Object wave retrieval using normalized holograms in three-step generalized phase-shifting digital holography

Digital hologram reconstruction algorithm based on the Fractional Fourier transform in non-telecentric digital holographic microscopy

A hologram reconstruction algorithm is proposed based on the fractional Fourier transform (FRFT) in non-telecentric digital holographic microscopy. The optimal fractional order representing the recorded hologram is estimated based on an evaluation metric. The FRFT-based hologram reconstruction enables noise robust amplitude and phase imaging with enhanced resolution. The effectiveness of the proposed approach is demonstrated in practical scenarios through both simulation and experimental results.

Fractional Fourier-transform filtering and reconstruction in off-axis digital holographic imaging

An off-axis digital holographic reconstruction method with fractional Fourier transform domain filtering is proposed. The theoretical expression and analysis of the characteristics of fractional-transform-domain filtering are given. It is proven that the filtering in a lower fractional-order transform domain can utilize more high-frequency components than that in a conventional Fourier transform domain under the same size of filtering regions. In simulation and experiment, the results demonstrate that the reconstruction imaging resolution can be improved by filtering in the fractional Fourier transform domain. The presented fractional Fourier transform filtering reconstruction provides a novel (to our knowlede) optional way for off-axis holographic imaging.

Accurate EOM-based phase-shifting digital holography with a monitoring interferometer

Phase-shifting digital holography (PSDH) can effectively remove the zero-order term and twin image in on-axis holography, but the phase-shifting error deteriorates the quality of reconstructed object images. In this paper, accurate PSDH with an electro-optic modulator (EOM) is proposed. The EOM is used to generate the required phase shift of on-axis digital holography, and the required phase shift is precisely measured with orthogonal detection of a homodyne interferometer and controlled with proportional-integral-derivative feedback in real time. The merits of our method are that it can achieve fast and accurate phase shifting without mechanical motion or sacrificing the resolution and field of view. The optical configuration was designed, an experimental setup was constructed, and real-time phase shifting was realized. Experiments of the phase-shifting accuracy evaluation, suppression effectiveness of the zero-order and twin image terms, and the specimen measurement demonstrate that the proposed method has significant application for precision topography measurement.

Zero-order-term elimination by using two hologram subtraction based on reference wave polarization adjustment in off-axis digital holography

We propose a method for the removal of the zero-order term by the subtraction of two off-axis holograms based on a reference wave polarization adjustment. The zero-order elimination hologram is generated by the subtraction of two off-axis holograms that are formed by the interference of two reference waves of different linear-polarization orientations with the same s-polarization object wave. The expression about the zero-order elimination hologram is derived according to the essential formula of holographic recording, which proves the validity of this method in principle. The experimental results show that imaging reconstruction from the zero-order elimination hologram can achieve a higher resolution than conventional reconstruction.

Random phase-shifting digital holography based on a self-calibrated system

Random phase-shifting digital holography based on a self-calibrated system is proposed. In the proposed method, the hologram and the calibration interference fringes can be recorded simultaneously in a single image based on the space-division-multiplexing technique. Three randomly phase-shifted holograms and corresponding interference fringes are recorded, and the phase-shifting amount between each two adjacent holograms is calculated by the sampling Moiré method from the calibration interference fringes. A reflective object is used to demonstrate the effectiveness of the proposed method in the numerical and experiment.

Novel Generalized Three-Step Phase-Shifting Interferometry with a Slight-Tilt Reference

A convenient and powerful method is proposed and presented to find the unknown phase shifts in three-step generalized phase-shifting interferometry. A slight-tilt reference of 0.1 degrees is employed. As a result, the developed theory shows that the unknown phase shifts can be simply extracted by subtraction operations. Also, from the theory developed, the tilt angle of the tilt reference can also be calculated, which is important as it allows us to extract the object wave precisely. Numerical simulations and optical experiments were performed to demonstrate the validity and efficiency of the proposed method. The proposed slight-tilt reference allows the full and efficient use of the space-bandwidth product of the limited resolution of digital recording devices as compared to the situation in standard off-axis holography where typically several degrees for off-axis angle is employed.