For more than 30 years, optical fiber sensors have made full use of their own unique advantages to continuously increase scientific research, technological development and commercial applications, and have achieved great success on a global scale.
     
         1. The concept and advantages of the sensor

　　(1) The concept of sensors

　　A sensor is a device, equipment or system that converts the absolute value or change of a physical quantity, electrical quantity or other quantity into a signal that can be observed or output by an instrument. The parameters that can be sensed are: temperature, pressure, strain, speed, rotation, light and radiation, electricity, magnetism, sound, gas and chemicals, surrounding objects, etc.

　　Almost all the physical properties of materials, which can change under certain excitations, can be used to form sensors. The widely used sensors include: resistance, inductance, capacitance, semiconductor, optoelectronic, piezoelectric, mechanical and MEMS, etc.

　　(2) Advantages of fiber optic sensors

　　1 Electrical insulation;

　　2 Anti-electromagnetic interference;

　　3 There is no need for electricity;

　　4 Inherent safety;

　　5 Can be used in many special working environments;

　　6 Can carry out long-distance and multi-channel multiplexing operation;

　　7 Small size and light weight;

　　8 Integrated telemetry, optical fiber itself is a data transmission channel;

　　9 wide bandwidth;

　　10 High sensitivity.

        2. Principle components and systems of optical fiber sensors

　　1. Basic types of fiber optic sensors

　　There are two basic types of fiber optic sensors:

　　(A) Intrinsic (functional) optical fiber sensor, the sensing signal is generated by the optical fiber itself;

　　(B) The extrinsic (light-guiding) optical fiber sensor requires an additional sensor to provide the sensing signal, and the optical fiber is used for optical signal transmission.

         2. Types of fiber optic sensors

　　(A) Intrinsic (functional) optical fiber sensor

　　Fiber optic gyroscope, fiber grating, fiber interference sensor, microbend fiber sensor, black body sensor.

　　(B) Extrinsic (light guiding) sensor

　　Optical time domain reflectometer, optical frequency domain reflectometer, Fabry-Perot interferometer, total internal reflection sensor, grating sensor, fluorescence sensor, absorption sensor, multi-point sensor WDM system.

    　Third, the application of optical fiber sensor

　　(1) Classification of fiber optic sensors

　　Fiber optic sensors are classified according to their response environmental parameters:

　　Temperature optical fiber sensor, pressure optical fiber sensor, acoustic optical fiber sensor (such as hydrophone), strain optical fiber sensor, displacement optical fiber sensor, rotating optical fiber sensor (such as optical fiber gyroscope), vibration optical fiber sensor, electric, magnetic optical fiber sensor (such as current optical fiber transformer), Gas and chemical fiber optic sensors, biological and medical fiber optic sensors.

　　(2) Application of optical fiber sensor

　　1 Oil and natural gas: P/T sensors, seismic arrays, energy industry, power plants, boilers and steam turbines, power cables, turbine transportation, oil refineries in oil reservoir monitoring wells;

　　2 Aerospace: jet engines, rocket propulsion systems, airframes;

　　3 Civil infrastructure construction: bridges, dams, roads, tunnels, landslides;

　　4 Transportation: railway monitoring, weight in motion, transportation safety;

　　5 Biomedicine: Medical temperature and pressure, intracranial pressure measurement, minimally invasive surgery, disposable probes.

 　　4. Fiber Bragg Grating (FBG)

　　Manufacturing FBG using phase mask

　　The core is co-doped with boron and intrinsically photosensitive, and does not need to carry hydrogen. The size of the core is compatible with the communication fiber. Using this fiber, a transmission grating with a width of 1nm and a length of 15mm can be written by excimer laser pulses (10Hz, 0.5 J/cm2, 248nm) within a few minutes.

　　Now we are in the information age, and building an intelligent society requires advanced sensing systems! Optical fiber sensing is a rookie in the sensor family, and the future is still incalculable. The current optical fiber sensor market is fragmented, but most applications have a common technical foundation, many devices and systems have entered the commercial stage, and the market share has been expanding year by year. The market has recovered from the recession in 2009, and the general consensus is that the annual growth rate will be in the range of 10% to 25%.

The main factors driving the growth of fiber optic sensors are:

　　1 The increasing demand for oil and natural gas;

　　2 Urgently search for alternative energy sources;

　　3 Establish a high degree of perimeter and homeland security;

　　4 Intelligent infrastructure;

　　5 Government support funding.

　　The challenging factors in the development of fiber optic sensors are:

　　1 Non-photonic technology competition (MEMS, wireless, etc.);

　　2 Formulate product standards as soon as possible;

　　3 Cost factor.

　　5. Global macroeconomic environment

　　Compared with traditional electromechanical and electronic sensors, fiber optic sensors have a series of unique advantages. In particular, the application of distributed optical fiber sensors in large-scale construction projects, bridges and tunnels, railways and highways, oil and gas pipelines, structural health management (monitoring) (SHM), etc. is almost unique and unmatched by other types of sensors. Judging from the current achievements of optical fiber sensors, the application scale of optical fiber sensors in the future may still be incalculable.

　　As we all know, optical fiber communication has almost completely defeated traditional copper wire communication in a short period of time. In fact, as far as optical fibers are concerned, only the excellent light transmission characteristics of silica optical fibers have been developed and utilized. The optical fiber sensor not only uses the light transmission characteristics of the optical fiber, but also uses the sensitivity of the optical fiber to environmental parameters. In fact, there are many characteristics of fiber that are being used or not yet utilized, such as fiber amplifiers, fiber lasers, fiber power transmission, and fiber signal processing.

　　Undoubtedly, it is completely believed that after optical fiber communication, optical fiber sensors will be another emerging industry in the field of optical fiber technology, which is rising rapidly, and it is believed that more emerging optical fiber industries will unearth, blossom, and bear fruit in the future.