Study On The Speckle Noise Reduction Algorithm Based On The Principle Of Lateral Shearing Interferometry

Holography not only can record and reconstruct the amplitude of optical field, but also can give unique advantages in recording and reconstructing the phase of optical field. So it is one of the most important advantage in holography to obtain the phase information of optical field. However, phase of optical field in an experiment is usually wrapped, so as to obtain the practical phase need phase unwrapping. Because of various noises, especially the speckle noise, the difficulty exists in phase unwrapping. In order to obtain right and high precision phase, it is necessary to reduce noise before phase unwrapping. Noise reduction can be completed in spatial domain, frequency domain and wavelet domain, the conventional denoising algorithms can achieve good results when the phase of optical field changes slowly; but when the phase of optical filed changes rapidly, it is difficult to separate noise form phase, because both of them have very high spatial variation frequency, the conventional denoising algorithms often cause loss of phase details and even breakage of interference fringes while reducing noise. So it is necessary to research a new denoising algorithm to solve the weakness of conventional denoising algorithms.To this our team introduced lateral shearing interferometry to noise reduction, the new denoising algorithm reduces the frequency of phase significantly and separates noise and phase in spatial variation frequency, thus the difficulty of noise reduction is reduced and good noise reduction result is achieved. On this basic, we will research on the influence of shearing quantity selection in lateral shearing interferometry, and compare different denoising algorithms based on lateral shearing interferometry.In order to compare the effect of different denoising algorithms based on lateral shearing interferometry through practical validation, this paper explores the experimental method to using liquid crystal spatial light modulator (LC-SLM) to simulate speckle noise, and a new method for measuring the phase modulation characteristics of LC-SLM is proposed, in which the principle of holographic interferometry and digital holographic zoom system are used.This paper gives relevant theoretical analysis, simulation computation and experimental validation for all research, and obtains some beneficial conclusions:in phase unwrapping, noise reduction is very difficult when phase of optical field has high spatial variation frequency, which can be effectively solved through introducing lateral shearing interferometry; the selection of shearing quantity has influence on linear correlation between phase of ideal shearing optical field (without noise) and phase of shearing optical field (with noise), the difficulty of new denoising algorithm can be minimized through selecting the shearing quantity of shearing optical field phase without wrapping; wavelet denoising algorithm based on lateral shearing interferometry is better than other algorithms; the new method for measuring the phase modulation characteristics of LC-SLM contains many advantages including simple system, low system error and fast measurement speed, and it is feasible to use LC-SLM to simulate speckle noise.