Phase retrieval in multicore fiber bundles

Abstract

Multicore fiber bundles are widely used in endoscopy due to their miniature size and their direct imaging capabilities. They have recently been used, in combination with spatial light modulators, in various realizations of endoscopy with little or no optics at the distal end. These schemes require characterization of the relative phase offsets between the different cores, typically done using off-axis holography, thus requiring both an interferometric setup and, typically, access to the distal tip. Here we explore the possibility of employing phase retrieval to extract the necessary phase information. We show that in the noise-free case, disordered fiber bundles are superior for phase retrieval over their periodic counterparts, and demonstrate experimentally accurate retrieval of phase information for up to 10 simultaneously illuminated cores. Thus, phase retrieval is presented as a viable alternative for real-time monitoring of phase distortions in multicore fiber bundles.

Joint estimation of object and probes in vectorial ptychography

“…The potential of our method relies on its capacity to address specimens of any size and to its ability to image, at optical resolution, both isotropic (transmittance, OPL) and anisotropic (birefringence, diattenuation, eigenmodes) properties contained in the Jones matrix. The specificity to these two aspects opens new imaging perspectives for characterizing systems offering unusual properties, such as optical metasurfaces [16], or spatially structured for wavefront control purpose (zone plates [17], spatial light modulators [18], multicore fiber bundles [19], etc.) and involving anisotropic materials.…”

Complex Wavefront Shaping through a Multi-Core Fiber

“…Recently, it is investigated that the performance of a precisely-twisted MCF is not affected by fiber bending [15], which shows the potential of MCFs becoming a more flexible waveguide beyond multi-mode fibers. Nevertheless, DOPC is required to compensate for the optical path difference between cores which can lead to phase distortion when light propagating through an MCF [16][17][18]. Focus scanning employing simple wavefront shaping through MCFs is thus achieved [19][20][21][22], paving the way to lensless endoscopy.…”

Single-shot noninterferometric measurement of the phase transmission matrix in multicore fibers

“…Amongst other advantages, this arrangement leads to an important reduction of side lobes when focusing light at the distal end. A key challenge in the deployment of lensless endoscopes is to achieve focusing at the fiber's distal end through non-interferometric methods such as iterative optimization [16] or phase retrieval to obtain the fiber's TM [17]. However, the characterization of the TM typically requires a sequential interferometric process [5].…”

“…We then focus on retrieving the phases φ n , measured with respect to the phase of the central core, φ 1 = 0. This problem has been examined through alternating projection (AP) algorithms for an aperiodic MCF [17]. Phase retrieval problems in 2D with source and far-field intensity measurements tend to lead to unique solutions [18], at least when important assumptions such as sparsity or low noise can be made.…”

“…For a perfectly periodic MCF, this autocorrelation is sparse and concentrated around discrete points, since different peaks due to the correlations of several pairs of points (with equal separation vector) overlap. AP algorithms can be susceptible to the sensor's limited dynamic range and readout noise, to minor aberrations in the optical system, and to small changes in the intensities of the emitting cores, especially when a large number of cores (≥ 10 ) is measured simultaneously [17]. Note that amplitude modulations are inevitable in experimental scenarios, so phase retrieval techniques with limited sensitivity to changes in relative amplitudes are mandatory.…”