Plane-wave decomposition of spatially random fields

Intensity-based adaptive optics with sequential optimization for laser communications

Wavefront distortions of optical waves propagating through the turbulent atmosphere are responsible for phase and amplitude fluctuations, causing random fading in the signal coupled into single-mode optical fibers. Wavefront aberrations can be confronted, in principle, with adaptive optics technology that compensates the incoming optical signal by the phase conjugation principle and mitigates the likeliness of fading. However, real-time adaptive optics requires phase wavefront measurements, which are generally difficult under typical propagation conditions for communication scenarios. As an alternative to the conventional adaptive optics approach, here, we discuss a novel phase-retrieval technique that indirectly determines the unknown phase wavefront from focal-plane intensity measurements. The adaptation approach is based on sequential optimization of the speckle pattern in the focal plane and works by iteratively updating the phases of individual speckles to maximize the received power. We found in our analysis that this technique can compensate the distorted phasefront and increase the signal coupled with a significant reduction in the required number of iterations, resulting in a loop bandwidth utilization well within the capacity of commercially available deformable mirrors.

Talbot effect with partially coherent interfering Bessel beams

We studied the free-space propagation of interfering partially coherent Bessel beams. The partially coherent superimposed Bessel beams were generated by diffracting a spatially incoherent light by two concentric circular slits. We observed a Talbot effect in the random intensity pattern and in the intensity correlation. We showed that the Talbot length depends only on the radii of the circular slits. We explained this effect on the basis of the plane-wave decomposition of spatially random fields.

Tomographic phase microscopy: principles and applications in bioimaging [Invited]

Tomographic phase microscopy (TPM) is an emerging optical microscopic technique for bioimaging. TPM uses digital holographic measurements of complex scattered fields to reconstruct three-dimensional refractive index (RI) maps of cells with diffraction-limited resolution by solving inverse scattering problems. In this paper, we review the developments of TPM from the fundamental physics to its applications in bioimaging. We first provide a comprehensive description of the tomographic reconstruction physical models used in TPM. The RI map reconstruction algorithms and various regularization methods are discussed. Selected TPM applications for cellular imaging, particularly in hematology, are reviewed. Finally, we examine the limitations of current TPM systems, propose future solutions, and envision promising directions in biomedical research.

Deterministic mode representation of random stationary media for scattering problems

Deterministic mode representation (DMR) is introduced for a three-dimensional random medium with a statistically stationary refractive index distribution. The DMR allows for the designing and fine tuning of novel random media by adjusting the weights of individual deterministic modes. To illustrate its usefulness, we have applied the decomposition to the problem of weak light scattering from a Gaussian Schell-model medium. In particular, we have shown how individual deterministic modes of the medium contribute to the scattered far-field spectral density distribution.

Synthesis of statistical properties of a randomly fluctuating polarized field

An experimental technique for the synthesis of statistical properties of a randomly fluctuating polarized field is investigated and experimentally demonstrated. The technique offers the controlled synthesis of coherence and polarization and subsequent analysis of the synthesized field is carried out by making use of two-point intensity correlation and the speckle holographic technique. The controlled synthesis is achieved by using an aperture of specific size at the source plane and generating a vortex in one of the orthogonal polarization components of the polarized field, thereby producing a singularity in off-diagonal elements of the coherence-polarization matrix.