1. Introduction

Optical fiber sensing takes advantage of the physical properties of light as it passes through the optical fiber to detect changes in temperature, strain and other parameters. Optical fiber has wide working frequency band and large dynamic range, which is suitable for remote measurement and remote control. It is an excellent low loss transmission line. Under certain conditions, optical fiber is particularly easy to accept the measured or field loading, and is an excellent sensing element. The optical fiber is electrically neutral, small in size, light in weight, flexible, anti electromagnetic interference, and good in radiation resistance. It is especially suitable for use in flammable, explosive, space restricted, strong electromagnetic interference and other harsh environments. Therefore, optical fiber sensing technology has received great attention since it came out. It has been studied and applied in almost all fields, and has become the leader of sensing technology, promoting the vigorous development of sensing technology.

Optical fiber sensing, including sensing and transmission of external signals (measured). The so-called perception (or sensitivity) refers to that the external signal changes the physical characteristic parameters of the optical wave transmitted in the optical fiber according to its change rule, such as intensity (power), wavelength, frequency, phase and polarization state. The change of the measured optical parameter is the change of 'perception' of the external signal. This kind of 'perception' is essentially the real time modulation of light waves propagating in optical fibers by external signals. The so-called transmission means that the optical fiber transmits the light wave modulated by the external signal to the photodetector for detection, extracts the external signal from the light wave and conducts data processing as required, that is, demodulation. Therefore, optical fiber sensing technology includes modulation and demodulation technologies, that is, the modulation technology (or loading technology) of how external signals (measured) modulate optical wave parameters in optical fibers and the demodulation technology (or detection technology) of how external signals (measured) are extracted from modulated optical waves.

2. Application

Optical fiber sensing technology has been widely used in military, national defense, aerospace, industrial and mining enterprises, energy and environmental protection, industrial control, medicine and health, measurement and testing, construction, household appliances and other fields. There are hundreds of optical fiber sensing technologies in the world, such as temperature, pressure, flow, displacement, vibration, rotation, bending, liquid level, speed, acceleration, sound field, current, voltage, magnetic field, radiation and other physical quantities have all achieved different performance sensing. There are also many application scenarios, for example:

①ECOAL Project—Delivering Solutions for Integrated Monitoring of Coal-Related Fires Supported on Optical Fiber Sensing Technology

https://www.mdpi.com/2076-3417/7/9/956

②Development of a monitoring and warning system based on optical fiber sensing technology for masonry retaining walls and trees

https://www.sciencedirect.com/science/article/pii/S1674775521001669?via%3Dihub

3. Product - optical fiber sensor

Optical fiber sensor is a kind of sensor that can change the state of the object to measurable optical signal. Its working principle is to send the light from the light source to the modulator through the optical fiber, so that after the parameters to be measured interact with the light entering the modulation area, the optical properties of the light (such as light intensity, wavelength, frequency, phase, skewness, etc.) will change, which is called the modulated signal light. After being sent to the photodetector through the optical fiber and demodulated, the measured parameters will be obtained. In the whole process, the light beam is introduced through the optical fiber, and then emitted through the modulator. The role of the optical fiber is to transmit the light beam first, and then to play the role of the light modulator. The sensor is developing in the direction of sensitivity, accuracy, adaptability, compactness and intelligence. It can play a role in people's ears and eyes in places that people cannot reach (such as high temperature areas or areas harmful to people, such as nuclear radiation areas), and it can also exceed the physiological limits of people and receive external information that people's senses cannot feel.