Introduction To Optical Fiber Sensing Technology

Technology, Gadget and Science

1. Basic principles and classification of optical fiber sensors

Optical fiber sensing technology is a new type of sensing technology developed in the 1970s. When light propagates in an optical fiber, under the influence of external temperature, pressure, displacement, magnetic field, electric field, and rotation, it is reflected by light and after series effects such as refraction and absorption effects, optical Doppler effect, acousto-optic, electro-optic, magneto-optic and elasto-optic effects, etc., directly or indirectly change the amplitude, phase, polarization state and wavelength of light waves.

It can be used as a sensitive element to detect various physical quantities.

The optical fiber sensor is mainly composed of a light source, a transmission fiber, a photodetector, and a signal processing part. The basic principle is to send the light from the light source to the sensor head (modulator) through the optical fiber. After the parameter to be measured interacts with the light entering the modulation area, the optical properties of the light (such as light intensity, wavelength, frequency, The phase and polarization state, etc.) change to become modulated signal light, which is then sent to the photodetector through an optical fiber to convert the optical signal into an electrical signal, and finally restore the measured physical quantity after signal processing. Fiber optic sensors can generally be divided into functional (sensing) sensors and non-functional (light-transmitting) sensors.

The functional sensor uses the characteristics of optical fiber with sensitivity and detection ability to external information. The optical fiber is used as a sensitive element. When the measurement is transmitted in the optical fiber, the light intensity, phase, frequency, or polarization state will change, and then realize the function of modulation. Then by demodulating the modulated signal, the measured signal is obtained. In this kind of sensor, the optical fiber not only plays the role of light transmission, but also plays the role of “sense”.

Non-functional sensors use other sensitive components to sense the changes being measured. Optical fibers are only used as information transmission media, that is, optical fibers only play a role in guiding light. Compared with traditional electrical sensors, optical fiber sensors have the advantages of strong anti-electromagnetic interference, good electrical insulation and high sensitivity, so they are widely used in various fields, such as environment, bridges, dams, oil fields, clinical medical testing and food safety Detection and other fields.

2. The development status of optical fiber sensors

Since the birth of the optical fiber sensor, its superiority and wide range of applications have received close attention and high attention from all over the world, and active research and development have been carried out on it. At present, more than 70 physical quantities such as displacement, pressure, temperature, speed, vibration, liquid level and angle have been measured by optical fiber sensors. Some countries such as the United States, the United Kingdom, Germany and Japan have focused their research on six aspects, including fiber optic sensor systems, modern digital fiber optic control systems, fiber optic gyroscopes, nuclear radiation monitoring, aircraft engine monitoring, and civil planning, and have made certain achievements.

Research on optical fiber sensors in my country began in 1983. The research on optical fiber sensors by some universities, research institutes and companies has led to rapid development of optical fiber sensing technology. In 2010, the “Continuous Distributed Optical Fiber Sensing Technology Based on Brillouin Effect” invented by Professor Zhang Xuping of the School of Engineering Management of Nanjing University passed the expert appraisal organized by the Ministry of Education. The appraisal expert group agreed that this technology is highly innovative, has a number of independent intellectual property rights, and has reached the domestic leading and international advanced level in technology, and has good application prospects. The essence of this technology is to use the concept of the Internet of Things, which fills the gap of the Internet of Things in my country.

Basic principles of the Internet of Things

The concept of the Internet of Things was proposed in 1999. The Internet of Things is based on the Internet using RFID (Radio Frequency Identification) technology, infrared sensors, global positioning systems, and laser scanners and other information sensing equipment to connect objects to the Internet to achieve information exchange and communication, thereby achieving intelligence Network for positioning, intelligent identification, tracking, monitoring and management. The technical architecture of the Internet of Things includes three levels: perception layer, network layer and application layer.

The perception layer is mainly to collect various data information that occurs in the physical world, mainly by temperature sensors, sound sensors, vibration sensors, pressure sensors, sensors, terminals, RFID tags and readers, and QR code tags. It is composed of various types of acquisition and control modules such as readers and sensor networks.

The network layer is divided into two parts: the access layer and the bearer network. This layer can realize large-scale information communication. Through the existing mobile network, Internet and other communication systems, the data information obtained by the perception layer can be transmitted to all parts of the earth to realize the earth Long-distance communication within range.

The application layer is composed of various application servers. The main task of this layer is to summarize all the information about items obtained after the work of the perception layer and the network layer is completed, and then process the information to further improve the comprehensive utilization of the information. This layer is the bridge between the Internet of Things and various industries, which can realize the application of Internet of Things technology to various industries, meet industry needs, and realize industry intelligence.

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