Higher-order Poincare Sphere Research Articles

Full characterization of vector eigenstates in symmetrically confined systems with photonic spin-orbit coupling.

The photonic spin-orbit (SO) coupling is a widely investigated effect in optical microcavities leading to various interesting physical phenomena and potential applications. We report the full sets of eigenenergies and eigenstates in a symmetrically confined potential under the effect of SO coupling induced by the transverse-electric transverse-magnetic (TE-TM) splitting, which are derived analytically via the degenerate perturbation theory. We obtained the eigenenergies and the eigenstates from the 1st to the 6th orders of excited manifold, and demonstrate unambiguously that universal rules governing the mode formation exist in such complicated photonic systems, making the modes exhibiting the features of solid and hollow skyrmions as well as spin vortices. We show that these eigenstates can be described by the SO coupled hyperspheres that can be decomposed into a series of higher-order Poincare spheres. Our results significantly extend the area of microcavity spin-optronics to the general theory of eigenvalues in confined systems, and provide an efficient theoretical frame for the information processing using microcavity-based high-dimensional vector states.

Interaction of four level closed loop atomic systems in the presence of two vector beams

In this manuscript, we have theoretically studied the four level closed loop atomic systems in the presence of two vector beams. A spatially dependent transparency for the probe vector beam is obtained based on the semiclassical model. We have explicitly shown that the number of petals formed for probe absorption depends on the value of orbital angular momentum (OAM) of the constituting beams. A detailed study for absorption and dispersion of right circularly polarized (RCP) and left circularly polarized (LCP) components of the probe beam is carried out and the importance of the polarization state of the beams on Higher Order Poincare Sphere (HOPS) is highlighted. An explicit effect of the interferometer phase of the vector beam which is geometric in nature, is shown for probe beam response. Three types of four level closed loop atomic system is studied with particular emphasis given for double Λ and Diamond atomic system. A dark state analysis of the atomic system is carried out which facilitate a physical understanding of the obtained results. Our study has explored the effects of inhomogeneity in both polarization and intensity for probe and coupling beam in a closed loop atomic system which is phase dependent.

Use of q-plate as a coupler.

A coupler is a device that allows interconversion of angular momentum of the optical beam among spin and orbital parts, without absorbing any angular momentum. In this paper, we demonstrate that a q-plate with q=1 can act as a coupler for any of the polarization distribution that can be represented by a point on a Poincare sphere (PS), or on a higher-order PS, or on a hybrid-order PS. A q-plate with any q-value can act as a coupler for polarization distribution that can be represented by an equatorial point on any of these spheres. It is also possible to find a q-plate with an appropriate q-value that can act as a creation or annihilation operator that raises or lowers the polarization singularity index. The q-plate being a coupler and made of half-wave plate segments, the singularity index change is concomitant with the helicity inversion of C-points. Interconversion of bright and dark C-points is possible by using a q-plate.

Evolution properties of vector vortex beams passing through a paraxial optical system

The arbitrary vector vortex beams on a higher-order Poincare sphere (HOPS) are generated and manipulated using the combination of a Mach–Zehnder interferometer and a spatial light modulator. In terms of the transfer matrix method, the analytical expressions of the arbitrary vector vortex beams on the HOPS through a paraxial optical system are derived. The characteristics of the transformation of vector vortex beams by three typical optical systems, such as free space, Fourier transform, and fractional Fourier transform system, are investigated theoretically and verified experimentally. The intensity distribution of the vector vortex beams is found to be form-invariant under paraxial transformations. In addition, the intensity and polarization properties of the vector vortex beams are closely related to the several independent complex parameters of the beams and the optical systems. This research provides a reliable and flexible approach to manipulating the vector vortex beams in practical optical systems.

Cylindrical vector beam generator using a two-element interferometer

We realize a robust and compact cylindrical vector beam generator that consists of a simple two-element interferometer composed of a beam displacer and a cube beamsplitter. The interferometer operates on the higher-order Poincaré sphere transforming a homogeneously polarized vortex into a cylindrical vector (CV) beam. We experimentally demonstrate the transformation of a single vortex beam into all the well-known CV beams and show the operations on the higher-order Poincaré sphere according to the control parameters. Our method offers an alternative to the Pancharatnam-Berry phase optical elements and has the potential to be implemented as a monolithic device.

Amplification of higher order Poincaré sphere beams through Nd:YLF and Nd:YAG crystals

Scalar and vector orbital angular momentum modes, generally described by the higher order Poincare sphere (HOPS), have found many applications to date, but limited to low-power levels. It has thus become topical to consider amplification of such structured light modes. Here, we employ recently developed characterisation tools for HOPS beams to study their purity through birefringent and non-birefringent amplifiers in a master oscillator power amplifier configuration. We outline a general theory for the problem that considers both vector and gain perspectives, and confirm the theory by experiment.

Multi-dimensional QAM equivalent constellation using coherently coupled orbital angular momentum (OAM) modes in optical communication.

In this work, a 1550 nm fiber-to-free-space optical communication link is successfully demonstrated employing the superposition of two coherently coupled orbital angular momentum (CCOAM) states. Information is encoded onto both the amplitude and phase of the CCOAM beams and is mapped to a three-dimensional (3D) constellation space using quadrature amplitude modulation (QAM) equivalent architecture. The 3D QAM constellation is based on a higher-order Poincare sphere equivalent for OAM states, and multiple spherical constellations are demonstrated for 64- and 128-QAM, providing a 6X and 7X increase in spectral efficiency by fully exploiting the available 3D space. The experimental results are presented showing a bit error rate (BER) below the forward error correction (FEC) limit. Multiple experimental parameters which could contribute to constellation distortions are also discussed.

Perfect Higher-Order Poincaré Sphere Beams from Digitalized Geometric Phases

The higher-order Poincare (HOP) sphere beam generalizes optical vortices and vector beams, vividly illustrating their higher-order polarization states. However, its doughnutlike intensity profile varies significantly with topological charge, restricting its application in optics. The authors study a perfect HOP sphere, whose annular intensity profile is $i\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}d\phantom{\rule{0}{0ex}}e\phantom{\rule{0}{0ex}}p\phantom{\rule{0}{0ex}}e\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}d\phantom{\rule{0}{0ex}}e\phantom{\rule{0}{0ex}}n\phantom{\rule{0}{0ex}}t$ of topological charge. Single- and multiringed beams are produced in anisotropic medium, by exploiting a spiral geometric phase and aptly designed gratings. This work provides an exciting technique for manipulating the angular momentum of light, to improve $e.g.$ optical tweezers, or multiplexing in optical communication.

Highly efficient generation of arbitrary vector beams with tunable polarization, phase, and amplitude

We propose an efficient and robust method to generate tunable vector beams by employing a single phase-type spatial light modulator (SLM). With this method, a linearly polarized Gaussian beam can be converted into a vector beam with arbitrarily controllable polarization state, phase, and amplitude. The energy loss during the conversion is greatly reduced and depends mainly on the reflectivity of the SLM. We experimentally demonstrate that conversion efficiency of about 47% is achieved by using an SLM with reflectivity of 62%. Several typical vector beams, including cylindrical vector beams, vector beams on higher order Poincare spheres, and arbitrary vector beams attached with phases and with tunable amplitude, are generated and verified experimentally. This method is also expected to create high-power vector beams and play important roles in optical fabrication and light trapping.

95.16-Gb/s Mode-Division-Multiplexing Signal Transmission in Free-Space Enabled by Effective-Conversion of Vector Beams

We introduce a high-efficient vector modes (VMs) conversion scheme by using Q-plate (QP) and half-waveplate based on higher-order Poincare sphere model. Enabled by this simple mode conversion scheme, we demonstrate a 95.16-Gb/s vector-mode-division-multiplexing (VMDM) transmission with direct-detection orthogonal-frequency-division-multiplexing signal over ∼20-cm free space optical link. The mode crosstalk of four typical cylindrical VMs (TE01, TM01, HE21e, and HE21o) are less than −10.3 dB and can be further optimized by high-quality QP. The experimental results indicate that the VMDM technique can be a powerful candidate for large-capacity short-reach optical interconnects.

Digitalized Geometric Phases for Parallel Optical Spin and Orbital Angular Momentum Encoding

Geometric phases have attracted considerable attention in recent years, due to their capability of arbitrary beam shaping in a most efficient and compact way, while traditional geometric phases are usually limited to handling single-structured beams and lack the capability of parallel manipulation. Here, we propose a digitalized geometric phase enabling parallel optical spin and orbital angular momentum encoding. The concept is demonstrated in inhomogeneous anisotropic media by imprinting a particularly designed binary phase into a space-variant geometric phase. We theoretically analyze its spin–orbit interaction of light and experimentally created higher-order Poincare sphere beam lattices, the order number and symmetry of which can be flexibly manipulated. Special lattices of cylindrical vector beams and orbital angular momentum modes with square and hexagonal symmetry are presented. This work discloses a new insight in programming geometric phases for tailoring the optical field and inspires various ph...

Controlled generation of higher-order Poincaré sphere beams from a laser

The angular momentum of light can be described by positions on a higher-order Poincare sphere, where superpositions of spin and orbital angular momentum states give rise to laser beams that have many applications, from microscopy to materials processing. Many techniques exist to create such beams but none so far allow their creation at the source. Here we report on a new class of laser that is able to generate all states on the higher-order Poincare sphere. We exploit geometric phase control inside a laser cavity to map polarization to orbital angular momentum, demonstrating that the orbital angular momentum degeneracy of a standard laser cavity may be broken, producing pure orbital angular momentum beams, and that generalized vector vortex beams may be created with high purity at the source. This work paves the way to new lasers for structured light based on intracavity geometric phase control. By exploiting geometric phase control inside a laser cavity to map polarization to orbital angular momentum, a new class of laser that is able to generate all states on the higher-order Poincare sphere is reported.