Vectorial coherence holography

Folded interferometer to measure coherence-polarization matrix

We present and experimentally demonstrate a new, to the best of our knowledge, technique to quantitatively measure coherence-polarization (BCP) matrix with correlations of only two Stokes fluctuations. The BCP matrix is a square matrix with four elements that involves two-point correlations among orthogonal polarization components. A theoretical framework of the technique is developed, and its viability is demonstrated by a proof of principle experiment. Experimental tests and measurement of the elements of the BCP matrix of statistically stationary beams are demonstrated.

Unscrambling OAM mode using digital phase-shifting in the Stokes fluctuations correlation

In this Letter, we propose and experimentally demonstrate a new, to the best of our knowledge, non-interferometric and highly stable technique to unscramble the incident orbital angular momentum (OAM) state and quantitatively measure the phase structure from the non-imaged random light. A new theoretical basis is developed and also verified by numerical simulation and experimental demonstration. We also quantitatively investigate the OAM modes of the incident light using orthogonal projection.

Imaging of polarimetric-phase object through scattering medium by phase shifting

Light propagating through a scattering medium generates a random field, which is also known as a speckle. The scattering process hinders the direct retrieval of the information encoded in the light based on the randomly fluctuating field. In this study, we propose and experimentally demonstrate a method for the imaging of polarimetric-phase objects hidden behind a scattering medium based on two-point intensity correlation and phase-shifting techniques. One advantage of proposed method is that it does not require mechanical rotation of polarization elements. The method exploits the relationship between the two-point intensity correlation of the spatially fluctuating random field in the observation plane and the structure of the polarized source in the scattering plane. The polarimetric phase of the source structure is determined by replacing the interference intensity in traditional phase shift formula with the Fourier transform of the cross-covariance of the intensity. The imaging of the polarimetric-phase object is demonstrated by comparing three different phase-shifting techniques. We also evaluated the performance of the proposed technique on an unstable platform as well as using dynamic diffusers, which is implemented by replacing the diffuser with a new one during each phase-shifting step. The results were compared with that obtained with a fixed diffuser on a vibration-isolation platform during the phase-shifting process. A good match is found among the three cases, thus confirming that the proposed intensity-correlation-based technique is a useful one and should be applicable with dynamic diffusers as well as in unstable environments.

Characterization of a spatial light modulator using polarization-sensitive digital holography

We show a digital holographic approach for polarimetric characterization of a twisted nematic liquid crystal spatial light modulator (TNLC-SLM). An experimental scheme is designed to perform polarization analysis of the SLM with gray levels. This is realized by simultaneous detection of the polarization states of the light from the SLM for a given gray level with the help of a specially designed spatial-frequency multiplex polarization interferometer. This provides amplitude and phase characteristics of the SLM in a single shot. In order to characterize the SLM, we perform Jones matrix imaging at its various gray values (driving voltages), and corresponding results are presented. These results are expected to be useful in designing and developing various SLM-based experiments in the scalar and vectorial domain.

Diatomic Metasurface for Vectorial Holography

The emerging metasurfaces with the exceptional capability of manipulating an arbitrary wavefront have revived the holography with unprecedented prospects. However, most of the reported metaholograms suffer from limited polarization controls for a restrained bandwidth in addition to their complicated meta-atom designs with spatially variant dimensions. Here, we demonstrate a new concept of vectorial holography based on diatomic metasurfaces consisting of metamolecules formed by two orthogonal meta-atoms. On the basis of a simply linear relationship between phase and polarization modulations with displacements and orientations of identical meta-atoms, active diffraction of multiple polarization states and reconstruction of holographic images are simultaneously achieved, which is robust against both incident angles and wavelengths. Leveraging this appealing feature, broadband vectorial holographic images with spatially varying polarization states and dual-way polarization switching functionalities have been demonstrated, suggesting a new route to achromatic diffractive elements, polarization optics, and ultrasecure anticounterfeiting.

Lensless Stokes holography with the Hanbury Brown-Twiss approach

The recording and reconstruction of the Stokes parameter is of paramount importance for the description of the vectorial interference of light. Polarization holography provides a complete vectorial wavefront, however, direct recording and reconstruction of the hologram is not possible in a situation where the object is located behind the random scattering layer. The Stokes holography plays an important role in such situations and makes use of the Fourier transform relation between the Stokes parameters (SPs) at the scattering plane and the generalized Stokes parameters (GSPs) of the random field. In this paper, we propose and experimentally demonstrate the Stokes holography with the Hanbury Brown-Twiss (HBT) interferometer. We also propose and implement a lensless Fourier configuration for the Stokes holography. This permits us to reconstruct the wavefront from the GSPs at any arbitrary distance from the scattering plane. The application of the proposed technique is experimentally demonstrated for the 3D imaging of two different objects lying behind the random scattering medium. Depth information of the 3D objects is obtained by digitally propagating the generalized Stokes parameters to a different longitudinal distance. The quality of the reconstruction is assessed by measuring the overall visibility, efficiency, and PSNR of the reconstruction parameters.

Controlled modulation of depolarization in laser speckle

A new technique based on superposition of two speckle patterns is proposed and demonstrated for controlled modulation of the spatial polarization distribution of the resultant speckle. It is theoretically and experimentally demonstrated that controlled modulation of the spatial polarization distribution of laser speckle can be achieved by proper choice of the polarization states as well as the average spatial intensity of the constituent speckles. It is shown that the proposed technique is useful to generate different speckle patterns with sinusoidal variation in their degree of polarization, which can be tuned from zero to unity. This technique can find application in sensing, biomedical studies, and in determining the rotation of an electric field vector after passing through a scattering medium.

Hybrid correlation holography with a single pixel detector

Correlation holography reconstructs three-dimensional (3D) objects as a distribution of two-point correlations of the random field detected by two-dimensional detector arrays. Here, we describe a hybrid method, a combination of optical and computational channels, to reconstruct the objects from only a single pixel detector. An experimental arrangement is proposed as a first step to realizing the technique; we have simulated the experimental model for both scalar and vectorial objects. The proposed technique provides depth focusing and 3D reconstruction with digital suppression of unwanted frequency spectrum.

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.

Generation of spatial coherence comb using Dammann grating

A new technique to generate a spatially varying coherence field, such as a coherence comb using a Dammann grating, is proposed and experimentally demonstrated. The principle of the technique lies with the vectorial van Cittert-Zernike theorem, which connects vectorial source structure with the coherence-polarization of the light. The Dammann grating is encoded into one of the polarization components of the light to shape the vectorial source structure and, consequently, the coherence-polarization of the light. Experimental results on the generation of a spatial coherence comb by the Dammann grating are presented for different orders.

Vectorial van Cittert-Zernike theorem based on spatial averaging: experimental demonstrations

The van Cittert-Zernike theorem is extended to the vectorial regime based on spatial averaging over the observation plane, and experimental demonstrations are presented. The theorem connects complex vectorial source structure to the degree of coherence and polarization of the spatially fluctuating vectorial field in the far field. Experimentation is carried out by making use of the space averages as a replacement of ensemble averages for the Gaussian stochastic field. For quantitative comparison with the theorem, analytical and experimental results are presented for a rectangular aperture with different vectorial source structures.

Stokes holography

A new technique, referred to as Stokes holography, is proposed and experimentally demonstrated for controlled synthesis of generalized Stokes parameters in 3D space using Stokes fringes. Stokes fringes are polarization fringes which permit to record and reconstruct complete wavefront. Full use of Stokes fringes in a single step is realized by scattering complex field and subsequently reconstructing using spatial averaging of the randomly scattered field. Mathematical formulations are derived and supported by experimental results of 3D object reconstruction in generalized Stokes parameters.