Development Route of Fiber Optic Sensing Technology in China: Current Status of Key Technologies

2022-9-7 20:23| Publisher: 2233| see: 290| comment: 0|come from: Photoelectric sink

abstract: After more than forty years of academic research and technological development, optical fiber sensing technology has formed an accelerating trend in recent years. There are two main reasons for this: firstly, optical fiber sensing technology has been widely applied in several practical scenarios; The second is the development and application of micro nano technology, material technology, and biotechnology, also known as optical fiber ...

After more than forty years of academic research and technological development, optical fiber sensing technology has formed an accelerating trend in recent years. There are two main reasons for this: firstly, optical fiber sensing technology has been widely applied in several practical scenarios; The second is the development and application of micro/nano technology, material technology, and biotechnology, which also provide many new methods for cross sensing in optical fiber sensing technology. The rapid development of China's economy not only provides a broad market for the practical application of fiber optic sensing technology, but also promotes the prosperity and progress of basic research in this field. Let's take a look at the development path of several key technologies in fiber optic sensing.

1.Special optical fibers and devices

In recent years, the rapid development of special optical fibers and their sensing devices has effectively pushed the level of optical fiber sensing technology to a new level. Compared with traditional sensors, fiber optic sensors have a series of unique advantages, such as good electrical insulation performance, strong resistance to electromagnetic interference, non-invasive, high sensitivity, flexible shape, corrosion resistance, explosion-proof, and easy to achieve remote monitoring of the measured signal.

With the rise of the Internet of Things and5GThe large-scale commercialization of technology and the application of special optical fibers and devices in sensing systems will also usher in vigorous development. The application of optical fiber in the sensing field has also undergone a series of technological changes. In order to meet different application environments, the development of special sensing optical fiber technology has also shifted from smaller size integration to more suitable technology for harsh environments. The practicality of optical fiber sensing has also made significant progress.

Special optical fibers mainly include bending resistant fibers, polarization maintaining fibers, high-temperature resistant fibers, radiation resistant fibers, rotating fibers, Rayleigh scattering enhanced fibers, etc.

1)Anti bending fiber,With low bending loss and high mechanical strength, it is suitable for small size vibration surround system and has important applications in optical fiber hydrophone. It is difficult for a single hydrophone to obtain the detailed information of the target, so it is necessary to deploy hundreds of detection elements to form a large detection array to achieve the positioning and pointing of underwater targets. For large-scale deployment, detection arrays and transmission optical cables are required to be small in size, light in weight, and easy to retract. Therefore, it is required that the sensing optical fiber used as a hydrophone should be small in size, able to withstand smaller bending radius and have lower bending loss. Anti bending optical fibers have also undergone a development process of gradually decreasing geometric dimensions, decreasing macro bending losses, and improving bending mechanical reliability. Their ultimate bending radius has reached5 mmThe maximum macroscopic bending loss is less than0.01 dB/turn。

2)Polarization maintaining fiber,The polarization state of an incident beam that can generate strong birefringence and maintain linear polarization in a certain direction, is often used in fiber optic gyroscopes. At present, for the application field of fiber optic gyroscopes, miniaturization and high precision are the development trends. Polarization maintaining optical fibers have also gone through a development process of smaller geometric dimensions, smaller bendable diameters, and more stable full temperature performance. The size of optical fibers has changed from125/250 μm(The diameters of the cladding and fiber core are respectively250 μm 125 μm)、80/170 μm,80/135 μm, developed to60/100 μmAt present, the core diameter has begun to shift towards40 μmDevelopment of dimensions.

3)High temperature resistant optical fiber,It is coated with special high temperature resistant polyimide coating, and the temperature resistance is up to300 ℃ is mainly used in distributed fiber optic temperature measurement systems, such as fire monitoring, pipeline leakage detection, and other special environments.

4)Radiation resistant fiberMainly used for communication and sensing in radiation environments such as space or nuclear power. The rare earth elements doped in optical fibers can cause radiative darkening effects when irradiated by high-energy particles in space, resulting in a sharp increase in fiber loss. Therefore, it is necessary to develop special optical fibers suitable for irradiation environments. At present, anti radiation optical fibers continuously reduce the radiation attenuation index from multiple directions such as doping material optimization, fiber pretreatment, and post-processing technology.

5)Rotating fiber optic,It has extremely outstanding anti environmental interference ability and is mainly used in fiber optic current transformers based on Faraday magneto optical effect. At present, relatively mature rotating optical fibers are prepared by rotating preforms during the drawing process. By optimizing the design of the torsion rate, the influence of linear birefringence caused by fiber bending can be greatly eliminated, and the mechanical strength of the rotating fiber is high, the process consistency is stable, and the stability of the product is greatly improved. It has been applied in fields such as power and metallurgy.

6)Rayleigh scattering enhanced fiberMainly used in distributed sensing systems based on Rayleigh scattering, such as Φ-OTDRSensing system.

Unlike communication, fiber optic sensing applications often come with special application environments. With the development of various industries in China, the sensing demand of the physical sensing layer has also followed, such as the demand for polarization maintaining fiber and its components in fiber optic gyroscope, fiber optic hydrophone, fiber optic current transformer, etc., and the demand for radiation resistant fiber and devices in nuclear power plants and space exploration. These demands not only promote the performance of sensing fiber, but also have a strong pull on the market.

However, in the application environment of special optical fibers, different application directions have different requirements for optical fibers, and achieving higher technical levels also puts forward unique technical requirements for various indicators of optical fibers. Special optical fibers have been widely used in the sensing field, and they can not be replaced in most fields, such as the application of bend resistant fibers in miniaturized hydrophone, and the application of fine diameter polarization maintaining fibers in high-precision gyroscopes. With the update of sensing technology, new requirements have been put forward for the indicators of various special optical fibers in practical applications.

Fiber optic is the carrier of fiber optic sensing technology. With the emergence of new fiber optic sensing technologies in the future and the upgrading and upgrading of existing sensing technologies, new types of fiber optic and various types of sensing fibers with higher technical requirements will inevitably emerge.

2.Fiber Bragg Grating Sensing Technology

Fiber Bragg Grating(FBG)It is widely recognized in the industry as the most diverse, commercialized, and widely used type of fiber optic sensing technology. Compared to other fiber optic sensing technologies,FBGThe sensing signal is strong, accurate, and responsive, unaffected by fluctuations in light sources and changes in link losses, with strong anti-interference ability; Through reasonable design and packaging, a single sensor can achieve strong environmental tolerance, while also possessing the characteristics of flexible and diverse networking and reuse methods.

FBGArray sensing, as a new generation of fiber optic grating sensing technology, organically combines the advantages of traditional "discrete fiber optic grating sensing" and "distributed fiber optic sensing", and is the most effective way to achieve large-capacity, high-precision, high-density, long-distance, and high reliability fiber optic sensing networks.

The photosensitive properties of optical fibers predate1978It was discovered in, but it wasn't until20century90In the 1990s, a series of milestone technological advancements in the fields of fiber optic communication and fiber optic sensing enabledFBGThe commercialization of has developed rapidly. surface1Summarized the development process of fiber Bragg grating sensing technology.

surface1 Summary of the Development of Fiber Bragg Grating Sensing Technology



Development Route of Fiber Optic Sensing Technology in China: Current Status of Key Technologies102 / author: / source:Photoelectric sink

Split typeFBGsensorSince its commercial launch, it has30Over the years of history, all key components of this technology have been domestically produced and widely applied in various fields, including monitoring of large buildings such as bridges, tunnels, slopes, and dams, monitoring of oil and gas fields, monitoring of large power facilities in thermal power, hydropower, wind power, nuclear power, and other fields, as well as monitoring of highways and high-speed railways/Intelligent monitoring of subway and airport pavement, etc. But faced with these main issues:

  • Under extreme working conditions, the reliability of fiber Bragg grating sensors and their fusion network is relatively low, such as their ability to withstand high temperature and pressure in oil and gas wells, as well as hydrogen damage, and their ability to withstand nuclear radiation environments is weak;
  • Discrete fiber optic grating sensors have a wide range of types and applications, but there is still a lack of unified industrial standards, greatly limiting their development and application.

andFBGArray sensing technologysince2003Since it was proposed in, it has been close to20Year. At present, the most representative work of three international institutions is the Leibniz Photonics Technology Research Institute in Germany(IPHT)BelgiumFBGSThe company, as well as the academician team of Jiang Desheng from the National Engineering Laboratory of Fiber Optic Sensing Technology at Wuhan University of Technology in China, have achieved industrial production of hundreds of thousands of fiber grating arrays per fiber, which have been widely applied in transportation, power, petrochemical and other fields, providing new sensing methods and methods for the intelligent development of multiple industries. Currently, they still face the following main problems:

  • Key technologies, large-scale production processes, and engineering installation specifications for fiber Bragg grating array sensing optical cables for many practical application scenarios;
  • Real time collection, storage, processing, and artificial intelligence pattern recognition of massive sensing big data using fiber Bragg grating arrays in combination with practical application scenarios;
  • Basic database for large-scale infrastructure Structural health monitoring and safety monitoring in key industries/Sample library construction, expert system and intelligent functional platform development.

3.Fiber optic gyroscope technology

Fiber optic gyroscope is a type of gyroscope based onSagnacThe fiber optic rotation sensor of the effect is a solid-state structure composed of fiber optic and optical wave devices. It has no moving components, is lightweight, has high reliability, and is flexible in configuration. Through optimization design, it can achieve high accuracy and low cost, and is currently the mainstream gyroscope instrument in the field of inertial technology.

The fiber resonant cavity of resonant fiber optic gyroscope is short, which has the characteristics of high reliability, high accuracy, easy maintenance, and long service life of laser gyroscope, and has important application potential. In recent years, researchers have used hollow fiber for fiber optic resonant rings, creating conditions for the development of resonant fiber optic gyroscopes and making them a relatively active research field.

The research and development process of fiber optic gyroscope technology can be regarded as a typical example of new technology development.1976-1986During the rapid development period of fiber optic gyroscopesInterference type open loop and closed loopThe scheme was proposed, and active, passive and integrated resonator gyroscopes were developed, symmetrical ring winding technology was invented, and polarization maintaining fiber and super radioluminescence light emitting diode were developed(SLD)Light source, integrated optical modulator, etc.1987-1996In, high-power and spectral stable erbium-doped fiber optic light sources were proposed, and the theory and suppression technology related to intensity noise were fully studied, which supported the development of high-precision fiber optic gyroscopes. The accuracy of interferometric fiber optic gyroscopes reached0.0003 (°)/hFiber optic gyroscopes are beginning to enter practical applications. In recent years, research on fiber optic gyroscope technology has mainly focused on high precision, noise reduction, temperature error suppression, and new solutions and applications.

With the maturity of technology, devices, and processes, as well as the continuous expansion of application fields, the market demand for medium precision fiber optic gyroscopes is increasing year by year. The fiber optic gyroscope technology has reached a high level of maturity, and currently all key components of this technology can be domestically produced. The serialized fiber optic gyroscope products have been widely used in fields such as sea, land, air, and sky, and have formed a supporting industrial cluster and a large market scale. However, facing the needs of ultra-high precision inertial systems and large-scale low-cost applications, the following main issues need to be overcome:

  • For the long-term observation requirements of long endurance high-precision inertial navigation and high-sensitivity, low-noise six component planetary seismology, there is still a big gap in the performance indicators of high-precision FOG;
  • The drift and noise introduced by temperature and its changes are the main factors affecting the on-site application performance of fiber optic gyroscopes. The existing technical effects are limited, and practical and effective solutions and technologies are expected;
  • Resonant fiber optic gyroscope has unique advantages and great potential for application. Currently, it is still in the stage of prototype research and has not formed practical solutions and technologies;
  • In order to control the production cost and improve production efficiency of fiber optic gyroscopes, there are still some unclear issues that need to be revealed and solved in terms of key processes, equipment, and online monitoring and control of key parameters;
  • Fiber optic gyroscopes have the potential for low-cost and mass production applications, but there is still a lack of suitable finalization plans, low-cost fiber optic materials, devices, and related mass production processes.

4.Optical fiber hydrophone technology

Optical fiber hydrophone is a new type of sensor that uses optical fiber as the information transmission and sensing medium. It can achieve high-precision measurement of underwater acoustic signals through highly sensitive optical coherence detection (Fig1)。 Compared with the traditional hydrophone, the optical fiber hydrophone has the advantages of high sensitivity, large dynamic range, anti electromagnetic interference, resistance to harsh environment, smart structure, easy remote transmission and large-scale array formation. It has important applications in military and civilian fields such as underwater target detection, oil and gas exploration, seismic detection, etc.

Development Route of Fiber Optic Sensing Technology in China: Current Status of Key Technologies873 / author: / source:Photoelectric sinkchart1 Physical drawing of optical fiber hydrophone probe and array

since1977After the United States Naval Laboratory published its first paper on optical fiber hydrophone in, developed countries actively carried out the research and development of optical fiber hydrophone. China's optical fiber hydrophone technology has exceeded20Year. since20century90In the late s, the National University of Defense Technology made breakthroughs in key optical fiber devices and key technologies of optical fiber hydrophone systems, and2000Since the first domestic sea trial of optical fiber hydrophone was carried out in, many domestic units have studied the optical fiber hydrophone technology and achieved a series of achievements. At present, the optical fiber hydrophone technology has been applied in many fields.

China's optical fiber hydrophone technology has overcome a series of problems from basic theory to practical application, and has entered the application stage in several fields, but still faces great challenges in the following aspects. The application of optical fiber hydrophone is expanding towards the deep sea field. How to achieve high sensitivity and low background noise of optical fiber hydrophone under the harsh conditions of high hydrostatic pressure in the deep sea is a key issue to be considered.

  • The optical fiber hydrophone is developing towards the remote direction. The number of optical fibers it can accommodate is limited. Long distance optical fiber transmission also introduces serious nonlinear effects, which greatly limits the multiplexing scale and transmission distance of the optical fiber hydrophone system.
  • Underwater target noise concentration100 HzIn the following frequency bands, how to realize the effective detection of underwater targets by optical fiber hydrophone under the background of large ocean noise is the current technical difficulty.
  • Compared with the discrete interferometric optical fiber hydrophone, the single fiber distributed optical fiber hydrophone greatly simplifies the wet end structure and improves the reliability, but the noise suppression ability and the stability of underwater acoustic signal detection need to be further improved.

5.Distributed Brillouin Fiber Optic Sensing Technology

Distributed Brillouin fiber optic sensing can achieve continuous measurement of parameters such as temperature and strain in space, with monitoring distances of up to 100 kilometers and monitoring points of up to one million. It has unparalleled advantages in large range, long distance, and large capacity sensing compared to traditional point sensors. After years of development, distributed Brillouin fiber optic sensing has been widely applied in the health monitoring of large-scale infrastructure such as oil and gas pipelines, high-voltage transmission lines, and bridges, as well as in the monitoring and warning of geological disasters such as landslides and road subsidence, as shown in the figure below2As shown in.

Development Route of Fiber Optic Sensing Technology in China: Current Status of Key Technologies319 / author: / source:Photoelectric sinkchart2 Schematic diagram of distributed Brillouin fiber optic sensing for infrastructure monitoring

After years of development, the performance of traditional distributed fiber optic sensors based on backward stimulated Brillouin scattering has been significantly improved. The spatial resolution has been increased from the meter level to the centimeter (time domain) and millimeter (correlation domain) levels, and the measurement time has been reduced from the minute level to the millisecond or even microsecond level. The measurement distance has exceeded100 km。 In addition, new distributed sensing mechanisms based on Brillouin dynamic gratings and forward stimulated Brillouin scattering have received great attention in recent years. Brillouin dynamic grating sensing can achieve the measurement of more parameters (including temperature, strain, salinity, static pressure, and lateral pressure), and forward stimulated Brillouin scattering can achieve the identification of external environmental substances in optical fibers.

The traditional distributed fiber optic sensors based on backward stimulated Brillouin scattering mainly develop in the following three aspects:

  1. High spatial resolution, ultra fast measurement, and ultra long distance;
  2. Brillouin dynamic grating sensing is mainly used for multi-parameter measurement;
  3. Forward stimulated Brillouin scattering sensing technology is in the ascendant, and exploring distributed measurement solutions and improving sensing performance are currently the main research directions.

The current challenges and difficulties faced by distributed Brillouin fiber optic sensing technology in practical applications include:

  • Implementation of Relay Free Amplification150~200 kmMeasuring distance is of great significance for monitoring railways, power grids, and oil and gas pipelines;
  • Integrating Brillouin scattering, Raman scattering, and Rayleigh scattering to achieve higher performance and richer functional sensing to meet some special applications;
  • Eliminating crosstalk between parameters while measuring multiple parameters;
  • The pump light and Stokes light in forward stimulated Brillouin scattering propagate in the same direction, making it difficult to directly utilize flight time for localization, which poses a challenge for achieving distributed sensing;
  • Miniaturization and high reliability of instruments are important prerequisites for promoting their application in multiple fields.

6.Φ-OTDR/DASFiber optic sensing technology

Ф-OTDRBy utilizing coherent backward Rayleigh scattering light in optical fibers for sensing, high sensitivity vibration can be achieved by demodulating the intensity or phase information of the backward Rayleigh scattering light/Distributed acoustic detection.

In recent years, it has been possible to quantitatively restore external vibrations/Phase Demodulation Type of Sound Wave Information Ф-OTDRTechnology, also known as fiber optic distributed acoustic sensing(DAS)Significant progress has been made in research and application of technology. This technology has outstanding advantages such as large sensing capacity, long sensing distance, high collection efficiency, low operating cost, and long service life. It has been successfully applied in fields such as seismic signal monitoring, oil and gas resource exploration, and pipeline safety monitoring. chart3Ultra sensitive fiber optic distributed acoustic sensor jointly developed by the University of Electronic Science and Technology and China National Petroleum Corporation Eastern Geophysical Exploration Co., Ltd(uDAS)Schematic diagram and physical photos of the seismograph architecture.

Development Route of Fiber Optic Sensing Technology in China: Current Status of Key Technologies382 / author: / source:Photoelectric sinkchart3 uDASSchematic diagram and physical diagram of the seismograph architecture. [Image courtesy of CNPC Aobo](Chengdu)Provided by Technology Co., Ltd

2014Year is Φ-OTDR/DAS The explosive period of technological development;2019yearuDASThe fiber optic distributed seismograph has passed the achievement appraisal organized by China Petroleum Corporation, reaching an international leading level as a whole, and has been applied on a large scale in dozens of oil fields. The results obtained have been selected by China Petroleum Corporation“2019The top ten technological advancements of the year. Overall, currently Ф-OTDR/DASTechnology is in a period of rapid development and is expected to be in the future5Reaching its peak within the year, it has become a new generation of distributed acoustic (vibration) sensing technology that is irreplaceable. However, there are still the following issues with this technology:

  • Sensitivity still needs to be improved;
  • At present, it is difficult to achieve distributed sensing of three component sound waves, as it can only perceive external disturbances and cannot determine their direction;
  • The sensing distance still needs to be increased, and achieving low noise distributed optical amplification to improve signal-to-noise ratio and increase sensing distance is extremely challenging;
  • The frequency response range is relatively small, and it is extremely challenging to expand the frequency response range at a distance of 100 meters to the ultrasonic band to achieve non-destructive testing;
  • The detection and recognition accuracy needs to be improved, and high-precision detection and recognition of weak signals in complex environmental noise needs to be improvedAIAlgorithm is a challenge.

7.OFDRFiber optic sensing technology

Light reflection detection technology is the foundation of distributed optical hearing devices,OFDRTechnology relative toOTDRTechnology has obvious advantages in spatial resolution and dynamic range, and is the main implementation solution for distributed sensing systems with sub millimeter to decimeter resolution. It is not only suitable for monitoring the status of medium and short distance fiber networks and optical devices, but also combines the analysis of fiber grating spectra or Rayleigh backscatter signals to achieve the detection of external physical parameters such as temperature, strain, vibration, shape, etc. In addition,OFDRThe technology is high-performance LiDAR and optical coherence tomography(OCT)Important implementation methods for technologies such as.

OFDRThe development of technology includes two main directions: hardware and signal processing. In terms of hardware systems, the main direction of development is towards swept frequency light source technology; In terms of signal processing, post-processing methods are mainly used to compensate for the phase noise of the swept laser, and distributed detection is achieved by analyzing the characteristics of backward Rayleigh scattering.

OFDRAfter decades of development, the basic principles of technology have been deeply studied and some commercial products have emerged. The main bottleneck limiting the promotion of this technology currently lies in the difficulty in implementing swept frequency light sources and optimizing signal technology processing.

  • High performanceOFDRThe technology requires a light source with a large sweep range and low phase noise, and currently only mechanically tuned external cavity diode lasers can be achieved simultaneously100 nmThe frequency sweep range of the stage is different from100 kHzInstantaneous linewidth of level, and the cost of this laser is difficult to reduce and its service life is difficult to extend;
  • The wavelength tuning range of sweep frequency light sources based on stable frequency lasers and external modulation methods is relatively small, and the implementation of high-order sideband modulation, nonlinear effect spread spectrum and other technologies is complex, and the modulation range is still difficult to exceed a few nanometers;
  • Semiconductor lasers based on direct modulation of current can be implemented at low costGHzTo dozensGHzThe tuning range is limited, but the phase noise and sweep nonlinearity are poor, and improvement plans need to be studied;
  • Real time phase noise compensation algorithms and signal analysis require a large amount of data operations, and the optimization of algorithms and the development of specialized processing circuits still need to be strengthened.

We will provide a detailed introduction on the application of fiber optic sensing technology in typical fields in the next article.

Author of this article:

Yuan Libo1,Tong Weijun2,Jiangshan3,Yang Yuanhong4,Mengzhou5,Dong Yongkang6,Raoyunjiang7, He Zuyuan8,Jin Wei9,Liu Tongyu10,Zou Qilin11,Bi Weihong12

1Photonics Research Center, College of Electronic Engineering and Automation, Guilin University of Electronic Science and Technology

2State Key Laboratory of Optical Fiber and Cable Preparation Technology of Changfei Optical Fiber and Cable Co., Ltd

3Wuhan Science and Technology Optoelectronics Co., Ltd

4School of Instrument Science and Optoelectronic Engineering, Beijing University of Aeronautics and Astronautics

5School of Meteorology and Oceanography, National University of Defense Technology

6State Key Laboratory of tunable laser Technology, Harbin Institute of Technology

7Fiber Optics Research Center, Key Laboratory of Fiber Sensing and Communication, Ministry of Education, School of Information and Communication Engineering, University of Electronic Science and Technology

8State Key Laboratory of Regional Optical Fiber Communication Network and New Optical Communication System of Shanghai Jiaotong University

9Department of Electrical Engineering, Hong Kong Polytechnic University

10Shandong Key Laboratory of Fiber Optic Sensing Technology,Qilu University of Technology(Shandong Academy of Sciences)Laser Research Institute of Shandong Academy of Sciences

11Beijing Perception Technology Co., Ltd

12School of Information Science and Engineering, Yanshan University,Key Laboratory of Special Fiber Optic and Fiber Optic Sensing in Hebei Province

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