Digital holographic speckle denoising method based on compound modulation of object light

In digital holography, the speckle noise caused by the high coherence of laser source will reduce the imaging quality. In order to overcome this problem, the combination of a quartz depolarizer and an electronically controlled liquid crystal diffuser for digital holography was proposed. By adding a quartz depolarizer to the object light path, the depolarization performance of the depolarizer was used to make the linearly polarized light in the object light path into randomly polarized light, which reduced the degree of coherence with the reference light and realized the suppression of speckle noise. By applying an electric field to the liquid crystal diffuser, the movement of the liquid crystal molecules and the orientation change of the optical axis could be caused. The liquid crystal driving voltage could be adjusted to change the different scattering effects on the incident light, thereby effectively reducing the coherence of the light source. The reconstructed images using the quartz depolarizer and the electronically controlled liquid crystal diffuser were compared and analyzed respectively with the reconstructed images of the combined device. The effectiveness of the proposed method was verified by experiments. The experimental results show that the peak signal to noise ratio of the reconstructed images of two experimental objects under the combined device reaches 16.91 and 18.30, the structural similarity is 0.47 and 0.43, the equivalent number of looks is 42% and 30% higher than the original reconstructed image, and the speckle index is 1.52 and 1.29, respectively. The proposed method can better remove the speckle noises and retain more details of the image.