Arbitrary state of polarization with customized degree of polarization generator

Metasurface-Based Solid Poincaré Sphere Polarizer

The combination of conventional polarization optical elements, such as linear polarizers and waveplates, is widely adopted to tailor light's state of polarization (SOP). Meanwhile, less attention has been given to the manipulation of light's degree of polarization (DOP). Here, we propose metasurface-based polarizers that can filter unpolarized incident light to light with any prescribed SOP and DOP, corresponding to arbitrary points located both at the surface and within the solid Poincaré sphere. The Jones matrix elements of the metasurface are inverse-designed via the adjoint method. As prototypes, we experimentally demonstrated metasurface-based polarizers in near-infrared frequencies that can convert unpolarized light into linear, elliptical, or circular polarizations with varying DOPs of 1, 0.7, and 0.4, respectively. Our Letter unlocks a new degree of freedom for metasurface polarization optics and may break new ground for a variety of DOP-related applications, such as polarization calibration and quantum state tomography.

Generalized polarization transformations with metasurfaces

Metasurfaces are arrays of sub-wavelength spaced nanostructures, which can be designed to control the many degrees-of-freedom of light on an unprecedented scale. In this work, we design meta-gratings where the diffraction orders can perform general, arbitrarily specified, polarization transformation without any reliance on conventional polarization components, such as waveplates and polarizers. We use matrix Fourier optics to design our devices and introduce a novel approach for their optimization. We implement the designs using form-birefringent metasurfaces and quantify their behavior - retardance and diattenuation. Our work is of importance in applications, such as polarization abberation correction in imaging systems, and in experiments requiring novel and compact polarization detection and control.

Measuring Stokes parameters by means of unitary operations

We propose an improved scheme to measure the Stokes polarization parameters by making the to-be-measured state evolve unitarily. An optical setup able to implement the scheme is presented theoretically and experimentally. Theoretical results indicate that at least two unitary operators should be employed to determine the Stokes parameters of light with arbitrary degrees of polarization. Compared with the results acquired by a commercial polarimeter, the proposed scheme is used to obtain the Stokes parameters of 13 representative states with degrees of polarization r=1 and r=0.5, experimentally. The fidelity between the two states gained by the above methods is in the range of 0.9802±0.0046 to 1.0000±0.0000.

Customized depolarization spatial patterns with dynamic retardance functions

In this work we demonstrate customized depolarization spatial patterns by imaging a dynamical time-dependent pixelated retarder. A proof-of-concept of the proposed method is presented, where a liquid-crystal spatial light modulator is used as a spatial retarder that emulates a controlled spatially variant depolarizing sample by addressing a time-dependent phase pattern. We apply an imaging Mueller polarimetric system based on a polarization camera to verify the effective depolarization effect. Experimental validation is provided by temporal integration on the detection system. The effective depolarizance results are fully described within a simple graphical approach which agrees with standard Mueller matrix decomposition methods. The potential of the method is discussed by means of three practical cases, which include non-reported depolarization spatial patterns, including exotic structures as a spirally shaped depolarization pattern.

Polarization state generation and measurement with a single metasurface

The constituent elements of metasurfaces may be designed with explicit polarization dependence, making metasurfaces a fascinating platform for new polarization optics. In this work we show that a metasurface grating can be designed to produce arbitrarily specified polarization states on a set of defined diffraction orders given that the polarization of the incident beam is known. We also demonstrate that, when used in a reverse configuration, the same grating may be used as a parallel snapshot polarimeter, requiring a minimum of bulk polarization optics. We demonstrate its use in measuring partially polarized light, and show that it performs favorably in comparison to a commercial polarimeter. This work is of consequence in any application requiring lightweight, compact, and low-cost polarization optics, polarimetry, or polarization imaging.

Generation of a coherent light beam with precise and fast dynamic control of the state and degree of polarization

Recent developments of polarized light sources with tunable state and degree of polarization (SOP and DOP) inherently provide a temporally incoherent beam, which makes them unsuitable for applications like interferometry. We present a method for generating a coherent beam with full, precise, and independent control of the SOP and DOP. Our approach is based on an imbalanced dual-frequency dual-polarization light source. We demonstrate that it offers three different working regimes, respectively providing perfectly depolarized light, DOP modulated light, or fully polarized light with a deterministic SOP trajectory. A simple implementation of this versatile approach is described and experimentally validated.

Stokes-vector and Mueller-matrix polarimetry [Invited]

This paper reviews the current status of instruments for measuring the full 4×1 Stokes vector S, which describes the state of polarization (SOP) of totally or partially polarized light, and the 4×4 Mueller matrix M, which determines how the SOP is transformed as light interacts with a material sample or an optical element or system. The principle of operation of each instrument is briefly explained by using the Stokes-Mueller calculus. The development of fast, automated, imaging, and spectroscopic instruments over the last 50 years has greatly expanded the range of applications of optical polarimetry and ellipsometry in almost every branch of science and technology. Current challenges and future directions of this important branch of optics are also discussed.

Parallel Polarization State Generation

The control of polarization, an essential property of light, is of wide scientific and technological interest. The general problem of generating arbitrary time-varying states of polarization (SOP) has always been mathematically formulated by a series of linear transformations, i.e. a product of matrices, imposing a serial architecture. Here we show a parallel architecture described by a sum of matrices. The theory is experimentally demonstrated by modulating spatially-separated polarization components of a laser using a digital micromirror device that are subsequently beam combined. This method greatly expands the parameter space for engineering devices that control polarization. Consequently, performance characteristics, such as speed, stability, and spectral range, are entirely dictated by the technologies of optical intensity modulation, including absorption, reflection, emission, and scattering. This opens up important prospects for polarization state generation (PSG) with unique performance characteristics with applications in spectroscopic ellipsometry, spectropolarimetry, communications, imaging, and security.

Optimal distribution of integration time for intensity measurements in degree of linear polarization polarimetry

We consider the degree of linear polarization (DOLP) polarimetry system, which performs two intensity measurements at orthogonal polarization states to estimate DOLP. We show that if the total integration time of intensity measurements is fixed, the variance of the DOLP estimator depends on the distribution of integration time for two intensity measurements. Therefore, by optimizing the distribution of integration time, the variance of the DOLP estimator can be decreased. In this paper, we obtain the closed-form solution of the optimal distribution of integration time in an approximate way by employing Delta method and Lagrange multiplier method. According to the theoretical analyses and real-world experiments, it is shown that the variance of the DOLP estimator can be decreased for any value of DOLP. The method proposed in this paper can effectively decrease the measurement variance and thus statistically improve the measurement accuracy of the polarimetry system.