Research And Implementation Of Three-dimensional Wavefront Coding Imaging System

Three-dimensional(3D)imaging technology is widely used in the material,biological,medical industries etc.However,the general 3D imaging system has some restrictions such as the limited flexibility.A two-step wavefront coding technology is applied to set up a passive 3D imaging system.Firstly,the intermediate images,captured by the Charge Coupled Device(CCD),are optically encoded by inserting a chiral phase mask in the pupil plane of the wavefront coding system.The encoded system becomes particularly sensitive to the object distance.Secondly,the 3D images can be digitally decoded from the intermediate images using the sensitivity to the object distance.We deducted the optical transfer function of the passive wavefront coding system with a chiral phase based on the theory of the Fourier optics.We also derived the analytical relationship between the object distance and the point spread function,as well as the object distance and the encoded intermediate image.Both of the point spread function and the processed spectrum of the encoded image have two spots,which will rotate with the variation of the object distance.Then the depth map,extracted from the encoded image,can be used to set up the 3D images.Instead of a fixed phase mask,a liquid-crystal spatial light modulator(LC-SLM)is used as the chiral phase mask to set up a wavefront coding system in the experiment.The object distances of the different parts of the object are extracted from the intermediate image captured by the CCD.Thus the 3D image of the object is reconstructed.The experimental results show that the error of the depth between the measured value and the actual value is less than 5%.The 3D wavefront coding imaging system has an acceptable accuracy.Compared to the traditional fixed phase mask,the phase generated by the LC-SLM is more feasible.It is especially suitable for observing the real-time object with a wide dynamic range.