A method and system for measuring reflectivity of a weakly reflecting grating array

Abstract

A kind of weak reflection grating array reflectivity measurement method, using optical time domain reflectometer OTDR, including direct current light source, modulator, erbium-doped fiber amplifier, circulator, photoelectric detector, data acquisition card, data analysis processing module and display module;1) weak reflection grating array is accessed to above-mentioned measurement system, the weak reflection grating array to be measured is accessed to the second port of circulator;2) the output port of laser is connected with the input port of modulator;Laser output direct current light signal is modulated into probe light pulse by modulator, is amplified after being amplified by erbium-doped fiber amplifier, forms probe signal by entering the weak reflection grating array to be measured through circulator;3) the input port of photoelectric detector is connected with the third port of circulator;The input port of data acquisition card is connected with the output port of photoelectric detector;It is sent to data acquisition card by photoelectric detector output port;4) the output port of data acquisition card is connected with data analysis processing module.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of optical fiber sensing measurement, and in particular to a method and system for measuring reflectivity of a weak reflection grating array. BACKGROUND

[0002] Distributed optical fiber sensing technology is a kind of distributed optical fiber sensor based on backscattering, which reflects the physical characteristics of the sensing optical fiber along the line by sending optical signals to the optical fiber and then measuring the backscattering. The backscattering based on Raman scattering, Brillouin scattering and Rayleigh scattering, etc. The signal provided by Rayleigh scattering has a signal-to-noise ratio significantly greater than the signal based on Raman scattering and Brillouin scattering, and therefore plays an important role in measuring physical quantities such as strain, temperature and shape. With the continuous development of technology, the optical time domain reflectometer (OTDR) has gradually developed from the functions of measuring fiber attenuation, joint loss and detecting fiber fault points into a multifunctional sensor with functions of measuring temperature, stress and acoustic waves, etc.

[0003] CN201510213700.3 discloses a method for measuring weak fiber grating reflectivity, comprising the following steps: placing the measured fiber grating in a low reflectivity fiber grating reflectivity test system; then cleaning the UPC type fiber joint end of the measured fiber grating and placing it in medium 1 to obtain the reflection spectrum of the measured fiber grating; then keeping the system fixed, quickly cleaning the UPC type fiber joint and placing it in medium 2 again to obtain the reflection spectrum of the measured fiber grating; finally, calculating the reflectivity of the measured weak fiber grating by using the peak values of the two reflection spectra. The weak fiber grating reflectivity is calculated by obtaining double reflection spectrum, which eliminates the influence of fiber end face and fiber joint connection on the measurement. The measurement method is large in workload and complicated.

[0004] CN2016107019489 discloses a low-reflectivity fiber grating reflectivity accurate measurement device for high-power fiber laser, comprising a broadband light source, a single-mode circulator, a mode field matcher, a first flange, a second flange, a winding column, a spectrometer and a low-reflectivity fiber grating. The output end of the broadband light source is connected with the port of the single-mode circulator through the first flange, the port of the single-mode circulator is connected with the spectrometer, the port of the single-mode circulator is connected with the single-mode end of the mode field matcher through the second flange, the multimode end of the mode field matcher is fused with one end of the low-reflectivity fiber grating, and the other end of the low-reflectivity fiber grating is wound on the winding column. This measurement method is also large in workload.

[0005] Due to the existence of fiber attenuation, the signal intensity propagating in the optical fiber decreases exponentially, and reaches a certain propagation distance, the signal-to-noise ratio will be reduced to a degree that makes the measurement result no longer accurate and reliable. The signal-to-noise ratio refers to the ratio of the power of the propagating signal to the power of the noise in the process of the propagating signal. At present, the power of the noise in the process of the propagating signal has been reduced to a certain extent, and the signal-to-noise ratio is improved mainly by enhancing the power of the propagating signal. Scattering occurs in all directions, but the proportion of light collected by the optical fiber core is limited by the numerical aperture of the optical fiber, so that 80% of the total attenuation of the propagating signal is caused by Rayleigh scattering. In order to increase the signal-to-noise ratio in the process of optical fiber sensing and better utilize Rayleigh scattering for optical fiber sensing, some enhanced back-reflection optical fibers with weak reflection gratings are born. For a weak reflection grating array, reflectivity is one of the most important physical parameters, and accurate measurement of the reflectivity of the weak reflection grating array is of great significance for the design and application of weak reflection grating array optical instruments and the further development of optical fiber sensing.

[0006] In recent years, with the continuous development of optical fiber sensing technology, OTDR as an optical fiber sensing device is widely used, which can measure optical fiber loss, optical reflectivity, etc. The optical time-domain reflectometer (OTDR) is an instrument that can understand the uniformity, defects, fractures, joint coupling and other performances of the optical fiber through analysis of the measurement curve. The information of attenuation is obtained by using the backscattered light generated when light propagates in the optical fiber, which can be used to measure the optical fiber attenuation, joint loss, optical fiber fault point positioning, optical fiber length, connector and joint loss, and understand the loss distribution along the length of the optical fiber. There is no OTDR to measure the reflectivity of the weak reflection grating array. SUMMARY

[0007] The purpose of the present application is to obtain a method and device for measuring the reflectivity of a weak reflection grating array using OTDR. The main purpose is to measure the weak reflection grating array to be measured based on the OTDR system.

[0008] The technical scheme of the present application is a weak reflection grating array reflectivity measurement method based on the following measurement system, using an optical time domain reflectometer (OTDR), including a direct current light source, a modulator, an erbium-doped fiber amplifier, a circulator, a photoelectric detector, a data acquisition card, a data analysis processing module and a display module; the optical path connection mode is as follows: the output port of the laser is connected to the input port of the modulator; the output port of the modulator is connected to the input port of the erbium-doped fiber amplifier; the output port of the erbium-doped fiber amplifier is connected to the first port of the circulator; the second port of the circulator is connected to the weak reflection grating array to be measured; the third port of the circulator is connected to the input port of the photoelectric detector; the output port of the photoelectric detector is connected to the input port of the data acquisition card; the output port of the data acquisition card is connected to the data analysis processing module; and the output port of the data analysis processing module is connected to the display module. The specific schematic diagram is shown in Figure 1 .

[0009] The present application converts the optical signal output from the third port of the circulator into voltage data through the photoelectric detector, collects the data output from the photoelectric detector through the data acquisition card, converts the collected voltage data into current data through the data analysis processing module, obtains the reflected optical power data from the photoelectric conversion efficiency, and displays the data on the display module. The specific reflected optical power data is shown in Figure 2 . The reflectivity is calculated from the reflectivity formula of the fiber grating, specifically, the reflectivity = reflected pulse power (considering the loss introduced by the fiber length) / incident pulse power (considering the loss introduced by the fiber length).

[0010] Specifically, the following steps are included:

[0011] Step 1, connecting the weak reflection grating array to the OTDR system, connecting the weak reflection grating array to be measured to the second port of the circulator;

[0012] Step 2, connecting the output port of the laser to the input port of the modulator; connecting the output port of the modulator to the input port of the erbium-doped fiber amplifier; connecting the output port of the erbium-doped fiber amplifier to the first port of the circulator; the laser output direct current light signal is modulated into a probe light pulse by the modulator, and after being amplified by the erbium-doped fiber amplifier, it enters the weak reflection grating array to be measured through the circulator to form a probe signal.

[0013] Step 3, connecting the third port of the circulator to the input port of the photoelectric detector; connecting the output port of the photoelectric detector to the input port of the data acquisition card; after the probe signal is reflected by the reflection point in the weak reflection grating array, it is sent to the photoelectric detector through the circulator; the photoelectric detector converts the output optical signal of the circulator into voltage data, and sends it to the data acquisition card through the output port of the photoelectric detector for data collection.

[0014] Step 4, the output port of the data acquisition card is connected with the data analysis processing module; the output port of the data analysis processing module is connected with the display device. The output port of the data acquisition card sends the data to the data analysis processing module for data analysis and processing, converts the collected voltage data into current data, and then obtains the reflected light power data by photoelectric conversion efficiency, and sends the reflected light power data to the display device through the output port of the data analysis processing module. The reflectivity of the fiber grating is calculated by the reflectivity formula of the fiber grating.

[0015] Further, the reflectivity of the fiber grating can be calculated by the formula , wherein is the reflectivity of the first fiber grating counted from the second port of the circulator, is the reflectivity of the th fiber grating, is the reflected pulse power of the th fiber grating (considering the loss introduced by the fiber length), is the incident pulse power at the position of the th fiber grating (considering the loss introduced by the fiber length), is the loss coefficient of the fiber, and the unit is . , wherein is the fiber loss, and the unit is .

[0016] Further, the reflected pulse power is obtained by the photodetector, the data acquisition card and the data analysis processing module. The specific processing procedure is that the photodetector converts the output optical signal of the circulator into voltage data, and sends the voltage data to the data acquisition card through the output port of the photodetector for data acquisition. The output port of the data acquisition card sends the data to the data analysis processing module for data analysis and processing, converts the collected voltage data into current data, and then obtains the reflected light power data by photoelectric conversion efficiency

[0017] Further, the incident pulse power , wherein is the incident light power, is the loss coefficient of the fiber, and the unit is . , wherein is the fiber loss, and the unit is .

[0018] The weak reflection grating array reflectivity measurement system of the application, the measuring device comprises a direct current light source, a modulator, an erbium-doped fiber amplifier, a circulator, a photoelectric detector, a data acquisition card, a data analysis processing module and a display module; the light path connection mode is as follows: the output port of the laser is connected with the input port of the modulator; the output port of the modulator is connected with the input port of the erbium-doped fiber amplifier; the output port of the erbium-doped fiber amplifier is connected with the first port of the circulator; the second port of the circulator is connected with the measured weak reflection grating array; the third port of the circulator is connected with the input port of the photoelectric detector; the output port of the photoelectric detector is connected with the input port of the data acquisition card; the output port of the data acquisition card is connected with the data analysis processing module; and the output port of the data analysis processing module is connected with the display module.

[0019] Beneficial effects: the application can produce the following advantages by adopting the above technical scheme: the application provides a method and system for measuring the reflectivity of weak reflection gratings, the reflectivity of each fiber grating in the weak reflection grating array is accurately measured by the simple quasi-OTDR, and important physical parameters are provided for designing and applying optical devices of the weak reflection grating array. Moreover, the detection system of the application is simple and reliable, the measurement method has small workload, and accurate measurement results can be obtained in time. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 It is a system structure schematic diagram of the application;

[0021] Figure 2 It is a measurement result of the application. DETAILED DESCRIPTION

[0022] In order to more clearly and clearly describe the application, one embodiment will be described below, but the application is not limited to this.

[0023] The system structure of the case includes 1, OTDR, 2 weak reflection grating array (to be measured).

[0024] The specific implementation steps of the case are as follows:

[0025] Step 1, connect the weak reflection grating array to the OTDR system, and connect the weak reflection grating array to be measured to the second port of the circulator.

[0026] Step 2, the output port of the laser is connected with the input port of the electro-optic modulator; the output port of the electro-optic modulator is connected with the input port of the erbium-doped fiber amplifier; the output port of the erbium-doped fiber amplifier is connected with the first port of the circulator; the direct current light signal output by the laser is modulated into a probe light pulse by the electro-optic modulator, is amplified by the erbium-doped fiber amplifier, and then enters the weak reflection grating array to be measured through the circulator to form a probe signal.

[0027] Step 3, the third port of the circulator is connected to the input port of the photoelectric detector; the output port of the photoelectric detector is connected to the input port of the data acquisition card; the detection signal is reflected by the reflection points in the weak reflection grating array and is sent to the photoelectric detector through the circulator. The photoelectric detector converts the circulator output optical signal into voltage data and sends it to the data acquisition card through the photoelectric detector output port for data acquisition.

[0028] Step 4, the output port of the data acquisition card is connected to the data analysis processing module; the output port of the data analysis processing module is connected to the display device. The voltage data collected by the data acquisition card is converted into current data through the data analysis processing module, and the reflected optical power data is obtained through the photoelectric conversion efficiency, and is sent to the display device through the output port of the data analysis processing module to give the reflected optical power data. The reflectivity of each fiber grating in the weak reflection grating array is calculated by the reflectivity formula of the fiber grating. The reflectivity of the first fiber grating is counted from the second port of the circulator, and the reflectivity of the

[0029] The voltage data converted into current data of the reflected pulse power of the standard fiber grating obtained by the photoelectric collector data acquisition and signal processing can be measured by a standard reflectivity fiber grating intervention measuring device at a position, and other fiber gratings are measured by comparing with the standard reflectivity fiber grating, which can better ensure the precision of the present application.​​​​​​​​​​​​​

Claims

1. A method for measuring the reflectivity of a weakly reflective grating array, characterized in that, The measurement system uses an Optical Time Domain Reflectometer (OTDR), comprising a DC light source, modulator, erbium-doped fiber amplifier, circulator, photodetector, data acquisition card, data analysis and processing module, and display module. The optical path connections are as follows: the laser output port is connected to the modulator input port; the modulator output port is connected to the erbium-doped fiber amplifier input port; the erbium-doped fiber amplifier output port is connected to port 1 of the circulator; port 2 of the circulator is connected to the weakly reflective grating array under test; port 3 of the circulator is connected to the photodetector input port; the photodetector output port is connected to the data acquisition card input port; the data acquisition card output port is connected to the data analysis and processing module; and the data analysis and processing module output port is connected to the display module. The reflectivity is calculated using the fiber grating reflectivity formula: Reflectivity = Reflected Pulse Power / Incident Pulse Power. Specifically, the following steps are included: Step 1: Connect the weak reflection grating array to the above measurement system, and connect the weak reflection grating array to be measured to the second port of the circulator; Step 2: Connect the output port of the laser to the input port of the modulator; the DC optical signal output by the laser is modulated into a probe optical pulse by the modulator, amplified by the erbium-doped fiber amplifier, and then enters the weak reflection grating array under test through the circulator to form a probe signal; Step 3: Connect the third port of the circulator to the input port of the photodetector; connect the output port of the photodetector to the input port of the data acquisition card; after the detection signal is reflected by the reflection point in the weak reflection grating array, it is sent to the photodetector through the circulator; the photodetector converts the output light signal of the circulator into voltage data and sends it to the data acquisition card through the output port of the photodetector for data acquisition. Step 4: Connect the output port of the data acquisition card to the data analysis and processing module; connect the output port of the data analysis and processing module to the display device; convert the acquired voltage data into current data, then obtain the reflected optical power data based on the photoelectric conversion efficiency, and send it to the display device through the output port of the data analysis and processing module to display the reflected optical power data; calculate the reflectivity using the formula for the reflectivity of a fiber Bragg grating; the reflectivity of a fiber Bragg grating is calculated using the formula... The calculation shows that, among which To start counting from the first fiber grating at port 2 of the circulator, the number of... The reflectivity of a fiber grating For the first The reflected pulse power of a fiber grating considering the loss introduced by fiber length. For the first The location of each fiber grating Considering the loss introduced by fiber length, the incident pulse power The loss factor of the optical fiber, in units of... Among them, fiber loss Units are .

2. The method for measuring the reflectivity of a weak-reflection grating array according to claim 1, characterized in that, Reflected pulse power The specific processing flow, derived from the photodetector, data acquisition card, and data analysis and processing module, is as follows: The photodetector converts the circulator's output optical signal into voltage data, which is then sent to the data acquisition card through the photodetector's output port for data acquisition. The data is then sent to the data analysis and processing module through the data acquisition card's output port for data analysis and processing. The acquired voltage data is converted into current data, and finally, the reflected optical power data is obtained based on the photoelectric conversion efficiency. Incident pulse power ,in The incident light power, The loss factor of the optical fiber, in units of... ; Among them, fiber loss The unit is .

3. The method for measuring the reflectivity of a weak-reflection grating array according to claim 1, characterized in that, By inserting a standard reflectivity fiber grating into a measurement device at a certain position, the voltage data corresponding to the reflected pulse power of this standard fiber grating, obtained after data acquisition and signal processing by the photoelectric collector, is converted into current data. Then, other fiber gratings are measured by comparing them with the standard reflectivity fiber grating.

4. A weak-reflection grating array reflectance measurement system for implementing the method of any one of claims 1-3, characterized in that, The measuring device includes a DC light source, a modulator, an erbium-doped fiber amplifier, a circulator, a photodetector, a data acquisition card, a data analysis and processing module, and a display module. The optical path connections are as follows: the output port of the laser is connected to the input port of the modulator; the output port of the modulator is connected to the input port of the erbium-doped fiber amplifier; the output port of the erbium-doped fiber amplifier is connected to port 1 of the circulator; port 2 of the circulator is connected to the weak reflection grating array under test; port 3 of the circulator is connected to the input port of the photodetector; the output port of the photodetector is connected to the input port of the data acquisition card; the output port of the data acquisition card is connected to the data analysis and processing module; and the output port of the data analysis and processing module is connected to the display module.

5. The weak reflection grating array reflectance measurement system according to claim 4, characterized in that, The modulator used in the device is an electro-optic modulator, an acousto-optic modulator, a spatial light modulator, or an optical switch.

6. The weak reflection grating array reflectance measurement system according to claim 4, characterized in that, The circulator ports are connected as follows: port 1 of the circulator is connected to the output port of the erbium-doped fiber amplifier, port 2 of the circulator is connected to the weak reflection grating array, and port 3 of the circulator is connected to the input port of the photodetector.

Images