1994). H. Iida, K. Toge, and F. Ito, "200-subchannel ultra-high-density frequency division multiplexed coherent OTDR with nonlinear effect suppression", in Proc. Optical Fiber Communication Conference 2013, paper OW1K. 5. M. Nazarathy, S. A. Newton, R.S. P. Giffard, D .; S. Moberly, F. Sischka, W. R. Trutna, S. Foster, "Real-time long range complementary correlation optical time domain reflectometer", J. Org. Lightw. Technol. 7 (1), 24-38 (1989). H. Nakamoto, N. Ohta, and Y. Koyamada, “Use of signal processing techniques to improve the dynamic range of coherent OTDRs”. Electronics and Communications in Japan (Part I: Communications) 75 (10), 42-54 (1992). M. D. Jones, “Using simplex codes to improve OTDR sensitivity”, IEEE Photon. Technol. Letters. 5 (7), 822-824 (1993).

  In FDM-OTDR, the dynamic range is expanded by increasing the number of frequency channels of test light. However, when the number of frequency channels is increased, the frequency interval between the channels is narrowed, crosstalk between test light frequencies occurs, and the accuracy of OTDR measurement is degraded. Another problem is that when using interpolated correlation Golay codes in C-OTDR measurement, the measurable FUT length is limited by the phase noise of the test light source (see, for example, Non-Patent Document 8). . Although the Simplex code provides greater coding gain than the Golay code, it suffers from the need for multiple measurement traces. Increasing the number of measurements for dynamic range expansion can seriously affect the OTDR measurement of submarine cables. For example, if the length of the FUT is 12000 km and Nmeas = 2 ^ 16, the total measurement time exceeds 2 hours.

  The present invention has been made in view of such problems, and it is an object of the present invention to provide an OTDR device capable of improving the dynamic range in one measurement trace and shortening the measurement time.

  In order to achieve the above object, the OTDR apparatus according to the present invention obtains an OTDR waveform by calculating the return light generated by the signal pulse train using a data pulse modulated signal pulse train instead of a single pulse as test light. I decided.

Specifically, the OTDR apparatus according to the present invention injects a test light pulse into the measured optical fiber, coherently receives the backscattered light generated in the measured optical fiber, and the loss distribution of the measured optical fiber An OTDR (Optical Time Domain Reflectometer) device that measures
An optical modulator that performs IQ modulation for each of the test light pulses with the input IQ modulation signal sequence;
Signal processing means for performing an operation for deriving a loss distribution with respect to the distance of the optical fiber to be measured from a reception signal coherently received using the IQ modulation signal sequence;
Equipped with

  The OTDR apparatus increases the power of the backscattered light generated in the FUT by using a data pulse modulated signal pulse train instead of a single pulse as the test light, and the signal to noise ratio at the receiver (signal to noise ratio) , SNR). As a result, the dynamic range of the OTDR waveform derived by signal processing after reception is larger than when a single pulse is used as the test light. Therefore, the present invention can provide an OTDR device that improves the dynamic range in one measurement trace and enables shortening of measurement time.

The OTDR apparatus according to the present invention performs the following calculation when signal processing of return light is performed in the time domain.
The operation performed by the signal processing means is
The IQ modulation signal sequence is vector x _probe = [x _probe (1), x _probe (2), ..., x _probe (N _probe )], and the received signal is vector x _obs = [x _obs (1) , X _obs (2), ..., x _obs (N _obs )],
_{Deriving the} Toeplitz matrix x _{probe, tpl} based on the signal column vector x _probe and the Moore-Penrose inverse matrix x _{probe, tpl} ^{+ of} the Toeplitz matrix x _{probe, tpl} ,
This is an operation for converting a column vector obtained by multiplying the Moore-Penrose inverse matrix x _{probe, tpl} ⁺ by the received signal vector x _obs into the distance dependency of the optical fiber to be measured.

  When the signal pulse train is incident on the FUT, the return light is light in which the backscattered light of each pulse is superimposed. The present OTDR apparatus obtains the OTDR waveform by separating and adding backscattered light information for each pulse from the received signal in which return light is received by the above calculation, and converting it into a loss distribution with respect to the distance of the FUT.

OTDR apparatus according to the present invention, the length range of the optical fiber to be measured are classified into N _length pieces, limit the setting value of the spatial resolution in the loss distribution measurement of the optical fiber to be measured in N _sr number, N _The memory device is further provided with a storage element that holds in advance (N _length × N _sr ) Moore-Penrose inverse matrix x _{probe, tpl} ⁺ corresponding to the number of combinations of _length and N _sr ,
The signal processing means takes out the Moore-Penrose inverse matrix x _{probe, tpl} ⁺ corresponding to the desired range of the length of the measured optical fiber and the desired setting value of the spatial resolution from the storage element, and performs the calculation. Is preferred.

  The longer the FUT and the smaller the test light pulse width, the larger the size of the Toeplitz matrix and the Moore-Penrose inverse matrix, leading to an increase in computational load in the signal processing unit. For this reason, the FUT length range and the spatial resolution of the OTDR waveform are limited to a plurality of types, and the Toeplitz matrix and Moore-Penrose inverse matrix are calculated in advance according to each combination, and the result can be read at high speed in the signal processing unit The calculation can be shortened by storing it in an appropriate memory.

  The signal processing means of the OTDR apparatus according to the present invention may perform Fourier transform on the IQ modulated signal sequence and the received signal, and perform the calculation in a frequency domain.

In this case, the following calculation is performed.
The operation performed by the signal processing means is
The IQ modulation signal sequence is vector x _probe = [x _probe (1), x _probe (2), ..., x _probe (N _probe )], and the received signal is vector x _obs = [x _obs (1) , X _obs (2), ..., x _obs (N _obs )],
Vector _{x probe} element number and vector _x the vector number of elements obtained by adding a zero elements in the vector _{x probe} to match the _{obs x probe '= (x probe} (1), x probe (2), ···, Fourier transform x _probe (N _probe ), 0, 0, ..., 0) and vector X _probe = (X _probe (1), X _probe (2), ..., X _probe (N _obs )) Derive the
Fourier transform vector x _obs to derive vector X _obs = (X _obs (1), X _obs (2), ..., X _obs (N _obs )),
This is an operation of converting a column vector obtained by inverse Fourier transform of a vector H obtained by dividing each element of the vector X _obs by each element of the vector X _probe into distance dependency of the optical fiber to be measured.

  The present invention can provide an OTDR device that improves the dynamic range in one measurement trace and enables shortening of measurement time.

It is a block diagram showing composition of a 1st embodiment of an OTDR device concerning the present invention. The figure which compares the time change of the receiving power in the OTDR device concerning the present invention about three kinds of test lights (single pulse, BPSK signal, QPSK signal), four kinds of test light pulse widths (10000 ns, 1000 ns, 100 ns, 10 ns) It is. It is a figure which compares the test light pulse width dependence of the average received power in the OTDR apparatus based on this invention about three types of test lights (a single pulse, a BPSK signal, a QPSK signal). It is a figure which compares the OTDR waveform in case test light is a single pulse about four types of test light pulse widths (10000 ns, 1000 ns, 100 ns, 10 ns). It is a figure which compares the OTDR waveform in OTDR apparatus based on this invention in case test light is a BPSK signal about four types of test light pulse widths (10000 ns, 1000 ns, 100 ns, 10 ns). It is a figure which compares the OTDR waveform in OTDR apparatus based on this invention when test light is a QPSK signal about four types of test light pulse widths (10000 ns, 1000 ns, 100 ns, 10 ns). It is a figure which compares the test light pulse width dependence of the dynamic range in the OTDR apparatus based on this invention about three types of test lights (a single pulse, a BPSK signal, a QPSK signal).

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The present invention is not limited to the embodiments described below. These implementation examples are merely illustrative, and the present invention can be implemented in various modifications and improvements based on the knowledge of those skilled in the art.

(Embodiment 1)
FIG. 1 is a block diagram for explaining an OTDR device 301 according to this embodiment. The OTDR apparatus 301 is an OTDR apparatus that injects a test light pulse into the measured optical fiber 50, coherently receives the backscattered light generated in the measured optical fiber 50, and measures the loss distribution of the measured optical fiber 50. ,
An optical modulator 13 that performs IQ modulation for each of the test light pulses with the input IQ modulation signal sequence;
Signal processing means 18 for performing an operation for deriving a loss distribution with respect to the distance of the measured optical fiber 50 from the reception signal coherently received using the IQ modulation signal sequence;
And the like.

  The operation principle of the present OTDR apparatus 301 will be described below. The CW light output from the laser light source 11 is split into two by the optical coupler 12, and one of the outputs is used as local light of the coherent receiver 16 and the other is an optical modulator 13 that generates a test light pulse. Combined with The test light pulse is coupled to the measured optical fiber (FUT) 50 through the optical circulator 14. A portion of the test light pulse is back-reflected by Rayleigh scattering in the measured optical fiber 50, or Fresnel reflection at a connection point or a failure point. The reflected test light pulse is coupled to the coherent receiver 16 via the optical circulator 14 and the amplitude and phase of the received test light are measured.

  In the conventional OTDR apparatus, a single pulse (impulse) signal is used as an electric signal for driving the optical modulator, whereas the OTDR apparatus 301 is configured to output a QPSK signal or the like output from the IQ modulated signal sequence generating means 15. The optical modulator 13 is driven by the IQ modulated signal sequence, and as a result, the optical modulator 13 outputs an IQ modulated signal light. Here, it is assumed that the signal information (signal pattern) of the IQ modulation signal sequence is a fixed pattern, and the user of the OTDR apparatus 301 grasps the signal information. The IQ modulation signal train generation means 15 is constituted by an apparatus such as a pulse pattern generator or a function generator, or an apparatus limitedly realizing the function of these apparatuses in a form suitable for the present invention.

本実施形態では、試験光として、単一パルス、ＢＰＳＫ信号、ＱＰＳＫ信号の３通りを考える。それぞれを次式で表わす。

Here, the test light is considered as a pulse train, and is represented by a column vector x _probe consisting of N _probe elements as in the following equation.

In this embodiment, three types of test light, single pulse, BPSK signal, and QPSK signal are considered. Each is expressed by the following equation.

ここで、ｃは真空中の光速度、Ｔ_０は試験光のパルス幅、ｎ_ｇは被測定光ファイバの群屈折率である。 The spatial resolution ΔL _{sr of} OTDR is given by the following equation.

Here, c is the speed of light in vacuum, T ₀ is the pulse width of the test light, and n _g is the group refractive index of the optical fiber to be measured.

Ｎ_ｈは次式で与えられる。

ここで、Ｌ_ＦＵＴは被測定光ファイバの長さ、Ｌ_{ｅｘｔｒａ}はＬ_ＦＵＴを超えた領域での雑音のパワーを考慮するために付与される長さである。 The backscattered impulse response of the optical fiber to be measured is a column vector h consisting of N _h elements as in the following equation.

N _h is given by the following equation.

Here, L _FUT is the length of the optical fiber to be measured, and L _extra is the length given to take into account the power of noise in the region beyond L _FUT .

h is a vector representing time dependency, and it is the OTDR waveform that is converted to fiber length dependency. Also, h is a complex vector, and the absolute value of each element is determined by the loss of the optical fiber to be measured, the Rayleigh backscattering coefficient, and the spatial resolution ΔL _sr . In this calculation, it is assumed that the phase of each element of h is a random fixed value.

ｘ_ｒｅｃの要素数は次式で与えられる。

数８の畳込みは、ｘ_{ｐｒｏｂｅ}をテプリッツ行列化したｘ_{ｐｒｏｂｅ、ｔｐｌ}とベクトルｈの乗算で表すことができる。

ここで行列ｘ_{ｐｒｏｂｅ、ｔｐｌ}は次式で与えられる。

ｘ_{ｐｒｏｂｅ、ｔｐｌ}の行数はＮ_ｒｅｃ、列数はＮ_ｈである。 Assuming that the signal received by the coherent receiver 16 is x _rec , x _rec is expressed as a convolution of x _probe and h.

The number of elements of x _rec is given by the following equation.

The convolution of Eq. 8 can be expressed by multiplication of x _{probe, t pl} and vector h _, which is x- _probe in the Toeplitz matrix.

Here, the matrix x _{probe and tpl} are given by the following equations.

The number of rows in x _{probe and tpl} is N _rec , and the number of columns is N _h .

コヒーレント受信器で観測される信号ｘ_ｏｂｓはｘ_ｒｅｃとｘ_ＷＧＮの和であることから、次式が得られる。

ｘ_{ｐｒｏｂｅ、ｔｐｌ}は縦長の行列であるから（Ｎ_ｒｅｃ＞Ｎ_ｈ）、ｘ_{ｐｒｏｂｅ、ｔｐｌ}のムーアペンローズ逆行列を数１３の両辺の左側から乗算することによって次式が得られる。

ここで、ｘ_{ｐｒｏｂｅ、ｔｐｌ} ^＋はｘ_{ｐｒｏｂｅ、ｔｐｌ}のムーアペンローズ逆行列であり、次の関係式が用いられた。

但し、Ｉ_Ｎｈは行数、列数がともにＮ_ｈである単位行列である。 The noise imparted by the coherent receiver is shot noise represented as white Gaussian noise. This shot noise is considered as a vector x _WGN of the element number N _rec as expressed by the following equation.

Since the signal x _obs observed by the coherent receiver is the sum of x _rec and x _WGN , the following equation is obtained.

Since x _{probe and tpl} are vertically elongated matrices (N _rec > N _h ), the following equation is obtained by multiplying the Moore-Penrose inverse matrix of x _{probe and tpl} from the left side of both sides of Eq.

Here, x _{probe and tpl} ⁺ are the Moore-Penrose inverse matrix of x _{probe and tpl} , and the following relation is used.

However, I _Nh is an identity matrix in which the number of rows and the number of columns are both N _h .

受信器で付与される雑音によって、ｈとｈ_ｅｔｍとの間の差が生じる。 Since information of noise x _WGN can not be obtained in actual measurement, it is necessary to estimate h only from x _obs by calculation using the following equation in the signal processing means. The estimated h is described as _hetm .

The noise imparted at the receiver causes a difference between h and _hetm .

数１７より、試験光パルス幅Ｔ_０とレーザ光源の線幅Δνの積が小さいほどＯＴＤＲのダイナミックレンジの拡大量が大きいことが分かる。 The power of the backscattered light incident on the coherent receiver increases as the number of elements N _probe of the test light vector increases, and the signal-to-noise ratio in the coherent receiver is improved. As a result, one measurement of the OTDR device Dynamic range in the trace is improved. However, the maximum value of the number of elements N _probe of the test light vector is limited by the phase noise (ie, line width Δν) of the laser light source. That is, when the phase of the laser light source changes during generation of the test light pulse train, h can not be estimated correctly. Here, it is assumed that the phase of the output light is constant during the coherence time τ _c of the laser light source. In this case, the maximum value of N _probe is given by the following equation.

From Equation 17, it is understood that the smaller the product of the test light pulse width T ₀ and the line width ΔΔ of the laser light source, the larger the amount of expansion of the OTDR dynamic range.

The longer the optical fiber to be measured and the smaller the test light pulse width, the larger the size of the matrix given by Equation 11, which leads to an increase in computational load in the signal processing unit. However, the length range of the optical fiber to be measured is classified and set to N _length , and the spatial resolution of the OTDR waveform is limited to N _sr types, and N _length × N _sr x _probes according to each combination. _{, Tpl} are calculated in advance, and the result is stored in a high-speed readable memory in the signal processing unit, whereby the calculation of _Equation 16 can be realized in a short time.

Subsequently, simulation results of the OTDR apparatus based on the operation principle described above will be shown. The line width of the laser light source was Δν = 1 kHz. This corresponds to a coherence time τ _c = 797.9 μs. The pulse widths of the single pulse, BPSK signal, and QPSK signal were set to any of T ₀ = 10,000, 1000, 100, and 10 ns. These pulse widths correspond to the upper limit N _probe = 80, 798, 7979, 79789 of the number of elements in the modulation signal, respectively. The signal patterns of the BPSK signal and the QPSK signal are random fixed values. The peak power of the test light incident on the measured optical fiber was 10 mW. The measured optical fiber had a length L _FUT = 100 km, a loss α = 0.2 dB / km, a group refractive index _ng = 1.46, and a Rayleigh backscattering coefficient Rrbs = 4.7E-8 m ⁻¹ . Further, the power ratio of Fresnel reflection at the end of the optical fiber to be measured was set to -14 dB.

FIG. 2 is a diagram showing a comparison of received power in a single trace when the test light is a single pulse, a BPSK signal, and a QPSK signal. 2 (a) is for T ₀ = 10,000 ns, FIG. 2 (b) is for T ₀ = 1000 ns, FIG. 2 (c) is for T ₀ = 100 ns, and FIG. 2 (d) is for T ₀ = 10 ns. That's the case. 2, the horizontal axis represents the time normalized by T _rt established if the T _rt and round-trip time of a single pulse test light in the optical fiber to be measured. In the case of single pulse test light, it is shown that the received power decreases with time, and the SNR decreases as the pulse width decreases. When a BPSK or QPSK signal sequence is input to the optical fiber to be measured, the received power fluctuates with time depending on the signal pattern, but many test light pulses are sequentially input to the optical fiber to be measured. Is much larger than in the case of single pulse test light.

  FIG. 3 is a diagram showing the relationship between the average received power (time average of received power) and the test light pulse width. It can be seen that the average received power of single pulse test light decreases as the test light pulse width is shortened. On the other hand, the average received power of the BPSK signal and the QPSK signal is substantially constant regardless of the pulse width, and the QPSK signal has an average received power larger by about 3 dB than the BPSK signal. FIG. 3 also shows the test light pulse width dependency of the shot noise power at the receiver. Since the bandwidth of the coherent receiver is proportional to the reciprocal of the test light pulse width, the shot noise power increases when the test light pulse width is shortened. This leads to the degradation of the dynamic range as the test light pulse width is reduced.

FIGS. 4, 5 and 6 are plots of OTDR waveforms calculated using Equation 16 for the case where the test light is a single pulse, a BPSK signal, and a QPSK signal, respectively. In each figure, (a) is for T ₀ = 10,000 ns, (b) for T ₀ = 1000 ns, (c) for T ₀ = 100 ns, and (d) for T ₀ = 10 ns. In any test light, it is understood that the SNR at the far end of the optical fiber to be measured decreases as the pulse width decreases. The deterioration of the SNR is significant when the test light is a single pulse, and when the test light pulse width is 10 ns, almost the entire OTDR waveform is buried in noise. On the other hand, in BPSK and QPSK signals, an OTDR waveform with a higher SNR as a whole than in the case of a single pulse is obtained. Even when the pulse width is as small as 10 ns, the position of the far end point of the measured optical fiber can be clearly identified.

FIG. 7 is a diagram showing the relationship between the dynamic range and the test light pulse width. As the pulse width of the test light is shortened, the dynamic range of the OTDR decreases, but the reduction rate is smaller for BPSK and QPSK signals than for single pulse test light. Therefore, as the pulse width of the test light is shortened, the BPSK and QPSK signals can realize a larger dynamic range. Also, the QPSK signal achieves a dynamic range 1.6 to 1.8 dB higher than that of the BPSK signal. It can be seen that by using a QPSK signal instead of a single pulse at T ₀ = 10 ns, an improvement of the dynamic range of over 20 dB is realized.

Second Embodiment
In the first embodiment, the signal processing unit 18 performs the calculation in the time domain. In the present embodiment, the signal processing unit 18 performs the calculation in the frequency domain. By performing the operation in the frequency domain, it is possible to complete the operation at any measured optical fiber length and at any spatial resolution (i.e., test light pulse width) in a short time. Below, the procedure for deriving the OTDR waveform by calculation in this frequency domain is shown.

数１８をフーリエ変換することで試験光ベクトルを周波数領域での表現に変換する。

First, x of which the number of appropriate elements is added after the vector x _probe so that the number of elements N _{probe of the} IQ modulated signal sequence x _probe matches the number of elements N _obs of the signal light x _obs observed at the receiver Think of ' _probe '.

The test light vector is converted to a frequency domain representation by Fourier transforming Eq.

ベクトルＸ_ｏｂｓの各々の要素をベクトルＸ_{ｐｒｏｂｅ}の各々の要素で除算することにより、要素数Ｎ_ｏｂｓのベクトルＨが得られる。

このＨの逆フーリエ変換を計算することによってＯＴＤＲ波形ｈが得られる。

The Fourier transform is also performed on the signal x _obs observed by the coherent receiver 16.

By dividing each element of the vector X _obs by each element of the vector X _probe , a vector H of the element number N _obs is obtained.

The OTDR waveform h is obtained by calculating the inverse Fourier transform of H.

In this embodiment, calculation of Fourier transform or inverse Fourier transform is necessary, but compared with the derivation of the Moore-Penrose inverse matrix in Eq. 14 of the embodiment 1, particularly when N _obs is large, the amount of calculation is small. It's over.

  The present invention realizes loss distribution measurement of an optical fiber, which is a transmission medium in an optical communication system, in a short time with high accuracy, and maintains the reliability of the existing optical communication system and a new optical communication system. It can be used for the purpose of construction.

11: light source 12: optical coupler 13: optical modulator 14: optical circulator 15: IQ modulation signal sequence generation means 16: coherent receiver 17: A / D converter 18: signal processing means 19: storage element 50: light to be measured Fiber 301: OTDR device

Claims (5)

This is an OTDR (Optical Time Domain Reflectometer) apparatus that injects a test light pulse into a measured optical fiber, coherently receives the backscattered light generated in the measured optical fiber, and measures the loss distribution of the measured optical fiber. ,
An optical modulator that performs IQ modulation for each of the test light pulses with the input IQ modulation signal sequence;
Signal processing means for performing an operation for deriving a loss distribution with respect to the distance of the optical fiber to be measured from a reception signal coherently received using the IQ modulation signal sequence;
An OTDR apparatus comprising: The operation performed by the signal processing means is
The IQ modulation signal sequence is vector x _probe = [x _probe (1), x _probe (2), ..., x _probe (N _probe )], and the received signal is vector x _obs = [x _obs (1) , X _obs (2), ..., x _obs (N _obs )],
_{Deriving the} Toeplitz matrix x _{probe, tpl} based on the signal column vector x _probe and the Moore-Penrose inverse matrix x _{probe, tpl} ^{+ of} the Toeplitz matrix x _{probe, tpl} ,
The method according to claim 1, characterized in that the column vector obtained by multiplying the Moore-Penrose inverse matrix x _{probe, tpl} ⁺ and the received signal vector x _obs is converted into the distance dependency of the optical fiber to be measured. OTDR device as described. Classifying length range of the optical fiber to be measured in _{N length} pieces, the set value of the spatial resolution in the loss distribution measurements of said measured optical fiber is limited to _{N sr number,} the number of combinations of _{N length} and _{N sr} The memory device further includes a storage element that holds in advance the corresponding (N _length × N _sr ) Moore penrose inverse matrix x _{probe, tpl} ⁺ ,
The signal processing means takes out the Moore-Penrose inverse matrix x _{probe, tpl} ⁺ corresponding to the desired range of the length of the measured optical fiber and the desired setting value of the spatial resolution from the storage element, and performs the calculation. The OTDR device according to claim 2, characterized in that:   The OTDR apparatus according to claim 1, wherein the signal processing means performs Fourier transform on the IQ modulated signal sequence and the received signal, and performs the calculation in a frequency domain. The operation performed by the signal processing means is
The IQ modulation signal sequence is vector x _probe = [x _probe (1), x _probe (2), ..., x _probe (N _probe )], and the received signal is vector x _obs = [x _obs (1) , X _obs (2), ..., x _obs (N _obs )],
Vector _{x probe} element number and vector _x the vector number of elements obtained by adding a zero elements in the vector _{x probe} to match the _{obs x probe '= (x probe} (1), x probe (2), ···, Fourier transform x _probe (N _probe ), 0, 0, ..., 0) and vector X _probe = (X _probe (1), X _probe (2), ..., X _probe (N _obs )) Derive the
Fourier transform vector x _obs to derive vector X _obs = (X _obs (1), X _obs (2), ..., X _obs (N _obs )),
It is characterized in that it is an operation to convert a column vector obtained by inverse Fourier transform of a vector H obtained by dividing each element of the vector X _obs by each element of the vector X _probe into distance dependency of the optical fiber to be measured. The OTDR apparatus according to claim 4, wherein

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