Device and method for preparing multi-period fiber grating sensor

Abstract

The invention provides a device and method for preparing a high-temperature-resistant multi-period fiber grating. The device comprises a femtosecond laser, a shutter, a variable attenuator, a cylindrical lens, a phase mask plate, a broadband light source, an optical fiber and a spectrograph. A femtosecond laser pulse emitted by the femtosecond laser passes through the cylindrical lens and the phase mask plate and forms interference fringes; different tensile forces are applied to the two ends of the optical fiber, the interference fringes are focused on an optical fiber core for inscribing, and the tensile forces are released after grating inscribing; the operation is repeated, the tension is released after each time of inscribing, and a plurality of fiber bragg gratings with different periods can be generated on a single optical fiber; therefore, the multi-period fiber grating array capable of monitoring the distributed temperature is formed.

Description

Technical Field

[0001] The present application relates to the technical field of fiber grating sensor preparation, and specifically to a method for preparing a high-temperature resistant multi-period fiber grating using a femtosecond laser, which is suitable for distributed temperature monitoring in a high-temperature environment, and is particularly suitable for motor carbon brush temperature monitoring. Background Art

[0002] Fiber Bragg grating sensors have been widely used in temperature and strain monitoring in complex environments due to their advantages of anti-electromagnetic interference, small size, and high sensitivity. However, traditional fiber Bragg grating preparation technology usually only supports single-period gratings, and multiple optical fibers need to be connected to achieve multi-point temperature measurement, resulting in complex structure, large space requirements, and high insertion loss, which makes it difficult to meet the needs of multi-point distributed measurement in high-temperature environments. In addition, the stability and accuracy of conventional fiber Bragg gratings in high-temperature environments are limited, and it is not easy to be used in the monitoring of high-temperature equipment such as generator carbon brushes.

[0003] The femtosecond laser combined with the phase mask writing method provides a feasible solution. The extremely short pulse width and high peak power of the femtosecond laser enable it to form a precise and high-temperature resistant refractive index modulation structure in the fiber core. The phase mask directly writes the interference fringes of the laser pulse into the optical fiber through spatial phase modulation, further improving the preparation efficiency and quality of the grating. Using this method, multiple fiber gratings of different periods can be written on a single optical fiber to achieve distributed temperature measurement and meet the needs of multi-point monitoring in high-temperature environments.

[0004] The phase mask method not only has high processing efficiency and good stability, but also has low requirements for the coherence of the processing light source, which is very suitable for batch preparation of fiber gratings using a light source with weak coherence, such as femtosecond laser. Therefore, the multi-period fiber grating prepared by combining femtosecond laser with phase mask technology can achieve stable multi-point temperature monitoring in complex high-temperature environments and has broad application prospects. Summary of the invention

[0005] In view of the problems that traditional fiber grating sensors are difficult to achieve multi-point monitoring on a single optical fiber, and are susceptible to electromagnetic interference, large insertion loss, and reduced sensitivity in high-temperature environments, this application proposes a preparation method using a femtosecond laser combined with a phase mask to prepare a high-temperature resistant multi-period fiber grating to meet the needs of multi-point temperature monitoring in high-temperature environments.

[0006] Through the method for preparing a high-temperature resistant multi-period fiber grating of the present application, multiple fiber gratings of different periods can be engraved on a single optical fiber to form a high-temperature resistant, multi-period grating structure, thereby realizing distributed temperature field monitoring.

[0007] This technology is particularly suitable for high-temperature application scenarios such as generator carbon brushes. It can provide higher accuracy, stability and reliability, and provides an efficient and low-cost solution for high-temperature monitoring applications.

[0008] A device for preparing a multi-period fiber grating comprises: a femtosecond laser (1), a shutter (2), a variable attenuator (3), a cylindrical lens (4), a phase mask (5), a broadband light source (6), an optical fiber (7), and a spectrometer (9). The optical fiber (7) is fixed on the phase mask (5), so that a femtosecond laser pulse emitted by the femtosecond laser (1) passes through the cylindrical lens (4) and the phase mask (5) to form interference fringes; the interference fringes are focused on a fiber core (8) of the optical fiber (7), generating a local refractive index change in the fiber core, thereby forming a fiber grating; and the spectrometer (9) is used to monitor the reflection and transmission peaks of the spectrum in real time to ensure the writing quality.

[0009] The high-energy pulses of femtosecond lasers combined with the spatial phase modulation technology of the phase mask enable the fiber Bragg grating to be written with high precision and stable structure, forming a high-quality grating with specific refractive index modulation.

[0010] By applying stress, multiple gratings of different periods are written on the same optical fiber (7). Specifically, the writing method for preparing a high-temperature resistant multi-period fiber grating is further as follows: a femtosecond laser pulse emitted by a femtosecond laser passes through a cylindrical lens and a phase mask to form interference fringes; different tensions are applied to both ends of the optical fiber, the interference fringes are focused on the optical fiber core, and writing is performed, and the tension is released after the grating is written, and the above operation is repeated, and the tension is released after each writing, so that multiple fiber gratings of different periods can be generated on a single optical fiber, thereby forming a multi-period fiber grating array that can monitor distributed temperature.

[0011] On the other hand, in order to meet the temperature monitoring requirements of the motor carbon brush (10) and slip ring (11) system. The present application proposes a carbon brush-slip ring temperature detection system, in which a multi-period fiber grating temperature sensor (12) is installed on the top surface of the carbon brush (10). The carbon brushes (10) in the system are arranged along the circumferential direction of the slip ring (11) to form a uniform temperature monitoring distribution point. By arranging the multi-period fiber grating sensor (12) on the top surface of each carbon brush (10), the distributed temperature field monitoring of each carbon brush (10) in the system can be achieved, ensuring that the temperature change is captured in real time and accurately in a high temperature environment such as the friction area between the slip ring (11) and the carbon brush (10).

[0012] This temperature monitoring method helps to warn of abnormal overheating in the carbon brush-slip ring system due to friction or current imbalance.

[0013] In addition to motor carbon brush temperature monitoring, the multi-period fiber grating sensor of the present application can be widely used in high-temperature environments such as petroleum, chemical industry, metallurgy, etc., and has broad application prospects.

[0014] This application has the following advantages and positive effects:

[0015] 1. Multi-point monitoring function: multiple temperature measurement points can be realized on a single optical fiber, which is suitable for quasi-distributed monitoring of carbon brush temperature and improves the density and accuracy of temperature monitoring;

[0016] 2. High temperature resistance and anti-electromagnetic interference: The grating prepared by femtosecond laser has high temperature stability and anti-electromagnetic interference performance, which is suitable for generator carbon brushes and other high-voltage environments;

[0017] 3. Easy installation and networking: Multi-period fiber Bragg gratings do not require additional splicing and complex operations during installation and networking, and can be easily integrated into the temperature monitoring network;

[0018] 4. High reliability and low cost: Compared with the traditional single-period grating structure, this application greatly reduces the system insertion loss and improves the monitoring accuracy and system reliability. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0020] Figure 1 A device diagram of a method for preparing a high temperature resistant multi-period fiber grating of the present application;

[0021] Figure 2a A schematic diagram of the specific structure of the carbon brush-slip ring temperature detection system of the present application;

[0022] Figure 2b It is a partially enlarged schematic diagram of the carbon brush-slip ring temperature detection system of the present application;

[0023] Reference numerals:

[0024] 1- femtosecond laser, 2- shutter, 3- variable attenuator, 4- cylindrical lens, 5- phase mask, 6- broadband light source, 7- optical fiber, 8- fiber core, 9- spectrometer, 10- carbon brush, 11- slip ring, 12- fiber Bragg grating temperature sensor; DETAILED DESCRIPTION

[0025] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. It should be noted that, in the absence of conflict, the various features in the embodiments of the present application can be combined with each other, and the combined embodiments are still within the scope of protection of the present application.

[0026] Example 1

[0027] like Figure 1 The device diagram of the method for preparing a high-temperature resistant multi-period fiber grating of the present application is shown, comprising: a femtosecond laser (1), a shutter (2), a variable attenuator (3), a cylindrical lens (4), a phase mask (5), a broadband light source (6), an optical fiber (7), and a spectrometer (9).

[0028] The optical fiber (7) is fixed on a phase mask (5), and a femtosecond laser pulse emitted by a femtosecond laser (1) is projected onto a core (8) of the optical fiber (7) through a cylindrical lens (4) and a phase mask (5), and a spectrometer (9) is used to monitor the reflection and transmission peaks of the spectrum in real time to ensure the writing quality.

[0029] The position of the optical fiber is adjusted through a three-dimensional mobile platform, so that the interference fringes are precisely focused on the core of the optical fiber, producing a local refractive index change in the core, thereby forming a fiber Bragg grating. The high-energy pulse of the femtosecond laser combined with the spatial phase modulation technology of the phase mask makes the fiber Bragg grating have high writing accuracy and stable structure, forming a high-quality grating with a specific refractive index modulation.

[0030] After writing the first grating, the periodic stretching of the optical fiber is adjusted by applying different tensions, and then the second grating is written. Repeat the above operation, the direction of the writing scan is roughly perpendicular to the stretching direction of the optical fiber (the direction of stress application), and the tensile stress is released after each writing, so that multiple fiber gratings with different periods can be generated on a single optical fiber. The grating segments of different periods formed are periodic refractive index modulation structures. During the writing scan process, a spectrometer (9) is used to monitor the reflection and transmission peaks of the spectrum in real time to ensure the writing quality.

[0031] Example 2

[0032] In order to meet the temperature monitoring requirements of the motor carbon brush (10) and slip ring (11) system. Figure 2aAs shown, the present application proposes a carbon brush-slip ring temperature detection system. In the carbon brush (10) and slip ring (11) system of the generator, each group of carbon brushes (10) is completely identical and arranged in a circumferential direction to form a uniform distribution of temperature monitoring points. The high-temperature resistant multi-period fiber grating temperature sensor (12) prepared by the preparation method of the present application is installed on the top surface of each carbon brush to accurately monitor its temperature change.

[0033] As attached Figure 2b As shown, a multi-period fiber Bragg grating temperature sensor (12) is installed on the top surface of the carbon brush (10) and fits closely to the surface, so as to realize distributed temperature field monitoring of each carbon brush (10) in the system, and ensure that temperature changes are captured in real time and accurately in a high temperature environment such as the friction area between the slip ring (11) and the carbon brush (10). The arrangement of the multi-period fiber Bragg grating temperature sensor can ensure that temperature data is evenly collected at different positions, and realize distributed monitoring of the temperature field.

[0034] The multi-period fiber Bragg grating temperature sensor is based on femtosecond laser writing technology and can maintain the stability of temperature response in high temperature environments. By monitoring the temperature changes of the carbon brush, the fiber Bragg grating temperature sensor can warn of abnormal friction or overheating, thereby improving the operating safety of the generator system. It contains multiple grating segments of different periods, which can achieve multi-point temperature measurement through a single optical fiber, ensuring high-precision temperature data at multiple locations.

[0035] The multi-period fiber Bragg grating temperature sensor is connected to the data acquisition system. The temperature data obtained by the sensor can be transmitted to the monitoring platform over a long distance, which is convenient for real-time monitoring of the temperature distribution of the carbon brush and slip ring system. The data of each monitoring point reflects the temperature change through the change of the central wavelength, realizing distributed monitoring in high temperature environment.

[0036] In addition to being used for motor carbon brush temperature monitoring, the multi-period fiber grating sensor of the present application is also suitable for high-temperature scenarios such as petroleum, chemical industry, and metallurgy, and has broad application potential.

[0037] Although the present application has been disclosed as above with preferred embodiments, the embodiments are not intended to limit the present application. Any equivalent changes or modifications made without departing from the spirit and scope of the present application also belong to the protection scope of the present application. Therefore, the protection scope of the present application should be based on the content defined by the claims of the present application.

Claims

1. A device for preparing a multi-period fiber grating, comprising: A femtosecond laser (1), a shutter (2), a variable attenuator (3), a cylindrical lens (4), a phase mask (5), a broadband light source (6), an optical fiber (7), and a spectrometer (9), characterized in that the optical fiber (7) is fixed on the phase mask (5), so that the femtosecond laser pulse emitted by the femtosecond laser (1) passes through the cylindrical lens (4) and the phase mask (5) to form interference fringes; the interference fringes are focused on the core (8) of the optical fiber (7), generating a local refractive index change in the core, thereby forming a fiber grating; and the spectrometer (9) is used to monitor the reflection and transmission peaks of the spectrum in real time to ensure the writing quality.

2. A method for preparing a multi-period fiber grating according to claim 1, characterized in that: The femtosecond laser pulses emitted by the femtosecond laser pass through a cylindrical lens and a phase mask to form interference fringes; different tensions are applied to both ends of the optical fiber, the interference fringes are focused on the optical fiber core, and the grating is written. The tension is released after the grating is written; the above operation is repeated, and the tension is released after each writing. Multiple fiber gratings with different periods can be generated on a single optical fiber; thereby, a multi-period fiber grating array that can monitor distributed temperature is formed.

3. A carbon brush-slip ring temperature detection system, using a multi-period fiber Bragg grating prepared by the preparation method according to claim 2, characterized in that: A multi-period fiber Bragg grating temperature sensor (12) is installed on the top surface of the carbon brush (10). The carbon brushes (10) in the system are arranged along the circumferential direction of the slip ring (11) to form uniform temperature monitoring distribution points. By arranging the multi-period fiber Bragg grating temperature sensor (12) on the top surface of each carbon brush (10), distributed temperature field monitoring of each carbon brush (10) in the system can be achieved, ensuring that temperature changes are captured in real time and accurately in a high-temperature environment such as a friction area between the slip ring (11) and the carbon brush (10).

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