KR102832600B1 - Active wavelength filter, distributed acoustic sensing apparatus using the same, and control method thereof - Google Patents

Abstract

According to one embodiment of the present disclosure, an active wavelength filter is provided, which includes a polarizing unit which receives unpolarized light from an optical input/output unit, separates it into two polarizations which are orthogonal to each other, and converts one of the two polarizations into the other polarization and outputs it, a wavelength separating unit which separates the light output from the polarizing unit according to wavelength and outputs it, and a wavelength selecting unit which selectively reflects one or more wavelengths from the light separated by wavelength by the wavelength separating unit, and the light selectively reflected by the wavelength selecting unit passes through the wavelength separating unit and the polarizing unit and is output to the optical input/output unit, and a distributed acoustic sensing device including the active wavelength filter and a control method thereof are provided, and even if the wavelength of the sensing light changes due to a cause such as deterioration of an element, distributed acoustic sensing can be performed normally by adjusting the passband of the active wavelength filter.

Description

{Active wavelength filter, distributed acoustic sensing apparatus using the same, and control method thereof}

The present disclosure relates to an active wavelength filter, a distributed acoustic sensing device using the same, and a control method thereof.

Distributed acoustic sensing technology is being used as a method for monitoring the conditions of pipelines such as gas and water pipes, roads, railways, and facilities. Distributed acoustic sensing technology monitors the conditions of facilities by irradiating laser light onto an optical fiber and measuring the backscattered light reflected at the point where force or sound is applied to the optical fiber. Distributed acoustic sensing technology is mainly used when the length of the facility to be monitored is long, such as several kilometers. Therefore, the intensity of the laser light input to the optical fiber must be strong. When the laser light is amplified, noise is also amplified for various reasons, and the noise lowers the signal-to-noise ratio, thereby lowering the sensing sensitivity. In addition, if the components that make up the distributed acoustic sensing device become old, the desired performance may not be exhibited.

KR 10-2330484 B1

A first aspect of the present disclosure is to provide an active wavelength filter capable of changing the center wavelength and bandwidth of a passband.

A second aspect of the present disclosure is to provide a distributed acoustic sensing device capable of matching the center wavelength of a passband of an active wavelength filter to the center wavelength of a laser light source.

According to a third aspect of the present disclosure, a method for controlling a distributed acoustic sensing device that automatically adjusts the center wavelength of a passband of an active wavelength filter according to a change in the center wavelength of a laser light source is provided.

An active wavelength filter according to a first aspect of the present disclosure may include a polarizing unit which receives unpolarized light from an optical input/output unit, separates it into two polarizations that are orthogonal to each other, and converts one of the two polarizations into the other polarization and outputs it, a wavelength separating unit which separates the light output from the polarizing unit according to wavelength and outputs the separated light, and a wavelength selecting unit which selectively reflects one or more wavelengths from the light separated by wavelength by the wavelength separating unit, and the light selectively reflected by the wavelength selecting unit may pass through the wavelength separating unit and the polarizing unit and be output to the optical input/output unit.

According to one embodiment, the polarizing unit may include a collimating lens that aligns light incident from the optical input/output unit into parallel beams, a beam displacer that separates light passing through the collimating lens into two polarizations that are perpendicular to each other, and a half-wave delay unit that delays one of the two polarizations output by the beam displacer to match the other polarization.

According to one embodiment, the wavelength separation unit may include a grating that reflects incident light in different directions according to the wavelength.

According to one embodiment, the wavelength selection unit may include an LC array whose arrangement is changed according to a control signal for each pixel to which light separated according to wavelength from the wavelength separation unit arrives to pass or block the light, and a mirror that reflects the light passed by the LC array.

A distributed acoustic sensing device including an active wavelength filter according to a second aspect of the present disclosure comprises: a light source generating laser light, a first optical coupler dividing light output from the light source into sensing light and reference light, an optical pulse modulator modulating the sensing light divided by the first optical coupler to output pulse light, an optical amplifier amplifying the pulse light, an active wavelength filter filtering the pulse light amplified by the optical amplifier to pass light in a pass band and capable of controlling the center wavelength or width of the pass band, an optical rotator outputting light input from the active wavelength filter connected to a first end to a second end and outputting backscattered light input from an optical fiber connected to the second end to a third end, a second optical coupler combining and outputting backscattered light received from a third end of the optical rotator and reference light received from the first optical coupler, an optical detector converting light received from the second optical coupler into an electrical signal and outputting it, It may include a signal processing unit that analyzes an electric signal received from a photodetector to detect vibration applied to an optical fiber and adjusts the center wavelength or width of the passband of the active wavelength filter.

According to one embodiment, the signal processing unit may analyze an electric signal received from the photodetector and, if the intensity of the backscattered light is less than a reference value, adjust the center wavelength of the passband of the active wavelength filter or adjust the width of the passband.

According to one embodiment, the signal processing unit may measure the intensity of the backscattered light while sequentially changing the center wavelength of the passband of the active wavelength filter, and control the active wavelength filter so that the center wavelength at which the size of the backscattered light is the largest becomes the center wavelength of the active wavelength filter.

According to one embodiment, the signal processing unit may measure the intensity of the backscattered light while changing the width of the pass band for each center wavelength of the pass band of the active wavelength filter, and control the active wavelength filter so that the width of the pass band in which the magnitude of the backscattered light is greater than a reference value becomes the width of the pass band of the active wavelength filter.

According to an embodiment of the third aspect of the present disclosure, a control method for a distributed acoustic sensing device including an active wavelength filter may include a first step in which an optical pulse modulator modulates light output by a light source into a pulse form and an optical amplifier amplifies the light to generate pulsed light, a second step in which an active wavelength filter filters the pulsed light, a third step in which pulsed light passing through the active wavelength filter is input to an optical fiber, backscattered light generated at an arbitrary point of the optical fiber is input to a photodetector and converted into an electric signal, and a signal processing unit analyzes the electric signal to detect a vibration applied to the optical fiber, and a fourth step in which the signal processing unit controls the active wavelength filter so that a center wavelength or width of a passband is changed.

A fourth step according to one embodiment may include a step 4-1 in which the signal processing unit analyzes an electric signal received from the photodetector and compares the intensity of the backscattered light with a reference value, and a step 4-2 in which, if the intensity of the backscattered light is smaller than the reference value, the signal processing unit adjusts the center wavelength or width of the passband of the active wavelength filter to adjust the intensity of the backscattered light to be larger than the reference value.

A step 4-2 according to an embodiment of the present invention may include a step of measuring the intensity of the backscattered light while the signal processing unit changes the center wavelength of the passband of the active wavelength filter, a step of determining whether the center wavelength with the greatest intensity of the backscattered light matches the existing center wavelength and a step of determining whether the greatest intensity of the backscattered light is greater than the reference value, thereby determining to perform one of the center wavelength adjustment step, the width adjustment step, and the center wavelength and the width adjustment step, and a step of performing one of the center wavelength adjustment step, the width adjustment step, and the center wavelength and the width adjustment step.

The central wavelength control step according to one embodiment may be to control the active wavelength filter so that the central wavelength at which the intensity of the backscattered light is the greatest becomes the central wavelength of the active wavelength filter.

The width control step according to one embodiment may be to control the active wavelength filter so that the width of the pass band becomes the width of the pass band of the active wavelength filter when the intensity of the backscattered light becomes higher than a reference value by allowing more wavelengths adjacent to the center wavelength of the active wavelength filter to pass through.

The above-described central wavelength and width control step according to one embodiment may be to determine the central wavelength at which the size of the backscattered light is the largest as the central wavelength of the active wavelength filter, and additionally control the passage of pixels corresponding to wavelengths adjacent to the central wavelength of the active wavelength filter, thereby controlling the active wavelength filter so that the width of the passband when the intensity of the backscattered light becomes a reference value or more becomes the width of the passband of the active wavelength filter.

The features and advantages of the present disclosure will become more apparent from the following detailed description based on the accompanying drawings.

Prior to this, the terms or words used in this specification and claims should not be interpreted in their usual or dictionary meanings, but should be interpreted in their meanings and concepts that are consistent with the technical idea of the present invention, based on the principle that the inventor can appropriately define the concept of the term in order to explain his or her own invention in the best way.

According to the first aspect of the present disclosure, an active wavelength filter can change the center wavelength and bandwidth of a passband.

According to the second aspect of the present disclosure, by controlling the center wavelength of the passband using an active wavelength filter, the sensing sensitivity can be maintained even when the center wavelength of the laser light source of the distributed acoustic sensing device changes.

According to a third aspect of the present disclosure, the center wavelength of the passband of an active wavelength filter can be automatically adjusted according to a change in the center wavelength of a laser light source of a distributed acoustic sensing device.

FIG. 1 is a drawing showing a distributed acoustic sensing device using an active wavelength filter according to one embodiment.
FIG. 2 is a drawing showing an active wavelength filter according to an embodiment.
Figure 3 is a graph showing the wavelength change due to a light source or filter.
Figure 4 is a graph showing the passband according to the type of filter.
Figure 5 is a graph comparing the output of a distributed photoacoustic sensing device according to the type of filter.
Figure 6 is a graph showing a change in the center wavelength of the passband of an active wavelength filter according to one implementation example.
Figure 7 is a graph showing a change in the width of the passband of an active wavelength filter according to one implementation example.
FIG. 8 is a flowchart showing steps of a control method for a distributed acoustic sensing device including an active wavelength filter according to one embodiment.
Figure 9 is a flowchart showing steps for controlling an active wavelength filter according to one embodiment.
Figure 10 is a flowchart showing a step of controlling the size of backscattered light to be greater than a reference value according to one implementation example.

The purpose, advantages, and features of the present disclosure will become more apparent from the following detailed description and preferred embodiments in conjunction with the accompanying drawings, but the present disclosure is not necessarily limited thereto. In addition, in describing the present disclosure, if it is determined that a detailed description of a related known technology may unnecessarily obscure the gist of the present disclosure, the detailed description thereof will be omitted.

When assigning reference numbers to components in a drawing, it should be noted that identical components are assigned the same reference numbers as much as possible even if they are shown in different drawings, and similar components are assigned similar reference numbers.

The terminology used to describe one embodiment of the present disclosure is not intended to limit the present disclosure. It should be noted that singular expressions include plural expressions unless the context clearly dictates otherwise.

The drawings may be schematic or exaggerated to illustrate the implementation.

In this document, the expressions "have," "can have," "include," or "may include" indicate the presence of a given feature (e.g., a numerical value, function, operation, or component such as a part), but do not exclude the presence of additional features.

Hereinafter, an embodiment of the present disclosure will be described in detail with reference to the attached drawings.

Fig. 1 is a drawing showing a distributed acoustic sensing device (1) using an active wavelength filter (50) according to one implementation example. In Fig. 1, an electrical signal is depicted as a dotted line, and an optical signal is depicted as a solid line.

A distributed acoustic sensing device (1) including an active wavelength filter (50) according to one embodiment of the present disclosure may include a light source (10), a first light coupler (21), a light pulse modulator (30), a light amplifier (40), an active wavelength filter (50), a light circulator (60), an optical fiber (70), a second light coupler (22), a photo detector (80), and a signal processing unit (90).

The light source (10) can generate continuous output laser light. The light source (10) can include a laser generator. The light source (10) can generate highly coherent laser light having a linewidth of several kHz or less. The light source (10) can generate unpolarized laser light.

The first optical coupler (21) can divide the light output from the light source (10) into sensing light and reference light. The sensing light is input to an optical fiber (70) and generates backscattered light by vibration applied to the optical fiber (70), and the reference light provides a reference for detecting vibration using the backscattered light. The first optical coupler (21) may have a first end (21a) connected to the light source (10), a second end (21b) connected to an optical pulse modulator (30), and a third end (21c) connected to the second optical coupler (22). The first optical coupler (21) may receive the light output from the light source (10) into the first end (21a), output 10% of the light as reference light to the third end (21c), and output 90% of the light as sensing light to the second end (21b).

The optical pulse modulator (30) can modulate the sensing light split by the first optical coupler (21) to output pulse light. The optical pulse modulator (30) can include an acousto-optic modulator (AOM). The sensing light can be modulated into pulse light while passing through the optical pulse modulator (30). The optical pulse modulator (30) can output the pulse light to an optical amplifier (40).

The optical amplifier (40) can amplify pulsed light. The optical amplifier (40) can include an erbium doped fiber amplifier (EDFA). The optical amplifier (40) can output the amplified pulsed light to an active wavelength filter (50). The amplified pulsed light can include Amplified Spontaneous Emission (ASE) noise. The ASE noise increases the background noise area of the pulsed light, which lowers the signal to noise ratio (SNR). The ASE noise can be generated when the pulsed light is amplified in the optical amplifier (40).

The active wavelength filter (50) can filter the pulse light amplified by the optical amplifier (40) and pass the light in the pass band. The active wavelength filter (50) can adjust the center wavelength of the pass band. The active wavelength filter can adjust the width of the pass band. The center wavelength of the pass band of the active wavelength filter (50) can be adjusted to correspond to the center wavelength of the light source (10). The width of the pass band can be adjusted so that the size of the sensing light is sufficiently large. The active wavelength filter (50) can remove noise and background noise generated in the optical amplifier (40). For example, the active wavelength filter (50) can remove natural amplification emission noise. A specific description of the active wavelength filter (50) will be described later. The pulse light from which noise has been removed by passing through the active wavelength filter (50) can be output to the optical rotator (60). Pulse light passing through an active wavelength filter (50) may have a narrow line width. Pulse light with a narrow line width has high coherence and is therefore suitable for measurement using backscattered light.

The optical rotator (60) can output sensing light input from an active wavelength filter (50) connected to a first end (60a) to a second end (60b), and output backscattered light input from an optical fiber (70) connected to the second end (60b) to a third end (60c). The optical rotator (60) can include an optical fiber circulator (OC) (70). The first end (60a) of the optical rotator (60) can be connected to an active wavelength filter (50), the second end (60b) can be connected to an optical fiber (70), and the third end (60c) can be connected to a second optical coupler (22).

The second optical coupler (22) can combine and output the backscattered light received from the third end (60c) of the optical rotator (60) and the reference light received from the first optical coupler (21). The first end (22a) of the second optical coupler (22) can be connected to the third end (21c) of the first optical coupler (21), and the second end (22b) can be connected to the third end (60c) of the optical rotator (60). The third end (22c) and the fourth end (22d) of the second optical coupler (22) can be connected to a photodetector (80). The second optical coupler (22) can output 50% of the light combined with the reference light input from the first stage (22a) and the backscattered light input from the second stage (22b) to the third stage (22c) and 50% to the fourth stage (22d).

The photodetector (80) can convert the light received from the second photocoupler (22) into an electrical signal and output it. The photodetector (80) can include a balanced photodetector. The photodetector (80) can generate an electrical signal that reflects the interference pattern of the backscattered light in the light received from the second photocoupler (22). The photodetector (80) can output an electrical signal including the pattern information of the backscattered light to the signal processing unit (90).

The signal processing unit (90) can detect vibration applied to the optical fiber (70) by analyzing the electric signal received from the photodetector (80). If vibration or sound is applied to any point of the optical fiber (70) into which pulsed light is input, backscattered light may be generated at the corresponding part of the optical fiber (70). The signal processing unit (90) can analyze the backscattered light using Rayleigh backscattered light. The signal processing unit (90) can analyze the electric signal to recognize which point of the optical fiber (70) the vibration or sound is applied to.

The signal processing unit (90) can adjust the center wavelength or width of the passband of the active wavelength filter (50). The signal processing unit (90) can output a control signal to the active wavelength filter (50), and the active wavelength filter (50) can operate according to the control signal to shift the center wavelength of the passband or widen or narrow the width of the passband.

Passive wavelength filters such as WDM (Wavelength division multiplexing) or FBG (Fiber Bragg Grating) cannot control the center wavelength or width of the passband. In addition, when a passive wavelength filter is used for a long period of time, it may deteriorate and change its characteristics. A deteriorated passive wavelength filter may have a different center wavelength or width of the passband. A deteriorated passive wavelength filter may cause noise to pass through the filter, thereby increasing the signal-to-noise ratio. Alternatively, some of the pulsed light may not pass through the deteriorated passive wavelength filter, thereby decreasing the intensity of the sensing light input to the optical fiber (70). In addition, the wavelength of the light emitted by the light source (10) may also change due to deterioration or other causes. If the wavelength of the light emitted by the light source (10) changes, some of the light may be blocked by the deteriorated passive wavelength filter, thereby decreasing the intensity of the light input to the optical fiber (70). If the intensity of the sensing light input to the optical fiber (70) decreases, the sensitivity of the distributed acoustic sensing device (1) may decrease. In this way, it is difficult for a passive wavelength filter to respond to wavelength changes due to deterioration of components constituting a distributed acoustic sensing device (1).

In contrast, the active wavelength filter (50) can respond by adjusting the center wavelength or width of the passband even if the wavelength of the pulse light changes due to changes in the elements constituting the distributed acoustic sensing device (1), so that the performance of the distributed acoustic sensing device (1) can be maintained.

The signal processing unit (90) may include a processor, a memory, and a bus. The signal processing unit (90) may further include a circuit that converts an electric signal received from the photodetector (80) into digital data. The processor may include various types of semiconductor devices having an information processing function. The memory may store data and program code. The bus may relay data transmission and reception between the processor and the memory, and may relay data transmission and reception with an external computer device. The signal processing unit (90) may be implemented in a manner in which the program code stored in the memory is driven by the processor. The program code stored in the memory may be written to perform a function of analyzing an electric signal to detect vibration, and a function of adjusting the center wavelength or width of the passband of the active wavelength filter (50). The program code stored in the memory may be written to perform a control method of a distributed acoustic sensing device including an active wavelength filter according to an embodiment of the present disclosure. The signal processing unit (90) may be included in a computer, PC, server, PLC, or other various information processing devices, or may be implemented as an independent information processing device.

Figure 2 is a drawing showing an active wavelength filter (50) according to one implementation example.

The active wavelength filter (50) may include a wavelength separation unit (53) and a wavelength selection unit (54). The active flat wavelength filter may further include a polarizing unit (52).

The polarizing unit (52) receives unpolarized light from the light input/output unit (51), separates it into two polarizations that are orthogonal to each other, and converts one of the two polarizations into the other polarization and outputs it.

The polarizing unit (52) may include a collimating lens (52a) that aligns light incident from the light input/output unit (51) into parallel beams, a beam displacer (52b) that separates light passing through the collimating lens (52a) into two polarizations that are perpendicular to each other, and a half-wave delayer (52c) that delays one of the two polarizations output by the beam displacer (52b) to match the other polarization. The polarizing unit (52) may further include a first lens (52d) that causes the polarization to enter the grating (53a) of the wavelength separation unit (53).

The optical input/output unit (51) may include an optical fiber (70). The optical input/output unit (51) may have an input terminal connected to an optical amplifier (40). The amplified pulse light output from the optical amplifier (40) may be input to the input terminal of the optical input/output unit (51) and output to a collimating lens (52a). The collimating lens (52a) may align the pulse light in parallel and provide it to a beam displayer (52b).

The beam displacer (52b) can separate unpolarized light into two polarizations that are perpendicular to each other. The two polarizations are a polarization that is perpendicular to the optic axis and a polarization that is horizontal to the optic axis.

The half-wave delay device (52c) can be placed in a portion where one of the two polarizations output by the beam displacer (52b) is output. The half-wave delay device (52c) can be placed in a portion where polarization horizontal to the optical axis is output, thereby changing the polarization horizontal to the optical axis into polarization perpendicular to the optical axis and outputting it.

The first lens (52d) may include an image lens. The first lens (52d) may allow light passing through the beam displacer (52b) and the half-wave delay unit (52c) to enter the grating (53a) of the wavelength separation unit (53).

In summary, light input from the input terminal of the input/output unit passes through a collimating lens (52a) and is aligned parallel, passes through a beam displacer (52b) and is separated into polarizations perpendicular to the optical axis and horizontal to the optical axis, and the polarization horizontal to the optical axis passes through a half-wave delay unit (52c) and is changed into polarization perpendicular to the optical axis, so that the polarization perpendicular to the optical axis can be output to the wavelength separation unit (53) through the first lens (52d).

The wavelength separation unit (53) can separate the light output from the polarization unit (52) according to wavelength and output it. The wavelength separation unit (53) can separate the light according to wavelength and provide it to the wavelength selection unit (54).

The wavelength separation unit (53) may include a grating (53a). The wavelength separation unit (53) may further include a second lens (53b).

The grating (53a) can reflect incident light in different directions according to the wavelength. The grating (53a) can include a reflective diffraction grating. The grating (53a) can split the input light into different wavelengths and output them. The light output from the polarizing unit (52) reaches the grating (53a) and is reflected in different directions according to the wavelength to reach the wavelength selecting unit (54) through the second lens (53b). The light output from the polarizing unit (52) has the same polarization and can be reflected in different directions according to the wavelength by the grating (53a). The light reflected in different directions according to the wavelength can pass through the second lens (53b) and the light of the same wavelength can reach the same pixel of the LC array (54a). For example, three light of the first wavelength (λ1) can reach any pixel of the LC array (54a), three light of the second wavelength (λ2) can reach another pixel of the LC array (54a), and three light of the third wavelength (λ3) can reach another pixel of the LC array (54a).

The wavelength selection unit (54) can selectively reflect one or more wavelengths from among the light separated by wavelength by the wavelength separation unit (53).

The wavelength selection unit (54) may include an LC array (54a) whose arrangement is changed according to a control signal for each part where light separated by wavelength from the wavelength separation unit (53) arrives to pass or block the light, and a mirror (54b) that reflects the light passed by the LC array (54a).

The LC array (Liquid Crystal Array, 54a) can change the alignment of the liquid crystal according to the control signal applied from the signal processing unit (90). The LC array (54a) can change the alignment of the liquid crystal on a pixel-by-pixel basis according to the control signal. Light of different wavelengths reaches each pixel of the LC array (54a). The smaller the pixel size, the more precisely the center wavelength and width of the passband of the active wavelength filter (50) can be adjusted. When the alignment of the liquid crystal is changed by applying a control signal to any pixel of the LC array (54a), the light is blocked, and when the alignment of the liquid crystal is not changed, the light can pass. Alternatively, the LC array (54a) can be configured so that when the alignment of the liquid crystal is changed, the light passes, and when the alignment of the liquid crystal is not changed, the light is blocked. This specification explains based on a method in which the alignment of the liquid crystal of the LC array (54a) is changed, the light is blocked.

A control signal may be applied to each pixel of the LC array (54a) to change the slope of the phase, thereby controlling the intensity of the light reflected by wavelength. The LC array (54a) can control the amount of light passing through any pixel by applying a control signal of a desired intensity. For example, the LC array (54a) can allow light of the first wavelength to pass through a pixel to which light of the first wavelength has reached without changing the alignment of the liquid crystal, can allow light of the second wavelength to pass through a pixel to which light of the second wavelength has reached by changing the alignment of the liquid crystal to block light of the second wavelength, and can allow light of the third wavelength to pass through a pixel to which light of the third wavelength has reached by changing the alignment of the liquid crystal to a desired degree. In other words, the LC array (54a) can control whether or not light is reflected and the intensity of the reflection by wavelength.

The mirror (54b) can reflect light that has passed through the LC array (54a). The mirror (54b) can be arranged in parallel with the LC array (54a). The mirror (54b) can be made of a material that reflects the wavelength of the laser light. The light that has passed through the LC array (54a) can be reflected by the mirror (54b) and pass through the LC array (54a) again to enter the wavelength separation unit (53).

In summary, the LC array (54a) controls the alignment of the liquid crystal of the pixel where light of each wavelength reaches according to the control signal of the signal processing unit (90) to allow the light to pass, block, or partially pass, and the light passing through the LC array (54a) can be reflected by the mirror (54b) and passed through the LC array (54a) again to be output to the wavelength separation unit (53).

The light selectively reflected from the wavelength selection unit (54) is directed to the optical input/output unit (51) through the same path as the incident path. The output terminal of the optical input/output unit (51) can be connected to the first terminal of the optical rotator (60). The wavelength selection unit (54) can adjust the wavelength at a minimum interval of 0.05 nm or less. The active wavelength filter (50) can be applied to various fields such as a wavelength tunable filter, a dispersion compensator, and a multi-channel laser.

Fig. 3 is a graph showing a wavelength change due to a light source (10) or a filter. Fig. 3 shows the results of testing a passive wavelength filter (WDM filter (Wavelength Division Multiplexing filter) and an FBG filter (Fiber Bragg Grating filter)) and an active wavelength filter (50) according to an embodiment of the present disclosure.

The light source (10) and filter of the distributed acoustic sensing device (1) may have different performances due to deterioration. If the light source (10) deteriorates, the center wavelength of the laser light may change. If the filter deteriorates, the center wavelength or width of the pass band may change. In Fig. 3, the normal state represents the intensity (Amplitude) of backscattered light according to location in a state where the light source (10) or the filter is not deteriorated. The light source (10) deterioration state represents the intensity of backscattered light according to location in a state where the light source (10) deteriorates and there is a change in the center wavelength of the laser light. The filter deterioration state represents the intensity of backscattered light according to location in a state where the passive wavelength filter deteriorates and there is a change in the center wavelength or width of the pass band.

In normal conditions, when using a passive wavelength filter and an active wavelength filter (50), the intensity of backscattered light is measured according to position. This is because the central wavelength of the laser light output from the light source (10) and the central wavelength of the filter are identical, so the sensing light normally enters the optical fiber (70).

When using a passive wavelength filter (WDM filter and FBG filter) in a state of light source deterioration, the intensity of backscattered light is measured to be very small regardless of the position. The center wavelength of the laser light changes due to the deterioration of the light source (10), and when the filter is normal, the laser light does not pass through the passive wavelength filter. Therefore, most of the sensing light does not enter the optical fiber (70), and the backscattered light is measured with a weak intensity.

On the other hand, when using an active wavelength filter (50) in a state of light source deterioration, the intensity of backscattered light according to the position is measured. Even if the center wavelength of the laser light changes due to the deterioration of the light source (10), the laser light can pass through the passive wavelength filter because the active wavelength filter (50) matches the center wavelength or width of the passband to the changed center wavelength of the laser light. Accordingly, since the sensing light enters the optical fiber (70) normally, the backscattered light can be measured.

When the passive wavelength filter (WDM filter and FBG filter) is deteriorated in the filter deterioration state, the intensity of the backscattered light is measured to be very small regardless of the position. When the center wavelength of the laser light output from the light source (10) does not change and the center wavelength or width of the pass band changes due to the deterioration of the passive wavelength filter, the laser light does not pass through the passive wavelength filter. Therefore, most of the sensing light does not enter the optical fiber (70), and the backscattered light is measured with a weak intensity.

On the other hand, when using an active wavelength filter (50) in a filter deterioration state, the intensity of backscattered light according to the position is measured. Even if the center wavelength or width of the pass band changes, the active wavelength filter (50) adjusts the center wavelength or width of the pass band again to match the center wavelength of the laser light, so that the laser light can pass through the passive wavelength filter. Accordingly, since the sensing light normally enters the optical fiber (70), the backscattered light can be measured.

In addition to deterioration, various external factors such as temperature change or impact may cause the center wavelength of the light source (10) to not exactly match the center wavelength of the filter. As in the present disclosure, by using an active wavelength filter (50), the center wavelength of the filter can be changed, so that the distributed acoustic sensing device (1) can operate normally.

As described, by using an active wavelength filter (50) in a distributed acoustic sensing device (1) and controlling the center wavelength and width of the passband of the active wavelength filter (50), the distributed acoustic device can perform normal functions even if the components constituting the distributed acoustic device deteriorate.

Fig. 4 is a graph showing the passband according to the type of filter. Fig. 4 shows the passband of a WDM filter (100 GHz DWDM filter), an FBG filter (Athermal packaged FBG filter), and an active wavelength filter (50) according to the present disclosure. Fig. 4 shows the results of comparing wavelength filters using a broadband light source and an optical spectrum analyzer.

The passband width of the FBG filter is 0.25 nm, the passband width of the WDM filter is 0.69 nm, and the passband width of the active wavelength filter (50) is 0.075 nm. The passband width of the active wavelength filter (50) is the narrowest. That is, the characteristic of the narrow passband width of the active wavelength filter (50) can effectively remove natural amplification emission noise in the distributed acoustic sensing device (1), thereby increasing the signal-to-noise ratio.

Fig. 5 is a graph comparing the output of a distributed photoacoustic sensing device according to the type of filter. Fig. 5 shows the intensity of backscattered light according to position when using a passive wavelength filter (WDM filter and FBG filter) and an active wavelength filter (50). The signal level is a range from the minimum to maximum value of the intensity of backscattered light, and the noise level is a range from the minimum to maximum value of the noise intensity.

For the WDM filter, the signal level is 11,599, the noise level is 5,378, and the signal-to-noise ratio is 6.67 dB. For the FBG filter, the signal level is 9,074, the noise level is 2,800, and the signal-to-noise ratio is 10.21 dB. For the active wavelength filter (50) according to the present disclosure, the signal level is 14,401, the noise level is 3,811, and the signal-to-noise ratio is 11.55 dB. In comparison, the active wavelength filter (50) exhibits the best signal-to-noise ratio performance because it has the characteristic of a narrow passband.

Figure 6 is a graph showing the change in the center wavelength of the passband of an active wavelength filter (50).

The active wavelength filter (50) can change the center wavelength of the pass band. In FIG. 6, the center wavelength of the pass band is shown to change from about 1550.3 nm to 1553.4 nm at intervals of about 0.18 nm. In this way, the active wavelength filter (50) can finely adjust the center wavelength so as to respond to even subtle changes in the center wavelength. The active wavelength filter (50) is not limited to that shown in FIG. 6, and can change the center wavelength in various ranges and can change the center wavelength more finely.

When the central wavelength of the light source (10) changes due to various causes such as external factors or deterioration, the passive wavelength filter cannot pass the sensing light, so the distributed acoustic sensing device (1) cannot operate normally. However, the active wavelength filter (50) can maintain coherence even when the central wavelength of the light source (10) changes by adjusting the central wavelength.

Figure 7 is a graph showing the change in the width of the passband of an active wavelength filter (50).

In general, the smaller the line width of the sensing light, the higher the coherence, and the lower the noise. However, in order for the backscattered light to have sufficient intensity, the intensity of the sensing light is also an important factor. The active wavelength filter (50) can adjust the width of the pass band so that the sensing light has sufficient intensity. If the intensity of the sensing light is not sufficient due to various reasons, such as a decrease in the intensity of the laser light output from the light source (10) or a decrease in the intensity of the pulse light amplified by the optical amplifier (40), the active wavelength filter (50) can increase the width of the pass band so that the sensing light with sufficient intensity can pass through.

The active wavelength filter (50) can only pass light of a wavelength that reaches an arbitrary pixel. If the active wavelength filter (50) controls the pixel through which light of about 1551.9 nm reaches to pass, it can have a shape like the first pass band (PB1) in FIG. 7. If the active wavelength filter (50) controls the pixel through which light of 1551.7 nm and light of 1552.1 nm reaches to pass, it can have a shape like the second pass band (PB2) in FIG. 7. If light reaching a plurality of pixels of the active wavelength filter (50) is passed, the width of the pass band can gradually widen, such as the third pass band (PB3), the fourth pass band (PB4), and the fifth pass band (PB5).

Fig. 8 is a flow chart showing steps of a control method of a distributed acoustic sensing device (1) including an active wavelength filter (50) according to one embodiment. See also Fig. 1.

A control method of a distributed acoustic sensing device (1) including an active wavelength filter (50) may include a first step (S1) in which an optical pulse modulator (30) modulates light output by a light source (10) into a pulse form and an optical amplifier (40) amplifies the light to generate pulse light, a second step (S2) in which an active wavelength filter (50) filters the pulse light, a third step (S3) in which pulse light passing through the active wavelength filter (50) is input to an optical fiber (70), backscattered light generated at an arbitrary point of the optical fiber (70) is input to a photodetector (80) and converted into an electric signal, and a signal processing unit (90) analyzes the electric signal to detect vibration applied to the optical fiber (70), and a fourth step (S4) in which the signal processing unit (90) controls the active wavelength filter (50) so that a center wavelength or width of a passband is changed.

The first step (S1) is a process prior to inputting sensing light to the active wavelength filter (50). In the first step (S1), the light source (10) generates laser light and provides it to the optical pulse modulator (30), the optical pulse modulator (30) modulates the laser light into a pulse shape and outputs the pulse light to the optical amplifier (40), and the optical amplifier (40) can amplify the pulse light and output it to the active wavelength filter (50). In the first step (S1), a part of the laser light is separated as reference light to the second optical coupler (22) by the first optical coupler (21) connected between the light source (10) and the optical pulse modulator (30), and the remainder can be input as sensing light to the optical pulse modulator (30).

In the second step (S2), the active wavelength filter (50) can block natural amplification emission noise by passing light included in the pass band and blocking light outside the pass band.

The third step (S3) is to measure the backscattered light generated when the sensing light input to the optical fiber (70) passes through the optical fiber (70) to calculate the position where vibration is applied to the optical fiber (70). The sensing light that has passed through the active wavelength filter (50) is input to the optical fiber (70) through the optical rotator (60), and the backscattered light input from the optical fiber (70) to the optical rotator (60) is output to the photodetector (80), so that the photodetector (80) can generate an electrical signal corresponding to the backscattered light. The signal processing unit (90) can analyze the electrical signal output by the photodetector (80) to calculate the position where vibration is applied to the optical fiber (70).

The fourth step (S4) is that the signal processing unit (90) automatically adjusts the center wavelength or width of the passband of the active wavelength filter (50). The signal processing unit (90) analyzes the electric signal received from the photodetector (80) and, if the intensity of the backscattered light is less than a reference value, adjusts the center wavelength or width of the passband of the active wavelength filter (50). The signal processing unit (90) can perform a step of controlling the active wavelength filter (50) independently of controlling the light source (10), the optical pulse modulator (30), and the amplifier to generate pulsed light. Alternatively, the signal processing unit (90) can perform a step of controlling the active wavelength filter (50) at set intervals.

If the intensity of the backscattered light is measured to be lower than the reference value, the signal processing unit (90) automatically adjusts the center wavelength or width of the passband of the active wavelength filter (50) and normal distributed acoustic sensing can be performed again.

Figure 9 is a flowchart showing steps for controlling an active wavelength filter according to one embodiment.

The fourth step (S4) of controlling the active wavelength filter may include a fourth step (S41) in which the signal processing unit (90) analyzes the electric signal received from the photodetector (80) and compares the intensity of the backscattered light with a reference value, and a fourth step (S42) in which, if the intensity of the backscattered light is lower than the reference value, the signal processing unit (90) adjusts the center wavelength or width of the passband of the active wavelength filter (50) to adjust the intensity of the backscattered light to be higher than the reference value.

In step 4-1 (S41), the reference value can be set to a value required for the distributed acoustic sensing to operate normally. The signal processing unit compares the intensity of the backscattered light with the reference value. If the intensity of the backscattered light is greater than the reference value (Y), it is a normal state (S4-3), so general distributed acoustic sensing can be continuously performed. If the intensity of the backscattered light is less than the reference value (N), it is not suitable for performing distributed acoustic sensing, so an operation of adjusting the active wavelength filter (50) can be performed. This is because if the intensity of the backscattered light is less than the reference value, it is difficult to recognize the position of the vibration applied to the optical fiber (70).

Step 4-2 (S42) is that the signal processing unit (90) controls the active wavelength filter (50). The signal processing unit (90) increases the intensity of the pulse light passing through the active wavelength filter (50) by shifting the center wavelength of the passband of the active wavelength filter (50) to a different wavelength or increasing the width of the passband, thereby increasing the intensity of the backscattered light.

Figure 10 is a flowchart showing a step of controlling the size of backscattered light to be greater than a reference value according to one implementation example.

Step 4-2 (S42) may include a step (S421) in which a signal processing unit (90) measures the intensity of backscattered light while changing the center wavelength of the passband of the active wavelength filter (50), a step (S423) in which a center wavelength adjustment step (S423a), a width adjustment step (S423b), and one of the center wavelength and width adjustment steps is determined to be performed by determining whether the center wavelength with the greatest intensity of the backscattered light matches the existing center wavelength and whether the intensity of the large backscattered light is greater than a reference value, and a step (S422) in which a step (S423) in which one of the center wavelength adjustment step (S423a), the width adjustment step (S423b), the center wavelength and the width adjustment step (S423c) is performed.

In step 4-2 (S42), the signal processing unit (90) measures the intensity of backscattered light while sequentially changing the center wavelength of the passband of the active wavelength filter (50), and can control the active wavelength filter (50) so that the center wavelength at which the size of the backscattered light is the largest becomes the center wavelength of the active wavelength filter (50). In step 4-2 (S42), the signal processing unit (90) measures the intensity of backscattered light while changing the width of the passband for each center wavelength of the passband of the active wavelength filter (50), and can control the active wavelength filter (50) so that the width of the passband at which the size of the backscattered light is greater than or equal to a reference value becomes the width of the passband of the active wavelength filter (50).

The step (S421) of measuring the intensity of backscattered light while changing the central wavelength is that the signal processing unit (90) measures and stores the intensity of backscattered light while sequentially or in a predetermined order changing the central wavelength of the active wavelength filter (50). At this time, the interval of the central wavelengths of the active wavelength filter (50) may vary depending on the smallest pixel size of the LC array (54a). By measuring the size of backscattered light for each central wavelength of the passband of the active wavelength filter (50), it is possible to know which central wavelength has the largest measured size of backscattered light.

The step (S422) of determining to perform either the center wavelength adjustment step (S423a), the width adjustment step (S423b), or the center wavelength and the width adjustment step may include a center wavelength matching test for determining whether the center wavelength having the largest intensity of the backscattered light matches the existing center wavelength. The center wavelength matching test may be performed to determine whether it is necessary to change the center wavelength of the passband of the active wavelength filter (50). The center wavelength matching test determines whether the existing center wavelength of the active wavelength filter (50) and the center wavelength having the largest intensity of the backscattered light measured in the step (S421) of measuring the backscattered light while changing the center wavelength match. If the existing center wavelength and the center wavelength having the largest intensity of the backscattered light match (Y), there is no need to change the center wavelength, but if they do not match (N), it is necessary to change the center wavelength.

The step of determining (S422) may include a backscattered light intensity test that determines whether the intensity of the largest backscattered light is greater than a reference value. The backscattered light intensity test may be performed to determine whether it is necessary to change the width of the passband of the active wavelength filter (50). The backscattered light intensity test determines whether the backscattered light with the largest intensity among the backscattered lights measured in the step (S421) of measuring the backscattered light while changing the center wavelength is greater than a reference value. If the backscattered light with the largest intensity is greater than the reference value (Y), there is no need to change the width of the passband, but if it is small (N), there is a need to expand the width of the passband.

The signal processing unit (90) may determine, in the determining step (S422), that if the center wavelength matching test result is 'N' and the backscattered light intensity test is 'Y', the center wavelength adjustment step (S423a) is performed, if the center wavelength matching test result is 'Y' and the backscattered light intensity test is 'N', the width adjustment step (S423b) is performed, and if the center wavelength matching test result is 'N' and the backscattered light intensity test is 'Y', the center wavelength and width adjustment step (S423b) is performed.

The signal processing unit (90) can perform one of the center wavelength adjustment step (S423a), the width adjustment step (S423b), and the center wavelength and width adjustment step (S423b) according to what is determined in the determining step (S422) (S423).

The central wavelength control step (S423a) controls the active wavelength filter (50) so that the central wavelength at which the intensity of the backscattered light is the greatest becomes the central wavelength of the active wavelength filter (50). The signal processing unit (90) controls the passage/blocking of pixels of the LC array (54a) of the active wavelength filter (50), so that light of a wavelength corresponding to the central wavelength at which the intensity of the backscattered light is the greatest passes through the pixel, thereby controlling the central wavelength of the active wavelength filter (50).

The width control step (S423b) controls the active wavelength filter (50) so that the width of the pass band when the intensity of backscattered light becomes higher than a reference value by allowing more wavelengths adjacent to the center wavelength of the active wavelength filter (50) to pass through, becomes the width of the pass band of the active wavelength filter (50). The signal processing unit (90) controls the passage/blocking of pixels of the LC array (54a) of the active wavelength filter (50), so that light passes through the pixel where the wavelength closest to the center wavelength reaches, and when light of the center wavelength and the adjacent wavelength passes through, the backscattered light is further measured and compared with a reference value, and if the intensity of the backscattered light is higher than the reference value, the width of the pass band can be determined to include the center wavelength and the adjacent wavelength. Even when allowing more adjacent wavelengths to pass through, if the intensity of the backscattered light is less than the reference value, the wavelengths adjacent to the adjacent wavelengths are controlled to pass through more, and when the center wavelength, the adjacent wavelength, and the wavelength adjacent to the adjacent wavelength pass through, the backscattered light is further measured and compared with the reference value, and if the intensity of the backscattered light is greater than the reference value, the width of the passband can be determined to include the center wavelength, the adjacent wavelength, and the wavelengths adjacent to the adjacent wavelength. As described, the adjacent wavelengths can be continuously added until the intensity of the backscattered light is greater than the reference value.

The central wavelength and width control step (S423b) determines the central wavelength at which the size of the backscattered light is the largest as the central wavelength of the active wavelength filter (50), and additionally controls pixels corresponding to wavelengths adjacent to the central wavelength of the active wavelength filter (50) to pass, thereby controlling the active wavelength filter (50) so that the width of the pass band when the intensity of the backscattered light becomes a reference value or more becomes the width of the pass band of the active wavelength filter (50). The signal processing unit (90) controls the on/off of the pixels of the LC array (54a) of the active wavelength filter (50) so as to pass light reaching the pixel corresponding to the center wavelength where the size of the backscattered light is the largest, while controlling light reaching the pixel corresponding to the wavelength adjacent to the center wavelength to pass more, and when light of the center wavelength and the adjacent wavelength passes, the backscattered light is further measured and compared with a reference value, and if the intensity of the backscattered light is greater than the reference value, the width of the pass band can be determined to include the center wavelength and the adjacent wavelength. The adjacent wavelengths can be continuously added until the intensity of the backscattered light is greater than the reference value.

As described above, the signal processing unit (90) can filter the sensing light input to the optical fiber (70) by adjusting the center wavelength and width of the passband of the active wavelength filter (50) so that sufficient intensity of backscattered light can be measured. Even when the characteristics of the light source (10) or the active wavelength filter (50) change due to various causes, the signal processing unit (90) can control the active wavelength filter (50) so that the intensity of the sensing light input to the optical fiber (70) is sufficiently strong, so that the distributed acoustic sensing device (1) can operate normally.

The above disclosure has been described in detail through specific implementation examples. The implementation examples are intended to specifically explain the disclosure, and the disclosure is not limited thereto. It will be apparent that modifications or improvements can be made by those skilled in the art within the technical spirit of the disclosure.

All simple modifications or changes of the present disclosure fall within the scope of the present disclosure, and the specific protection scope of the present disclosure will be made clear by the appended claims.

This application was conducted as part of the Open Innovation R&D (20-A-T-002) project of Korea Water Resources Corporation (K-water).

1: Distributed acoustic sensing device using active wavelength filter
10: Light source 21: 1st optical coupler
22: Second optocoupler 30: Optical pulse modulator
40: Optical amplifier 50: Active wavelength filter
60: Optical Rotator 70: Optical Fiber
80: Photodetector 90: Signal processing unit
51: Optical input/output section 52: Polarizing section
52a: Collimating lens 52b: Beam displacer
52c: Half-wave delay 52d: First lens
53: Wavelength separation section 53a: Grating
53b: Second lens 54: Wavelength selector
54a: LC array 54b: Mirror

Claims (14)

A polarizing unit that receives unpolarized light from an optical input/output unit, separates it into two polarized lights that are orthogonal to each other, and converts one of the two polarizations into the other polarization and outputs it;
A wavelength separation unit that separates and outputs light output from the polarizing unit according to wavelength; and
It includes a wavelength selection unit that selectively reflects one or more wavelengths from among the light separated by wavelength by the wavelength separation unit,
The above wavelength selection section
An LC array whose arrangement is changed according to a control signal for each pixel where light separated by wavelength arrives in the wavelength separation unit to pass or block the light; and
A mirror is included that reflects light passed through the LC array,
An active wavelength filter in which light selectively reflected from the wavelength selection section passes through the wavelength separation section and polarization section and is output to the optical input/output section. In claim 1,
The above polarizing part
A collimating lens that aligns light incident from the above optical input/output unit into parallel beams;
A beam displayer that separates light passing through the collimating lens into two polarizations that are perpendicular to each other; and
An active wavelength filter including a half-wave delayer that delays one of the two polarizations output by the beam displacer to match the other polarization. In claim 1,
The above wavelength separation section
An active wavelength filter comprising a grating that reflects incoming light in different directions depending on its wavelength. delete A light source that generates laser light;
A first optical coupler that divides light output from the light source into sensing light and reference light;
An optical pulse modulator that modulates the sensing light split by the first optical coupler to output pulse light;
An optical amplifier for amplifying the above pulsed light;
An active wavelength filter that filters the pulse light amplified by the optical amplifier to pass light in the pass band and has the ability to control the center wavelength or width of the pass band;
An optical rotator that outputs light input from the active wavelength filter connected to the first stage to the second stage and outputs backscattered light input from the optical fiber connected to the second stage to the third stage;
A second optical coupler that combines and outputs the backscattered light received from the third stage of the optical rotator and the reference light received from the first optical coupler;
A photodetector that converts light received from the second optical coupler into an electrical signal and outputs it;
A distributed acoustic sensing device including an active wavelength filter, the device including a signal processing unit that analyzes an electric signal received from the photodetector to detect vibration applied to an optical fiber and adjusts the center wavelength or width of the passband of the active wavelength filter. In claim 5,
The above signal processing unit
A distributed acoustic sensing device including an active wavelength filter that analyzes an electric signal received from the photodetector and, if the intensity of the backscattered light is less than a reference value, adjusts the center wavelength of the passband of the active wavelength filter or adjusts the width of the passband. In claim 6,
The above signal processing unit
A distributed acoustic sensing device including an active wavelength filter, which measures the intensity of the backscattered light while sequentially changing the center wavelength of the passband of the active wavelength filter, and controls the active wavelength filter so that the center wavelength at which the size of the backscattered light is the largest becomes the center wavelength of the active wavelength filter. In claim 6,
The above signal processing unit
A distributed acoustic sensing device including an active wavelength filter, which measures the intensity of the backscattered light while changing the width of the pass band for each center wavelength of the pass band of the active wavelength filter, and controls the active wavelength filter so that the width of the pass band in which the magnitude of the backscattered light is greater than a reference value becomes the width of the pass band of the active wavelength filter. A first step in which an optical pulse modulator modulates light output by a light source into a pulse form and an optical amplifier amplifies the same to generate pulse light;
A second step in which an active wavelength filter filters the pulse light;
A third step in which pulse light passing through the active wavelength filter is input to an optical fiber, backscattered light generated at any point of the optical fiber is input to a photodetector and converted into an electric signal, and a signal processing unit analyzes the electric signal to detect vibration applied to the optical fiber; and
A control method for a distributed acoustic sensing device including an active wavelength filter, comprising a fourth step of controlling the active wavelength filter so that the center wavelength or width of the passband is changed. In claim 9,
The fourth step above is,
Step 4-1, in which the signal processing unit analyzes the electric signal received from the photodetector and compares the intensity of the backscattered light with a reference value; and
A method for controlling a distributed acoustic sensing device including an active wavelength filter, comprising a step 4-2 in which, when the intensity of the backscattered light is less than a reference value, the signal processing unit adjusts the center wavelength or width of the passband of the active wavelength filter to adjust the intensity of the backscattered light to be greater than the reference value. In claim 10,
Step 4-2
A step of measuring the intensity of the backscattered light while the signal processing unit changes the center wavelength of the passband of the active wavelength filter;
A step of determining whether the center wavelength of the greatest intensity of the backscattered light is identical to the existing center wavelength, and determining whether the greatest intensity of the backscattered light is greater than the reference value, and thereby determining to perform one of the center wavelength adjustment step, the width adjustment step, and the center wavelength and width adjustment step; and
A control method for a distributed acoustic sensing device including an active wavelength filter, the method comprising: performing a center wavelength adjustment step, a width adjustment step, or one of the center wavelength and width adjustment steps. In claim 11,
The above central wavelength adjustment step
A control method for a distributed acoustic sensing device including an active wavelength filter, wherein the active wavelength filter is controlled so that the center wavelength at which the intensity of the backscattered light is the greatest becomes the center wavelength of the active wavelength filter. In claim 11,
The above width adjustment step is
A control method for a distributed acoustic sensing device including an active wavelength filter, wherein the active wavelength filter is controlled so that the width of the passband when the intensity of backscattered light exceeds a reference value becomes the width of the passband of the active wavelength filter by further passing wavelengths adjacent to the center wavelength of the active wavelength filter. In claim 11,
The above central wavelength and width adjustment steps are
A control method for a distributed acoustic sensing device including an active wavelength filter, wherein the center wavelength at which the magnitude of the backscattered light is the largest is determined as the center wavelength of the active wavelength filter, and pixels corresponding to wavelengths adjacent to the center wavelength of the active wavelength filter are additionally controlled to pass, so that the width of the pass band when the intensity of the backscattered light becomes a reference value or more is controlled to become the width of the pass band of the active wavelength filter.

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