Control Of Orbital Angular Momentum Research Articles

Berry-phase-mediated polarization control of orbital angular momentum in microcoil fiber resonators

Berry-phase-mediated polarization control of orbital angular momentum in microcoil fiber resonators

Spatial Full Degree‐Of‐Freedom Scattered Optical Field Modulation

AbstractScattered optical field modulations can enable the function of traditional optical technologies, such as the dynamic holographic display, in a scattering environment. Nonetheless, only part of the degrees of freedom in the optical field can be effectively modulated so far. Here, this work proposes spatial full degree‐of‐freedom scattered optical field modulation (SF‐SOM) to impose a control on the amplitude, phase, and polarization of the optical field. To do so, this method independently modulates the complex amplitude of two orthogonally polarized components. It also contains a full degree‐of‐freedom vector transmission matrix model to describe the transformation from the incident field to the scattered field. Compared with the single degree‐of‐freedom modulation methods against the same scattering environment, SF‐SOM increases the contrast of focus by a factor of five. Furthermore, the experiments demonstrate a holographic display and orbital angular momentum control with SF‐SOM to show its ubiquitous utility in optics.

Structured light transformations and orbital angular momentum control in a three-coil optical snake

In this paper, we studied transformations of structured light and its angular momentum in a three-coil optical snake – a coil resonator composed of 3 evanescently uniformly coupled coils of a multimode fiber. We have suggested a fully vectorial theory of normal modes of the 3-coil resona-tor, which takes account of the spin-orbit interaction. On the basis of the analytical expressions for such normal modes and their propagation constants we have studied transmission of some types of structured light beams – optical vortices, Hermite-Gaussian-like and Laguerre-Gaussian beams – through such a system. We have shown the possibility of a super-efficient parametric control over the topological charge, orbital and spin angular momenta of the outcoming optical field by this system. We have theoretically demonstrated implementation of logic X and Y Pauli gates for light beams carrying orbital angular momentum on the basis of such a 3-coil resonator.

Control of orbital angular momentum of optical vortex beams with complex wandering perturbations.

This work investigates how independent perturbations and cross-correlation perturbations affect optical vortex beams. Theoretical and experimental results show that both perturbations cause the intensity, average orbital angular momentum (OAM), and the OAM spectrum of the vortex beam to vary periodically with the perturbation direction, but with different periods. When the beam is subjected to independent perturbations, the average OAM changes periodically with θ in every π/2; when the beam is subjected to cross-correlation perturbations, the average OAM varies with θ in every π. The results of this work provide a method to control the OAM and regulate low-coherence vortex beams in turbulent environments.

Synthetic ultrawideband orbital angular momentum radar

Control of orbital angular momentum (OAM) offers the potential for increases in control and sensitivity for high-performance microwave systems. EM waves with properties dependent on spatial distribution are said to be “structured.” Control of OAM in microwave systems is an example of a wave structure that exploits EM degrees of freedom, which most conventional systems do not use. OAM is characterized by an integer OAM mode in which zero represents the case of a plane wave and nonzero OAM modes propagate with a helical wavefront. A uniform circular phased array approach is utilized to produce helix-shaped OAM wavefronts. This method offers a critical advantage over common fixed-frequency dielectric lenses; the phases of all antenna elements are programmable across a wide frequency range, which is necessary for ultrawideband (UWB) radar imaging. Simulations and laboratory experiments are performed to determine the requirements and capabilities of an UWB OAM radar that uses the circular phased array approach. Key results include OAM phase front characterization, detection of specified OAM modes, and configuration of a network analyzer UWB radar with synthetic OAM mode-control via signal post-processing.

Spin-constrained orbital-angular-momentum control in high-harmonic generation

The interplay between spin and orbital angular momentum in the up-conversion process allows us to control the macroscopic wave front of high harmonics by manipulating the microscopic polarizations of the driving field. We demonstrate control of orbital angular momentum in high harmonic generation from both solid and gas phase targets using the selection rules of spin angular momentum. The gas phase harmonics extend the control of angular momentum to extreme-ultraviolet wavelength. We also propose a bi-color scheme to produce spectrally separated extreme-ultraviolet radiation carrying orbital angular momentum.

Single-step shaping of the orbital angular momentum spectrum of light.

Control of orbital angular momentum (OAM) in optical fields has seen tremendous growth of late, with a myriad of tools existing for their creation and detection. What has been lacking is the ability to arbitrarily modify the OAM spectrum of a superposition in amplitude and phase, especially if a priori knowledge of the initial OAM spectrum is absent. Motivated by a quasi-mapping that exists between the position and OAM of Laguerre-Gaussian modes, we propose an approach for a single-step modulation of a field's OAM spectrum. We outline the concept and implement it through the use of binary ring apertures encoded on spatial light modulators. We show that complete control of the OAM spectrum is achievable in a single step, fostering applications in classical and quantum information processing that utilise the OAM basis.

Control of orbital angular momentum with partially coherent vortex beams.

We investigate the orbital angular momentum of partially coherent beams which are constructed by a superposition of mutually incoherent vortex modes, each mode having a different beam width and topological charge. It is shown that these simple beams nevertheless provide great flexibility in controlling orbital angular momentum through adjustment of the beam parameters and have significant potential for particle rotation and trapping.

Control of orbital angular momentum of light in optofluidic infiltrated circular photonic crystal fibers

Orbital angular momentum (OAM) of light has been of great interest to enhance the data transmission capacity in optical communication systems. In this regards, new designs of optical fibers have been developed to transmit OAM modes. Circular photonic crystal fibers (C-PCFs) with an air-core in the center are good candidates for guiding OAM of light. By changing the geometrical parameters of the C-PCFs, one can control the topological charge (l) associated with OAM order. However, practically it is of significant interest to keep the geometrical parameters fixed and control the OAM characteristics by introducing optical fluid into the C-PCF. Therefore, in this paper, we propose for the first time controlling OAM characteristics such as l, dispersion and confinement loss based on optofluidic infiltrated C-PCFs. To this end, optofluidics with various refractive indices are introduced into the first ring of air holes in the cladding and mode characteristics are compared with those of uninfiltrated C-PCF. The results show that the OAM modes can be well controlled in optofluidic-infiltrated C-PCFs over the wavelength range of 1.25–2.0μm with good dispersion and loss characteristics. Also, the dispersion curve can be flattened when an optical fluid with a proper refractive index is infiltrated into the C-PCF.

Simultaneous control of orbital angular momentum and beam profile in two-mode polarization-maintaining fiber.

We report simultaneous control of the orbital angular momentum (OAM) and beam profile of vortex beams generated in two-mode polarization-maintaining optical fiber. Two higher-order eigenmodes of the fiber are combined to form optical vortices. Reduced coherence between the fiber modes decreases the mode purity. Varying the coherence of the fiber modes changes the average OAM while maintaining a constant annular intensity profile. Additionally, a donut mode has been shown to be insensitive to bends and twists in the fiber.

Orbital angular momentum control by a multihelicoidal fibre with a twist defect

We have theoretically demonstrated that by creating a controllable twist defect in an l-helicoidal fibre one can control the orbital angular momentum of the generated beam at a constant power. We have studied the passage of the Gaussian beam through such a defect fibre and shown that by varying the twist defect angle one can change the total orbital angular momentum of the generated optical field from 0 to l (in dimensionless units). We have also studied the distribution of the angular momentum density in the cross-section of the generated optical field.

Control of orbital angular momentum of light with optical fibers

We present a fiber-based method for generating vortex beams with a tunable value of orbital angular momentum from -1ℏ to +1ℏ per photon. We propose a new (to our knowledge) method to determine the modal content of the fiber and demonstrate high purity of the desired vortex state (97% after 20 m, even after bends and twists). This method has immediate utility for the multitude of applications in science and technology that exploit vortex light states.