A method and system for determining reflection position in optical fiber

Abstract

A method and system for determining the reflection position in an optical fiber, relating to the field of online monitoring of optical fiber lines, is disclosed. The method includes: a signal transmitting end generating a correlation sequence, dynamically adjusting the duty cycle of the correlation sequence, and modulating it onto a detection wavelength before transmitting it to the optical fiber under test; a signal receiving end receiving the reflected light signal from the optical fiber under test, processing the signal, and performing correlation calculation with the correlation sequence from the transmitting end, determining the reflection position by the time delay of the correlation peak; wherein the reflected light signals from each reflection point of the optical fiber under test are interleaved in time, reducing the overlap of strong and weak reflection signals in time, and the correlation peaks of different reflection signals can still be obtained based on correlation detection, thereby accurately determining the reflection position based on the time delay of the correlation peak.

Description

Technical Field

[0001] This application relates to the field of online monitoring of optical fiber lines, specifically to a method and system for determining the reflection position in an optical fiber. Background Technology

[0002] An optical time-domain reflectometer (OTDR) can test the continuity of a single optical fiber under test and locate the fault point based on the reflected signal of the link. However, it is difficult to use in point-to-multipoint networks such as optical access networks because when the OTDR is connected to a passive optical network (PON), the backscattered signal received is the superposition of the various branches of the PON network, making it difficult to distinguish which branch the signal comes from and thus impossible to locate the fault.

[0003] Correlation-based OTDR is another promising detection method. It uses digital circuits and optical transceivers to modulate a direct spread spectrum sequence onto an optical signal. The reflected signal returns to the OLT during transmission, is filtered, amplified, and then converted back into an electrical signal. This signal is then correlated with the original transmitted sequence, and the reflection location is precisely determined based on the time delay of the correlation peak. This method offers high detection sensitivity and spatial resolution, reducing the cost of line monitoring systems. However, in real-world environments, the signals reflected from the fiber under test are highly complex, with strong and weak signals often differing by tens of dB. During correlation detection, the spectra of signals containing the same information overlap, with strong signals masking weak signals, making weak reflections unobservable. Signals requiring close monitoring are thus obscured, reducing the usability of the OTDR system. Therefore, the application of correlation-based OTDR in practical line monitoring remains challenging. Summary of the Invention

[0004] This application provides a method and system for determining the reflection position in an optical fiber, which can solve the technical problem in the prior art where the signal spectrum of the same content overlaps during correlation detection, and strong signals mask weak signals, making weak reflections unobservable.

[0005] In a first aspect, embodiments of this application provide a method for determining the reflection position in an optical fiber, the method comprising:

[0006] The signal transmitting end generates a correlation sequence, and after dynamically adjusting the duty cycle of the correlation sequence, it is modulated onto the detection wavelength and sent to the optical fiber under test.

[0007] The signal receiving end receives the reflected light signal from the optical fiber under test. After signal processing, it performs correlation operation with the correlation sequence of the transmitting end and determines the reflection position by the time delay of the correlation peak. The reflected light signals from each reflection point of the optical fiber under test are interleaved in time.

[0008] In this embodiment, by dynamically adjusting the duty cycle of the relevant sequence, the weak reflection signal is staggered from the strong reflection signal in time and will not be completely covered. By dynamically adjusting the duty cycle of the transmission 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 conjunction with the first aspect, in one implementation, the dynamic adjustment of the duty cycle of the relevant sequence includes:

[0010] By adding a certain length of 0 sequence after the relevant sequence or turning off the emitted light, the transmission pauses for several cycles after the relevant sequence is sent before starting to transmit again.

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

[0012] In conjunction with the first aspect, in one implementation, the dynamic adjustment of the duty cycle of the relevant sequence includes:

[0013] The relevant sequence content 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 under test is discontinuous; the length of the content retained in the relevant sequence is 1 / M of the total length of the relevant sequence, where M is an integer less than the total length of the relevant sequence.

[0014] In conjunction with the first aspect, in one implementation, the correlation peaks obtained by each weak reflection for different values ​​of M are recorded, and the time delay of the correlation peak is determined based on the highest correlation peak of each weak reflection.

[0015] Secondly, this application provides a system for determining the reflection position in an optical fiber, comprising:

[0016] The transmitting device, located at the signal transmitting end, is used to generate a correlation sequence, dynamically adjust the duty cycle of the correlation sequence, and then modulate it onto the detection wavelength and transmit it to the optical fiber under test.

[0017] The receiving end device, located at the signal receiving end, is used to receive the reflected light signal from the optical fiber under test. After signal processing, it performs correlation operations with the correlation sequence from the transmitting end, and determines the reflection position by the time delay of the correlation peak. The reflected light signals from each reflection point of the optical fiber under test are interleaved in time.

[0018] A coupler is used to couple both the transmitting and receiving devices to the optical fiber under test.

[0019] In conjunction with the second aspect, in one embodiment, the generating device includes:

[0020] The sequence generation module is used to generate relevant sequences;

[0021] The sequence adjustment module is used to dynamically adjust the duty cycle of the relevant sequence so that the reflected light signals at each reflection point of the optical fiber under test are interleaved in time.

[0022] The digital-to-analog converter module is used to convert dynamically adjusted digital signals into analog signals;

[0023] The optoelectronic modulation module is used to modulate the correlation sequence after digital-to-analog conversion onto the detection wavelength and transmit it to the optical fiber under test through a coupler.

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

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

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

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

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

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

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

[0031] A filter is used to filter the reflected light signal from the optical fiber under test.

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

[0033] A photodetector is used to detect amplified optical signals and perform photoelectric conversion.

[0034] The signal processor is used to perform correlation operations between the photoelectric converted sequence and the correlation sequence of the transmitting end, and to determine the reflection position by the time delay of the correlation peak.

[0035] The beneficial effects of the technical solutions provided in this application include:

[0036] By generating a correlation sequence at the signal transmitter and dynamically adjusting the duty cycle of the correlation sequence, the reflected light signals from each reflection point of the optical fiber under test can be interleaved in time. This reduces the overlap of strong and weak reflection signals in time, making weak reflection signals easier to observe. Based on correlation detection, correlation peaks of different strong and weak reflection signals can still be obtained. Then, the reflection position can be accurately determined based on the correlation peak delay, thus improving the robustness and detection capability of the correlation OTDR system under complex conditions. Attached Figure Description

[0037] Figure 1 This is a schematic flowchart of the method for determining the reflection position in an optical fiber according to an embodiment of this application;

[0038] Figure 2 This is a schematic diagram illustrating the principle of dynamically adjusting related sequences in an embodiment of this application;

[0039] Figure 3 This is a schematic diagram of a system for determining the reflection position in an optical fiber according to an embodiment of this application. Detailed Implementation

[0040] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present application.

[0041] To make the objectives, technical solutions, and advantages of this application clearer, the embodiments of this application will be described in further detail below with reference to the accompanying drawings.

[0042] Firstly, an embodiment of a method for determining the reflection position in an optical fiber is provided, which solves the technical problem in the prior art where the signal spectrum of the same content overlaps during related detection, and strong signals mask weak signals, making weak reflections unobservable.

[0043] In one embodiment, reference is made to Figure 1 , Figure 1 This is a flowchart illustrating an embodiment of the method for determining the reflection position in the optical fiber of this 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, and modulates it onto the detection wavelength before transmitting it to the optical fiber under test. Preferably, the correlation sequence is a direct spread spectrum sequence.

[0045] S2: The signal receiving end receives the reflected light signal from the optical fiber under test. After signal processing, it performs correlation operation with the correlation sequence of the transmitting end and determines the reflection position by the time delay of the correlation peak. The reflected light signals from each reflection point of the optical fiber under test are interleaved in time.

[0046] In this embodiment, by dynamically adjusting the duty cycle of the relevant sequence, the weak reflection signal is staggered from the strong reflection signal in time and will not be completely covered. By dynamically adjusting the duty cycle of the transmission 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 typical correlation OTDR system, the correlation sequence is usually transmitted repeatedly at a fixed period, and the probe light carrying the correlation sequence is reflected back at different locations in the fiber under test. For example... Figure 2 As shown in (a), due to the varying distances and reflectivities of each reflection point from the signal transmitter, the intensity of the reflected light signals differs. When the correlation sequence is repeatedly transmitted, the reflected light signals from each reflection point completely overlap, resulting in a combination of strong and weak reflected signals, as shown in (a). Figure 2 As shown in (b), it can be seen that the strong reflection signal completely overwhelms 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 zero sequence after the correlation sequence, or by directly turning off the emitted light after the correlation sequence. This allows for a pause of several cycles after transmitting the correlation sequence before resuming transmission, with the correlation sequences interleaved in timing. The reflected light signal is divided into strong reflection signal and weak reflection signal. In this embodiment, the strong reflection signal and weak reflection signal are as follows: Figure 2 As shown in (c). In this embodiment, the duration of the 0 sequence after the correlation sequence, which is extended by a certain length, or the duration of the emitted light being directly turned off 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 sequence exposure. The length of the 0 sequence extended after the correlation sequence follows the principle of being as short as possible, so that the reflection signals of different sequences do not overlap as much as possible.

[0049] Furthermore, in one embodiment, the method of dynamically adjusting the duty cycle of the correlation sequence can also be: setting the content interval in the correlation sequence to 0, or turning off the emitted light at the content interval in the correlation sequence, so that the reflected light signals from each reflection point of the optical fiber under test are discontinuous and interleaved in time; and the length of the content retained in the correlation sequence is 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 different lengths of weak reflection sequence exposure. The reflected light signal is divided into strong reflection signal and 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 value of M needs to be dynamically adjusted. One possible approach is to record the correlation peaks obtained by each weak reflection with different values ​​of M, and determine the time delay of the correlation peak based on the highest correlation peak of each weak reflection.

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

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

[0053] The transmitting device is located at the signal transmitting end and is used to generate a correlation sequence. After dynamically adjusting the duty cycle of the correlation sequence, it is modulated onto the detection wavelength and sent to the optical fiber under test.

[0054] The receiving end device is located at the signal receiving end and is used to receive the reflected light signal of the optical fiber under test. After signal processing, it performs correlation operation with the correlation sequence of the transmitting end and determines the reflection position by the time delay of the correlation peak. The reflected light signals from each reflection point of the optical fiber under test are interleaved in time.

[0055] A coupler is used to couple both the transmitting and receiving devices to the optical fiber under test.

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

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

[0058] The sequence adjustment module is used to dynamically adjust the duty cycle of the relevant sequences generated by the sequence generation module, so that the reflected light signals of each reflection point of the optical fiber under test are interleaved in time.

[0059] The digital-to-analog converter module is used to convert dynamically adjusted digital signals into analog signals.

[0060] The optoelectronic modulation module is used to modulate the correlation sequence of the analog signal after digital-to-analog conversion onto the detection wavelength and transmit it to the optical fiber under test through a coupler.

[0061] In another embodiment, the receiving device includes a filter, an amplifier, a photodetector, and a signal processor.

[0062] Among them, the filter is used to filter the reflected light signal of the optical fiber under test.

[0063] An amplifier is used to amplify the optical signal after it has been filtered by a filter.

[0064] A photodetector is used to detect optical signals amplified by an amplifier and to perform photoelectric conversion.

[0065] The signal processor is used to perform correlation operations between the photoelectric converted sequence and the correlation sequence of the transmitting end, and to determine the reflection position by the time delay of the correlation peak.

[0066] In the above system, the sequence adjustment module can adjust the duty cycle of the relevant sequence in two ways. One way is that the sequence adjustment module adds a certain length of 0 sequence or turns off the emitted light after the relevant sequence. Furthermore, the duration of the 0 sequence or the duration of the emitted light being turned off is 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 approach is for the sequence adjustment module to set the interval of the relevant sequence content to 0 or to turn off the emitted light. Furthermore, the length of the retained content in the relevant sequence is 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] Thirdly, based on the aforementioned system for determining the reflection position in an optical fiber, an embodiment of an optical fiber line monitoring method is provided, which includes 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 by the sequence adjustment module, so that the reflected light signals from each reflection point of the optical fiber under test are interleaved in time. The dynamically adjusted digital signal is converted into an analog signal by the digital-to-analog converter module, and then the correlation sequence of the analog signal is modulated onto the detection wavelength by the optoelectronic modulation module and sent to the optical fiber under test through the coupler. At the same time, the content of the correlation sequence and the corresponding time of optical signal emission are recorded.

[0070] Step 2: Possible reflection points in the optical fiber under test will cause the optical signal to be reflected and retrieved by a coupler. The filter of the receiving device filters the reflected optical signal from the optical fiber under test, and then the amplifier amplifies the optical signal. The amplified optical signal is detected by a photodetector and undergoes photoelectric conversion. Then, signal processing is performed. Specifically, the photoelectric converted sequence is correlated with the corresponding sequence from the transmitting end, and the time delay and peak value of the correlation peak are analyzed.

[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. The light intensity change of each reflection point is monitored based on the relevant amplitude change 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 from each reflection point of the optical fiber under test received by the receiving device are interleaved in time. Based on correlation detection, correlation peaks of reflection signals with different strengths can still be obtained, and the reflection position can be accurately determined according to the time delay, thereby improving the robustness and detection capability of the correlation OTDR system under complex conditions.

[0073] It should be noted that the sequence numbers of the embodiments in this application are for descriptive purposes only and do not represent the superiority or inferiority of the embodiments.

[0074] The terms "comprising" and "having," and any variations thereof, in the specification, claims, and accompanying drawings of this application are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or apparatus that includes a series of steps or units is not limited to the listed steps or units, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to such process, method, product, or apparatus. The terms "first," "second," and "third," etc., are used to distinguish different objects, etc., and do not indicate a sequence, nor do they limit "first," "second," and "third" to different types.

[0075] In the description of the embodiments of this application, terms such as "exemplary," "for example," or "for instance" are used to indicate examples, illustrations, or explanations. Any embodiment or design described as "exemplary," "for example," or "for instance" in the embodiments of this application should not be construed as being more preferred or advantageous than other embodiments or designs. Specifically, the use of terms such as "exemplary," "for example," or "for instance" is intended to present the relevant concepts in a specific manner. Furthermore, in the description of the embodiments of this application, "a plurality of" refers to two or more.

[0076] In some processes described in the embodiments of this application, multiple operations or steps are included in a specific order. However, it should be understood that these operations or steps may not be executed in the order they appear in the embodiments of this application, or they may be executed in parallel. The sequence number of the operation is only used to distinguish 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 sequentially or in parallel, and these operations or steps may be combined.

[0077] Through the above description of the embodiments, those skilled in the art can clearly understand that the methods of the above embodiments can be implemented by means of software plus necessary general-purpose hardware platforms. Of course, they can also be implemented by hardware, but in many cases the former is a better implementation method. Based on this understanding, the technical solution of this application, in essence, or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product is stored in a storage medium (such as ROM / RAM, magnetic disk, optical disk) as described above, and includes several instructions to cause a terminal device to execute the methods described in the various embodiments of this application.

[0078] The above are merely preferred embodiments of this application and do not limit the patent scope of this application. Any equivalent structural or procedural transformations made using the content of this application's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of this application.

Claims

1. A method for determining the reflection position in an optical fiber, characterized in that, The method includes: The signal transmitting end generates a correlation sequence, and after dynamically adjusting the duty cycle of the correlation sequence, it is modulated onto the detection wavelength and sent to the optical fiber under test. The signal receiving end receives the reflected light signal from the optical fiber under test. After signal processing, it performs correlation operation with the correlation sequence of the transmitting end and determines the reflection position by the time delay of the correlation peak. The reflected light signals from each reflection point of the optical fiber under test are interleaved in time.

2. The method for determining the reflection position in an optical fiber as described in claim 1, characterized in that, The dynamic adjustment of the duty cycle of the relevant sequence includes: By adding a certain length of 0 sequence after the relevant sequence or turning off the emitted light, the transmission pauses for several cycles after the relevant sequence is sent before starting to transmit again.

3. The method for determining the reflection position in an optical fiber as described in claim 2, characterized in that, The duration of the 0 sequence is extended or the duration of the emitted light is turned off is an integer multiple of the duration of the relevant sequence.

4. The method for determining the reflection position in an optical fiber as described in claim 1, characterized in that, The dynamic adjustment of the duty cycle of the relevant sequence includes: The relevant sequence content 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 under test is discontinuous; the length of the content retained in the relevant sequence is 1 / M of the total length of the relevant sequence, where M is an integer less than the total length of the relevant sequence.

5. The method for determining the reflection position in an optical fiber as described in claim 4, characterized in that, Record the correlation peaks obtained from each weak reflection for different values ​​of M, and determine the time delay of the correlation peak based on the highest correlation peak of each weak reflection.

6. A system for determining the reflection position in an optical fiber, characterized in that, include: The transmitting device, located at the signal transmitting end, is used to generate a correlation sequence, dynamically adjust the duty cycle of the correlation sequence, and then modulate it onto the detection wavelength and transmit it to the optical fiber under test. The receiving end device, located at the signal receiving end, is used to receive the reflected light signal from the optical fiber under test. After signal processing, it performs correlation operations with the correlation sequence from the transmitting end, and determines the reflection position by the time delay of the correlation peak. The reflected light signals from each reflection point of the optical fiber under test are interleaved in time. A coupler is used to couple both the transmitting and receiving devices to the optical fiber under test.

7. The system for determining the reflection position in an optical fiber as described in claim 6, characterized in that, The transmitting device includes: The sequence generation module is used to generate relevant sequences; The sequence adjustment module is used to dynamically adjust the duty cycle of the relevant sequence so that the reflected light signals at each reflection point of the optical fiber under test are interleaved in time. The digital-to-analog converter module is used to convert dynamically adjusted digital signals into analog signals; The optoelectronic modulation module is used to modulate the correlation sequence after digital-to-analog conversion onto the detection wavelength and transmit it to the optical fiber under test through a coupler.

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

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

10. The system for determining the reflection position in an optical fiber as described in any one of claims 6-9, characterized in that, The receiving device includes: A filter is used to filter the reflected light signal from the optical fiber under test. An amplifier, used to amplify filtered optical signals; A photodetector is used to detect amplified optical signals and perform photoelectric conversion. The signal processor is used to perform correlation operations between the photoelectric converted sequence and the correlation sequence of the transmitting end, and to determine the reflection position by the time delay of the correlation peak.

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