Suppression of Speckle Noise in Digital Holography With Spatial and Temporal Domain Depolarization

Abstract

Speckle noise in digital holography has a great influence on image quality, and one of the reasons for the formation of speckle noise is that the degree of coherence for the reference light and the object light is too high and unnecessary noise is introduced to the recorded hologram. In this paper, the spatial depolarization and the temporal domain depolarization are analyzed to reduce the speckle noise. The spatial depolarization utilizes the depolarization performance of the depolarizer. By adding a quartz depolarizer to the object light, the linearly polarized light in the object light becomes randomly polarized light, thereby reducing the degree of coherence with the reference light, realizing the suppression of speckle noise, and by utilizing the characteristics of pupil parameters towards the depolarization degree, it is to realize the control for the degree of coherence. The temporal domain depolarization uses two quarter-wave plates and adjustable liquid crystal to realize the depolarization superposition. By controlling the phase delay of the liquid crystal phase variable retarder, the multi-depolarization accumulation in a short time is realized, and the experimental results show that this method preserves the detail portion of the image while better removing speckle noise. Finally, the Non-Local Means filtering algorithm is used to make the reconstructed image smoother. The method proposed in this paper has great applicable value for improving the image quality of digital holography system. INDEX TERMS Digital holography speckle noise, depolarization, quartz depolarizer, liquid crystal.

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