Automatic filtering for zero-order and twin-image elimination in off-axis digital holography

Windowing the Fourier spectra is usually used to filter the zero-order and twin image in off-axis digital holography (DH). However, during the filtering process, manual operation is often needed. In our work, we present an automatic filtering method. The filtered zone is a circle in the Fourier domain. The point with the highest intensity in the +1st order is chosen as its center, the location of which is related to the angle between the reference and the objective beams. Considering that the size of the zero-order spectra is twice of that of the +1st order, the radius of the circle is set to be a third of the distance between the circle center and the very center of the Fourier spectra. With this filtering method, the desired spectra can be filtered out automatically and noniteratively. This method has been tested and validated on several samples. Compared with the iterative filtering method, it spends about 2‰ of the processing time and obtains the reconstructed images with high similarity. This approach can result in real-time use of the off-axis DH and holographic microscopy.