With the rapid development of optical fiber and optical fiber communication technologies, optical fiber sensing technology emerged. Since its birth, fiber optic sensors have been rapidly developed due to their small size, light weight, high sensitivity, fast response, strong anti-electromagnetic interference capability and ease of use, and are widely used in chemical medicine, materials industry, water conservancy and electric power, ships, Coal mines and civil engineering in various fields. Especially today, with the rapid development of the Internet of Things, the status of optical fiber sensing technology can not be ignored.
1 Basic principle and development status of fiber optic sensors
1.1 Basic Principles and Classification of Fiber Optic Sensors
Optical fiber sensing technology is a new type of sensing technology developed in the 1970s. When light propagates through an optical fiber, it is reflected by light under the influence of external temperature, pressure, displacement, magnetic field, electric field and rotation. , refractive and absorption effects, optical Doppler effect, acousto-optic, electro-optic, magneto-optical and elastic effects, etc., can directly or indirectly change the amplitude, phase, polarization state and wavelength of the light wave, thus the fiber As a sensitive component to detect various physical quantities.
The fiber optic sensor is mainly composed of a light source, a transmission fiber, a photodetector, and a signal processing part. The basic principle is that the light from the light source is sent to the sensing head (modulator) through the optical fiber, so that the parameters to be measured interact with the light entering the modulation area, resulting in the optical properties of the light (such as the intensity, wavelength, frequency of the light, The phase, polarization state, etc. are changed to become modulated signal light, which is then sent to the photodetector through the optical fiber to convert the optical signal into an electrical signal, and finally the signal is processed to restore the measured physical quantity. There are many types of optical fiber sensors, and they can be generally classified into functional (sensing type) sensors and non-functional type (light transmitting type) sensors.
The functional sensor is characterized by the ability of the optical fiber to be sensitive to the external information and the detection capability. When the optical fiber is used as a sensitive component, when measured in the optical fiber, the characteristics of the intensity, phase, frequency or polarization state of the light will change. The function of modulation is realized. Then, the signal to be measured is obtained by demodulating the modulated signal. 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 measured changes. The optical fiber acts only as a transmission medium for information, that is, the optical fiber only serves as a light guide [3]. Compared with traditional electric sensors, fiber optic sensors have strong anti-electromagnetic interference capability, 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. Testing and other fields.
1.2 Development Status of Fiber Optic Sensors
Since the birth of the fiber sensor, its superiority and wide application have been closely watched and highly valued by all countries in the world, and it has been actively researched and developed. At present, optical fiber sensors have been measured for more than 70 physical quantities such as displacement, pressure, temperature, speed, vibration, liquid level and angle. Some countries such as the United States, Britain, Germany and Japan have focused on six aspects of fiber-optic sensor systems, modern digital fiber control systems, fiber optic gyros, nuclear radiation monitoring, aircraft engine monitoring and civil programs, and have achieved certain achievements.
The research work of fiber optic sensors in China began in 1983. The research on fiber optic sensors by some universities, research institutes and companies has led to the rapid development of fiber optic sensing technology. On May 7, 2010, People‘s Daily reported that the "continuous distributed optical fiber sensing technology based on the Brillouin effect" invented by Zhang Xuping, a professor at the School of Engineering and Management of Nanjing University, passed the expert appraisal organized by the Ministry of Education. The appraisal expert group unanimously believes that this technology has strong innovation, possesses a number of independent intellectual property rights, and has reached the domestic leading level and international advanced level in technology, and has a good application prospect. The essence of this technology is the use of the concept of the Internet of Things, which fills the gap in the Internet of Things in China.
2 The basic principles of the Internet of Things
The concept of the Internet of Things was proposed in 1999, and its English name is "The Internet of Things", which is "the network of things connected." The Internet of Things is based on the Internet and uses information technology such as RFID (radio frequency identification) technology, infrared sensors, global positioning systems, and laser scanners to connect items to the Internet to realize information exchange and communication. A network that locates, intelligently identifies, tracks, monitors, and manages. The technical architecture of the Internet of Things consists of three levels: the perception layer, the network layer, and the application layer.
