Sensors are evolving towards sensitivity, accuracy, adaptability, compactness and intelligence. In this process, fiber-optic sensors, a new member of the sensor family, are gaining popularity.

  Optical fiber sensor is a kind of sensor based on optical quantity conversion, using optical signal as a carrier for conversion and transmission, and using optical fiber to convey optical signal. Fiber optic sensor is mainly composed of light source, optical fiber (referred to as optical fiber), light detector and additional devices. There are many types of light sources, commonly used light sources such as tungsten lamps, lasers and light-emitting diodes. Optical fiber is very thin, soft, bendable, is a transparent fiber can guide light.

I. Development status of fiber optic sensors

  The global development of fiber optic sensing technology began in 1977, and in recent years, it has been developed and promoted in the production process and automatic control, online detection and fault diagnosis in the fields of machinery, electronic instrumentation, aerospace, petroleum, chemical industry, food safety, etc.The U.S. fiber optic sensor research started early, fiber optic sensing technology is the most advanced in the world, representing the world's largest regional market for fiber optic sensors. The global consumption value of fiber optic sensors (both point-split and distributed) increased at an average annual rate of 20.3% between 2012 and 2017. The U.S. holds the vast majority of the global fiber optic sensors market share. Meanwhile, Asia Pacific is expected to be the fastest growing market with a CAGR of 12.7% from 2015 to 2020. In recent years, China has become the most important market for fiber optic sensing products in the Asia-Pacific region. 2011, the market size of fiber optic fire alarm products in the transportation and petrochemical industries was at the level of 200 million yuan, the scale of fiber optic sensing temperature detection and application of power equipment reached the level of 200 million yuan, the market of fiber optic sensing environmental monitoring and fiber optic gyro products reached the level of 200 million yuan, and the market of fiber optic perimeter was at the level of 0.5 billion yuan.

  Unlike fiber optic communication products, fiber optic sensing products have the characteristics of small volume and multiple varieties, distributed in various market segments, and there are indeed no large foreign companies specializing in fiber optic sensing; But many foreign oil giants, military giants, and big power equipment companies like ABB and Siemens have their own fiber optic sensing business, only that it is difficult for outsiders to figure out the development of these businesses. In some emerging fields, such as distributed sensing, there are also a number of small and medium-sized specialized companies.

  Currently, the products that have gained mature application and high acceptance in the market are: fiber optic grating temperature/pressure/strain sensors; point type fluorescent fiber optic temperature sensor products; point type fiber optic F-P pressure/temperature/vibration sensing products, fiber optic current sensing products; fiber optic gyroscope products; distributed fiber optic Raman temperature measurement system; fiber optic interference type intrusion monitoring system.

  Although the fiber optic sensor technology has achieved some applications in practical inspection, there are still some problems, such as the process problem of fiber optic buried in the structure, although it can be improved by the installation method, but at the same time, it also leads to the strain to be transmitted through the metal first, and then the strain is indirectly sensed by the fiber, so it needs to be corrected by experiment before accurate measurement can be made. At the same time, the output signal of fiber-optic sensors can be affected by fluctuations in the light source, changes in fiber-optic transmission loss, and detector aging, all of which can reduce the accuracy of fiber-optic sensor measurements. Furthermore, the practicality of fiber optic sensors is still to be developed, while their production cost is quite expensive. A large portion of fiber optic sensors are still in the laboratory stage, so the experimental results need to be put into use as soon as possible.

Ⅱ, China's fiber optic sensor enterprise status

  In terms of fiber optic sensing technology alone, the achievements made by Chinese scholars are very close to the world's advanced level, and the gap is narrowing. In the past few years, many schools and companies have a full set of fiber optic sensing and demodulation solutions. China's fiber optic sensor production and service enterprises by region can be divided into four major industry groups, respectively, Jiangsu, Zhejiang, Shanghai, Anhui-based East China Yangtze River Delta industry group, Beijing, Hebei-based Bohai industry group in northern China, Hubei-based Central China industry group and Guangdong-based Pearl River Delta industry group, the total number of enterprises in these four industry groups accounted for 90% of the total number of fiber optic sensor production and service enterprises.

  Domestic fiber optic sensor manufacturing and service companies are divided into the following categories according to their business:

(1) Focus on a certain type or several fiber optic sensor research and development and production enterprises;

(2) Agents of foreign fiber optic sensors and domestic market support;

(3) System integrators and integrated solution providers with distinct industry application backgrounds;

(4) New business expansion or business transformation in the communications industry and other companies.

  Currently, the business models of fiber optic sensor manufacturers in the Chinese market are divided into two main types:

  One is that foreign manufacturers are mainly engaged in the production and promotion of instruments in China, and the system integration work is done by domestic partner manufacturers. This business model has a high utilization rate of resources, but whether the products can meet customer needs depends largely on the technical level and quality control level of the partner.

  Another is that domestic manufacturers usually directly imported instruments, integrated supporting equipment and software, and then the formation of the entire monitoring system. This integrated business model does not require manufacturers to have a strong R & D and production capacity, and the barriers to entry are low.

  Domestic enterprises by the level of technology research and development and market business development restrictions can only master one or several technologies, not yet able to participate in international market competition. The scale of enterprises is small, most of them are high-tech enterprises, and there is no association organization in the industry.

Ⅲ, the main applications of fiber optic sensors

  Optical fiber has many excellent properties, such as: with electromagnetic and atomic radiation interference performance, fine diameter, soft, light weight mechanical properties; insulation, non-inductive electrical properties; water resistance, high temperature resistance, corrosion resistance chemical properties, etc., it can be in places where people can not reach (such as high temperature areas), or areas harmful to people (such as nuclear radiation areas), to play the role of the human ear, and also beyond the human physiological boundaries, receiving external information that is not perceived by the human senses.

  Fiber optic sensors have been widely used in national defense, electric power, petroleum, construction, medicine and other fields, along with the development of Internet of Things technology, fiber optic sensors will play a more important role in the Internet of Things together with wireless sensing technology.

1、Oil and gas applications

  Fiber optic sensors can overcome the harsh downhole environment to replace traditional electronic sensors and achieve the measurement of gas holding rate, water content, pressure, temperature, multiphase flow and acoustic wave in oil wells. A large number of experiments have been conducted in domestic onshore oil fields, represented by the Xinjiang Karamay and Liaohe oil fields. In China, many institutions are conducting cooperative research with oil companies on fiber optic sensing. For example, the 152 G6 fiber optic velocity sensor is used for non-contact velocity measurement using a long optical probe with 100 KHz bandwidth and TTL output.    

2、Coal mine application

  China's coal mines dominate China's energy landscape, at about 94%, and our coal mine accidents are more than four times the total number of coal mine fatalities in the world's major coal mining countries. Underground operations in coal mines, water, fire, gas, coal dust, roof and other disasters are all over the place. The gas safety integrated monitoring system based on fiber optic sensing technology can monitor gas, mine pressure, water pressure, temperature, acoustic emission, seismic waves, etc. within 10 km.For example, the 152 G6 fiber optic speed sensor for non-contact speed measurements with long optical probes, 100 KHz bandwidth and TTL output. For example, 152 G7 fiber optic speed sensor for non-cyclic, torsional vibration and belt slippage measurements at high speed. Bandwidth 260 KHz and TTL output, with ICT, DIN, SUB-D, custom connection variants.

3、Urban architecture application

  In construction projects, fiber-optic sensors can be used to monitor physical quantities such as temperature, stress, pressure, vibration, and inclination of bridges, dams, and important buildings in real time to assess their short-term and long-term structural safety performance. For example, interferometric gyroscopes and grating pressure sensors can be pre-embedded in materials such as concrete to test stress relaxation, construction stresses and dynamic load stresses.In large projects, because of the need for real-time monitoring, and a wide range, so the main use of continuous distributed fiber optic sensors. In addition, the information system of urban corridor, at least half of the need to use fiber optics, the system can easily be a kilometer of tens of millions of dollars, the fiber optic system, even if only a small part of the inside, there is a large market.At present, the overall solution of urban corridor monitoring fiber optic sensing does not account for a high proportion, representative cities are Qingdao, Zhuhai, etc.. For example, 152 G8 fiber optic speed sensor, used to measure non-cyclic, torsional vibration and speed measurement in F1 and motorsport with high speed sensor, 600KHz bandwidth, TTL output.

4、Electricity system

  In power systems, parameters such as temperature and current need to be measured, and because electrical sensors are susceptible to interference from strong electromagnetic fields, they cannot be used in these applications, and only fiber optic sensors can be used. There is also an important application is the use of OPGW, OPPS and other power composite cable distributed monitoring of cable line temperature, ice cover, dance, theft, tower collapse and other accidents.Domestic companies such as Changfei and Shanghai Kangguo have passed several tests in the field of fiber optic current transformers, but are still some time away from practical applications. For example, 152M fiber optic speed sensor, high speed sensor for balancing turbomachinery, speed sensor calibration, bandwidth more than 1MHz, TTL and analog output.

5、Military field

  There is also a huge market demand for fiber optic sensing in the military sector. Fiber optic sensors for military applications can be used for hydroacoustic diving (fiber optic hydrophone), fiber optic guillotine guidance, attitude control (fiber optic gyro), structural damage detection of aerospace vehicles (smart skin), and detection of battlefield environments.

In aerospace, tactical missiles are precisely guided with fiber optic gyros. Fiber optic gyro can also be applied to attitude control of radar unmanned control helicopters.

The maritime defense sensing network system composed of fiber optic hydrophones is an emerging defense system being developed, which has begun to be used for maritime border defense and maritime defense vigilance in important military areas. The fiber optic network security alert system based on fiber optic sensing technology developed in recent years has also started to be promoted and applied in border defense and key area defense.