CN212482510U

CN212482510U - An OTDR-based F-P sensing head multi-point measurement sensing device

Info

Publication number: CN212482510U
Application number: CN202021104243.7U
Authority: CN
Inventors: 赵春柳; 洪婉玲; 王剑锋; 徐贲; 康娟
Original assignee: China Jiliang University
Current assignee: China Jiliang University
Priority date: 2020-06-16
Filing date: 2020-06-16
Publication date: 2021-02-05
Anticipated expiration: 2030-06-16

Abstract

The utility model discloses an OTDR-based F-P sensing head multipoint measurement sensing device, which comprises an OTDR (optical time domain reflectometer), a long-distance single-mode optical fiber delay line, a filter and an F-P sensing head; when the m-th path to be measured is changed, the interference spectrum of the corresponding F-P sensing head drifts, the wavelength drift is converted into the intensity change after the interference spectrum passes through the filter, and the intensity change is received by the OTDR. Because the specific position detected by the OTDR is determined by 2 times of the optical path, and the length of the delay line of each optical path is different, the signal light returned by each optical path has a certain interval in the time domain. By observing the light intensity changes of OTDR at different points in time domain, for N²The outside of each FP sensing head is measured and measured in real time, thereby realizing real-time measurementThe multiplexing and multi-point measurement of the F-P sensing head are realized. The utility model has the advantages of but sensitivity is high, while multiple spot measurement, cost of manufacture are low, be applicable to remote measurement etc.

Description

F-P sensing head multipoint measurement sensing device based on OTDR

Technical Field

The utility model belongs to the technical field of the optical fiber sensing, in particular to F-P sensing head multiple spot measurement sensing device based on OTDR.

Background

The human being has entered the information age, and the sensor technology is an important basis of the information technology and is a main technical approach for acquiring information. Fiber optic sensors have been an important area in research and industrial applications over the years, the primary reason for this being the fundamental difference between optical fibers and metal wires. The most advantages of using light as sensing and waveguide medium are large transmission capacity, high sensitivity, anti-electromagnetic interference, low cost, and chemical inertness and flexibility of optical fiber (optical waveguide) as light wave carrier, convenient multiplexing and easy web formation. Fiber optic sensors are the most competitive measurement tools in the fields of smart materials, smart and large-scale structure monitoring, high voltage, high magnetic fields, nuclear radiation, and biomedicine. And it can act as the otology of a person in places where the person cannot reach (e.g. high temperature areas), or in areas harmful to the person (e.g. nuclear radiation areas). But also can exceed the physiological limit of the human body and receive external information which can not be sensed by the sense organ of the human body. Although the optical fiber sensor has many advantages, the problems of cross sensitivity and the like still exist, and the practical application is limited.

The principle of the optical fiber sensor is to integrate various optical waveguides and optical fibers by using an optical waveguide technology and a semiconductor integrated optoelectronic technology. When a change in the quantity to be measured occurs, the properties of the optical fiber change, resulting in a change in the optical characteristics of the light transmitted in the optical fiber (e.g., intensity, wavelength, frequency, phase, polarization, etc. of the light). The variable to be measured can be measured by detecting and analyzing the relationship between the change of the optical characteristic of the output light and the corresponding variable to be measured.

The main directions for the development of fiber optic sensor technology are: (1) it is multipurpose. That is, an optical fiber sensor is capable of measuring a plurality of physical quantities simultaneously, not only for one physical quantity. (2) The spatial resolution and the sensitivity of the distributed sensor are improved, the cost is reduced, and a complex sensor network project is designed. Note the influence of the parameters of the distributed sensor, i.e. pressure, temperature, in particular chemical parameters (hydrocarbons, some contaminants, humidity, PH, etc.) on the optical fiber. (3) Development of novel sensing materials, sensing technologies, and the like. (4) Development and application of low cost sensors (bracket, connection, mounting) under harsh conditions (high temperature, high pressure, chemical corrosion). (5) Fiber optic connectors and micro-optics combined with other micro-technologies.

Currently common optical fiber sensors include Fiber Bragg Grating (FBG) sensors, interferometric optical fiber sensors, and the like. A fiber bragg grating (FBS) is the most frequently used and widely used fiber optic sensor that changes the wavelength of light reflected by the fiber bragg grating sensor according to changes in ambient temperature and/or strain. A small segment of photosensitive fiber is exposed to a light wave with a light intensity period distribution by holographic interference method or phase mask method. The optical refractive index of the fiber is thus permanently changed according to the intensity of the light wave it is illuminated. The periodic variation in the refractive index of light caused by this method is called a fiber bragg grating. The sensor is a mature sensor in the prior art, is widely applied to quasi-distributed measurement, and has lower sensitivity compared with an interference type optical fiber sensor.

The interference type optical fiber sensor such as an M-Z (Mach-Zehnder) interferometer type, an F-P (Fabry-Perot) interferometer type and the like has the advantages of high sensitivity, simple structure, low cost, easiness in operation and the like. The F-P interference type sensor is characterized in that two reflecting surfaces are manufactured in an optical fiber, so that an F-P cavity is formed in the two reflecting surfaces. When the light beam enters along the optical fiber, the light beam is reflected by the two end faces and returns along the original path to form interference light. When external change to be measured acts on the F-P cavity, the optical path difference of the F-P cavity is changed, and the spectrum of the output reflected light is shifted. The variable quantity to be measured can be obtained by detecting the drift quantity of the spectrum of the reflected light. However, the reflection spectrum of the F-P sensing head is generally quasi-positive rotation, has peaks and troughs, and has complex spectral components, so that the F-P interference type sensing head is difficult to realize multipoint measurement, and cannot meet the requirements of practical application occasions of multipoint simultaneous measurement.

To the difficult multiple spot measurement that realizes of F-P interference type sensing head, can't satisfy the demand scheduling problem of multiple spot simultaneous measurement's practical application occasion, the utility model provides a sensing device is measured to F-P sensing head multiple spot based on OTDR. The utility model has the advantages of but sensitivity is high, while multiple spot measurement, cost of manufacture are low, be applicable to remote measurement etc.

SUMMERY OF THE UTILITY MODEL

The utility model discloses the purpose is: to the difficult problem that realizes the multiple spot measurement of F-P interference type sensing head, the utility model provides a sensitivity is high, the cost of manufacture is low, but simultaneous multiple spot measurement, be applicable to remote measurement's F-P sensing head multiple spot measurement sensing device based on OTDR.

The utility model discloses a technical scheme who solves technical problem and take does:

an OTDR-based F-P sensing head multipoint measurement sensing device is characterized by comprising an OTDR (optical time domain reflectometer), a filter, a coupler, a single-mode fiber delay line and an F-P sensing head. The central wavelength and bandwidth of the filter are consistent with a certain main peak of the OTDR light source. The center wavelength of the F-P sensor head is required to be consistent with that of the filter, and the Free Spectral Range (FSR) of the F-P sensor head is required to be larger than the bandwidth of the filter.

The optical output end of the OTDR is connected with the optical input end of the filter through a single-mode transmission optical fiber, the output end of the filter filters out a narrow-band optical pulse, the narrow-band optical pulse is connected with the signal input end of the coupler through the single-mode optical fiber, the optical path is equally divided into N pieces, and the N pieces of optical pulse are output through N signal output ends. Each signal output end is connected with the signal input end of another coupler through a single-mode fiber, the optical path is divided into N routes and N signal output ends are output again, and N routes are formed in total²The strip measures the optical path. Each light path is connected with a single-mode optical fiber delay line with different lengths, the lengths of the delay lines are sequentially increased, and finally each single-mode optical fiber delay line is connected with an F-P sensing head.

The utility model has the advantages that: high sensitivity, simultaneous multi-point measurement, low manufacturing cost and suitability for remote measurement.

Drawings

Fig. 1 is a schematic diagram of an F-P multipoint measurement sensing device based on OTDR.

Detailed Description

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

Fig. 1 is a schematic diagram of a multi-point measurement sensing device for an F-P sensing head based on OTDR of the present invention, which includes an OTDR 1, a filter 2, a coupler 3, a delay line 4, and an F-P sensing head 5. The optical output end of the OTDR 1 is connected with the optical input end of the filter 2 through a single-mode transmission optical fiber, a narrow-band optical pulse is filtered out, the optical path is equally divided into N pieces after the narrow-band optical pulse is connected with the coupler 3 through the single-mode optical fiber, light on each branch is connected with the coupler through the single-mode optical fiber, and the optical path is divided into N pieces to form N pieces²The strip measures the optical path. Each measuring light path is connected with a single-mode optical fiber delay line 4 with different lengths, the lengths of the single-mode optical fiber delay lines are sequentially increased in an increasing mode, and finally each single-mode optical fiber delay line is connected with an F-P sensing head 5.

The utility model discloses a working method does: the signal light from OTDR 1 is input from a single-mode transmission fiber to the optical input of filter 2, and a narrow-band optical pulse is filtered from the optical output. The pulse bandwidth of the narrow-band light is consistent with a certain main peak of the OTDR light source and is opposite to the interference main peak of the F-P sensing head. And then is connected with the signal input end of the coupler 3 through the single mode fiber, and equally divides a beam of signal light into N pieces which are output by N signal output ends. Each output end is connected with the signal input end of the coupler through a single-mode transmission optical fiber and is divided into N branches. In total N²The strip measuring optical route is output by a signal output end and then passes through delay lines 4 and N with sequentially increasing lengths²The single mode fiber ends of the F-P sensor heads 5 are connected. N is a radical of²The light beams are coupled into a path after being reflected by the F-P sensing head and received by the OTDR.

The reflection spectrum I of the F-P sensor head changing along with the measured value is as follows:

when the external environment of the mth path is to be measured and changed, the interference spectrum of the corresponding F-P sensing head will drift.

Reflected light intensity S of mth optical path received by OTDR_mCan be expressed as:

as can be seen from equation (2), the optical intensity received by the OTDR is related to the F-P cavity refractive index n and the cavity length L, and thus to the outside world to be measured. The OTDR can obtain the corresponding change to be measured by monitoring the change of the reflected light intensity of the mth optical path at a specific position. Similarly, when all optical paths are coupled into one path and received by the OTDR, the specific position detected by the OTDR is determined by 2 times of the optical path, so that the signal light returned by each optical path has a certain interval in the time domain, and the interval is determined by the difference in length of the delay line. By observing the light intensity changes of OTDR at different points in time domain, for N²The outside of each FP sensing head is measured to be measured, so that the multiplexing and multi-point measurement of the F-P sensing heads are realized.

The device can realize the key technologies of multiplexing and multipoint measurement of the F-P interference type sensing head based on OTDR, and comprises the following steps:

1. the central wavelength of the reflected light of the F-P sensing head is consistent with the central wavelength of the transmission spectrum of the filter, so that the wavelength drift is converted into the light intensity change.

2. The time interval between the action of the delay line and each optical path needs to be far greater than the precision (more than or equal to 10 times) of the OTDR, so that the system can well distinguish the optical signal of each branch.

In this example, the OTDR emits laser light in the wavelength range of 1530-1557nm and pulse width of 5 ns. The bandwidth of the filter is 0.5nm, the filter is opposite to a 1550nm main peak connected with the OTDR, a narrow-band optical pulse is filtered out, the optical path is equally divided into 4 paths after passing through the 1 x 4 coupler, light on each branch is divided into 4 paths after passing through the 1 x 4 coupler, and 16 optical paths are formed in total. Each light path is connected with a single-mode fiber delay line with different lengths, and the lengths of the delay lines are respectively 100 meters, 200 meters and 300 meters … … 1600 meters. And finally, each delay line is connected with an F-P sensing head, the central wavelength of the F-P sensing head is 1550nm, and the free spectral range of the F-P sensing head is 12.5 nm. Experimental results show that the sensitivity of the F-P interference type multipoint measurement temperature sensor based on the OTDR can reach 1.210 dB/DEG C in the temperature range of 25-75 ℃.

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, which fall within the scope of the invention as claimed.

Claims

1. An OTDR-based FP sensing head multi-point measurement sensing device is characterized in that comprising an OTDR (optical time domain reflectometer), a filter, a coupler, a long-distance single-mode fiber delay line, an FP sensing head ; The optical output end of the OTDR is connected to the optical input end of the filter through a single-mode transmission fiber, and the optical output end of the filter is connected to the coupler through a single-mode transmission fiber. It is divided into N optical paths, and each branch is then transmitted through a single mode. The optical fiber is connected to the coupler and is divided into N optical paths, a total of N ² measurement optical paths are respectively connected to the single-mode fiber end of the FP sensor head through the single-mode fiber delay line of unequal length; the center wavelength of the filter is And the bandwidth is consistent with a certain main peak of the OTDR light source, the center wavelength of the FP sensor head needs to be consistent with the filter, and the free spectral range (FSR) needs to be larger than the bandwidth of the filter.