For more than 30 years, fiber optic sensors have made full use of their unique advantages to continuously increase scientific research, technological development and commercial applications, and have achieved great success worldwide.
      
        1. Concept and advantages of sensors

(1) Concept of sensor

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 include: temperature, pressure, strain, speed, rotation, light and radiation, electricity, magnetism, sound, gas and chemicals, surrounding objects, etc.

Almost all physical properties of materials that can change under certain stimuli can be used to form sensors. Widely used sensors include: resistors, inductors, capacitors, semiconductors, optoelectronics, piezoelectrics, mechanical and MEMS, etc.

(2) Advantages of fiber optic sensors

1 Electrical insulation;

2 Anti-electromagnetic interference;

3 No need for electricity;

4 Intrinsic safety;

5 Can be used in many special working environments;

6 Can perform remote and multi-channel multiplexing operations;

7 Small size and light weight;

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

9 Wide bandwidth;

10 High sensitivity.

        2. Principle components and systems of optical fiber sensors

1. Basic types of optical fiber sensors

There are two basic types of optical fiber sensors:

(a) Intrinsic (functional) optical fiber sensors, the sensing signal is generated by the optical fiber itself;

(b) Non-intrinsic (light-guiding) optical fiber sensors, which require an external 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) fiber optic sensor

Fiber optic gyroscope, fiber grating, fiber interferometer sensor, micro-bend fiber optic sensor, black body sensor.

(b) Non-intrinsic (light-guiding) type 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.

    　III. Application of Fiber Optic Sensors

(1) Classification of Fiber Optic Sensors

Fiber optic sensors are classified according to the environmental parameters they respond to:

Temperature fiber optic sensors, pressure fiber optic sensors, acoustic fiber optic sensors (such as hydrophones), strain fiber optic sensors, displacement fiber optic sensors, rotation fiber optic sensors (such as fiber optic gyroscopes), vibration fiber optic sensors, electric and magnetic fiber optic sensors (such as current fiber optic transformers), gas and chemical fiber optic sensors, biological and medical fiber optic sensors.

(2) Application of fiber optic sensors

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

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

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

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

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

 Fourth, Fiber Bragg Grating (FBG)

FBG is manufactured using a phase mask

The core is co-doped with boron and intrinsically photosensitive, and does not require hydrogen. The size of the core is compatible with communication optical fibers. Using this fiber, a 1nm wide and 15mm long transmission grating can be written by an excimer laser pulse (10Hz, 0.5 J/cm2, 248nm) in a few minutes.

Now we are in the information age, and building an intelligent society requires advanced sensing systems! Fiber optic sensing is a newcomer in the sensor family, and its future is still difficult to estimate. The current fiber optic 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 is expanding year by year. The market has begun to recover 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 growing demand for oil and gas;

2 Urgently seeking alternative energy;

3 Establishing high perimeter and homeland security;

4 Smart infrastructure;

5 Government support funding.

Challenges in developing fiber optic sensors include:

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

2 Formulate product standards as soon as possible;

3 Cost factors.

V. 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 fiber optic 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 fiber optic sensors, the scale of future fiber optic sensor applications is probably immeasurable.

As we all know, fiber optic communication has almost completely defeated traditional copper wire communication in a short period of time. In fact, for optical fiber, only the excellent light transmission characteristics of quartz optical fiber have been developed and utilized. Fiber optic sensors not only utilize the light transmission characteristics of optical fiber, but also utilize the sensitive characteristics of optical fiber to environmental parameters. In fact, there are many characteristics of optical fiber that are being used or have not yet been used, such as fiber amplifiers, fiber lasers, fiber power transmission, and fiber signal processing.

There is no doubt that after fiber optic communication, fiber optic sensors will be another emerging industry in the field of optical fiber technology that is rapidly rising, and it is believed that more emerging optical fiber industries will emerge, bloom, and bear fruit in the future.