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2 Optica Applicata

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Fast phase reconstruction in off-axis digital holography with zero-order term suppression

100%

Luan G. , Shan M. , Zhong Z. , Xia B.

2020

tom Vol. 50, nr 3

425--432

A fast phase reconstruction method (FPRM) employing a free-sample hologram can improve the efficiency of phase reconstruction in off-axis digital holography. However, the space-bandwidth product is still confined by spectrum aliasing in the hologram owing to the zero-order term. In this paper, we propose an FPRM that features an efficient zero-order term suppression method called the average gray that can eliminate spectrum shifting. We can implement phase reconstruction by considering both speed and the space-bandwidth product. We verified the validity of our approach for off-axis digital holography using laser and white-light illumination.

Optical multiple-image encryption in discrete multiple-parameter fractional Fourier transform scheme using complex encoding, theta modulation and spectral fusion

100%

Luan G. , Zhong Z. , Shan M.

Optica Applicata

2021

tom Vol. 51, nr 1

121--134

We present a novel encryption method for multiple images in a discrete multiple-parameter fractional Fourier transform scheme, using complex encoding, theta modulation and spectral fusion. All pairs of original images are encoded separately into a complex signal. The spectrum of each complex signal can then be scattered into various positions in the spectral plane and multiplexed into one spectral image with a combination of theta modulation and spectral fusion. After Fourier transforming back to the spatial domain, the multiplexed signal is encrypted in the discrete multiple-parameter fractional Fourier transform domain. Information about the original images can only be successfully decrypted given the possession of all correct keys. The parameters of chaotic pixel scrambling for the proposed method enlarge the key space. Moreover, the proposed method solves the crosstalk problem of multiple images and improves the multiplexing capacity. Numerical simulations demonstrate the effectiveness of the proposed method.