Loss analysis device and loss analysis method

Abstract

To provide a loss analysis device and loss analysis method to detect an event with good producibility when an SN ratio is small or an event interval is short.SOLUTION: A loss analysis device includes: an OTDR waveform acquisition part that acquires OTDR waveform of a measured optical fiber; and a calculation part that nonlinearly fits an event model function to the OTDR waveform using a location of a start point of each event in the OTDR waveform, a level of the start point of each event, a loss of each event, and a reflection loss of each event as parameters, and calculates the location, the level, the loss and the reflection loss of each event.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a loss analysis device and a loss analysis method using an event model function. [Background technology]

[0002] There is a known method for detecting an event that occurs in an optical fiber under test based on a measured OTDR (Optical Time Domain Reflectometer) waveform (see, for example, Patent Document 1). In a device according to the related art, the OTDR waveform of the optical fiber under test is measured, a change point in the measured OTDR waveform is extracted, and an ideal waveform is generated in the case where an event occurs at the change point. After that, the difference between the measured OTDR waveform and the ideal waveform is extracted, and if there is a difference, it is determined that there is an undetected event at the position where the difference is present, and all events included in the OTDR waveform are detected.

[0003] Specifically, in the device according to the related art, in order to calculate the position of an event, a change point in the slope of the OTDR waveform is detected, and in the device according to the related art, in order to calculate the loss of the event, a least-squares approximation line is used for the OTDR waveform. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2012-167935 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the related technology has a problem that the reproducibility of the starting point position of an event is low when the signal-to-noise ratio is poor, and the related technology has a problem that the reproducibility of the loss value of an event is low when the events are adjacent to each other.

[0006] In order to solve the above-mentioned problems, an object of the present disclosure is to provide a loss analysis device and a loss analysis method that detect events with good reproducibility when the SNR is small or the event interval is short. [Means for solving the problem]

[0007] In order to achieve the above object, the loss analysis device disclosed herein performs nonlinear fitting of an event model function to an OTDR waveform.

[0008] Specifically, the loss analysis device according to the present disclosure includes: an OTDR waveform acquisition unit for acquiring an OTDR waveform of an optical fiber under test; a calculation unit that performs nonlinear fitting of an event model function, which has parameters including a position of a start point of each event included in the OTDR waveform, a level of the start point of each event, a loss of each event, and a return loss of each event, to the OTDR waveform, and calculates the position, the level, the loss, and the return loss; Equipped with.

[0009] Specifically, the loss analysis method according to the present disclosure includes: An OTDR waveform acquisition step of acquiring an OTDR waveform of an optical fiber to be measured; and a calculation step of nonlinearly fitting an event model function, the parameters of which are the position of a start point of each event included in the OTDR waveform, the level of the start point of each event, the loss of each event, and the return loss of each event, to the OTDR waveform, and calculating the position, the level, the loss, and the return loss.

[0010] The above-mentioned inventions can be combined as much as possible. Effect of the Invention

[0011] According to the present disclosure, it is possible to provide a loss analysis device and a loss analysis method that detect events with good reproducibility when the SN ratio is small or the event interval is short. [Brief description of the drawings]

[0012] [Figure 1] 1 shows an example of a schematic configuration of a loss analysis device according to a first embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, the embodiments of the present disclosure will be described in detail with reference to the drawings. Note that the present disclosure is not limited to the embodiments shown below. These implementation examples are merely illustrative, and the present disclosure can be implemented in various forms with various modifications and improvements based on the knowledge of those skilled in the art. Note that components with the same reference numerals in this specification and drawings are assumed to indicate the same components.

[0014] (Embodiment 1) An example of a schematic configuration of the loss analysis device according to the present embodiment is shown in Fig. 1. The loss analysis device according to the present embodiment includes an OTDR waveform acquisition unit 11 that acquires an OTDR waveform of a measured optical fiber 20, and a calculation unit 12 that performs nonlinear fitting of an event model function, which has parameters of the position of the start point of each event included in the OTDR waveform, the level of the start point of each event, the loss of each event, and the return loss of each event, to the OTDR waveform, and calculates the position of the start point of each event, the level of the start point of each event, the loss of each event, and the return loss of each event. Hereinafter, the "loss" of an event will be described as a "loss value." The parameters of an event refer to the position [km] of the start point of the event, the level [dB] of the start point of the event, the loss value [dB] of the event, and the return loss [dB] of the event.

[0015] (OTDR waveform acquisition step) The OTDR waveform acquisition unit 11 acquires an OTDR waveform from the measured optical fiber 20. For example, the OTDR waveform acquisition unit 11 inputs an optical pulse into one end of the measured optical fiber 20, and acquires, as an OTDR waveform, the time distribution of the intensity of the backscattered light output from the one end of the measured optical fiber 20 into which the optical pulse is input. Hereinafter, the "distance from the one end of the measured optical fiber 20 into which the optical pulse is input" will be referred to as "distance".

[0016] (Calculation step) The calculation unit 12 performs nonlinear fitting of an event model function to the OTDR waveform acquired by the OTDR waveform acquisition unit 11, and calculates the position of the start point of the event, the level of the start point of the event, the loss value of the event, and the return loss of the event.

[0017] Specifically, the calculation unit 12 calculates the event model function y fit Equation (1) may be used as follows.

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[0018] Backscatter function y bs may be defined as equation (2).

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[0019] Loss function y loss may be defined as equation (4).

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[0020] Reflection function y refl may be defined by equations (7) and (8).

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[0021] The calculation unit 12 calculates an event model function y fit The nonlinear fitting according to this embodiment is a nonlinear fitting of the event model function y fit is a nonlinear function, and the OTDR waveform and the event model function y fit For example, the calculation unit 12 performs nonlinear fitting using the Trust Region Method, which is a nonlinear least squares approximation algorithm. The calculation unit 12 calculates the optimal event start point position s by this nonlinear fitting. x , the level s of the event start point y , loss value l, and return loss r are calculated.

[0022] Note that the position s of the start point of the event xThe initial value of may be the event candidate point detected from the OTDR waveform minus the number of pulse width points if the event is a non-reflective event, and may be the minimum level within the range from the start point of the event candidate detected from the OTDR waveform to the maximum level if the event is a reflective event. Here, the event candidate point may be the peak point of the absolute value of the slope detected by using a differentiation method on the OTDR waveform, or may be the peak point of the absolute value of the wavelet coefficient detected by using a wavelet transform on the OTDR waveform. In addition, the level s of the event start point y The initial value of is the position s of the event start point. x The initial value of the loss value l is the position s of the start point of the event. x The initial value of the return loss r may be the ratio of the level at the start point s of the event to the level at the end point of the event, converted into dB. x Alternatively, the difference between the first level and the maximum level may be converted into a return loss.

[0023] The fitting range may be set to a range from the start point of the event candidate to be fitted to the end point of the event candidate, which is expanded by twice the pulse width.

[0024] The loss analysis device according to this embodiment detects the start point of an event at the position s x In order to set the initial value and fitting range of , the event detection unit may be provided with an event detection unit that detects event candidates from the OTDR waveform. For example, the event detection unit may detect event candidates by using a differentiation method on the OTDR waveform acquired by the OTDR waveform acquisition unit 11 before the calculation unit 12 performs nonlinear fitting. Also, the event detection unit may detect event candidate points by using a wavelet transform on the OTDR waveform acquired by the OTDR waveform acquisition unit 11 before the calculation unit 12 performs nonlinear fitting.

[0025] When the OTDR waveform includes a plurality of events, the calculation unit 12 uses the formula (9) instead of the formula (1) as the event model function.

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[0026] When the OTDR waveform contains two events, the calculation section 12 may simultaneously optimize the parameters of the two events.

[0027] Furthermore, when the OTDR waveform includes three or more events, the calculation unit 12 optimizes the parameters for each event. The calculation unit 12 may perform nonlinear fitting on events for which nonlinear fitting has not been completed in order from the event with the largest initial loss value.

[0028] For example, let us consider a case where an OTDR waveform contains events 1 to 3. If the initial loss values ​​for each event are largest for event 1, followed by event 2 and then event 3, then the initial loss value for event 1 is the largest among the events for which nonlinear fitting has not been completed. Therefore, nonlinear fitting is performed for event 1 while fixing the parameters for event 2 and event 3 at their initial values. As a result, the position s of the start point for event 1 is x,1 , the starting level s y,1 , loss value l1, and return loss r1 are calculated. Next, the initial value of the loss value of event 2 is the largest among the events for which nonlinear fitting has not been completed. The parameters of event 3 are fixed at their initial values, and the parameters of event 1 are fixed at the calculated values, and nonlinear fitting is performed for event 2. As a result, the position s of the start point for event 2 is calculated.x,2 , the starting level s y,2 , loss value l2, and return loss r2 are calculated. Finally, while fixing the parameters of event 1 and event 2 at the calculated values, nonlinear fitting is performed on event 3, for which nonlinear fitting has not been completed. As a result, the position s x,3 , the starting level s y,3 , loss value l3, and return loss r3 are calculated.

[0029] As described above, the loss analysis apparatus and loss analysis method according to the present disclosure can detect events with good reproducibility when the SNR is small or the event interval is short by nonlinearly fitting an event model function to an OTDR waveform. [Industrial Applicability]

[0030] The loss analysis device and loss analysis method according to the present disclosure can be applied to the optical measuring instrument industry. [Explanation of symbols]

[0031] 10:Loss analysis device 11:OTDR waveform acquisition section 12: Calculation section 20: Optical fiber under test

Claims

1. An OTDR waveform acquisition unit for acquiring an OTDR waveform of an optical fiber to be measured; a calculation unit that uses a position of a start point of each event included in the OTDR waveform, a level of the start point of each event, a loss of each event, and a return loss of each event as parameters, performs nonlinear fitting of an event model function including a backscatter function, a loss function, and a reflection function to the OTDR waveform, and calculates the position, the level, the loss, and the return loss; A loss analysis device comprising: The loss analysis device, wherein the event model function is expressed by equation (1). [0010] where x is the distance and y ｂｓ is the backscatter function, y ｌｏｓｓ is the loss function, y ｒｅｆｌ is the reflection function, s ｘ is the location of the start point of the event [km], s ｙ is the level [dB] of the start point of the event, l is the loss value [dB], and r is the return loss [dB].

2. An OTDR waveform acquisition unit for acquiring an OTDR waveform of an optical fiber to be measured; a calculation unit that uses a position of a start point of each event included in the OTDR waveform, a level of the start point of each event, a loss of each event, and a return loss of each event as parameters, performs nonlinear fitting of an event model function including a backscatter function, a loss function, and a reflection function to the OTDR waveform, and calculates the position, the level, the loss, and the return loss; A loss analysis device comprising: The loss analysis device, wherein the event model function is expressed by equation (9). [0097] Here, n is an event number assigned in order from the event on the input end side of the optical fiber under test, Π is a product, Σ is a product sum, x is a distance, and y is a ｂｓ is the backscatter function, y ｌｏｓｓ is the loss function, y ｒｅｆｌ is the reflection function, s ｘ，ｎ is the location of the start point of the event [km], s ｙ，ｎ is the level [dB] of the start point of each of the events, ｎ is the loss value [dB] of each of the events, r ｎ is the return loss [dB] of each of the events.

3. 3. The loss analysis device according to claim 1, wherein the backscatter function is expressed by equation (2), the loss function is expressed by equation (4), and the reflection function is expressed by equation (7). [0025] Here, α ｄＢ is the backscatter slope [dB / km], and s' ｙ is ｙ and is calculated from equation (3). [0030] [0045] Here, l' is calculated from the loss value l and equation (5), and y' ｌｏｓｓ is calculated from equation (6). [0050] [006] Here, τ is a time constant [km], and w is a pulse width [km]. [0070] Here, r' is calculated using the following formula. [0080] Here, T ｒ is the pulse rise distance [km], and b is the backscatter coefficient [dB]. The loss value l n of each event is calculated using the following formula. [0089] ##EQU00011##

4. 3. The loss analysis device according to claim 1, further comprising an event detection unit that detects event candidates from the OTDR waveform.

5. an initial value of the position of the start point of the event is set to a point obtained by subtracting the pulse width of the optical pulse incident on the measured optical fiber from the peak point of the event candidate detected from the OTDR waveform when the event is a non-reflective event, and set to a minimum level within a range from the start point of the event candidate detected from the OTDR waveform to a maximum level when the event is a reflective event; The initial value of the level of the start point of the event is set to the level [dB] of the OTDR waveform at the position of the start point of the event; The initial value of the loss value is a value obtained by converting a level at the start point of the event to a level at the end point of the event into dB; and The initial value of the return loss is set to a value obtained by converting the difference between the level at the start point of the event and the maximum level into a return loss.

5. The loss analysis device according to claim 4,

6. 5. The loss analysis device according to claim 4, wherein the range of the nonlinear fitting is a range from the start point of the event candidate to the end point of the event candidate expanded by twice the pulse width of the optical pulse input to the measured optical fiber.

7. 3. The loss analysis device according to claim 1, wherein when the OTDR waveform includes three or more of the events, the calculation unit performs the nonlinear fitting in order from the event having the largest initial value of the loss value among the events for which the nonlinear fitting has not been completed.

8. an OTDR waveform acquisition step of acquiring an OTDR waveform of the optical fiber under test; a calculation step of nonlinearly fitting an event model function including a backscatter function, a loss function, and a reflection function to the OTDR waveform using the position of a start point of each event included in the OTDR waveform, the level of the start point of each event, the loss of each event, and the return loss of each event as parameters, and calculating the position, the level, the loss, and the return loss; A loss analysis method comprising: The loss analysis method, wherein the event model function is expressed by equation (1). [0010] Here, x is the distance, y bs is the backscatter function, y loss is the loss function, y refl is the reflection function, s x is the position [km] of the start point of the event, s y is the level [dB] of the start point of the event, l is the loss value [dB], and r is the return loss [dB].

9. an OTDR waveform acquisition step of acquiring an OTDR waveform of the optical fiber under test; a calculation step of nonlinearly fitting an event model function including a backscatter function, a loss function, and a reflection function to the OTDR waveform using the position of a start point of each event included in the OTDR waveform, the level of the start point of each event, the loss of each event, and the return loss of each event as parameters, and calculating the position, the level, the loss, and the return loss; A loss analysis method comprising: The loss analysis method, wherein the event model function is expressed by equation (9). [0097] Here, n is the event number assigned in order from the event on the incident end side of the measured optical fiber, Π is the multiplication, Σ is the product, x is the distance, y bs is the backscatter function, y loss is the loss function, y refl is the reflection function, s x,n is the position [km] of the start point of the event, s y,n is the level [dB] of the start point of each of the events, l n is the loss value [dB] of each of the events, and r n is the return loss [dB] of each of the events.

10. 10. The loss analysis method according to claim 8, further comprising an event detection step of detecting an event candidate from the OTDR waveform, and setting an initial value of a position of a start point of the event and a range of the nonlinear fitting from the event candidate.

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