CN212482511U

CN212482511U - Device based on cavity ring-down large-range high-precision fiber grating sensing

Info

Publication number: CN212482511U
Application number: CN202021638989.6U
Authority: CN
Inventors: 赵春柳; 吴锴; 毛邦宁
Original assignee: China Jiliang University
Current assignee: China Jiliang University
Priority date: 2020-08-10
Filing date: 2020-08-10
Publication date: 2021-02-05
Anticipated expiration: 2030-08-10

Abstract

The utility model relates to a device based on optical cavity declines and swings high accuracy fiber grating sensing on a large scale. The device comprises an LED broadband light source, a signal generator, a 2 x 1 optical fiber coupler, a transmission optical fiber, an optical fiber delay line, a circulator, an optical fiber grating FBG, an edge filter, a photoelectric detector, an optical fiber grating, a PC and an oscilloscope. The present invention uses a fiber ring cavity ring down (FLRD) technique. The spectrum of the broadband light source has a certain range, and when the fiber bragg grating is influenced by external parameters and wavelength conversion occurs, effective reflected light can be generated. The edge filter can make the light intensity after passing through the edge filter and the wavelength of the fiber grating in a linear one-to-one correspondence relationship, so that the output loss in the cavity and the wavelength of the fiber grating are in a linear relationship. Because the ring-down time is determined by the loss in the cavity, the effective measurement of the parameters acting on the fiber grating can be realized by measuring the ring-down time, thereby realizing the measurement with large range and high precision.

Description

Device based on cavity ring-down large-range high-precision fiber grating sensing

Technical Field

The utility model belongs to the technical field of the optical fiber sensing, in particular to device based on optical cavity declines and swings high accuracy fiber grating sensing on a large scale.

Background

The fiber grating is formed by writing a coherent field pattern of incident light into a fiber core by ultraviolet light exposure using the photosensitivity of the fiber material, and generating a periodic variation of the refractive index in the fiber core along the axial direction of the fiber core, which essentially forms a narrow-band (transmissive or reflective) edge filter or mirror in the fiber core. In practical measurement, the fiber grating is equivalent to form a narrow-band edge filter in the fiber to reflect light with a specific central wavelength, when the fiber grating is subjected to external physical quantity change, the effective refractive index and the grating period of the fiber grating can be changed, the central wavelength is changed accordingly, and the change of the external physical quantity can be measured by detecting the offset of the central wavelength of the fiber grating. The fiber grating has the characteristics of small volume, good wavelength selectivity, no influence of nonlinear effect, insensitive polarization, easy connection with a fiber system, convenient use and maintenance, large bandwidth range, small additional loss, miniaturized device, good coupling, capability of being fused with other fiber devices and the like, and the fiber grating has mature manufacturing process, easy formation of mass production and low cost, so the fiber grating has good practicability and the superiority that other devices cannot be replaced. This makes fiber gratings and fiber grating-based devices important as photoelectric sensing devices.

The fiber ring cavity ring-down (FLRD) technology is a new fiber sensing technology. The technology simulates the concept of ring-down, light passes through the substance to be detected for multiple times to form a circular ring-down, then an output optical signal is converted into an electrical signal by using a photoelectric detector, a ring-down pulse curve can be seen in an oscilloscope, and the information of the substance to be detected can be obtained by detecting the ring-down time of the pulse curve. Because the ring-down time is detected, the influence of the fluctuation of the light source on the detection can be avoided. The fiber ring cavity consists of a fiber coupler and a section of long fiber, a sample to be measured is placed in the ring cavity, and the relevant information of the parameter to be measured can be calculated by measuring the attenuation time. Compared with the traditional spectrum technology, the technology avoids the use of a spectrometer, so that the whole system is low in cost, short in response time and capable of having strong advantages in rapid detection and line detection. The fiber ring cavity ring-down technology has the advantages of no influence of light source fluctuation, high response speed, high sensitivity, good stability and the like. Through development and research in the last decade, the technology gradually matures, and can be applied to measurement of parameters such as liquid refractive index, gas concentration, temperature, strain and the like.

The Fiber Bragg Grating (FBG) -based FLRD sensing system also has the advantages of the fiber ring-down (FLRD) technology, the detection sensitivity of the sensing system is in direct proportion to the round-trip times of optical pulses propagating in an optical fiber loop, and the optical fiber loop can be as long as several kilometers, so that the long-distance sensing detection is facilitated; unlike direct measurement of light intensity attenuation or wavelength drift, the sensing system is insensitive to light source fluctuations, thus also ensuring accuracy. However, the measuring range of the sensing system is not large, and some measuring requirements cannot be met.

SUMMERY OF THE UTILITY MODEL

The problem that the sensing system of the fiber ring cavity ring-down (FLRD) technology cannot measure in a large range is solved. The utility model provides a simple structure, stability are good and based on the device that the optical cavity declines and swings high accuracy fiber grating sensing on a large scale.

Utility model is a device that solution technical problem took:

the cavity ring-down large-range high-precision fiber grating sensing device comprises: the device comprises an LED broadband light source, a signal generator, a 2X 1 optical fiber coupler, a transmission optical fiber, an optical fiber delay line, a circulator, an optical fiber grating FBG, an edge filter, a photoelectric detector, an optical fiber grating, a PC and an oscilloscope.

The 2 x 1 fiber coupler includes a first coupler and a second coupler.

The broadband light source is connected with an output port of the signal generator through a cable, two ports on one side of the first coupler are respectively connected with the broadband light source and one end of the optical fiber delay line, the other end of the optical fiber delay line is connected with one end of a port of the second coupler, port 1 of the circulator is connected with one end of the second coupler, port 2 of the circulator is connected with the Fiber Bragg Grating (FBG), port 3 of the circulator is connected with one end of the edge filter, the other end of the edge filter is connected with one end of the first coupler, an input port of the photoelectric detector is connected with one end of the second coupler, the PC is connected with the photoelectric detector through a USB line, and an output port of the photoelectric detector is connected with the oscilloscope through an optical cable. The first coupler, the optical fiber delay line, the second coupler, the circulator, the Fiber Bragg Grating (FBG) and the edge filter form a ring-down cavity structure, the Fiber Bragg Grating (FBG) is used as a sensing area, and the photoelectric detector, the PC and the oscilloscope are used as demodulators of the sensors; monitoring the attenuation change curve of light intensity when different light intensity is to be measured, and realizing the measurement to be measured by measuring the ring-down time of the curve.

The utility model has the advantages that:

the utility model discloses a broadband light source has been used to the light source to add edge filter, broadband light source has the energy spectrum of certain width, after edge filter's signal linear modulation again, makes device system measuring range grow, and measurement accuracy becomes more accurate.

The utility model discloses light source intensity changes and does not have the influence to ring down chamber system measurement result, as long as the light intensity can in detection range. And the ring-down cavity technology measures a ring-down time value which is a relative value, does not need calibration and is not easy to be submerged by background light.

Drawings

Fig. 1 is the utility model discloses the cavity ring-down technique is high accuracy fiber grating sensing device's on a large scale schematic diagram.

Fig. 2 is how to realize the principle and schematic diagram of the large-range high-precision measurement of the utility model.

Detailed Description

The present invention will be further described with reference to the accompanying drawings.

As shown in fig. 1, the cavity ring-down technique large-range high-precision fiber grating sensing device includes a signal generator 1, a broadband light source 2, a first coupler 3, a fiber delay line 4, a second coupler 5, a circulator 6, a fiber grating (FBG)7, an edge filter 8, a photodetector 9, a PC 10, and an oscilloscope 11. The broadband light source 2 is connected with an output port of the signal generator 1 through a cable, a port 301 of the first coupler 3 is connected with the broadband light source 2, a port 302 of the first coupler 3 is connected with an optical fiber delay line 4, the other end of the optical fiber delay line 4 is connected with a port 501 of the second coupler, a port 601 of the circulator is connected with a port 503 of the second coupler, a port 602 of the circulator is connected with an optical fiber grating (FBG)7, a port 603 of the circulator is connected with one end of an edge filter 8, the other end of the edge filter 8 is connected with a port 303 of the first coupler, an input port of the photoelectric detector 9 is connected with a port 502 of the second coupler 3, the PC 10 is connected with the photoelectric detector 9 through a USB line, and an output port of the photoelectric detector 9 is connected with the oscilloscope 11 through an optical cable. The first coupler 3, the optical fiber delay line 4, the second coupler 5, the circulator 6, the Fiber Bragg Grating (FBG)7 and the edge filter 8 form a ring-down cavity structure, the Fiber Bragg Grating (FBG)7 serves as a sensing area, and the photoelectric detector 9, the PC 10 and the oscilloscope 11 serve as demodulators of sensors.

The utility model discloses a working method does: the light wave of the broadband light source 2 generates time sequence pulse signal light through the signal generator 1, the time sequence pulse signal light is input into the first coupler 3 through the optical fiber, then is transmitted to the optical fiber delay line 4 from the port 302 of the first coupler 3, and is transmitted to the second coupler 5 through the optical fiber delay line 4, one part of the pulse signal light is transmitted to the circulator 6 through the port 503 of the second coupler 5, and the other part of the light signal is transmitted to the photoelectric detector through the port 502. The signal light passing through the circulator 6 is input from the port 601, is sensed by the Fiber Bragg Grating (FBG)7 through the port 602, the sensed signal light is transmitted to the edge filter 8 through the port 603 for linear selection processing, and the signal passing through the edge filter 8 enters the next ring-down cycle through the port 303 of the first coupler 3. The electric signal passing through the photodetector 9 is converted into an optical signal, amplified by a parameter adjusting signal of the PC 10, and finally displayed on the oscilloscope 11.

The device for sensing the large-range high-precision fiber bragg grating by cavity ring-down is characterized in that an LED broadband light source with a certain width is used, a spectrum of the LED broadband light source has a certain range as shown in a figure 2-1, and when a system device carries out measurement, the fiber bragg grating is influenced by external parameters and can generate effective reflected light when wavelength is changed. By adding an edge filter to the device, the light after passing through the edge filterThe intensity is in linear one-to-one correspondence with the wavelength of the fiber grating, so that the output loss in the cavity is in linear relationship with the wavelength of the fiber grating. The energy spectrum output by the broadband light source after being acted on by the edge filter can be seen from fig. 2-2, and the output energy is linearly selected, as can be seen from fig. 2-3. The accuracy of the finally detected signal after linear processing is further improved. The signal generator controls the broadband light source to output a pulse sequence, and detects that the output light intensity is changed into the input light intensity under the conditions of the same pulse sequence and different to-be-measured values

The time required. Different losses and ring-down times correspond to different quantities to be measured. The loss in the ring-down cavity is only related to the measurement to be measured and is unrelated to other factors, and the influence of other factors on the measurement is eliminated, so that the accurate measurement of the band measurement is completed. The device can enlarge the measuring range and improve the accuracy.

The key technology of the device for realizing the optical cavity ring-down large-range high-precision fiber grating sensing method and the device is as follows:

1. a broadband light source is chosen instead of a single wavelength light source. The spectrum of the broadband light source has a certain range, and the fiber bragg grating is influenced by external parameters and can generate effective reflected light when the wavelength is changed.

2. The edge filter is added in the device, so that the light intensity after passing through the filter and the wavelength of the fiber grating are in linear one-to-one correspondence, and the output loss in the cavity and the wavelength of the fiber grating are in linear relationship. Because the ring-down time is determined by the loss in the cavity, the effective measurement of the parameters acting on the fiber grating can be realized by measuring the ring-down time, thereby realizing the measurement with large range and high precision.

In one embodiment of the present invention, the broadband light source SLED-1550 has a spectral width of 55 nm; the modulation frequency of the pulse wave of the signal generator is 10 kHz. The sensing fiber grating (FBG) is prepared on a G.652 single-mode fiber, the length is 15mm, the working wavelength is 1547.3nm, the bandwidth is 3dB,the loss is 0.01 dB. An edge filter with an action range of 1540nm to 1555nm and a slope K of 0.68,1540nm, and the zero output wavelength lambda of the edge filter₀(ii) a The method comprises the following steps that axial stress is measured, two ends of a sensing Fiber Bragg Grating (FBG) are fixed on a clamp of a moving platform, the sensing Fiber Bragg Grating (FBG) moves towards two sides through the clamp, and the axial stress is applied to the sensing Fiber Bragg Grating (FBG); the optical fiber is G.652 single-mode optical fiber; the photoelectric detector is an Avalanche Photodiode (APD), the working wavelength is 1.0-2.9 μm, the range to be measured is 0-300 μm, and the measurement precision can reach 0.005 μm.

The basic principles and essential features of the invention have been shown and described above, and various changes and modifications may be made without departing from the spirit and scope of the invention, all of which fall within the scope of the claimed invention.

Claims

1. The utility model provides a device based on optical cavity ring-down is high accuracy fiber grating sensing on a large scale which characterized in that includes: the system comprises an LED broadband light source, a signal generator, a 2X 1 optical fiber coupler, a transmission optical fiber, an optical fiber delay line, a circulator, an optical fiber grating (FBG), an edge filter, a photoelectric detector, a PC and an oscilloscope; the 2 x 1 optical fiber coupler comprises a first coupler and a second coupler;

the broadband light source is connected with an output port of the signal generator through a cable, two ports on one side of the first coupler are respectively connected with the broadband light source and one end of an optical fiber delay line, the other end of the optical fiber delay line is connected with one end of a port of the second coupler, a port 1 of the circulator is connected with one end of the second coupler, a port 2 of the circulator is connected with an optical fiber grating (FBG), a port 3 of the circulator is connected with one end of an edge filter, the other end of the edge filter is connected with one end of the first coupler, an input port of the photoelectric detector is connected with one end of the second coupler, the PC is connected with the photoelectric detector through a USB line, and an output port of the photoelectric detector is connected with the oscilloscope through an optical cable; the first coupler, the optical fiber delay line, the second coupler, the circulator, the Fiber Bragg Grating (FBG) and the edge filter form a ring-down cavity structure, the Fiber Bragg Grating (FBG) is used as a sensing area, and the photoelectric detector, the PC and the oscilloscope are used as demodulators of the sensors; monitoring the attenuation change curve of light intensity when different light intensity is to be measured, and realizing the measurement to be measured by measuring the ring-down time of the curve.