Target and cantilever supported seawater velocity sensor based on panda fiber polarization interferometer.

It is necessary to develop a novel optical low velocity sensor for seawater. In this paper, a fiber optic seawater velocity sensor based on a target cantilever reflective polarization interferometer is presented theoretically and experimentally. Height: width of equal strength cantilever is determined by finite element method as 22:5, and the seawater velocity sensing experiment is carried out using this parameter. The sensitivity obtained by experiment is consistent with the theory, whose correlation coefficient is 0.96, and the mean relative error is 3.65%. The velocity measurement results of the sensor were also compared by Acoustic doppler velocimetry, the correlation coefficient and the mean relative error are 0.92 and 4.5% respectively, which realized the high precision measurement of water velocity. The maximum sensitivity of the sensor is 355.55 nm/(m·s) when the velocity is 0.09 m/s. In addition, when the thickness of the cantilever is 0.5 mm, the velocity measurement can be realized in the range of 0-0.22 m/s. Finally, the influence factors of sensor sensitivity are discussed, which shows that the sensitivity is related to wavelength, velocity and the size of the cantilever structure, and is independent on the length of the panda fiber. The fiber optic velocity sensor based on the target cantilever is expected to play an important role in the field of seawater measurement due to its advantages of small size, stable structure and high sensitivity.