Nanophotonic Materials for Twisted-Light Manipulation

Constructing a Comprehensive Nanopattern Library through Morphological Transitions of Block Copolymer Surface Micelles via Direct Solvent Immersion

This study establishes a comprehensive library of nanopatterns achievable by a single block copolymer (BCP), ranging from spheres to complex structures like split micelles, flower-like clusters, toroids, disordered micelle arrays, and unspecified unique shapes. The ordinary nanostructures of polystyrene-b-poly(2-vinylpyridine) (PS-b-P2VP) surface micelles deposited on a SiOx surface undergo a unique morphology transformation when immersed directly in solvents. Investigating parameters such as immersion solvents, BCP molecular weight, substrate interactions, and temperature, this work reveals the influence of these parameters on the thermodynamics and kinetics governing the morphology transformation. Additionally, the practical application of BCP nanopattern templates for fabricating metal nanostructures through direct solvent immersion of surface micelles is demonstrated. This approach offers an efficient and effective method for producing diverse nanostructures, with the potential to be employed in nanolithography, catalysts, electronics, membranes, plasmonics, and photonics.

Self-Assembly for Creating Vertically-Aligned Graphene Micro Helices with Monolayer Graphene as Chiral Metamaterials

Graphene's emergence enables creating chiral metamaterials in helical shapes for terahertz (THz) applications, overcoming material limitations. However, practical implementation remains theoretical due to fabrication challenges. This paper introduces a dual-component self-assembly technique that enables creating vertically-aligned continuous monolayer graphene helices at microscale with great flexibility and high controllability. This assembly process not only facilitates the creation of 3D microstructures, but also positions the 3D structures from a horizontal to a vertical orientation, achieving an aspect ratio (height/width) of ≈2700. As a result, an array of vertically-aligned graphene helices is formed, reaching up to 4 mm in height, which is equivalent to 4 million times the height of monolayer graphene. The benefit of these 3D chiral structures made from graphene is their capability to infinitely extend in height, interacting with light in ways that are not possible with traditional 2D layering methods. Such an impressive height elevates a level of interaction with light that far surpasses what is achievable with traditional 2D layering methods, resulting in a notable enhancement of optical chirality properties. This approach is applicable to various 2D materials, promising advancements in innovative research and diverse applications across fields.

On-chip photodetection of angular momentums of vortex structured light

Structured vortex light with orbital angular momentum (OAM) shows great promise for high-bandwidth optical communications, quantum information and computing, optical tweezers, microscopy, astronomy, among others. Generating, controlling, and detecting of vortex light by all-electrical means is at the heart of next generation nanophotonic platforms. However, on-chip electrical photodetection of structured vortex light remains challenging. Here, we propose an on-chip photodetector based on 2D broadband thermoelectric material (PdSe2) with a well-designed spin-Hall couplers to directly characterize angular momentum modes of vortex structured light. Photothermoelectric responses in the PdSe2 nanoflake, excited by the focusing surface plasmons, show a magnitude proportional to the total angular momentum modes of the infrared vortex beams, thereby achieving direct detection of spin and orbital angular momentum, as well as the chirality and ellipticity of scalar vortex lights. Our works provide a promising strategy for developing on-chip angular momentum optoelectronic devices, which play a key role in the next-generation high-capacity optical communications, quantum information and computing, imaging, and other photonic systems.

Multiplexed manipulation of orbital angular momentum and wavelength in metasurfaces based on arbitrary complex-amplitude control

Due to its unbounded and orthogonal modes, the orbital angular momentum (OAM) is regarded as a key optical degree of freedom (DoF) for future information processing with ultra-high capacity and speed. Although the manipulation of OAM based on metasurfaces has brought about great achievements in various fields, such manipulation currently remains at single-DoF level, which means the multiplexed manipulation of OAM with other optical DoFs is still lacking, greatly hampering the application of OAM beams and advancement of metasurfaces. In order to overcome this challenge, we propose the idea of multiplexed coherent pixel (MCP) for metasurfaces. This approach enables the manipulation of arbitrary complex-amplitude under incident lights of both plane and OAM waves, on the basis of which we have realized the multiplexed DoF control of OAM and wavelength. As a result, the MCP method expands the types of incident lights which can be simultaneously responded by metasurfaces, enriches the information processing capability of metasurfaces, and creates applications of information encryption and OAM demultiplexer. Our findings not only provide means for the design of high-security and high-capacity metasurfaces, but also raise the control and application level of OAM, offering great potential for multifunctional nanophotonic devices in the future.

Nonlinear Boost of Optical Angular Momentum Selectivity by Hybrid Nanolaser Circuits

Selective control of light is essential for optical science and technology, with numerous applications. However, optical selectivity in the angular momentum of light has been quite limited, remaining constant by increasing the incident light power on previous passive optical devices. Here, we demonstrate a nonlinear boost of optical selectivity in both the spin and orbital angular momentum of light through near-field selective excitation of single-mode nanolasers. Our designed hybrid nanolaser circuits consist of plasmonic metasurfaces and individually placed perovskite nanowires, enabling subwavelength focusing of angular-momentum-distinctive plasmonic fields and further selective excitation of nanolasers in nanowires. The optically selected nanolaser with a nonlinear increase of light emission greatly enhances the baseline optical selectivity offered by the metasurface from about 0.4 up to near unity. Our demonstrated hybrid nanophotonic platform may find important applications in all-optical logic gates and nanowire networks, ultrafast optical switches, nanophotonic detectors, and on-chip optical and quantum information processing.

Metafiber transforming arbitrarily structured light

Structured light has proven useful for numerous photonic applications. However, the current use of structured light in optical fiber science and technology is severely limited by mode mixing or by the lack of optical elements that can be integrated onto fiber end-faces for wavefront engineering, and hence generation of structured light is still handled outside the fiber via bulky optics in free space. We report a metafiber platform capable of creating arbitrarily structured light on the hybrid-order Poincaré sphere. Polymeric metasurfaces, with unleashed height degree of freedom and a greatly expanded 3D meta-atom library, were 3D laser nanoprinted and interfaced with polarization-maintaining single-mode fibers. Multiple metasurfaces were interfaced on the fiber end-faces, transforming the fiber output into different structured-light fields, including cylindrical vector beams, circularly polarized vortex beams, and arbitrary vector field. Our work provides a paradigm for advancing optical fiber science and technology towards fiber-integrated light shaping, which may find important applications in fiber communications, fiber lasers and sensors, endoscopic imaging, fiber lithography, and lab-on-fiber technology.

Multichannel Quantum Emission with On-Chip Emitter-Coupled Holographic Metasurfaces

Multichannel quantum emission is in high demand for advanced quantum photonic applications such as quantum communications, quantum computing, and quantum cryptography. However, to date, the most common way for shaping photon emission from quantum emitters (QEs) is to utilize free-standing (external) bulky optical components. Here, we develop the multichannel holography approach for flexibly designing on-chip QE-coupled metasurfaces that make use of nonradiatively QE-excited surface plasmon polaritons for generating far-field quantum emission, which propagates in designed directions carrying specific spin and orbital angular momenta (SAM and OAM, respectively). We further design, fabricate, and characterize on-chip quantum light sources of multichannel quantum emission encoded with different SAMs and OAMs. The holography-based inverse design approach developed and demonstrated on-chip quantum light sources with multiple degrees of freedoms, thereby enabling a powerful platform for quantum nanophotonics, especially relevant for advanced quantum photonic applications, e.g., high-dimensional quantum information processing.

Dynamic control of hybrid grafted perfect vector vortex beams

Perfect vector vortex beams (PVVBs) have attracted considerable interest due to their peculiar optical features. PVVBs are typically generated through the superposition of perfect vortex beams, which suffer from the limited number of topological charges (TCs). Furthermore, dynamic control of PVVBs is desirable and has not been reported. We propose and experimentally demonstrate hybrid grafted perfect vector vortex beams (GPVVBs) and their dynamic control. Hybrid GPVVBs are generated through the superposition of grafted perfect vortex beams with a multifunctional metasurface. The generated hybrid GPVVBs possess spatially variant rates of polarization change due to the involvement of more TCs. Each hybrid GPVVB includes different GPVVBs in the same beam, adding more design flexibility. Moreover, these beams are dynamically controlled with a rotating half waveplate. The generated dynamic GPVVBs may find applications in the fields where dynamic control is in high demand, including optical encryption, dense data communication, and multiple particle manipulation.

Organic Synthetic Photonic Systems with Reconfigurable Parity-Time Symmetry Breaking for Tunable Single-Mode Microlasers

Synthetic photonic materials exploiting the quantum concept of parity-time (PT) symmetry lead to an emerging photonic paradigm-non-Hermitian photonics, which is revolutionizing the photonic sciences. The non-Hermitian photonics dealing with the interplay between gain and loss in PT synthetic photonic material systems offers a versatile platform for advancing microlaser technology. However, current PT-symmetric microcavity laser systems only manipulate imaginary parts of the refractive indices, suffering from limited laser spectral bandwidth. Here, an organic composite material system is proposed to synthesize reconfigurable PT-symmetric microcavities with controllable complex refractive indices for realizing tunable single-mode laser outputs. A grayscale electron-beam direct-writing technique is elaborately designed to process laser dye-doped polymer films in one single step into microdisk cavities with periodic gain and loss distribution, which enables thresholdless PT-symmetry breaking and single-mode laser operation. Furthermore, organic photoisomerizable compounds are introduced to reconfigure the PT-symmetric systems in real-time by tailoring the real refractive index of the polymer microresonators, allowing for a dynamically and continuously tunable single-mode laser output. This work fundamentally enhances the PT-symmetric photonic systems for innovative design of synthetic photonic materials and architectures.

Polarization-directed growth of spiral nanostructures by laser direct writing with vector beams

Chirality is pivotal in nature which attracts wide research interests from all disciplines and creating chiral matter is one of the central themes for chemists and material scientists. Despite of significant efforts, a simple, cost-effective and general method that can produce different kinds of chiral metamaterials with high regularity and tailorability is still demanding but greatly missing. Here, we introduce polarization-directed growth of spiral nanostructures via vector beams, which is simple, tailorable and generally applicable to both plasmonic and dielectric materials. The self-aligned near field enhances the photochemical growth along the polarization, which is crucial for the oriented growth. The obtained plasmonic chiral nanostructures present prominent optical activity with a g-factor up to 0.4, which can be tuned by adjusting the spirality of the vector beams. These spiral plasmonic nanostructures can be used for the sensing of different chiral enantiomers. The dielectric chiral metasurfaces can also be formed in arrays of sub-mm scale, which exhibit a g-factor over 0.1. However, photoluminescence of chiral cadmium sulfide presents a very weak luminescence g-factor with the excitation of linearly polarized light. A number of applications can be envisioned with these chiral nanostructures such as chiral sensing, chiral separation and chiral information storage.

Planar Optical Cavities Hybridized with Low-Dimensional Light-Emitting Materials

Low-dimensional light-emitting materials have been actively investigated due to their unprecedented optical and optoelectronic properties that are not observed in their bulk forms. However, the emission from low-dimensional light-emitting materials is generally weak and difficult to use in nanophotonic devices without being amplified and engineered by optical cavities. Along with studies on various planar optical cavities over the last decade, the physics of cavity-emitter interactions as well as various integration methods are investigated deeply. These integrations not only enhance the light-matter interaction of the emitters, but also provide opportunities for realizing nanophotonic devices based on the new physics allowed by low-dimensional emitters. In this review, the fundamentals, strengths and weaknesses of various planar optical resonators are first provided. Then, commonly used low-dimensional light-emitting materials such as 0D emitters (quantum dots and upconversion nanoparticles) and 2D emitters (transition-metal dichalcogenide and hexagonal boron nitride) are discussed. The integration of these emitters and cavities and the expect interplay between them are explained in the following chapters. Finally, a comprehensive discussion and outlook of nanoscale cavity-emitter integrated systems is provided.

Smart Modulators Based on Electric Field-Triggering of Surface Plasmon-Polariton for Active Plasmonics

Design and properties of a plasmonic modulator in situ tunable by electric field are presented. Our design comprises the creation of periodic surface pattern on the surface of an elastic polymer supported by a piezo-substrate by excimer laser irradiation and subsequent selective coverage by silver by tilted angle vacuum evaporation. The structure creation was confirmed by AFM and FIB-SEM techniques. An external electric field is used for fine control of the polymer pattern amplitude, which tends to decrease with increasing voltage. As a result, surface plasmon-polariton excitation is quenched, leading to the less pronounced structure of plasmon response. This quenching was checked using UV-Vis spectroscopy and SERS measurements, and confirmed by numerical simulation. All methods prove the proposed functionality of the structures enabling the creation smart plasmonic materials for a very broad range of advanced optical applications.

Terahertz quasi non-diffraction Bessel vortex beam generation using three lattice types reflective metasurface

Bandwidth, orbital-angular momentum (OAM) divergence, and mode purity are the three critical issues for the practical terahertz orbital angular momentum manipulation, especially in the next sixth-generation (6G) communication system. Here we propose the broadband high-order Bessel vortex beam carrying multiple OAM modes reflective metasurface in the terahertz domain. The simulation results agree with the theoretical expectation, and the diffracting divergence of OAM vortex beam characteristics has been alleviated. The research on the relationship between the varieties of lattice type and mode purity is also relatively scarce. Henceforth, a comparison study has been conducted between three lattice types, i.e., square lattice, triangular lattice, and concentric ring lattice. And corresponding results of the relationship of mode purity with those lattice types show that the concentric ring lattice has the best performance.

Towards higher-dimensional structured light

Structured light refers to the arbitrarily tailoring of optical fields in all their degrees of freedom (DoFs), from spatial to temporal. Although orbital angular momentum (OAM) is perhaps the most topical example, and celebrating 30 years since its connection to the spatial structure of light, control over other DoFs is slowly gaining traction, promising access to higher-dimensional forms of structured light. Nevertheless, harnessing these new DoFs in quantum and classical states remains challenging, with the toolkit still in its infancy. In this perspective, we discuss methods, challenges, and opportunities for the creation, detection, and control of multiple DoFs for higher-dimensional structured light. We present a roadmap for future development trends, from fundamental research to applications, concentrating on the potential for larger-capacity, higher-security information processing and communication, and beyond.