The Study Of Underwater Scattered Light Focusing For Acousto-optic Imaging

In turbid water especially some offshore waters,it is difficult to directly achieve optical imaging under water due to severe scattering of light.The focus of scattered light is the premise of optical imaging,which is significant in underwater rescue,scientific investigation,safeguarding national maritime rights and so on.The acoustooptic imaging technology using optical phase conjugation is an important mean to realize the optical focusing and imaging in scattering medium.Aiming at the focus of underwater scattered light,adapted from the acousto-optic imaging technology,the study on scattered light,acousto-optic effect,digital phase conjugation,focusing of ordinary and ultrasonic modulated scattered light are carried out step by step.In this paper,the propagation characteristics of underwater scattered light are analyzed first,and the verification experiments of acousto-optic modulation are also expounded.The key to focusing of scattered light is the combination of digital holography and phase conjugation technology.The basic theory of digital optical phase conjugation is discussed in detail.Two digital optical phase conjugation systems based on polarization phase shift and off-axis holography are designed.The scattered light is focused successfully through scattering media by those systems.The speed of off-axis holography is faster because it only needs one interference picture.So the focusing ultrasonic probe is introduced into the off-axis digital holographic optical phase conjugation system to realize focusing inside the scattering medium,in which the colloid is used as the experimental scattering medium.Above all,this study will provide theoretical basis and technical experience for the future development of underwater acousto-optic imaging technology.