Method and system for determining reflection position in optical fiber

Abstract

A method and system for determining a reflection position in an optical fiber relates to the field of on-line monitoring of an optical fiber line, and the method comprises the following steps: a signal sending end generates a correlation sequence, dynamically adjusts the duty ratio of the correlation sequence, modulates the correlation sequence to a detection wavelength, and sends the correlation sequence to a to-be-detected optical fiber; the signal receiving end receives the reflected light signal of the optical fiber to be measured, after signal processing, correlation operation is carried out on the signal and the correlation sequence of the sending end, and the reflection position is determined through the time delay of a correlation peak; reflection light signals from all reflection points of the optical fiber to be detected are mutually staggered in time sequence, so that overlapping of strong and weak reflection signals is reduced in time, correlation peaks of the strong and weak reflection signals can still be obtained based on correlation detection, and then the reflection position is accurately determined according to correlation peak time delay.

Description

Technical Field

[0001] The present application relates to the field of online monitoring of optical fiber lines, and in particular to a method and system for determining a reflection position in an optical fiber. Background Art

[0002] The Optical Time-Domain Reflectometer (OTDR) can test the continuity of a single optical fiber to be tested and locate the fault point based on the reflection signal of the link. However, it is difficult to use in point-to-multipoint networks such as optical access networks. This is because when the OTDR accesses the Passive Optical Network (PON), the backscattered signal received is the superposition of each branch of the PON network. It is difficult to distinguish which branch the signal comes from and it is impossible to locate the fault location.

[0003] OTDR based on correlation detection is another promising detection method. It modulates the direct spread spectrum sequence onto the optical signal based on digital circuits and optical transceiver devices. After the reflected signal returns to the OLT in the transmission path, it is filtered, amplified, and then converted into an electrical signal. After that, it is correlated with the original transmission sequence, and the reflection position is accurately located according to the time delay of the correlation peak. This method has high detection sensitivity and spatial resolution, and can reduce the cost of the line monitoring system. However, in the actual environment, the signal reflected back from the optical fiber to be tested is very complex, and the power of strong and weak signals often differs by tens of dB (decibels). During correlation detection, the signal spectra of the same content overlap, and the strong signal covers the weak signal, making the weak reflection impossible to observe. The signal that needs to be focused on is submerged, reducing the availability of the OTDR system. Therefore, there are still challenges in using correlation OTDR for actual line monitoring. Summary of the invention

[0004] The present application provides a method and system for determining the reflection position in an optical fiber, which can solve the technical problems in the prior art that the signal spectra of the same content overlap during correlation detection, and the strong signal covers the weak signal, making the weak reflection unobservable.

[0005] In a first aspect, an embodiment of the present application provides a method for determining a reflection position in an optical fiber, the method comprising:

[0006] The signal transmitting end generates a correlation sequence, dynamically adjusts the duty cycle of the correlation sequence, modulates it to the detection wavelength and sends it to the optical fiber to be tested;

[0007] The signal receiving end receives the reflected light signal of the optical fiber to be tested, and after signal processing, performs correlation operation with the correlation sequence of the transmitting end, and determines the reflection position through the time delay of the correlation peak; wherein, the reflected light signals from each reflection point of the optical fiber to be tested are interlaced in time sequence.

[0008] In this embodiment, by dynamically adjusting the duty cycle of the relevant sequence, the weak reflection signal is staggered with the strong reflection signal in timing and will not be completely covered. By dynamically adjusting the duty cycle of the sending sequence, both strong and weak reflection signals can be detected, thereby improving the robustness and detection capability of the system under complex conditions.

[0009] In combination with the first aspect, in one implementation, dynamically adjusting the duty cycle of the related sequence includes:

[0010] A certain length of 0 sequence is added after the correlation sequence or the emission light is turned off, so that after the correlation sequence is sent, it pauses for several cycles before starting to send again.

[0011] In combination with the first aspect, in one implementation, the duration of the 0 sequence is lengthened or the duration of turning off the emitted light is an integer multiple of the duration of the relevant sequence.

[0012] In combination with the first aspect, in one implementation, dynamically adjusting the duty cycle of the related sequence includes:

[0013] The content of the correlation sequence is set to 0 or the emitted light is turned off, so that the reflected light signal from each reflection point of the optical fiber to be tested becomes intermittent; the length of the retained content in the correlation sequence accounts for 1 / M of the total length of the correlation sequence, where M is an integer less than the total length of the correlation sequence.

[0014] In combination with the first aspect, in one implementation, the correlation peaks obtained for each weak reflection when M takes different values ​​are recorded, and the time delay of the correlation peak is determined according to the highest correlation peak of each weak reflection.

[0015] In a second aspect, the present application provides a system for determining a reflection position in an optical fiber, comprising:

[0016] The transmitting device is arranged at the signal transmitting end, and is used to generate a correlation sequence, dynamically adjust the duty cycle of the correlation sequence, modulate it to the detection wavelength, and send it to the optical fiber to be tested;

[0017] The receiving device is arranged at the signal receiving end, and is used to receive the reflected light signal of the optical fiber to be tested, and after signal processing, perform correlation operation with the correlation sequence of the transmitting end, and determine the reflection position through the time delay of the correlation peak; wherein the reflected light signals from each reflection point of the optical fiber to be tested are interlaced in time sequence;

[0018] The coupler is used to couple the emitting device and the receiving device to the optical fiber to be tested.

[0019] In conjunction with the second aspect, in one implementation, the originating device includes:

[0020] A sequence generation module, which is used to generate related sequences;

[0021] A sequence adjustment module, which is used to dynamically adjust the duty cycle of the related sequence so that the reflected light signals of each reflection point of the optical fiber to be tested are staggered in time sequence;

[0022] A digital-to-analog conversion module, which is used to convert the dynamically adjusted digital signal into an analog signal;

[0023] The optoelectronic modulation module is used to modulate the correlation sequence after digital-to-analog conversion to the detection wavelength and send it to the optical fiber to be tested through the coupler.

[0024] In combination with the second aspect, in one implementation, the sequence adjustment module adjusts the duty cycle of the related sequence, including:

[0025] The sequence adjustment module adds a certain length of 0 sequence after the relevant sequence or turns off the emission light;

[0026] The duration of the 0 sequence is lengthened or the duration of turning off the emitted light is an integer multiple of the duration of the relevant sequence.

[0027] In combination with the second aspect, in one implementation, the sequence adjustment module adjusts the duty cycle of the related sequence, including:

[0028] The sequence adjustment module sets the relevant sequence content interval to 0 or turns off the emission light;

[0029] The length of the retained content in the correlation sequence accounts for 1 / M of the total length of the correlation sequence, where M is an integer less than the total length of the correlation sequence.

[0030] In conjunction with the second aspect, in one implementation, the receiving device includes:

[0031] A filter, which is used to filter the reflected light signal of the optical fiber to be tested;

[0032] An amplifier, used to amplify the filtered optical signal;

[0033] A photodetector, which is used to detect the amplified light signal and perform photoelectric conversion;

[0034] The signal processor is used to perform correlation operation on the sequence after photoelectric conversion and the correlation sequence of the transmitting end, and determine the reflection position through the time delay of the correlation peak.

[0035] The beneficial effects brought by the technical solution provided in the embodiments of the present application include:

[0036] By generating a correlation sequence at the signal transmitting end and dynamically adjusting the duty cycle of the correlation sequence, the reflected light signals from each reflection point of the optical fiber to be tested can be interlaced in timing, so that the strong and weak reflection signals can be less overlapped in time, and the weak reflection signal can be easily observed. Based on the correlation detection, the correlation peaks of the strong and weak reflection signals can still be obtained, and then the reflection position can be accurately determined according to the correlation peak delay, thereby improving the robustness and detection capability of the related OTDR system under complex conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 A schematic flow chart of a method for determining a reflection position in an optical fiber according to an embodiment of the present application;

[0038] Figure 2 A schematic diagram of the principle of dynamically adjusting the related sequence according to an embodiment of the present application;

[0039] Figure 3 Schematic diagram of a system for determining reflection positions in optical fibers according to an embodiment of the present application. DETAILED DESCRIPTION

[0040] In order to enable those skilled in the art to better understand the solution of the present application, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0041] In order to make the objectives, technical solutions and advantages of the present application clearer, the implementation methods of the present application will be further described in detail below with reference to the accompanying drawings.

[0042] On the first aspect, an embodiment of a method for determining a reflection position in an optical fiber is provided to solve the technical problems existing in the prior art that signal spectra of the same content overlap during correlation detection, and strong signals mask weak signals, making weak reflections unobservable.

[0043] In one embodiment, referring to Figure 1 , Figure 1 Schematic diagram of the process of an embodiment of the method for determining the reflection position in an optical fiber of the present application. Figure 1 As shown, the method includes:

[0044] S1: The signal transmitting end generates a correlation sequence, dynamically adjusts the duty cycle of the correlation sequence, modulates it to the detection wavelength and sends it to the optical fiber to be tested. Preferably, the correlation sequence is a direct spread spectrum sequence.

[0045] S2: The signal receiving end receives the reflected light signal of the optical fiber to be tested, and after signal processing, performs correlation operation with the correlation sequence of the transmitting end, and determines the reflection position through the time delay of the correlation peak; wherein, the reflected light signals from each reflection point of the optical fiber to be tested are interlaced in time sequence.

[0046] In this embodiment, by dynamically adjusting the duty cycle of the relevant sequence, the weak reflection signal is staggered with the strong reflection signal in timing and will not be completely covered. By dynamically adjusting the duty cycle of the sending sequence, both strong and weak reflection signals can be detected, thereby improving the robustness and detection capability of the system under complex conditions.

[0047] In a common correlation OTDR system, the correlation sequence is usually sent repeatedly at a fixed period, and the detection light carrying the correlation sequence is reflected back at different positions of the optical fiber to be tested. Figure 2 As shown in (a), due to the different distances between each reflection point and the signal transmitter and the different reflectivity of each reflection point, the strength of the reflected light signal varies. When the related sequence is sent repeatedly, the reflected light signals of each reflection point completely overlap, and the reflected light signals are divided into strong reflection signals and weak reflection signals, as shown in Figure 2 As shown in (b), it can be seen that the strong reflection signal completely submerges the weak reflection signal.

[0048] Furthermore, in one embodiment, the duty cycle of the correlation sequence is dynamically adjusted by adding a certain length of 0 sequence after the correlation sequence, or directly turning off the emission light after the correlation sequence, so that after sending the correlation sequence, it can pause for several cycles before starting to send again, and the correlation sequences are interlaced in timing. The reflected light signal is divided into a strong reflection signal and a weak reflection signal. In this embodiment, the strong reflection signal and the weak reflection signal are as follows: Figure 2 (c) In this embodiment, the duration of the 0 sequence that is lengthened to a certain length after the correlation sequence, or the duration of directly shutting off the emitted light after the correlation sequence, are both integer multiples of the duration of the correlation sequence, so as to achieve the effect of different lengths of weak reflection sequences. The length of the 0 sequence that is lengthened after the correlation sequence follows the principle of being as short as possible, so that the successive reflection signals do not overlap as much as possible.

[0049] Furthermore, in one embodiment, the duty cycle of the correlation sequence can be dynamically adjusted by: setting the content intervals in the correlation sequence to 0, or turning off the emitted light at the content intervals in the correlation sequence, so that the reflected light signals from each reflection point of the optical fiber to be tested are intermittent and staggered in time sequence; and the length of the content retained in the correlation sequence accounts for 1 / M of the total length of the correlation sequence, where M is an integer less than the total length of the correlation sequence, so as to achieve the effect of weak reflection sequences showing different lengths. The reflected light signal is divided into a strong reflection signal and a weak reflection signal. In this embodiment, the strong reflection signal and the weak reflection signal are as follows: Figure 2 (d).

[0050] Furthermore, in order to maximize the exposure length of the weak reflection sequence, the M value needs to be dynamically adjusted. The method that can be adopted is: sequentially record the correlation peaks obtained for each weak reflection when M values ​​are different, and determine the delay of the correlation peak according to the highest correlation peak of each weak reflection.

[0051] In a second aspect, an embodiment of a system for determining a reflection position in an optical fiber is provided, which can be used to implement the above-mentioned method embodiments.

[0052] like Figure 3 FIG. 1 is a schematic diagram of an embodiment of a system for determining a reflection position in an optical fiber; the system includes a emitting device, a receiving device and a coupler.

[0053] The transmitting device is arranged at the signal transmitting end, and is used to generate a correlation sequence, dynamically adjust the duty cycle of the correlation sequence, modulate it to the detection wavelength and send it to the optical fiber to be tested.

[0054] The receiving device is arranged at the signal receiving end, and is used to receive the reflected light signal of the optical fiber to be tested. After signal processing, the reflected light signal is correlated with the correlation sequence of the transmitting end, and the reflection position is determined by the time delay of the correlation peak; wherein, the reflected light signals from each reflection point of the optical fiber to be tested are interlaced in time sequence.

[0055] The coupler is used to couple the emitting device and the receiving device to the optical fiber to be tested.

[0056] Furthermore, in one embodiment, the transmitting device includes a sequence generating module, a sequence adjusting module, a digital-to-analog conversion module, and an optoelectronic modulation module.

[0057] The sequence generation module is used to generate related sequences.

[0058] The sequence adjustment module is used to dynamically adjust the duty cycle of the correlation sequence generated by the sequence generation module so that the reflected light signals of each reflection point of the optical fiber to be tested are interlaced in time sequence.

[0059] The digital-to-analog conversion module is used to digitally convert the dynamically adjusted signal into an analog signal.

[0060] The optoelectronic modulation module is used to modulate the relevant sequence of the analog signal after digital-to-analog conversion onto the detection wavelength and send it to the optical fiber to be tested through the coupler.

[0061] Furthermore, in one embodiment, the receiving device includes a filter, an amplifier, a photodetector, and a signal processor.

[0062] The filter is used to filter the reflected light signal of the optical fiber to be tested.

[0063] The amplifier is used to amplify the optical signal filtered by the filter.

[0064] The photodetector is used to detect the optical signal amplified by the amplifier and perform photoelectric conversion.

[0065] The signal processor is used to perform correlation operation on the sequence after photoelectric conversion and the correlation sequence of the transmitting end, and determine the reflection position through the time delay of the correlation peak.

[0066] In the above system, the sequence adjustment module adjusts the duty cycle of the relevant sequence in two ways, one of which is: the sequence adjustment module lengthens a certain length of 0 sequence or turns off the emission light after the relevant sequence. In addition, the duration of the 0 sequence is lengthened or the duration of the emission light is turned off to an integer multiple of the duration of the relevant sequence, so as to achieve the effect of different lengths of weak reflection sequence exposure.

[0067] Another way is: the sequence adjustment module sets the content of the relevant sequence to 0 or turns off the emission light. In addition, the length of the content retained in the relevant sequence accounts for 1 / M of the total length of the relevant sequence, where M is an integer less than the total length of the relevant sequence.

[0068] In a third aspect, according to the system for determining a reflection position in an optical fiber, an embodiment of an optical fiber line monitoring method is provided, and the optical fiber line detection method comprises the following steps:

[0069] Step 1: After the sequence generation module of the transmitting device generates the correlation sequence, the duty cycle of the generated correlation sequence is dynamically adjusted through the sequence adjustment module, so that the reflected light signals of each reflection point of the optical fiber to be tested are interlaced in timing. After the dynamically adjusted digital signal is converted into an analog signal through the digital-to-analog conversion module, the correlation sequence of the analog signal after the digital-to-analog conversion is modulated to the detection wavelength through the photoelectric modulation module and sent to the optical fiber to be tested through the coupler. At the same time, the content of the correlation sequence and the time when the corresponding optical signal is sent are recorded.

[0070] Step 2: The possible reflection points in the optical fiber to be tested reflect the optical signal through the coupler to the recovery end device. After the filter of the receiving end device filters the reflected optical signal of the optical fiber to be tested, the amplifier amplifies the optical signal. The amplified optical signal is detected by the photoelectric detector and then photoelectrically converted. Then the signal is processed. Specifically, the sequence after photoelectric conversion is correlated with the relevant sequence of the sending end, and the delay and peak value of the correlation peak are measured.

[0071] Step 3: Different reflection points in the optical path are distinguished and marked according to the time delay of different reflected light signal peaks, and the light intensity change of each reflection point is monitored according to the change of the relevant amplitude of the reflected light signal at each reflection point.

[0072] In this embodiment, the duty cycle of the generated correlation sequence is dynamically adjusted by the sequence adjustment module of the transmitting device, so that the reflected light signals received by the receiving device from the various reflection points of the optical fiber to be tested are staggered in time sequence. Based on the correlation detection, the correlation peaks of the different reflection signals can still be obtained, and then the reflection position is accurately determined according to the time delay, thereby improving the robustness and detection capability of the related OTDR system under complex conditions.

[0073] It should be noted that the serial numbers of the above-mentioned embodiments of the present application are only for description and do not represent the advantages or disadvantages of the embodiments.

[0074] The terms "including" and "having" and any variations thereof in the specification and claims of this application and the above-mentioned drawings are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not limited to the listed steps or units, but optionally includes steps or units that are not listed, or optionally includes other steps or units inherent to these processes, methods, products or devices. The terms "first", "second" and "third" are used to distinguish different objects, etc., and do not represent a sequence, nor do they limit "first", "second" and "third" to different types.

[0075] In the description of the embodiments of the present application, "exemplary", "for example" or "for example" are used to indicate examples, illustrations or descriptions. Any embodiment or design described as "exemplary", "for example" or "for example" in the embodiments of the present application should not be interpreted as being more preferred or more advantageous than other embodiments or designs. Specifically, the use of words such as "exemplary", "for example" or "for example" is intended to present related concepts in a concrete way. In addition, in the description of the embodiments of the present application, "plurality" refers to two or more than two.

[0076] In some processes described in the embodiments of the present application, multiple operations or steps that appear in a specific order are included, but it should be understood that these operations or steps may not be executed in the order in which they appear in the embodiments of the present application or in parallel, and the sequence number of the operation is only used to distinguish the different operations, and the sequence number itself does not represent any execution order. In addition, these processes may include more or fewer operations, and these operations or steps may be executed in sequence or in parallel, and these operations or steps may be combined.

[0077] Through the description of the above implementation methods, those skilled in the art can clearly understand that the above-mentioned embodiment methods can be implemented by means of software plus a necessary general hardware platform, and of course by hardware, but in many cases the former is a better implementation method. Based on such an understanding, the technical solution of the present application is essentially or the part that contributes to the prior art can be embodied in the form of a software product, which is stored in a storage medium (such as ROM / RAM, disk, CD) as described above, and includes a number of instructions for a terminal device to execute the methods described in each embodiment of the present application.

[0078] The above are only preferred embodiments of the present application, and are not intended to limit the patent scope of the present application. Any equivalent structure or equivalent process transformation made using the contents of the present application specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present application.

Claims

1. A method for determining a reflection position in an optical fiber, characterized in that: The method comprises: The signal transmitting end generates a correlation sequence, dynamically adjusts the duty cycle of the correlation sequence, modulates it to the detection wavelength and sends it to the optical fiber to be tested; The signal receiving end receives the reflected light signal of the optical fiber to be tested, and after signal processing, performs correlation operation with the correlation sequence of the transmitting end, and determines the reflection position through the time delay of the correlation peak; wherein, the reflected light signals from each reflection point of the optical fiber to be tested are interlaced in time sequence.

2. The method for determining a reflection position in an optical fiber according to claim 1, characterized in that: The dynamically adjusting the duty cycle of the related sequence includes: A certain length of 0 sequence is added after the correlation sequence or the emission light is turned off, so that after the correlation sequence is sent, it pauses for several cycles before starting to send again.

3. The method for determining a reflection position in an optical fiber according to claim 2, characterized in that: The duration of the 0 sequence is lengthened or the duration of turning off the emitted light is an integer multiple of the duration of the relevant sequence.

4. The method for determining a reflection position in an optical fiber according to claim 1, characterized in that: The dynamically adjusting the duty cycle of the related sequence includes: The content of the correlation sequence is set to 0 or the emitted light is turned off, so that the reflected light signal from each reflection point of the optical fiber to be tested becomes intermittent; the length of the retained content in the correlation sequence accounts for 1 / M of the total length of the correlation sequence, where M is an integer less than the total length of the correlation sequence.

5. The method for determining a reflection position in an optical fiber according to claim 4, characterized in that: The correlation peaks obtained for each weak reflection when different M values ​​are taken are recorded, and the time delay of the correlation peak is determined according to the highest correlation peak of each weak reflection.

6. A system for determining a reflection position in an optical fiber, characterized in that: include: The transmitting device is arranged at the signal transmitting end, and is used to generate a correlation sequence, dynamically adjust the duty cycle of the correlation sequence, modulate it to the detection wavelength, and send it to the optical fiber to be tested; The receiving device is arranged at the signal receiving end, and is used to receive the reflected light signal of the optical fiber to be tested, and after signal processing, perform correlation operation with the correlation sequence of the transmitting end, and determine the reflection position through the time delay of the correlation peak; wherein the reflected light signals from each reflection point of the optical fiber to be tested are interlaced in time sequence; The coupler is used to couple the emitting device and the receiving device to the optical fiber to be tested.

7. The system for determining a reflection position in an optical fiber according to claim 6, characterized in that: The originating device comprises: A sequence generation module, which is used to generate related sequences; A sequence adjustment module, which is used to dynamically adjust the duty cycle of the related sequence so that the reflected light signals of each reflection point of the optical fiber to be tested are staggered in time sequence; A digital-to-analog conversion module, which is used to convert the dynamically adjusted digital signal into an analog signal; The optoelectronic modulation module is used to modulate the correlation sequence after digital-to-analog conversion to the detection wavelength and send it to the optical fiber to be tested through the coupler.

8. The system for determining a reflection position in an optical fiber according to claim 7, characterized in that: The sequence adjustment module adjusts the duty cycle of the related sequence, including: The sequence adjustment module adds a certain length of 0 sequence after the relevant sequence or turns off the emission light; The duration of the 0 sequence is lengthened or the duration of turning off the emitted light is an integer multiple of the duration of the relevant sequence.

9. The system for determining a reflection position in an optical fiber according to claim 7, characterized in that: The sequence adjustment module adjusts the duty cycle of the related sequence, including: The sequence adjustment module sets the relevant sequence content interval to 0 or turns off the emission light; The length of the retained content in the correlation sequence accounts for 1 / M of the total length of the correlation sequence, where M is an integer less than the total length of the correlation sequence.

10. The system for determining a reflection position in an optical fiber according to any one of claims 6 to 9, characterized in that: The receiving device comprises: A filter, which is used to filter the reflected light signal of the optical fiber to be tested; An amplifier, used to amplify the filtered optical signal; A photodetector, which is used to detect the amplified light signal and perform photoelectric conversion; The signal processor is used to perform correlation operation on the sequence after photoelectric conversion and the correlation sequence of the transmitting end, and determine the reflection position through the time delay of the correlation peak.

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