Off-axis digital holographic multiplexing for rapid wavefront acquisition and processing

Abstract

Off-axis holographic multiplexing involves capturing several complex wavefronts, each encoded into off-axis holograms with different interference fringe orientations, simultaneously, with a single camera acquisition. Thus, the multiplexed off-axis hologram can capture several wavefronts at once, where each one encodes different information from the sample, using the same number of pixels typically required for acquiring a single conventional off-axis hologram encoding only one sample wavefront. This gives rise to many possible applications, with focus on acquisition of dynamic samples, with hundreds of scientific papers already published in the last decade. These include field-of-view multiplexing, depth-of-field multiplexing, angular perspective multiplexing for tomographic phase microscopy for 3-D refractive index imaging, multiple wavelength multiplexing for multiwavelength phase unwrapping or for spectroscopy, performing super-resolution holographic imaging with synthetic aperture with simultaneous acquisition, holographic imaging of ultrafast events by encoding different temporal events into the parallel channels using laser pulses, measuring the Jones matrix and the birefringence of the sample from a single multiplexed hologram, and measuring several fluorescent microscopy channels and quantitative phase profiles together, among others. Each of the multiplexing techniques opens new perspectives for applying holography to efficiently measure challenging biological and metrological samples. Furthermore, even if the multiplexing is done digitally, off-axis holographic multiplexing is useful for rapid processing of the wavefront, for holographic compression, and for visualization purposes. Although each of these applications typically requires a different optical system or processing, they all share the same theoretical background. We therefore review the theory, various optical systems, applications, and perspectives of the field of off-axis holographic multiplexing, with the goal of stimulating its further development.

High Bandwidth‐Utilization Digital Holographic Multiplexing: An Approach Using Kramers–Kronig Relations

“…The multiplexing limit bandwidth utilization is 58.9% with six channels in a single hologram. [ 41 ] The multiplexing bandwidth utilization in Figure 1f surpasses the current multiplexing limit to 78.5%, which is the highest with the circular pupil function of the diffraction‐limited optical imaging system; however, it inevitably leads to the overlap between the AC and CC spectra. It can be reconstructed by acquiring two phase‐shifted holograms [ 50,54–56 ] but consumes multiframe images or more pixels, reducing at least half of the SBU.…”

Generation and Detection of Structured Light: A Review

“…Then, the autocorrelation term is filtered out and the cross-correlation term is kept in the spatial frequency domain. Implementing the two-dimensional reversal fast Fourier transforms to the crosscorrelation term, the complex amplitude distribution of the output beam can be computed to calculate the mode spectrum of the output light field [89]. A 45 × 45 mode transfer matrix of MMF can be fast characterized, using only 45 measurements within 0.3 s [87].…”

Flipping Interferometric Module for Simultaneous Dual-Wavelength Unwrapping of Quantitative Phase Maps of Biological Cells

“…This can be done by multiplexing two offaxis holograms of the same sample imaged under different wavelengths on the same sensor, providing real-time holographic capabilities without 2π phase ambiguities. In this case, the camera records a multiplexed off-axis hologram composed of two 90 • -rotated, or orthogonal, off-axis interference fringes [6][7][8][9]. These methods use separate reference beams, independent of the sample beam along most of the optical path, yielding increased temporal noise.…”