Differential group delay measurement method, device, equipment, storage medium and computer program product

Abstract

The present application relates to the technical field of optical fiber characteristic measurement, and discloses a differential group delay measurement method, device, equipment, storage medium and computer program product, including: obtaining a mixed signal transmitted in a few-mode optical fiber to be tested, the mixed signal including at least two spatial mode optical signals; collecting electrical signal change information based on the mixed signal, and generating a light field interference signal according to the electrical signal change information; performing a cepstrum analysis on the light field interference signal through Fourier transform to determine the peak position in the light field interference signal; and calculating the differential group delay between two spatial modes in the few-mode optical fiber to be tested according to the peak position. Performing a cepstrum analysis on the received signal data, extracting the cepstrum features of the signal through Fourier transform, and then extracting the feature information of the differential mode group delay, while ensuring high measurement accuracy and reliability, reducing the dependence on special signal sources and expensive equipment, and reducing the cost of actual operation.

Description

Technical Field

[0001] The present application relates to the technical field of optical fiber characteristic measurement, and in particular to a differential group delay measurement method, device, equipment, storage medium and computer program product. Background Art

[0002] Existing methods for measuring differential mode group delay include time-domain flight method, broadband spectrum analysis, microwave interferometry, spatial and spectral imaging analysis, Fourier domain mode-locked laser method, digital resampling method, etc. Although these methods have certain accuracy and feasibility, most of them require expensive and cumbersome equipment and rely on specific signal sources. In actual application scenarios, especially field testing, it is usually preferred to adopt technologies that do not require dedicated signal sources, and the difficulty and cost of actual operations cannot be reduced. Summary of the invention

[0003] The main purpose of the present application is to provide a differential group delay measurement method, apparatus, device, storage medium and computer program product, aiming to solve the technical problem that the existing methods for measuring differential mode group delay, although having certain accuracy and feasibility, mostly require expensive and cumbersome equipment, rely on specific signal sources, and increase the difficulty and cost of actual operation.

[0004] To achieve the above object, the present application proposes a differential group delay measurement method, the differential group delay measurement method comprising:

[0005] Acquire a mixed signal transmitted in the few-mode optical fiber to be tested, wherein the mixed signal includes optical signals of at least two spatial modes;

[0006] Collecting electrical signal change information based on the mixed signal, and generating a light field interference signal according to the electrical signal change information;

[0007] Performing a cepstrum analysis on the light field interference signal by Fourier transform to determine a peak position in the light field interference signal;

[0008] The differential group delay between two spatial modes in the few-mode optical fiber to be tested is calculated according to the peak position.

[0009] Optionally, the step of performing cepstrum analysis on the light field interference signal by Fourier transform to determine the peak position in the light field interference signal includes:

[0010] Converting the light field interference signal into a frequency domain signal based on Fourier transform;

[0011] The frequency domain signal is processed by a preset function operation, and the processing result is subjected to inverse Fourier transform to obtain delay information;

[0012] A peak position in the light field interference signal is determined according to the delay information.

[0013] Optionally, the step of collecting the electric signal change information based on the mixed signal and generating the light field interference signal according to the electric signal change information includes:

[0014] Demultiplexing the mixed signal based on a mode demultiplexer to generate a target signal, and combining the target signal into a single light beam based on a first coupler;

[0015] The single light beam is converted into an electrical signal by a photoelectric converter, and data of changes of current in the electrical signal over time are collected to obtain information on changes in the electrical signal;

[0016] The electrical signal change information is processed offline to obtain a light field interference signal.

[0017] Optionally, before the step of obtaining the mixed signal transmitted in the few-mode optical fiber to be tested, the method further includes:

[0018] Modulating a continuous wave laser signal emitted by a preset light source to obtain a modulated signal;

[0019] Inputting the modulated signal into a second coupler to generate a first optical signal and a second optical signal;

[0020] The first optical signal and the second optical signal are converted into the mixed signal based on a mode multiplexer, and the mixed signal is input into the few-mode optical fiber to be tested.

[0021] Optionally, the step of converting the first optical signal and the second optical signal into the mixed signal based on a mode multiplexer and inputting the mixed signal into the few-mode optical fiber to be tested comprises:

[0022] Adjusting the output power of the first optical signal by an optical attenuation unit to obtain a third optical signal;

[0023] Inputting the second optical signal and the third optical signal into the corresponding mode ports of the mode multiplexer to perform spatial mode conversion and determine the stimulated mode;

[0024] The mixed signal is generated according to the stimulated mode and input into the few-mode optical fiber to be tested.

[0025] Optionally, the step of calculating the differential group delay between two spatial modes in the few-mode optical fiber to be tested according to the peak position comprises:

[0026] Taking mode crosstalk into consideration, correcting the erroneous peak value in the peak position to obtain a target peak value;

[0027] The differential group delay between two spatial modes in the few-mode optical fiber to be tested is calculated based on the target peak value and the length of the few-mode optical fiber to be tested.

[0028] In addition, to achieve the above-mentioned purpose, the present application also proposes a differential group delay measurement device, the differential group delay measurement device comprising:

[0029] A signal acquisition module, used to acquire a mixed signal transmitted in the few-mode optical fiber to be tested, wherein the mixed signal includes at least two optical signals of spatial modes;

[0030] A photoelectric conversion module, used for collecting electrical signal change information based on the mixed signal, and generating a light field interference signal according to the electrical signal change information;

[0031] A cepstrum analysis module, used to perform cepstrum analysis on the light field interference signal through Fourier transform to determine the peak position in the light field interference signal;

[0032] A delay calculation module is used to calculate the differential group delay between two spatial modes in the few-mode optical fiber to be tested according to the peak position.

[0033] In addition, to achieve the above-mentioned purpose, the present application also proposes a differential group delay measurement device, which includes: a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the computer program is configured to implement the steps of the differential group delay measurement method described above.

[0034] In addition, to achieve the above-mentioned purpose, the present application also proposes a storage medium, which is a computer-readable storage medium, and a computer program is stored on the storage medium. When the computer program is executed by a processor, the steps of the differential group delay measurement method described above are implemented.

[0035] In addition, to achieve the above-mentioned purpose, the present application also provides a computer program product, which includes a computer program, and when the computer program is executed by a processor, the steps of the differential group delay measurement method as described above are implemented.

[0036] The present application discloses obtaining a mixed signal transmitted in a few-mode optical fiber to be tested, wherein the mixed signal includes optical signals of at least two spatial modes; collecting electrical signal change information based on the mixed signal, and generating an optical field interference signal according to the electrical signal change information; performing a cepstrum analysis on the optical field interference signal through Fourier transform to determine the peak position in the optical field interference signal; and calculating the differential group delay between the two spatial modes in the few-mode optical fiber to be tested according to the peak position. Cepstrum analysis is performed on the received signal data, and the cepstrum features of the signal are extracted through Fourier transform, thereby extracting the characteristic information of the differential mode group delay, which reduces the dependence on special signal sources and expensive equipment and the cost of actual operation while ensuring high measurement accuracy and reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present application and, together with the description, serve to explain the principles of the present application.

[0038] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0039] Figure 1 This is a flow chart of a first embodiment of a differential group delay measurement method of the present application;

[0040] Figure 2 The signal processing flow chart of the cepstrum analysis for this application;

[0041] Figure 3 Schematic diagram of the experimental device for measuring the differential mode group delay of few-mode optical fiber in this application;

[0042] Figure 4 It is a schematic diagram of the delay between LP01 mode and LP11a mode;

[0043] Figure 5 It is a schematic diagram of the delay between LP01 mode and LP11b mode;

[0044] Figure 6 It is a schematic diagram of the delay between LP01 mode and LP21a mode;

[0045] Figure 7 It is a schematic diagram of the delay between LP01 mode and LP21b mode;

[0046] Figure 8 It is a schematic diagram of the delay between LP01 mode and LP02 mode;

[0047] Fig. 9 The relationship between the differential mode group delay measurement results and wavelength of the cepstrum method and the reference method is shown in FIG.

[0048] Fig.10 It is the difference diagram of the measurement results between the C-band cepstrum method and the reference method;

[0049] Fig.11 This is a flow chart of a second embodiment of a differential group delay measurement method of the present application;

[0050] Fig.12 Schematic diagram of a measurement system for differential mode group delay of few-mode optical fiber of the present application;

[0051] Fig.13 This is a flow chart of a third embodiment of a differential group delay measurement method of the present application;

[0052] Fig.14 This is a schematic diagram of the module structure of a differential group delay measurement device according to an embodiment of the present application;

[0053] Fig.15 Schematic diagram of the device structure of the hardware operating environment involved in the differential group delay measurement method in the embodiment of the present application.

[0054] The purpose, features and advantages of this application will be further described in conjunction with the embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0055] It should be understood that the specific embodiments described herein are only used to explain the technical solutions of the present application and are not used to limit the present application.

[0056] In order to better understand the technical solution of the present application, a detailed description will be given below in conjunction with the accompanying drawings and specific implementation methods.

[0057] The main solution of the embodiment of the present application is: obtaining a mixed signal transmitted in the few-mode optical fiber to be tested, wherein the mixed signal includes optical signals of at least two spatial modes; collecting electrical signal change information based on the mixed signal, and generating a light field interference signal according to the electrical signal change information; performing a cepstrum analysis on the light field interference signal through Fourier transform to determine the peak position in the light field interference signal; and calculating the differential group delay between the two spatial modes in the few-mode optical fiber to be tested according to the peak position.

[0058] With the rapid development of information technology, the demand for transmission capacity of optical fiber communication links continues to grow. However, the transmission capacity of optical fiber communication systems using single-mode fiber (Single Mode Fiber) as the transmission medium is approaching its theoretical limit - the Shannon limit. To solve this capacity bottleneck, space division multiplexing (SDM) technology came into being. By introducing multiple paths that can independently transmit signals in the lateral spatial dimension, the transmission capacity of the system is greatly improved. Among all the implementation schemes of SDM technology, mode-division multiplexing (MDM) technology based on few-mode fiber (FMF) can use a limited number of orthogonal transmission modes as independent channels for parallel transmission in the same optical fiber, which can significantly improve the transmission capacity of optical fiber communication systems and has become the focus of research on next-generation optical communication systems.

[0059] Few-mode optical fibers have problems such as mode coupling, differential mode group delay (DMGD) and mode-related loss during transmission. These damages limit the transmission performance and transmission distance of the mode division multiplexing system. Currently, most few-mode optical fiber transmission experiments use multi-input multi-output (MIMO) equalization technology to compensate for the impact of mode coupling. The complexity of the equalization technology is closely related to the size of the differential mode group delay. The differential mode group delay is the delay difference caused by the propagation of different modes of optical signals in the optical fiber. Under the same optical fiber length, the larger the differential mode group delay value, the more significant the time difference between different modes arriving at the receiving end, resulting in an increase in the complexity of the MIMO calculation. Therefore, in order to optimize the theoretical model of few-mode optical fibers and the design of optical transmission systems, it is necessary to accurately measure the differential mode group delay of few-mode optical fibers. Existing methods for measuring differential mode group delay include time-domain flight method, broadband spectrum analysis, microwave interferometry, spatial and spectral imaging analysis, Fourier domain mode-locked laser method, digital resampling method, etc. Although these methods have certain accuracy and feasibility, most of them require expensive and cumbersome equipment, or rely on specific signal sources, which increases the difficulty and cost of actual operation.

[0060] Therefore, the present application provides a method for measuring the differential mode group delay of few-mode optical fiber based on cepstrum signal processing technology, which realizes the accurate measurement of the differential mode group delay of few-mode optical fiber by utilizing the random cache data and a single photodetector (PD) in the existing transceiver without adding additional hardware.

[0061] It should be noted that the execution subject of this embodiment can be a computing service device with data processing, network communication and program running functions, such as a computer, or an electronic device capable of realizing the above functions. The following takes the measurement system as an example to illustrate this embodiment and the following embodiments.

[0062] Based on this, the embodiment of the present application provides a differential group delay measurement method, referring to Figure 1 , Figure 1 This is a flow chart of the first embodiment of the differential group delay measurement method of the present application.

[0063] In this embodiment, the differential group delay measurement method includes:

[0064] Step S10, obtaining a mixed signal transmitted in the few-mode optical fiber to be tested, wherein the mixed signal includes optical signals of at least two spatial modes.

[0065] It should be noted that few-mode fiber is a type of fiber that can support a limited number of transmission modes. Compared with single-mode fiber, it can use multiple modes to transmit signals simultaneously, thereby improving the transmission capacity of the optical fiber communication system. A mixed signal is a signal composed of optical signals of at least two spatial modes. In few-mode fiber, different spatial modes have different electromagnetic field distributions and propagation characteristics. When optical signals of these modes are transmitted simultaneously in the optical fiber, they are superimposed on each other to form a mixed signal. For example, in a few-mode fiber that supports LP01 and LP11 modes, the mixed signal is a complex optical signal containing LP01 mode optical signals and LP11 mode optical signals. Spatial mode refers to the distribution form of optical signals in optical fibers when they propagate in the form of electromagnetic fields, such as LP01, LP11, etc.

[0066] Step S20: collecting electrical signal change information based on the mixed signal, and generating a light field interference signal according to the electrical signal change information.

[0067] It should be noted that the electrical signal change information refers to the data related to the change of current or voltage in the electrical signal over time after the optical information in the mixed signal is converted into an electrical signal. In the photoelectric conversion process, the intensity, frequency and other characteristics of the optical signal are converted into corresponding changes in the electrical signal. These changes contain information about different spatial modes in the mixed signal. For example, changes in the intensity of the optical signal will cause changes in the output current of the photoelectric converter. By collecting the data on the change of these currents over time, the electrical signal change information is obtained. The light field interference signal is a signal form obtained after offline processing of the electrical signal change information, which reflects the interference between optical signals of different spatial modes in the mixed signal.

[0068] It should be understood that when collecting information on changes in electrical signals, the mixed signal can first be demultiplexed using a mode demultiplexer to decompose it into signals of different spatial modes. Then, these demultiplexed signals are combined into a single light beam through a coupler, so that signals of different modes can be transmitted on the same optical path, which is convenient for subsequent processing. Next, a photoelectric converter is used to convert the single light beam into an electrical signal. The photoelectric converter converts the intensity change of the optical signal into a change in current based on the photoelectric effect. In this process, data on the change of current in the electrical signal over time is collected through data acquisition equipment (such as an oscilloscope, data acquisition card, etc.), thereby obtaining information on changes in the electrical signal.

[0069] Step S30: Perform cepstrum analysis on the light field interference signal by Fourier transform to determine the peak position of the light field interference signal.

[0070] It should be noted that cepstrum analysis is a signal processing technique used to extract hidden periodic information or delay information from a signal. The peak position refers to the time or frequency position corresponding to the point where the signal amplitude reaches the maximum value in the cepstrum of the light field interference signal.

[0071] It should be understood that in the original light field interference signal, the differential mode group delay information may be masked by other signal components, but by converting the signal to the frequency domain through Fourier transform, and then converting the spectral features related to the delay into peaks in the cepstrum through logarithmic operations and inverse Fourier transform processing, the delay information can be made more obvious and easier to extract. For example, in the frequency domain, the phase difference caused by the differential mode group delay of the frequency components of different modes will be reflected in the phase characteristics of the spectrum. After cepstrum analysis, this phase difference-related information is converted into the peak position, so that the features related to the differential mode group delay can be accurately identified from the signal.

[0072] In one example, reference Figure 2 , Figure 2 This is the signal processing flow chart of the cepstrum analysis of this application. This is the light field interference signal. Next, we use the cepstrum method to Through Fourier transformation, Convert to frequency domain , then square( ) and then perform exponential operation and take the logarithm to get , and finally the inverse Fourier transform is performed to determine the objective function. From the objective function, it can be seen that the interference of noise may affect the peak size at the delay, but the position of the peak at the delay is not affected. Therefore, the group delay difference between a pair of spatial modes can be calculated by identifying the position of the peak.

[0073] Step S40, calculating the differential group delay between two spatial modes in the few-mode optical fiber to be tested according to the peak position.

[0074] It is understandable that in few-mode optical fibers, light signals in different spatial modes have different propagation speeds, which results in time delay differences during transmission, and the time delay differences are the differential group delays between different modes. A series of processing (such as Fourier transform, cepstrum analysis, etc.) is performed on the light field interference signal to obtain the cepstrum of the light field interference signal. The peak position in the cepstrum is directly related to the differential group delay between the two spatial modes. By determining the peak information in the cepstrum, the differential group delay between different modes can be calculated.

[0075] It should be understood that when calculating the differential group delay between the two spatial modes in the few-mode optical fiber to be tested according to the peak position, the size of the differential mode group delay can be calculated based on a preset delay relationship formula, or it can be determined by a corresponding mapping relationship table class.

[0076] In one example, reference Figure 3 , Figure 3 Schematic diagram of the experimental device for measuring the differential mode group delay of the few-mode fiber in this application. In the data generation module, the continuous wave laser emits a four-level pulse amplitude modulation (PAM4) signal with a baud rate of 50 Gbaud. The signal is upsampled by the arbitrary waveform generator (AWG) through an electro-absorption modulator. After being modulated by the Mach-Zehnder Modulator (MZM), the modulated signal is divided into two paths by a 50:50 coupler in the mode multiplexing module, one of which is adjusted in power by an optical attenuator, and the other remains unchanged. The signals of the two paths are sent to the two ports of the spatial mode multiplexer to excite a pair of spatial modes. The LP01 and LP11a modes are excited in the figure. The multiplexed signal is transmitted through a 5 km long few-mode fiber, which supports six spatial modes (LP01, LP11a, LP11b, LP02, LP21a, LP21b). After the transmission is completed, the signal in the mode demultiplexing module is demultiplexed by the spatial mode demultiplexer to demultiplex the LP01 and LP11a mode signals, and then the two signals are combined by the coupler. The combined signal is detected by the photodetector in the photoelectric detection module and processed by the analog-to-digital converter (ADC) to obtain the light field signal. Finally, the pilot analysis module performs offline processing to demodulate the delay. Finally, the formula can be used Calculate the differential mode group delay, where is the transmission distance of the optical fiber. is the differential group delay between the two modes.

[0077] Furthermore, in order to consider the small peak effect caused by non-ideal mode crosstalk, the accuracy of differential group delay measurement is improved. The step S40 may include:

[0078] The erroneous peak in the peak position is corrected by taking mode crosstalk into consideration to obtain a target peak; and the differential group delay between two spatial modes in the few-mode optical fiber to be tested is calculated based on the target peak and the length of the few-mode optical fiber to be tested.

[0079] It should be noted that mode crosstalk is the mutual interference phenomenon caused by the imperfection of the optical fiber (such as uneven refractive index, bending, etc.) during the transmission of optical signals in few-mode optical fibers. When performing cepstrum analysis on the optical field interference signal to determine the peak position to calculate the differential mode group delay, due to the influence of factors such as mode crosstalk, the peak that does not correspond to the true differential mode group delay appears in the cepstrum.

[0080] It is understandable that before correcting the error peak, it is necessary to identify the error peak caused by mode crosstalk, and by analyzing the peak changes in the inverse spectrum of the light field interference signal obtained under different fiber lengths, different input optical powers, etc., to determine which peaks appear stably and in accordance with physical laws, and which peaks appear randomly due to mode crosstalk. After identifying the error peak, the error peak is corrected according to certain algorithms and rules. For example, based on statistical analysis, the probability of peak occurrence and the stability of position in multiple measurements can be calculated. For those peaks with low probability of occurrence and unstable position, they are judged as error peaks and are eliminated or corrected.

[0081] In one example, reference Figure 4 , Figure 5 , Figure 6 , Figure 7 and Figure 8 . Figure 4 This is a schematic diagram of the delay between LP01 mode and LP11a mode. Figure 5 This is a schematic diagram of the delay between LP01 mode and LP11b mode. Figure 6 This is a schematic diagram of the delay between LP01 mode and LP21a mode. Figure 7 This is a schematic diagram of the delay between LP01 mode and LP21b mode. Figure 8Schematic diagram of the delay between the LP01 mode and the LP02 mode. The figure shows the delay between spatial modes measured at 1550 nm using this scheme. The horizontal axis is the time delay Delay (picoseconds ps), and the vertical axis is the peak height (Peaks Height). Taking LP01 as a reference, the time delays of the other five modes and the fundamental mode are measured. The delays of LP11a (a), LP11b (b), LP21a (c), LP21b (d) and LP02 (e) are 36200 ps, ​​36760 ps, ​​75540 ps, ​​77820 ps and 85960 ps, ​​respectively. Figure 5 , Figure 7 and Figure 8 The small peaks in the figure are due to the non-ideal mode crosstalk in the spatial multiplexer and demultiplexer. In addition, in addition to the fundamental mode, the time delay of other spatial mode pairs can also be measured using the method proposed in the present invention. For example, the delay difference between LP11a and LP11b is about 560 ps, ​​and the delay difference between LP21a and LP21b is about 280 ps. Finally, the obtained time delay is used using the formula The differential mode group delay can be calculated.

[0082] In another example, reference Fig. 9 and Fig.10 , Fig. 9 The relationship between the differential mode group delay measurement results of the cepstrum method and the reference method and the wavelength is shown in the figure. Fig.10 This is the difference diagram of the measurement results of the C-band cepstrum method and the reference method. In order to verify the accuracy of the scheme, this scheme is compared with the traditional method. Fig. 9 The wavelength dependence of the differential group delay of each mode is shown using two methods ((a) cepstrum method and (b) traditional time-of-flight method). The horizontal axis represents wavelength (Wavelength) in nanometers (nm), and the vertical axis represents differential mode group delay (DMGD) in picoseconds per meter (ps / m). It can be seen from the results that the mode differential group delay has little dependence on wavelength. Fig.10 Further comparison of the measurement difference (Error) between the two methods shows that within the C band range (c), the measurement results based on the cepstrum analysis method are highly consistent with the test results of the traditional method, with a small difference. In the 1540 nm~1555 nm band range, all mode measurement results are basically the same, with slight fluctuations in other bands. These results show that the method proposed in this scheme has high accuracy and reliability.

[0083] In this embodiment, a mixed signal transmitted in the few-mode optical fiber to be tested is obtained, and the mixed signal includes at least two spatial mode optical signals; based on the mixed signal, the electric signal change information is collected, and the light field interference signal is generated according to the electric signal change information; the light field interference signal is subjected to cepstrum analysis through Fourier transform to determine the peak position in the light field interference signal; and the differential group delay between the two spatial modes in the few-mode optical fiber to be tested is calculated according to the peak position. The received signal data is subjected to cepstrum analysis, and the cepstrum features of the signal are extracted through Fourier transform, and then the characteristic information of the differential mode group delay is extracted, which reduces the dependence on special signal sources and expensive equipment and the cost of actual operation while ensuring high measurement accuracy and reliability.

[0084] Reference Fig.11 , Fig.11 This is a flow chart of a second embodiment of a differential group delay measurement method of the present application. Based on the above first embodiment, a second embodiment of a differential group delay measurement method of the present application is proposed.

[0085] In the second embodiment, the step S20 includes:

[0086] Step S201 : demultiplexing the mixed signal based on a mode demultiplexer to generate a target signal, and combining the target signal into a single light beam according to a first coupler.

[0087] It should be noted that a mode demultiplexer is a device used to separate a mixed optical signal containing multiple spatial modes into individual independent spatial mode signals, and realizes the demultiplexing function based on the differences in propagation characteristics (such as phase, polarization, etc.) of optical signals of different spatial modes in optical fibers. A coupler is a device that can merge multiple optical signals into one optical path or split an optical signal into multiple optical paths. The first coupler is a coupler used to merge the target signal obtained after mode demultiplexing into a single light beam.

[0088] It should be understood that when the mixed signal enters the mode demultiplexer, the mode demultiplexer performs demultiplexing operations according to the characteristic differences of different spatial mode optical signals. After obtaining each target signal, these target signals enter the first coupler. The first coupler uses its internal optical coupling mechanism to precisely control the coupling area of ​​the optical fiber or use the optical field coupling principle of the optical microstructure to superimpose the target signals of different modes in the coupler, and finally form a single light beam output.

[0089] Step S202, converting the single light beam into an electrical signal through a photoelectric converter, collecting data on the change of current in the electrical signal over time, and obtaining electrical signal change information.

[0090] It should be understood that the photoelectric converter can effectively convert the optical signal into an electrical signal, which facilitates the subsequent signal processing based on electronic devices. When measuring the differential mode group delay of few-mode optical fiber, the inter-mode delay information in the optical signal is difficult to measure directly, but after conversion to an electrical signal, the electronic device can be used to accurately measure the current change in the electrical signal, and then extract the information related to the differential mode group delay.

[0091] It is understandable that for a single light beam whose intensity varies with time, the magnitude of the current generated in the photoelectric converter will also vary with time accordingly. If the intensity of the light beam increases, the current generated will also increase; conversely, if the intensity of the light beam decreases, the current will also decrease. When collecting data on the change of current over time, the waveform of the current changing with time can be displayed in real time through an oscilloscope, and appropriate parameters such as time scale and voltage sensitivity can be set to clearly observe the change of current.

[0092] Step S203: Offline processing is performed on the electrical signal change information to obtain a light field interference signal.

[0093] In one example, to simplify the analysis, it is assumed that the signal in the input few-mode fiber excites a pair of spatial modes. Then the electric field at the output end of the few-mode fiber is It can be expressed as:

[0094]

[0095] in and are the normalized mode field distributions of the two spatial modes, is the relative amplitude of the two spatial modes, is the differential group delay between the two modes. and is the information of the electrical signal change. After square law detection, the interference signal of the two spatial modes is:

[0096]

[0097] Under ideal mode excitation conditions, , , and the last product cross term in the formula The spatial integral of is zero. However, in practical applications, mode excitation is non-ideal, and its spatial integral is generally not zero, so the output light field can be expressed as:

[0098]

[0099]

[0100]

[0101]

[0102] Next, we need to use the cepstrum to be processed.

[0103] In the second embodiment, the step S30 includes:

[0104] Step S301: convert the light field interference signal into a frequency domain signal based on Fourier transform.

[0105] It should be noted that frequency domain signal is a way to describe the signal, which is opposite to time domain. Frequency domain signal can be obtained by Fourier transforming the time domain signal, which represents the distribution of the signal in the frequency domain.

[0106] In one example, the Fourier transform Converting to frequency domain:

[0107]

[0108] In the formula represents convolution, and the convolution relationship between the two functions can be expressed as:

[0109]

[0110] After calculation, we can get The expression is:

[0111]

[0112] if is a small amount, Only with Regarding frequency and There are only minor dependencies.

[0113] Step S302: Process the frequency domain signal by using a preset function operation, and perform inverse Fourier transform on the processing result to obtain delay information.

[0114] It should be noted that the preset function operation refers to a mathematical function that is pre-set according to a specific algorithm or processing requirement, such as square, logarithm, exponential and other operations. Certain features in the signal can be extracted, enhanced or converted so that the required information can be accurately obtained later. Delay information refers to the time delay caused by factors such as the difference in propagation speed of different paths, different media or different modes during the transmission of the signal, which can be reflected in the waveform change of the time domain signal, such as the delay in the occurrence time of the signal peak, or in the phase change of the frequency domain signal.

[0115] In one example, the frequency domain signal is squared to obtain:

[0116]

[0117] At the same time, perform exponential operation on it. According to Taylor expansion principle, if , then we have:

[0118]

[0119] Substituting the above formula into the equation:

[0120]

[0121] In the formula , the second term can be used The harmonic multiples of are expressed as:

[0122]

[0123] in

[0124]

[0125] Combining the above formulas, Performing inverse Fourier transform yields:

[0126]

[0127]

[0128] In the formula yes The inverse Fourier transform of , yes About oneself Convolution. Generally speaking, the high-order terms in the above formula can be ignored, so it can be simplified to:

[0129]

[0130] It can be seen that the interference of noise may affect the peak size at the delay, but the position of the peak at the delay is not affected. Therefore, the group delay difference between a pair of spatial modes can be calculated by identifying the position of the peak.

[0131] Step S303: determining a peak position in the light field interference signal according to the delay information.

[0132] It is understandable that in the light field interference process, light signals of different spatial modes will form a specific phase difference when interfering due to their different propagation speeds (i.e., there is a delay). This phase difference will be reflected in the light field interference signal, which will cause the signal to have peaks at certain moments. By analyzing the delay information, the locations where these peaks appear can be determined.

[0133] In one example, reference Fig.12 , Fig.12 This is a schematic diagram of a measurement system for differential mode group delay of few-mode optical fiber of the present application. The system includes the following modules: data generation module, mode multiplexing module, mode demultiplexing module, photoelectric conversion module, and cepstrum analysis module. The data generation module generates a continuous light wave signal through a continuous wave signal source unit, the arbitrary wave generator unit generates a signal of arbitrary waveform, and the intensity modulation unit modulates the intensity of the light wave signal to generate a four-level pulse amplitude modulation signal and performs filtering processing on it; the mode multiplexing module divides the generated signal into two paths through a coupling unit, one of which needs to be controlled by an optical attenuator to control the size of the optical power. After that, the two signals are sent to the mode multiplexer to respectively excite different modes to obtain a few-mode optical signal, which is injected into the few-mode optical fiber to be tested; the mode demultiplexing module is used to perform mode demultiplexing on the output signal of the few-mode optical fiber to obtain two optical signals, and the above two signals are combined through a coupler; the photoelectric conversion module is used to perform photoelectric conversion on the combined signal, and obtain the output signal through the data acquisition unit; the cepstrum analysis module performs cepstrum analysis on the output signal through the cepstrum analysis unit, demodulates the peak position, and calculates the size of the differential mode group delay.

[0134] In this embodiment, by converting the optical signal into an electrical signal, the data of the current change over time in the electrical signal is more conveniently sampled and quantified, thereby accurately extracting information related to the differential mode group delay. At the same time, when Fourier transform is used to process the light field interference signal, the complex signal operation and interaction analysis between modes involved are simplified, thereby improving the calculation speed.

[0135] Reference Fig.13 , Fig.13 This is a flow chart of a third embodiment of a differential group delay measurement method of the present application. Based on the above second embodiment, the third embodiment of the differential group delay measurement method of the present application is proposed.

[0136] In the third embodiment, before step S10, the method further includes:

[0137] Step S01, modulating a continuous wave laser signal emitted by a preset light source to obtain a modulated signal.

[0138] It should be noted that the preset light source is a device that can generate light and is pre-selected and set in the experiment or system. This light source usually has specific characteristics, such as wavelength range, optical power, beam quality, etc., to meet the requirements of subsequent operations and measurements. Continuous wave laser signal refers to the continuous and uninterrupted output of laser in time, and its light intensity remains relatively stable over a period of time without obvious pulse characteristics.

[0139] Step S02: input the modulated signal into a second coupler to generate a first optical signal and a second optical signal.

[0140] It should be understood that the modulated signal can be accurately separated into the first optical signal and the second optical signal by the second coupler. The separated optical signals can be processed differently respectively. For example, one of the optical signals may be subjected to power adjustment and other operations, and then mode-multiplexed with the other optical signal and input into the few-mode optical fiber to generate a mixed signal for subsequent measurement.

[0141] Step S03: converting the first optical signal and the second optical signal into the mixed signal based on a mode multiplexer, and inputting the mixed signal into the few-mode optical fiber to be tested.

[0142] It should be understood that after the first optical signal and the second optical signal enter the mode multiplexer, the mode multiplexer operates based on the spatial mode characteristics of different optical signals, and utilizes optical principles, such as through specially designed waveguide structures, refractive index distributions, etc., to merge the different spatial modes represented by the first optical signal and the second optical signal.

[0143] It is understandable that during the input process, the mixed signal will excite different spatial modes at the input end of the optical fiber, and the optical signals of these spatial modes will propagate along the axial direction of the optical fiber in the few-mode fiber. By subsequently processing and analyzing the mixed signal obtained from the output end of the optical fiber (such as photoelectric conversion, signal processing, cepstrum analysis, etc.), these characteristic parameters can be measured to evaluate the performance of the few-mode fiber.

[0144] Furthermore, in order to reduce inter-code interference, the step S03 may include:

[0145] The output power of the first optical signal is adjusted by an optical attenuation unit to obtain a third optical signal; the second optical signal and the third optical signal are input into the mode ports corresponding to the mode multiplexer to perform spatial mode conversion and determine the stimulated mode; the mixed signal is generated according to the stimulated mode and input into the few-mode optical fiber to be tested.

[0146] It should be noted that the optical attenuation unit is an optical device used to adjust the intensity of optical signals, and can reduce the power of optical signals by absorption, scattering or reflection. In this process, the optical attenuation unit can accurately control the output power of the optical signal to reach the required level.

[0147] It is understandable that the first optical signal enters the optical attenuation unit. The optical attenuation unit adjusts the power of the first optical signal according to a preset attenuation parameter. For example, if the power of the original first optical signal is P1, after passing through the optical attenuation unit, its power is reduced to P3, thereby obtaining a third optical signal. This power adjustment can be achieved in a variety of ways, such as using a material with a specific absorption rate in the optical attenuation unit to absorb a portion of the light energy, or by changing the propagation path length of the optical signal to achieve light loss, thereby adjusting the power. By adjusting the power, the system can simulate the different paths and changes that the optical signal may experience in actual transmission. The stimulated mode optical signals obtained after the mode multiplexer performs spatial mode conversion on the second optical signal and the third optical signal are superimposed on each other to form a mixed signal. The mixed signal contains optical signals of multiple spatial modes. Finally, the generated mixed signal is input into the few-mode optical fiber to be tested for transmission in the optical fiber and subsequent characteristic measurement.

[0148] In this embodiment, the continuous wave laser signal emitted by the preset light source is modulated to obtain a modulated signal; the modulated signal is input into the second coupler to generate a first optical signal and a second optical signal; the first optical signal and the second optical signal are converted into the mixed signal based on the mode multiplexer, and input into the few-mode optical fiber to be tested. The modulated signal is divided into two paths by the second coupler, and the signals are processed differently respectively, which can simulate the different paths and changes that the optical signal may experience in actual transmission, and accurately reflect the differential mode group delay information.

[0149] It should be noted that the above examples are only used to understand the present application and do not constitute a limitation on the differential group delay measurement method of the present application. More simple transformations based on this technical concept are all within the protection scope of the present application.

[0150] The present application also provides a differential group delay measurement device, please refer to Fig.14 , the differential group delay measurement device comprises:

[0151] A signal acquisition module 10, used to acquire a mixed signal transmitted in the few-mode optical fiber to be tested, wherein the mixed signal includes optical signals of at least two spatial modes;

[0152] The photoelectric conversion module 20 is used to collect the electric signal change information based on the mixed signal, and generate the light field interference signal according to the electric signal change information;

[0153] A cepstrum analysis module 30, configured to perform cepstrum analysis on the light field interference signal by Fourier transform to determine a peak position in the light field interference signal;

[0154] The delay calculation module 40 is used to calculate the differential group delay between two spatial modes in the few-mode optical fiber to be tested according to the peak position.

[0155] The differential group delay measurement device provided by the present application adopts the differential group delay measurement method in the above embodiment, which can solve the technical problem that the existing methods for measuring differential mode group delay have certain accuracy and feasibility, but most of them require expensive and cumbersome equipment, rely on specific signal sources, and increase the difficulty and cost of actual operation. Compared with the prior art, the beneficial effects of the differential group delay measurement device provided by the present application are the same as the beneficial effects of the differential group delay measurement method provided by the above embodiment, and the other technical features in the differential group delay measurement device are the same as the features disclosed in the above embodiment method, which will not be repeated here.

[0156] The present application provides a differential group delay measurement device, which includes: at least one processor; and a memory communicatively connected to the at least one processor; wherein the memory stores instructions executable by the at least one processor, and the instructions are executed by the at least one processor so that the at least one processor can execute the differential group delay measurement method in the above-mentioned embodiment 1.

[0157] Reference below Fig.15 , which shows a schematic diagram of the structure of a differential group delay measurement device suitable for implementing the embodiment of the present application. The differential group delay measurement device in the embodiment of the present application may include but is not limited to mobile terminals such as mobile phones, laptop computers, digital broadcast receivers, PDAs (Personal Digital Assistants), PADs (Portable Application Descriptions), PMPs (Portable Media Players), vehicle-mounted terminals (such as vehicle-mounted navigation terminals), etc., and fixed terminals such as digital TVs, desktop computers, etc. Fig.15 The differential group delay measurement device shown is only an example and should not bring any limitation to the functions and scope of use of the embodiments of the present application.

[0158] like Fig.15As shown, the differential group delay measurement device may include a processing device 1001 (e.g., a central processing unit, a graphics processor, etc.), which can perform various appropriate actions and processes according to a program stored in a read-only memory (ROM: Read Only Memory) 1002 or a program loaded from a storage device 1003 to a random access memory (RAM: Random Access Memory) 1004. In RAM1004, various programs and data required for the operation of the differential group delay measurement device are also stored. The processing device 1001, ROM1002, and RAM1004 are connected to each other through a bus 1005. An input / output (I / O) interface 1006 is also connected to the bus. Generally, the following systems can be connected to the I / O interface 1006: an input device 1007 including, for example, a touch screen, a touch pad, a keyboard, a mouse, an image sensor, a microphone, an accelerometer, a gyroscope, etc.; an output device 1008 including, for example, a liquid crystal display (LCD: Liquid Crystal Display), a speaker, a vibrator, etc.; a storage device 1003 including, for example, a magnetic tape, a hard disk, etc.; and a communication device 1009. The communication device 1009 can allow the differential group delay measurement device to communicate with other devices wirelessly or by wire to exchange data. Although the differential group delay measurement device with various systems is shown in the figure, it should be understood that it is not required to implement or have all the systems shown. More or fewer systems can be implemented or have alternatively.

[0159] In particular, according to the embodiments disclosed in the present application, the process described above with reference to the flowchart can be implemented as a computer software program. For example, the embodiments disclosed in the present application include a computer program product, which includes a computer program carried on a computer-readable medium, and the computer program includes a program code for executing the method shown in the flowchart. In such an embodiment, the computer program can be downloaded and installed from a network through a communication device, or installed from a storage device 1003, or installed from a ROM 1002. When the computer program is executed by the processing device 1001, the above-mentioned functions defined in the method of the embodiment disclosed in the present application are executed.

[0160] The differential group delay measurement device provided by the present application adopts the differential group delay measurement method in the above embodiment, which can solve the technical problem that the existing methods for measuring differential mode group delay have certain accuracy and feasibility, but most of them require expensive and cumbersome equipment, rely on specific signal sources, and increase the difficulty and cost of actual operation. Compared with the prior art, the beneficial effects of the differential group delay measurement device provided by the present application are the same as the beneficial effects of the differential group delay measurement method provided by the above embodiment, and the other technical features in the differential group delay measurement device are the same as the features disclosed in the method of the previous embodiment, which will not be repeated here.

[0161] It should be understood that the various parts disclosed in this application can be implemented by hardware, software, firmware or a combination thereof. In the description of the above embodiments, specific features, structures, materials or characteristics can be combined in any one or more embodiments or examples in a suitable manner.

[0162] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any person skilled in the art who is familiar with the present technical field can easily think of changes or substitutions within the technical scope disclosed in the present application, which should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

[0163] The present application provides a computer-readable storage medium having computer-readable program instructions (ie, computer programs) stored thereon, and the computer-readable program instructions are used to execute the differential group delay measurement method in the above-mentioned embodiment.

[0164] The computer-readable storage medium provided in the present application may be, for example, a USB flash drive, but is not limited to electrical, magnetic, optical, electromagnetic, infrared, or semiconductor systems, systems or devices, or any combination of the above. More specific examples of computer-readable storage media may include, but are not limited to: an electrical connection with one or more wires, a portable computer disk, a hard disk, a random access memory (RAM: Random Access Memory), a read-only memory (ROM: Read Only Memory), an erasable programmable read-only memory (EPROM: Erasable Programmable Read Only Memory or flash memory), an optical fiber, a portable compact disk read-only memory (CD-ROM: CD-Read Only Memory), an optical storage device, a magnetic storage device, or any suitable combination of the above. In this embodiment, the computer-readable storage medium may be any tangible medium containing or storing a program, which may be used by or in combination with an instruction execution system, system or device. The program code contained on the computer-readable storage medium may be transmitted using any appropriate medium, including but not limited to: wires, optical cables, RF (Radio Frequency: Radio Frequency), etc., or any suitable combination of the above.

[0165] The computer-readable storage medium may be included in the differential group delay measurement device; or may exist independently without being assembled into the differential group delay measurement device.

[0166] The computer-readable storage medium carries one or more programs. When the one or more programs are executed by the differential group delay measurement device, the differential group delay measurement device performs the differential group delay measurement method described above.

[0167] Computer program code for performing the operations of the present application may be written in one or more programming languages ​​or a combination thereof, including object-oriented programming languages ​​such as Java, Smalltalk, C++, and conventional procedural programming languages ​​such as "C" or similar programming languages. The program code may be executed entirely on the user's computer, partially on the user's computer, as a separate software package, partially on the user's computer and partially on a remote computer, or entirely on a remote computer or server. In the case of a remote computer, the remote computer may be connected to the user's computer via any type of network, including a local area network (LAN) or a wide area network (WAN), or may be connected to an external computer (e.g., via the Internet using an Internet service provider).

[0168] The flow chart and block diagram in the accompanying drawings illustrate the possible architecture, function and operation of the system, method and computer program product according to various embodiments of the present application. In this regard, each square box in the flow chart or block diagram can represent a module, a program segment or a part of a code, and the module, the program segment or a part of the code contains one or more executable instructions for realizing the specified logical function. It should also be noted that in some alternative implementations, the functions marked in the square box can also occur in a sequence different from that marked in the accompanying drawings. For example, two square boxes represented in succession can actually be executed substantially in parallel, and they can sometimes be executed in the opposite order, depending on the functions involved. It should also be noted that each square box in the block diagram and / or flow chart, and the combination of the square boxes in the block diagram and / or flow chart can be implemented with a dedicated hardware-based system that performs a specified function or operation, or can be implemented with a combination of dedicated hardware and computer instructions.

[0169] The modules involved in the embodiments described in this application may be implemented by software or hardware, wherein the name of the module does not constitute a limitation on the unit itself in some cases.

[0170] The readable storage medium provided by the present application is a computer-readable storage medium, which stores computer-readable program instructions (i.e., computer programs) for executing the above-mentioned differential group delay measurement method, and can solve the technical problem that the existing methods for measuring differential mode group delay have certain accuracy and feasibility, but most of them require expensive and cumbersome equipment, rely on specific signal sources, and increase the difficulty and cost of actual operation. Compared with the prior art, the beneficial effects of the computer-readable storage medium provided by the present application are the same as the beneficial effects of the differential group delay measurement method provided by the above-mentioned embodiment, and will not be repeated here.

[0171] The present application also provides a computer program product, including a computer program, and when the computer program is executed by a processor, the steps of the differential group delay measurement method as described above are implemented.

[0172] The computer program product provided by the present application can solve the technical problem that the existing methods for measuring differential mode group delay, although having certain accuracy and feasibility, mostly require expensive and cumbersome equipment, rely on specific signal sources, and increase the difficulty and cost of actual operation. Compared with the prior art, the beneficial effects of the computer program product provided by the present application are the same as the beneficial effects of the differential group delay measurement method provided by the above embodiment, and will not be elaborated here.

[0173] The above descriptions are only some embodiments of the present application, and are not intended to limit the patent scope of the present application. All equivalent structural changes made using the contents of the present application specification and drawings under the technical concept of the present application, or direct / indirect applications in other related technical fields are included in the patent protection scope of the present application.

Claims

1. A differential group delay measurement method, characterized in that: The differential group delay measurement method includes: Acquire a mixed signal transmitted in the few-mode optical fiber to be tested, wherein the mixed signal includes optical signals of at least two spatial modes; collecting electrical signal change information based on the mixed signal, and generating a light field interference signal according to the electrical signal change information; Performing a cepstrum analysis on the light field interference signal by Fourier transform to determine a peak position in the light field interference signal; Calculating the differential group delay between two spatial modes in the few-mode optical fiber to be tested according to the peak position; Before the step of obtaining the mixed signal transmitted in the few-mode optical fiber to be tested, the method further includes: Modulating a continuous wave laser signal emitted by a preset light source to obtain a modulated signal; inputting the modulated signal into a second coupler to generate a first optical signal and a second optical signal; Converting the first optical signal and the second optical signal into the mixed signal based on a mode multiplexer, and inputting the mixed signal into the few-mode optical fiber to be tested; The step of converting the first optical signal and the second optical signal into the mixed signal based on a mode multiplexer and inputting the mixed signal into the few-mode optical fiber to be tested comprises: adjusting the output power of the first optical signal by an optical attenuation unit to obtain a third optical signal; Inputting the second optical signal and the third optical signal into corresponding mode ports of a mode multiplexer to perform spatial mode conversion and determine an excited mode; The mixed signal is generated according to the stimulated mode and input into the few-mode optical fiber to be tested.

2. The differential group delay measurement method according to claim 1, wherein: The step of performing cepstrum analysis on the light field interference signal through Fourier transform to determine the peak position in the light field interference signal includes: Converting the light field interference signal into a frequency domain signal based on Fourier transform; Processing the frequency domain signal by a preset function operation, and performing an inverse Fourier transform on the processing result to obtain delay information; A peak position in the light field interference signal is determined according to the delay information.

3. The differential group delay measurement method according to claim 1, wherein: The step of collecting electrical signal change information based on the mixed signal and generating a light field interference signal according to the electrical signal change information includes: Demultiplexing the mixed signal based on a mode demultiplexer to generate a target signal, and combining the target signal into a single light beam based on a first coupler; Converting the single light beam into an electrical signal through a photoelectric converter, collecting data on changes in current over time in the electrical signal, and obtaining electrical signal change information; The electrical signal change information is processed offline to obtain a light field interference signal.

4. The differential group delay measurement method according to claim 1, wherein: The step of calculating the differential group delay between two spatial modes in the few-mode optical fiber to be tested according to the peak position comprises: Correcting an erroneous peak value in the peak position by taking mode crosstalk into consideration to obtain a target peak value; The differential group delay between two spatial modes in the few-mode optical fiber to be tested is calculated based on the target peak value and the length of the few-mode optical fiber to be tested.

5. A differential group delay measurement device, characterized in that: The device comprises: A signal acquisition module, configured to acquire a mixed signal transmitted in the few-mode optical fiber to be tested, wherein the mixed signal includes optical signals of two spatial modes; a photoelectric conversion module, configured to collect electrical signal change information based on the mixed signal, and generate a light field interference signal according to the electrical signal change information; a cepstrum analysis module, configured to perform cepstrum analysis on the light field interference signal through Fourier transform to determine a peak position in the light field interference signal; a delay calculation module, configured to calculate the differential group delay between two spatial modes in the few-mode optical fiber to be tested according to the peak position; The differential group delay measurement device is further used for: Modulating a continuous wave laser signal emitted by a preset light source to obtain a modulated signal; inputting the modulated signal into a second coupler to generate a first optical signal and a second optical signal; converting the first optical signal and the second optical signal into the mixed signal based on a mode multiplexer, and inputting the mixed signal into the few-mode optical fiber to be tested; The output power of the first optical signal is adjusted by an optical attenuation unit to obtain a third optical signal; the second optical signal and the third optical signal are input into the corresponding mode ports of the mode multiplexer to perform spatial mode conversion and determine the stimulated mode; the mixed signal is generated according to the stimulated mode and input into the few-mode optical fiber to be tested.

6. A differential group delay measurement device, characterized in that: The device comprises: a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the computer program is configured to implement the steps of the differential group delay measurement method according to any one of claims 1 to 4.

7. A storage medium, characterized in that: The storage medium is a computer-readable storage medium, and a computer program is stored on the storage medium. When the computer program is executed by a processor, the steps of the differential group delay measurement method according to any one of claims 1 to 4 are implemented.

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