Low-cost optical fiber length measuring system and method

Abstract

The invention discloses a low-cost optical fiber length measuring system and method. The system comprises a first clock crystal oscillator and a second clock crystal oscillator, the first clock crystal oscillator and the second clock crystal oscillator are connected with the central processing unit, the central processing unit carries out pulse driving on the laser driver by referring to the second clock crystal oscillator, and the output end of the laser driver is connected with the input end of the laser diode; the output end of the laser diode is connected with one end of a to-be-measured optical fiber, and the other end of the to-be-measured optical fiber is connected with the receiving end of the photoelectric receiving module; the output end of the photoelectric receiving module is connected with the input end of the analog-to-digital converter, and the output end of the analog-to-digital converter is connected with the central processing unit. The method has the advantages of being high in precision, low in cost, simplified in implementation, high in robustness and the like, can greatly reduce complexity and improve system efficiency, has high expansibility and flexibility, and is suitable for being widely applied to various optical measurement, sensing and communication systems.

Description

Technical Field

[0001] The present invention relates to the technical field of optical fiber measurement, and in particular to a low-cost optical fiber length measurement system and method. Background Art

[0002] With the development of fiber optic networks, the demand for a large number of high-precision optical devices has exploded, and the demand for measuring optical fiber length has become more and more.

[0003] The solutions that can be used to measure the length of optical fiber at present mainly include OTDR (optical time domain reflectometer), OFDR (optical frequency domain reflectometer), and OLCR (white light interferometer). The advantages and disadvantages of these solutions are analyzed as follows: 1. OTDR: This method performs length analysis by measuring the time of flight. Limited by the sampling rate, the minimum resolution can reach the order of ~0.1m. The advantages are that it is relatively easy to implement and low cost, and can be used for long-distance optical fiber links. The disadvantage is that it is not suitable for ultra-short distance application scenarios such as optical devices. 2. OFDR: This method performs frequency scanning through a linear swept light source and performs length analysis by calculating the beat frequency. The theoretical minimum resolution can reach 10nm; the disadvantage is that it has high requirements for the light source, especially the long-distance version, and the cost is high. 3. OLCR: This method maps the information of the optical fiber into the high-precision lead screw motion range through delayed line scanning, and can obtain an accuracy of 0.1mm. However, the measurement accuracy and range depend on the lead screw, which determines that the device cannot measure short-distance and long-distance samples at the same time, and the cost is relatively high.

[0004] Therefore, it is necessary to propose a low-cost optical fiber length measurement system and method that can simplify the equipment structure and improve the system flexibility, so as to accurately measure the length of long-distance and short-distance optical fibers at a lower cost, and improve the breadth and practicality of the optical fiber measurement system and method. Summary of the invention

[0005] The present invention provides a low-cost optical fiber length measurement system and method, which are used to solve the technical problems of poor measurement versatility and high measurement cost in the existing optical fiber measurement technology.

[0006] In order to solve the above problems, on the one hand, the present invention provides a low-cost optical fiber length measurement system, including: a first clock crystal oscillator and a second clock crystal oscillator;

[0007] The first clock crystal oscillator and the second clock crystal oscillator are connected to a central processing unit, the central processing unit is connected to a laser driver, and the output end of the laser driver is connected to the input end of a laser diode; the central processing unit drives the laser diode based on a second clock; the output end of the laser diode is connected to one end of the optical fiber to be tested, and the other end of the optical fiber to be tested is connected to the receiving end of a photoelectric receiving module; the output end of the photoelectric receiving module is connected to the input end of an analog-to-digital converter, and the output end of the analog-to-digital converter is connected to the central processing unit;

[0008] The first clock crystal oscillator is used to provide a local reference clock for the central processing unit;

[0009] The second clock crystal oscillator is used to provide clock drive for the laser diode driver;

[0010] The laser diode driver is used to receive an enable signal from the central processing unit and drive the laser diode to emit a modulated pulse laser;

[0011] The optoelectronic receiving module is used to receive the modulated pulse laser emitted by the laser diode transmitted through the optical fiber to be tested, and convert the optical signal into an analog electrical signal;

[0012] The analog-to-digital converter is used to convert the analog electrical signal output by the photoelectric receiving module into a digital signal and send it to the central processor;

[0013] The central processing unit is used to receive the digital signal output by the analog-to-digital converter, and calculate the length of the optical fiber to be measured based on the digital signal.

[0014] Furthermore, the central processing unit is an FPGA chip.

[0015] On the other hand, the present invention also provides a low-cost optical fiber length measurement method, which is applied to the low-cost optical fiber length measurement system described in the above technical solution, comprising:

[0016] The main scale frequency of the first clock crystal oscillator and the secondary scale frequency of the second clock crystal oscillator are respectively set based on the processing frequency of the central processor; wherein the main scale frequency is less than the secondary scale frequency;

[0017] A main scale clock is obtained according to the main scale frequency, and a secondary scale clock is obtained according to the secondary scale frequency; the main scale clock is used as a local counting clock of a central processor, and the secondary scale clock is used as a driving clock of a laser diode, and a modulated pulse laser is emitted to the optical fiber to be tested;

[0018] The photoelectric receiving module receives the modulated pulse laser emitted by the laser diode transmitted through the optical fiber to be tested, and converts the optical signal into an analog electrical signal and transmits it to the analog-to-digital converter; the analog-to-digital converter converts the analog electrical signal into a digital signal and inputs it into the central processing unit;

[0019] The central processor determines the rising edge information of the return pulse according to the main scale clock, and obtains the length of the optical fiber to be measured according to the periodic phase relationship between the rising edge information of the return pulse and the main scale clock and the auxiliary scale clock.

[0020] Furthermore, the central processor determines the rising edge information of the return pulse according to the main scale clock, and obtains the length of the optical fiber to be measured according to the periodic phase relationship between the rising edge information of the return pulse and the main scale clock and the secondary scale clock, including:

[0021] The central processor determines the main scale clock counting period m of the return signal of the first pulse sent according to the main scale clock;

[0022] Compare the i-th returned light pulse with the rising edge of the m+i-th main scale clock one by one, find the n-th light pulse whose rising edge occurs at a time less than or equal to the rising edge of the main scale clock, and record the secondary scale clock counting period corresponding to the n-th light pulse as n;

[0023] The optical fiber length is calculated based on the main scale clock counting period m and the secondary scale clock counting period n.

[0024] Further, the optical fiber length is calculated according to the main scale clock counting period m and the secondary scale clock counting period n, including:

[0025] The calculation formula of the optical fiber length L is:

[0026] L=[m*T1+n*(T1-T)]*c / fiber_n

[0027] Where m is the main scale clock counting period, n is the sub-scale clock counting period, T1 is the clock period corresponding to the main scale frequency, T is the clock period corresponding to the optical pulse, c is the speed of light, and fiber_n is the refractive index of the optical fiber to be measured.

[0028] Furthermore, the time difference between the main scale clock period T1 and the secondary scale clock period T2 satisfies:

[0029] T1-T2=T1 / y

[0030] Wherein, y is an integer greater than 0.

[0031] Furthermore, the value of y is 200.

[0032] Furthermore, the main frequency of the central processing unit is not lower than the frequency of the secondary clock.

[0033] Compared with the prior art, the beneficial effects of the present invention include: the present invention adopts precise synchronous control of the main scale frequency and the secondary scale frequency, avoids the common clock drift or signal error problems in traditional optical fiber measurement, can reduce the cost of optical fiber length measurement, and the system can maintain stability in long-term use. Especially at high frequencies, the accuracy of clock synchronization directly affects the reliability of the measurement results. The design of this system can effectively reduce errors and ensure measurement accuracy. The length of the optical fiber can be accurately calculated by the relationship between the time difference of the optical pulse returning after passing through the optical fiber to be measured and the clock cycle. In addition, the system does not rely on expensive optical instruments, but uses conventional photodetectors and digital signal processing hardware (such as FPGA), which makes the system cost-effective. Therefore, it can be widely used in low-cost optical fiber length detection equipment, especially suitable for scenarios that require large-scale deployment, and has important application value in the fields of optical fiber communication, optical fiber network construction, optical fiber testing and maintenance. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 A schematic diagram of the structure of a low-cost optical fiber length measurement system provided by the present invention;

[0035] Figure 2 A schematic diagram of an implementation of the optical fiber length measurement principle provided by the present invention;

[0036] Figure 3 A schematic diagram of an implementation of an optical fiber length measurement process provided by the present invention. DETAILED DESCRIPTION

[0037] The preferred embodiments of the present invention are described in detail below in conjunction with the accompanying drawings, wherein the accompanying drawings constitute a part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not used to limit the scope of the present invention.

[0038] This embodiment provides a low-cost optical fiber length measurement system. Figure 1 As shown, Figure 1 is a structural schematic diagram of the low-cost optical fiber length measurement system, the system comprising: a first clock crystal oscillator and a second clock crystal oscillator;

[0039] The first clock crystal oscillator and the second clock crystal oscillator are connected to a central processing unit, the central processing unit is connected to a laser driver, and the output end of the laser driver is connected to the input end of a laser diode; the central processing unit drives the laser diode based on a second clock; the output end of the laser diode is connected to one end of the optical fiber to be tested, and the other end of the optical fiber to be tested is connected to the receiving end of a photoelectric receiving module; the output end of the photoelectric receiving module is connected to the input end of an analog-to-digital converter, and the output end of the analog-to-digital converter is connected to the central processing unit;

[0040] The first clock crystal oscillator is used to provide a local reference clock for the central processing unit;

[0041] The second clock crystal oscillator is used to provide clock drive for the laser diode driver;

[0042] The laser diode driver is used to receive a central processor enable signal and drive the laser diode to emit a modulated pulse laser;

[0043] The optoelectronic receiving module is used to receive the modulated pulse laser emitted by the laser diode transmitted through the optical fiber to be tested, and convert the optical signal into an analog electrical signal;

[0044] The analog-to-digital converter is used to convert the analog electrical signal output by the photoelectric receiving module into a digital signal and send it to the central processor;

[0045] The central processing unit is used to receive the digital signal output by the analog-to-digital converter, and calculate the length of the optical fiber to be measured based on the digital signal.

[0046] The low-cost optical fiber length measurement system provided in this embodiment adopts the precise synchronous control of the main scale frequency and the secondary scale frequency, avoids the common clock drift or signal error problems in traditional optical fiber measurement, can reduce the cost of optical fiber length measurement, and the system can maintain stability in long-term use. Especially at high frequencies, the accuracy of clock synchronization directly affects the reliability of the measurement results. The design of this system can effectively reduce errors and ensure measurement accuracy. The length of the optical fiber can be accurately calculated by the relationship between the time difference and the clock cycle after the optical pulse passes through the optical fiber to be measured. In addition, this system does not rely on expensive optical instruments, but uses conventional photodetectors and digital signal processing hardware (such as FPGA), so that the system has advantages in cost. Therefore, it can be widely used in low-cost optical fiber length detection equipment, especially suitable for scenes that need large-scale deployment, and has important application value in the fields of optical fiber communication, optical fiber network construction, optical fiber testing and maintenance.

[0047] As a preferred embodiment, the central processor is an FPGA chip. FPGA has the characteristics of high speed, programmability, parallel processing, etc., and can meet the real-time signal processing requirements in optical fiber length measurement.

[0048] Specifically, in practical applications, the FPGA chip model can be selected as XA7S6-2CSGA225. The XA7S6-2CSGA225 chip is equipped with approximately 6,800 logic units (LUTs) and 2,160 Flip-Flops, which are sufficient to support complex clock synchronization, signal processing, data transmission, high-speed timing and other tasks. For optical pulse measurement solutions based on clock synchronization, these resources can support more complex computing logic and data processing. Compared with other high-end FPGA chips, the Artix-7 series provides higher performance and moderate prices, and is suitable for low-cost application scenarios of measuring optical fiber length.

[0049] As a specific embodiment, the model of the analog-to-digital converter is AD9215 chip. AD9215 has the advantages of fast sampling speed, high precision, high integration, low power consumption and strong anti-interference ability. It can provide reliable signal conversion performance, reduce the complexity of system design and improve system efficiency.

[0050] The embodiment of the present invention further provides a low-cost optical fiber length measurement method, which is applied to any low-cost optical fiber length measurement system described in the above scheme, comprising:

[0051] The main scale frequency of the first clock crystal oscillator and the secondary scale frequency of the second clock crystal oscillator are respectively set based on the processing frequency of the central processor; wherein the main scale frequency is less than the secondary scale frequency;

[0052] A main scale clock is obtained according to the main scale frequency, and a secondary scale clock is obtained according to the secondary scale frequency; the main scale clock is used as a local counting clock of a central processor, and the secondary scale clock is used as a driving clock of a laser diode, and a modulated pulse laser is emitted to the optical fiber to be tested;

[0053] The photoelectric receiving module receives the modulated pulse laser emitted by the laser diode transmitted through the optical fiber to be tested, and converts the optical signal into an analog electrical signal and transmits it to the analog-to-digital converter; the analog-to-digital converter converts the analog electrical signal into a digital signal and inputs it into the central processing unit;

[0054] The central processor determines the rising edge information of the return pulse according to the main scale clock, and obtains the length of the optical fiber to be measured according to the periodic phase relationship between the rising edge information of the return pulse and the main scale clock and the auxiliary scale clock.

[0055] As a preferred embodiment, the central processor determines the rising edge information of the return pulse according to the main scale clock, and obtains the length of the optical fiber to be measured according to the periodic phase relationship between the rising edge information of the return pulse and the main scale clock and the secondary scale clock, including:

[0056] The central processor determines the main scale clock counting period m of the return signal of the first pulse sent according to the main scale clock;

[0057] Compare the i-th returned light pulse with the rising edge of the m+i-th main scale clock one by one, find the n-th light pulse whose rising edge occurs at a time less than or equal to the rising edge of the main scale clock, and record the secondary scale clock counting period corresponding to the n-th light pulse as n;

[0058] The optical fiber length is calculated based on the main scale clock counting period m and the secondary scale clock counting period n.

[0059] As a preferred embodiment, calculating the optical fiber length according to the main scale clock counting period m and the secondary scale clock counting period n includes:

[0060] The calculation formula of the optical fiber length L is:

[0061] L=[m*T1+n*(T1-T)]*c / fiber_n

[0062] Where m is the main scale clock counting period, n is the sub-scale clock counting period, T1 is the clock period corresponding to the main scale frequency, T is the clock period corresponding to the optical pulse frequency, c is the speed of light, and fiber_n is the refractive index of the optical fiber to be measured.

[0063] As a preferred embodiment, the time difference between the main scale clock period T1 and the secondary scale clock period T2 satisfies:

[0064] T1-T2=T1 / y

[0065] Wherein, y is an integer greater than 0.

[0066] As a preferred embodiment, the value of y is 200.

[0067] As a preferred embodiment, the main frequency of the central processing unit is not lower than the frequency of the secondary scale clock.

[0068] Combine the following Figure 2 and Figure 3 The method of the present invention is described in detail with a specific embodiment.

[0069] Firstly, the main scale frequency of the first clock crystal oscillator and the secondary scale frequency of the second clock crystal oscillator are respectively set based on the processing frequency of the central processing unit;

[0070] It should be noted that the following requirements are imposed on the main scale frequency and the secondary scale frequency:

[0071] 1. The main scale frequency is less than the secondary scale frequency;

[0072] 2. The time difference between the main scale clock cycle T1 and the secondary scale clock cycle T2 satisfies: T1-T2=T1 / y, where y is an integer greater than 0;

[0073] 3. The main scale frequency and the sub-scale frequency are limited by the maximum main frequency of the FPGA processing chip, that is, the sub-scale frequency needs to be as much lower than the working main frequency of the FPGA as possible.

[0074] Here we choose to set the main scale frequency of the first clock crystal oscillator to 100MHz, and the secondary scale frequency of the second clock crystal oscillator to 100.502513MHz. The first clock crystal oscillator is used to provide a local reference clock for the FPGA, and the second clock crystal oscillator is used to provide clock drive for the laser diode driver.

[0075] When starting the measurement, we send a modulated pulse light to one end of the optical fiber through a laser diode, and the optical pulse frequency is set to 100.502513MHz; Figure 2 As shown, when sending optical pulses, since the main scale frequency of the local clock is 100MHz, the main scale clock period is 10ns; the sub-scale frequency is 100.502513MHz, and the laser diode is driven by the 100.502513MHz clock to emit pulses.

[0076] In the initial state of laser transmission, that is, the 0th time is the 0th coincidence, the main scale clock coincides with the modulated light pulse for 200 pulse cycles after 199 pulse cycles, which is equivalent to 10ns being divided into 200 parts, each time period is 0.05ns. At this time, the theoretical minimum measurement distance accuracy is: T1 / y*c / fiber_n; T1 is the clock cycle corresponding to the main scale frequency, c is the speed of light, fiber_n is the refractive index of the fiber to be measured, y is 200 in this scenario, and the theoretical accuracy of the measured fiber length is 1mm, so the theoretical accuracy of the final fiber length is 1mm.

[0077] At the other end of the optical fiber, an optoelectronic receiving module is used to receive the modulated pulse light signal, and the received pulse light signal is sent to the FPGA for real-time processing after optoelectronic conversion and analog-to-digital conversion. When the FPGA processes the main scale clock count and the secondary scale clock count, it uses the measurement principle of the main scale and secondary scale of the vernier caliper, which is divided into "main scale measurement" and "vernier scale measurement", such as Figure 3 As shown:

[0078] 1. The measurement process of the main scale includes:

[0079] According to the cycle of the local master counting clock, the front end of the receiving optical pulse is searched and judged through FPGA to find the clock cycle counting cycle m closest to the 0th pulse of the returned pulse optical signal on the local master clock;

[0080] 2. The measurement process of the vernier scale includes:

[0081] Compare the i-th returning optical pulse with the rising edge of the m+i-th local main counting clock one by one, find the time when the first optical pulse rising edge appears <= the rising edge of the local clock, and record the vernier scale (counting cycle of the secondary scale clock) at this time as n;

[0082] Calculate the fiber length: L = (m*10 / 1e9+n*0.05 / 1e9)*c / fiber_n

[0083] Where m is the main scale clock counting period, 10 / 1e9 is the main scale clock period, n is the sub-scale clock counting period, 0.05 / 1e9 is the minimum time resolution, that is, the main scale period of 10ns is divided into 200 parts; c is the speed of light, and fiber_n is the refractive index of the optical fiber to be measured.

[0084] The theoretical accuracy of the optical fiber length in the above embodiment is 1 mm.

[0085] In the processing method of this embodiment, the emission of laser pulses, the reception of optical signals and the signal processing accuracy of the central processor are guaranteed by the precise setting and synchronization of the main scale and the secondary scale clocks. Based on the phase relationship of the clock cycle, the time difference of the return pulse can be accurately measured, so as to accurately calculate the length of the optical fiber. The accuracy of signal conversion is further guaranteed by a high-precision analog-to-digital converter and a signal processing algorithm, thereby improving the measurement accuracy. At the same time, the system does not have to rely on expensive measuring equipment. Through reasonable design and configuration, high-precision optical fiber length measurement is achieved, which reduces the measurement cost of the optical fiber length while ensuring high measurement accuracy. It has strong scalability and flexibility and is suitable for wide application in various optical measurement, sensing and communication systems.

[0086] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A low-cost optical fiber length measurement system, characterized in that: include: a first clock crystal oscillator and a second clock crystal oscillator; The first clock crystal oscillator and the second clock crystal oscillator are connected to a central processing unit, the central processing unit is connected to a laser driver, and the output end of the laser driver is connected to the input end of a laser diode; the central processing unit drives the laser diode based on a second clock; the output end of the laser diode is connected to one end of the optical fiber to be tested, and the other end of the optical fiber to be tested is connected to the receiving end of a photoelectric receiving module; the output end of the photoelectric receiving module is connected to the input end of an analog-to-digital converter, and the output end of the analog-to-digital converter is connected to the central processing unit; The first clock crystal oscillator is used to provide a local reference clock for the central processing unit; The second clock crystal oscillator is used to provide clock drive for the laser diode driver; The laser diode driver is used to receive an enable signal from the central processing unit and drive the laser diode to emit a modulated pulse laser; The optoelectronic receiving module is used to receive the modulated pulse laser emitted by the laser diode transmitted through the optical fiber to be tested, and convert the optical signal into an analog electrical signal; The analog-to-digital converter is used to convert the analog electrical signal output by the photoelectric receiving module into a digital signal and send it to the central processor; The central processing unit is used to receive the digital signal output by the analog-to-digital converter, and calculate the length of the optical fiber to be measured based on the digital signal.

2. The low-cost optical fiber length measurement system according to claim 1, characterized in that: The central processing unit is an FPGA chip.

3. A low-cost optical fiber length measurement method, applied to the low-cost optical fiber length measurement system as claimed in any one of claims 1 or 2, characterized in that: include: The main scale frequency of the first clock crystal oscillator and the secondary scale frequency of the second clock crystal oscillator are respectively set based on the processing frequency of the central processor; wherein the main scale frequency is less than the secondary scale frequency; A main scale clock is obtained according to the main scale frequency, and a secondary scale clock is obtained according to the secondary scale frequency; the main scale clock is used as a local counting clock of a central processor, and the secondary scale clock is used as a driving clock of a laser diode, and a modulated pulse laser is emitted to the optical fiber to be tested; The photoelectric receiving module receives the modulated pulse laser emitted by the laser diode transmitted through the optical fiber to be tested, and converts the optical signal into an analog electrical signal and transmits it to the analog-to-digital converter; the analog-to-digital converter converts the analog electrical signal into a digital signal and inputs it into the central processing unit; The central processor determines the rising edge information of the return pulse according to the main scale clock, and obtains the length of the optical fiber to be measured according to the periodic phase relationship between the rising edge information of the return pulse and the main scale clock and the auxiliary scale clock.

4. The low-cost optical fiber length measurement system according to claim 1, characterized in that: The central processor determines the rising edge information of the return pulse according to the main scale clock, and obtains the length of the optical fiber to be measured according to the periodic phase relationship between the rising edge information of the return pulse and the main scale clock and the secondary scale clock, including: The central processor determines the main scale clock counting period m of the return signal of the first pulse sent according to the main scale clock; Compare the i-th returned light pulse with the rising edge of the m+i-th main scale clock one by one, find the n-th light pulse whose rising edge occurs at a time less than or equal to the rising edge of the main scale clock, and record the secondary scale clock counting period corresponding to the n-th light pulse as n; The optical fiber length is calculated based on the main scale clock counting period m and the secondary scale clock counting period n.

5. The low-cost optical fiber length measurement system according to claim 1, characterized in that: The optical fiber length is calculated according to the main scale clock counting cycle m and the secondary scale clock counting cycle n, including: The calculation formula of the optical fiber length L is: L=[m*T1+n*(T1-T)]*c / fiber_n Where m is the main scale clock counting period, n is the sub-scale clock counting period, T1 is the clock period corresponding to the main scale frequency, T is the clock period corresponding to the optical pulse, c is the speed of light, and fiber_n is the refractive index of the optical fiber to be measured.

6. The low-cost optical fiber length measurement system according to claim 3, characterized in that: The time difference between the main scale clock cycle T1 and the secondary scale clock cycle T2 satisfies: T1-T2=T1 / y Wherein, y is an integer greater than 0.

7. The low-cost optical fiber length measurement system according to claim 6, characterized in that: The value of y is 200.

8. The low-cost optical fiber length measurement system according to claim 3, characterized in that: The main frequency of the central processing unit is not lower than the frequency of the secondary scale clock.

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