Interferometric Fiber Optic Hydrophone
The main mystery of the high sensitivity of the interference fiber optic hydrophone is that the length change of the sensing fiber is extremely sensitive to the small fluctuation of the underwater sound pressure. He usually adopts the air-vest mandrel structure, and the sensing fiber is wound on a compliant mandrel that expands and contracts with the fluctuation of the sound pressure. to small fluctuations in the sound pressure of the underwater sound.
According to the way of picking up sound waves, interference fiber optic hydrophones can be divided into scalar interference fiber optic hydrophones and vector interference fiber optic hydrophones. The main difference between the two is that a single scalar interference type hydrophone can only feel the presence or absence of sound waves, but cannot judge the direction of sound waves, and its directivity diagram is circular; while a single vector interference type hydrophone can not only feel the presence or absence of sound waves. With or without, the direction of the sound wave can also be judged, and its typical directivity diagram is in the shape of "8".
Interferometric fiber optic hydrophones can be used alone or linked into an array. The fiber optic hydrophone array can detect farther and more complex underwater acoustic signals.
Fiber Bragg Grating Hydrophone
Compared with the interference fiber optic hydrophone, although the sensitivity of the fiber grating hydrophone is slightly lower, it can realize the miniaturization and miniaturization of the fiber optic hydrophone. Therefore, the fiber grating hydrophone has special features in some complex environments. application space.
Fiber Bragg grating hydrophones use fiber Bragg gratings as sensitive components. When sound waves act on fiber Bragg grating hydrophones, the resonant coupling wavelength of fiber Bragg gratings moves with the change of sound waves. information.
Fiber Bragg grating (Bragg) is a typical structure of fiber Bragg grating hydrophone. After the light output by the broadband light source enters the fiber Bragg grating (FBG), the underwater acoustic sound pressure modulates the wavelength of the reflected signal light, and the sound pressure information can be obtained by detecting the shift of the central reflected wavelength.
Fiber Bragg grating hydrophones not only have the advantages of high sensitivity, no electromagnetic interference, and long-distance transmission of interferometric fiber optic hydrophones, but also have the advantages of miniaturized probes and convenient wavelength division multiplexing. In addition, it is also possible to use the method of writing multiple gratings with different wavelengths on one optical fiber to realize the simultaneous detection of underwater multi-point signals, which makes it more convenient to form thin-line towed arrays. In the military field of underwater unmanned vehicles, these The advantages will make fiber grating hydrophone technology promising.
