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Fiber Optic Hydrophone: Underwater Submarine Listening Underwater The Great Wall
Nov 19, 2018

The silent battlefield calls for sensitive ears.

The seemingly peaceful sea is never calm. Underwater submarines are like "stealth fighters" in the water, which put forward higher and higher requirements for underwater acoustic signal interception. In February 2009, Britain's Vanguard nuclear submarine and France's Triumph nuclear submarine staged a "kiss of affection" in the deep Atlantic. At that time, both submarines were underwater. There were about 250 crew members on the submarine at the time of collision, but none of them used sonar devices to find each other.


Sound wave is not only the only substance that can be transmitted over a long distance in water, but also reflected back when it encounters an object in water. Sound waves of different frequencies are absorbed and reflected differently in water. Sonars are invented according to the characteristics of sound waves. In recent years, all kinds of "silent" advanced submarines have joined the active service successively, and the difficulty of using traditional sonar devices for interception has greatly increased. The "silent" battlefield of anti submarine warfare has also become one of the difficult problems recognized by the Navy.


Optical fiber hydrophone is an underwater acoustic signal detector based on optical fiber sensing and optoelectronic technology. It transforms underwater acoustic signals directly into optical signals by high sensitivity optical fiber coherent detection technology, and transmits them to signal processing system through optical fibers, just like magicians. After subsequent processing, we can extract the unique sound of "uninvited visitors" in the ocean from seemingly quiet signals.



"Fiber optic hydrophone era" has arrived.

As early as 1937, researchers discovered that there was a "deep-sea channel" in the deep ocean that allowed sound waves to travel farther. On the basis of the development of "deep-sea channel" and anti-submarine technology, the first paper of optical fiber hydrophone was published by the US Naval Research Laboratory in 1977, which opened a new era of underwater interception belonging to optical fiber hydrophone. Since then, the U.S. Naval Research Laboratory has begun to implement the Optical Fiber Sensor System (FOSS) program, and the optical fiber hydrophone is one of the important contents of the experimental system.


The U.S. Navy conducted its first offshore experiment on a plastic-core optical fiber hydrophone in the "Mobile Noise Barge" system and successfully deployed it in the Bahamas in July 1983. Since then, the U.S. Navy has carried out many experiments on towed fiber optic hydrophone arrays at sea, and achieved great success. With the formal formulation of the "Standard for Optical Fiber Hydrophone Systems" for submarines by the US Naval Research Laboratory, optical fiber hydrophones have also begun to make great strides towards practical weapon systems.


As an important development direction of underwater listening system in the future, Britain, France, Italy and other countries have also carried out research in the field of optical fiber hydrophones. Fiber optic hydrophone can effectively overcome the problems of traditional sonar, such as large number of underwater electronic components, high price, heavy weight, poor sealing, and can effectively improve the detection accuracy of underwater acoustic signals and the stability of the system. It is no wonder that some researchers have proudly said, "The era of optical fiber hydrophone technology has arrived!"


The British Navy mainly focuses on the shallow sea surveillance and coastline surveillance technology using arrays, and has successfully developed the optical fiber submarine array system, which can realize the long-distance formation of optical fiber hydrophone array technology with great application prospects. France, Italy and Norway cooperated in the implementation of the All-Fiber Optic Hydrophone Linear Array Project, which aims to develop static fiber optic hydrophone arrays, and later continued to develop into part of the European Long-Term Defence Alliance project.


Three dimensional antisubmarine "water listening network" is ready to come out

Compared with traditional hydrophone, fiber optic hydrophone can be said to be "a lot of advantages". Fiber optic hydrophones have the "special ability" to form large-scale arrays because they can transmit a large number of signals from an optical fiber. In addition, the module unit of the fiber optic hydrophone can also be designed flexibly, and the response bandwidth is wide and the sensitivity is very high. There is no need to worry about the interference of the electromagnetic environment in signal transmission and unit layout, so it has great potential to form a large-scale detection array of the fiber optic hydrophone.


Fiber optic hydrophone can form a three-dimensional anti-submarine hydrophone network with insight into the ocean by "strong combination" with anti-submarine patrol aircraft and anti-submarine ships. In the future, the optical fiber hydrophone can be woven into an integrated sky, earth and sea detection network with terrestrial ground listening stations and space exploration satellites, or it will become an important part of the Military Material Link Sensing Network.


Fiber optic hydrophone can not only be used in anti-submarine warfare and underwater weapon test, but also become a "steel wall" of underwater anti-submarine interception and a "versatile person" in the civil field. Previously, American researchers and the British Defense Research Agency have successfully developed a marine and terrestrial borehole imaging system, which relies on all-optical fiber hydrophones and can be used for underground oil or gas exploration. Optical fiber hydrophones can also be used to check whether there are malfunctions in offshore platforms, underwater oil storage tanks, submarine cables, submarine pipelines and other facilities. In addition, optical fiber hydrophones can also be used for marine seismic wave detection and marine environment detection, and will play an increasingly important role in military and civil fields.

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