Backscattered light field control based on self-adaptive genetic algorithm

Modulating the light field scattered by scattering media has potential applications in biological tissue imaging, military anti-terrorism, and optical information transmission. However, light reflected by complex scattering media, such as biological tissues, clouds and fog, multi-mode fiber, and white paper, will produce disorderly scattering, and then disturb the wavefront of incident light. It has always been the main obstacle to optical imaging and effective information transmission. Therefore, the control of backscattered light field is also a research field worthy of attention, which is of great significance for the transmission of non-line-of-sight optical information. It is also very important to find a method of efficiently controlling backscattered light field for the breakthrough of related applications. It has been found that iterative wavefront shaping technology is an effective solution, which gradually modulates the amplitude or phase distribution of wavefront according to the feedback of the light intensity distribution in the target area of charge coupled device (CCD). An improved genetic algorithm, self-adaptation genetic algorithm (SAGA), is proposed, which can be used to rapidly modulate the backscattered light field. The amplitude distribution of wavefront is controlled, which makes it form the required pattern at the target position through the interference of light. During the implementation of the algorithm, the SAGA performs gene crossover and mutation separately, and selects gene crossover and mutation operations according to the number of iterations. At the beginning of evolution, the probability of selecting gene mutations is higher because the population needs to adapt to the environment, while at the end of evolution, the probability of selecting gene mutations is lower because it gradually adapts to the environment. In the experimental measurement, the effective modulation area of digital-micromirror device (DMD) is 1024×1024, which is divided into 64×64 modulation segments by pixel merging. Each segment number is assigned a value of 0 or 1. Focusing and image projection performance of scattered light field are evaluated based on peak-to-background ratio (PBR) and Pearson correlation coefficient (Cor), respectively. By comparing the scattered light focusing and image projection of SAGA and genetic algorithm (GA), it is found that SAGA can accurately control the backscattered light field and converge to the optimal value in a few iterations. After 1000 iterations, the GA still has a clear speckle background. With the increase of iteration times, GA will also show bright focus and clear projection image. Compared with GA, SAGA has a modulation speed that is 8.3 times faster in light focusing and 14.38 times faster in image projection, greatly improving the modulation speed of the scattered light field. The fast control technology for scattered light field can lead to numerous new optical communication applications and offer fresh insights into the study of optics and information science.