The full vector nature of light provides an additional degree of freedom, namely, the angular momentum (AM) which includes both spin angular momentum (SAM) and orbital angular momentum (OAM). This full AM space holds a great promise for multi-dimensional high capacity data modulation and multiplexing in both classical and quantum regimes, confronting the exploding demands for information. The dynamical generation and control of optical vortices carrying SAM-OAM states mainly rely on tabletop optics. Vortex microlasers offer more compact and robust solution. However, the recently developed vortex microlasers either lack reconfigurability or require extremely low temperature operation environment, limiting the potential real world applications. By harnessing the properties of total angular momentum conservation, spin-orbit interaction and optically controlled non-Hermitian symmetry breaking, we demonstrate an on-chip integrated SAM-OAM-tunable vortex microlaser at room temperature, providing up to 5 different SAM-OAM states at a single telecom wavelength. Moreover, by utilizing fast transient optical gain dynamics in semiconductor materials, we experimentally demonstrate the ultrafast control of fractional OAM emission continuously from 0 to +2 in less than 100 ps. Our toolbox of flexible generation and control of vortex emission at a single wavelength provides a feasible route for the development of the next generation of multi-dimensional high capacity information system in both classical and quantum regimes.
A Weyl semimetal carries topological charges at the Weyl nodes; a light beam can also carry a topological charge, when it has an orbital angular momentum (OAM). Recently there has been a lot of interest in understanding how the spin angular momentum (SAM) of light interacts with materials to induce photocurrents (circular photogalvanic effect, CPGE), but not many studies have focused on photocurrents generated by the OAM of light. Here we report a unique orbital photogalvanic effect (OPGE) in a type-II Weyl semimetal WTe2, featured by a photocurrent winding around the axis of OAM-carrying beams, whose intensity is directly proportional to the topological winding number of the light field, and can be attributed to a discretized dynamical Hall effect. In addition to obtaining evidence of OAM induced electron excitations, our measurements show promise for on-chip detection of the phase of light.
Through systematically manipulating the couplings in the photonic lattice, the topological nature emerges associated with edge state dynamics. Here, we demonstrate a robust photonic zero mode sustained by a spatial non-Hermitian phase transition in a parity-time (PT) symmetric lattice despite the same topological order across the entire system and a flexible topological photonic lattice with multiple topologically nontrivial dispersion bands. Heterodyne measurements clearly reveal the ultrafast transport dynamics and energy of the edge states at a femtosecond scale, validating the designed topological features.
Structured light and structured matter are two fascinating branches of modern optics that recently started having a significant impact on each other. However, integrating structured light, which commonly is created using bulk optics, on miniaturized silicon chips represents a significant challenge. In this talk, we discuss fundamental optical phenomena at the interface of structured light and engineered optical structures, including theoretical and experimental studies of light-matter interactions of vector and singular optical beams in optical metamaterials and microcavities. The synergy of complex beams, such as the beams carrying an orbital angular momentum (OAM), with nanostructured “engineered” media is likely to bring new dimensions to the science and applications of structured light ranging from fundamentally new regimes of spin-orbit interaction to novel ways of information encoding for the future optical communication systems.
We show that unique optical properties of engineered micro- and nanosctructures open unlimited prospects to “engineer” light itself. We discuss several approaches to ultra-compact structured light wavefront shaping using metal-dielectric and all-dielectric resonant metasurfaces. Moreover, by exploiting the emerging non-Hermitian photonics design at an exceptional point, we demonstrate a microring laser generating a single-mode OAM vortex lasing with the ability to precisely define the topological charge of the OAM mode. We show that the polarization associated with OAM lasing can be further manipulated on demand, creating a radially polarized vortex emission. Our OAM microlaser could find applications in the next generation of integrated optoelectronic devices for optical communications in both quantum and classical regimes.
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