Multifunctional Optical Devices Research Articles

Dielectric metasurface Fresnel zone plates for polarization conversion

Abstract Conventional Fresnel zone plates (FZPs) can only achieve a single focusing function and require the combination with other optical elements to achieve multiple optical functions. This contradicts the development trends for miniaturized, integrated and multifunctional optical devices. However, the emergence of metasurfaces offers new solutions for this problem. In this paper, we design two different types of multifunctional metasurface Fresnel zone plates (MFZPs). One is based on amplitude modulation, and the other is based on phase modulation, both of which can achieve linear polarization conversion and focusing functions. The realization of these functions is based on the ability of silicon diatomic nanopillars to decouple and control the amplitude, phase, and polarization of electromagnetic waves. The designed ultrathin dielectric metasurface effectively combines the functions of conventional half-wave plates and FZPs, thereby reducing the volume of the optical system. The designed MFZPs have enormous potential for application in integrated and compact optical systems.

Wavelength and spin-decoupled metasurface based on single-parameter modulation.

Metasurfaces provide an unprecedented platform for precise and subwavelength-scale modulation of optical phases, leading to innovative advancements in wavefront shaping and holography devices. This study presents a single-layer umbrella-like metasurface capable of multichannel holography, encoded with both polarization and wavelength. By leveraging a unique chiral-assisted strategy, we achieve simultaneous decoupling of wavelength and spin states through single-parameter modulation. This approach circumvents the complex structure designs and multi-parameter adjustments typically required in previous methods. Numerical simulations confirm the effectiveness of this metasurface, demonstrating wavelength- and spin-decoupled phase modulation at 1550 and 980 nm. Furthermore, we successfully demonstrate a four-channel hologram operable in both transmission and reflection modes, showcasing the potential applications of this metasurface in compact functional integration, information encryption, and 3D displays. This work paves the way for the development of multifunctional optical devices with enhanced integration and performance.

Full-space metasurfaces for independent manipulation of transmission and reflection.

In recent years, beam manipulation using metasurfaces has evolved from being limited to either a transmission or reflection space to encompassing a full space. However, existing methods still inevitably require complex systems and are unable to achieve continuous and arbitrary phase manipulation. Here, one type of a bilayer metasurface is proposed to simultaneously manipulate reflection and transmission phases continuously and independently, which also makes the optical system more compact without requiring any analyzers and enhances the degree of freedom for full-space beam manipulation. As a proof-of-concept demonstration, one device is designed to show different holograms in transmission and reflection spaces. Additionally, the Dammann grating designed in the reflection hologram increases the information capacity. The proposed method may pave the way toward achieving a variety of applications such as multi-channel beam manipulation and multifunctional optical devices.

Non-interleaved quad-channel metasurfaces for simultaneous nanoprinting and holography enabled by phase and bidirectional intensity modulation

Metasurfaces, with their unparalleled ability to manipulate light-field characteristics, have brought forth numerous advantages in ultra-compact and high-resolution image displays, particularly in multifunctional metadevices for simultaneous nanoprinting and holography. However, current efforts are hindered by challenges such as increased fabrication complexity, low efficiencies, or being confined to classic two/three-channel configurations, limiting their further applications. In this study, we propose a single-cell non-interleaved metasurface platform capable of simultaneously and independently generating two holographic images in the far field and two nanoprinting images in the near field. Through a spin-decoupled phase modulation, the metasurface can produce two far-field holographic images under orthogonal circularly polarized incidences. By fully unlocking the Malus's law-assisted bidirectional intensity modulation, the metasurface enables the reconstruction of two near-field nanoprinting images with two distinct orthogonal polarization optical setups as decoding keys. Moreover, the quad-channel metasurface we proposed exhibits broadband response and on-off binary switching performance enabled by the phase transition of Ge2Sb2Se4Te1. We envision that the proposed design paradigm opens up new possibilities for expanding the functionality and enhancing the capacity of metasurfaces without burdening their design, thereby paving the way for compact multifunctional optical devices in image display, information encoding, anti-counterfeiting, and other related fields.

Anisotropic van der Waals Tellurene-Based Multifunctional, Polarization-Sensitive, In-Line Optical Device.

Polarization plays a paramount role in scaling the optical network capacity. Anisotropic two-dimensional (2D) materials offer opportunities to exploit optical polarization-sensitive responses in various photonic and optoelectronic applications. However, the exploration of optical anisotropy in fiber in-line devices, critical for ultrafast pulse generation and modulation, remains limited. In this study, we present a fiber-integrated device based on a single-crystalline tellurene nanosheet. Benefiting from the chiral-chain crystal lattice and distinct optical dichroism of tellurene, multifunctional optical devices possessing diverse excellent properties can be achieved. By inserting the in-line device into a 1.5 μm fiber laser cavity, we generated both linearly polarized and dual-wavelength mode-locking pulses with a degree of polarization of 98% and exceptional long-term stability. Through a twisted configuration of two tellurene nanosheets, we realized an all-optical switching operation with a fast response. The multifunctional device also serves as a broadband photodetector. Notably, bipolar polarization encoding communication at 1550 nm can be achieved without any external voltage. The device's multifunctionality and stability in ambient environments established a promising prototype for integrating polarization as an additional physical dimension in fiber optical networks, encompassing diverse applications in light generation, modulation, and detection.

Dual-band high quality-factor perfect absorber based on uniaxial/biaxial anisotropic van der Waals polar crystals

Phonon polaritons (PhPs) in two-dimensional van der Waals crystals, such as hexagonal boron nitride (hBN) and α-phase molybdenum trioxide (α-MoO3), exhibit remarkable spatial confinement and extremely low optical losses, offering possibilities for the development of novel micro and nanophotonic devices at mid-infrared wavelengths. Here, we demonstrate the potential of the proposed Tamm structure to achieve dual-band high quality-factor perfect absorption within the mid-infrared range. This structure utilizes upper and lower spacer layers to isolate the anisotropic materials hBN and α-MoO3 from one-dimensional photonic crystals, where the Tamm phonon polaritons (TPhPs) are respectively excited at the interfaces, facilitating strong coupling with incident light and leading to significant dual-band perfect absorption phenomena. The results demonstrate that due to polariton resonances, the absorption peaks exhibit extremely narrow absorption bandwidths, with the maximum quality-factor reaching up to 297. In addition, tunable resonant wavelengths and polarization-dependent absorption properties are also demonstrated in the proposed Tamm structure. This study provides an alternative and straightforward approach for constructing dynamic and multifunctional optical devices such as optical modulators, tunable multi-band filters and biosensors.

Twist-Angle-Controlled Nonlinear Circular Dichroism on Gold-Crystal Hybrid Metasurfaces.

Optical chirality, which plays important roles in liquid crystal display and biological and chemical detection, has been attracting scientists' attention due to its potential applications in optical information processing. Usually, the chiral optical response of natural molecules is very weak. However, the emergence of metasurfaces offers a promising solution to solve this issue. By judiciously designing the geometry of meta-atoms, we have realized strong optical circular dichroism (CD) in both linear and nonlinear optical regimes. However, tuning of the CD with a metasurface remains challenging. Here, we propose the twist-angle-controlled nonlinear CD effect by using the second-harmonic generation process on a gold-crystal hybrid metasurface. The CD effect of the second-harmonic waves can be tuned well by controlling the twist angle between the two constituent materials. The proposed hybrid metasurface may open new avenues for developing ultracompact and multifunctional nonlinear optical devices.

Design and time-domain finite element simulation of multi-functional transformation optical device

In this paper, we first proposed mathematical model equations for wave propagation in a multi-functional transformation optical device, namely, an electromagnetic rotation concentrator. This device can concentrate electromagnetic energy while rotating electromagnetic waves. We also demonstrate the stability of the model equation in the continuous case. Next, we designed the multi-functional device with multiple layers. We then proposed a time-domain finite element method for simulating wave propagation in this device and conducted a stability analysis of the model equations in the discrete case. Finally, we implemented the proposed algorithm and obtained numerous numerical results that demonstrate the validity of our model equations. To the best of our knowledge, this is the first work on time-domain modeling and analysis of multi-functional electromagnetic devices.

Dual‐Layer Metasurface Enhanced Capacity of Polarization Multiplexing

AbstractPolarization is the nature of optics. Exploiting metasurface's polarizations can enhance the multiplexing capacity but face a limited number of channels. For example, a single‐layer metasurface can offer three independent channels with six degrees of freedom (DoFs) including the amplitude and phase of Ex, Exy(yx), and Ey of the Jones matrix. In this work, it is theoretically demonstrated that the degrees of freedom of dual‐layer metasurfaces can reach eight, overcoming the polarization multiplexing constraints of single‐layer metasurfaces and that the cross‐talk can be largely reduced as compared with single‐layer metasurfaces when the channel number is larger than three. Numerical calculations manifest a decrease of 100%, 63%, and 50% for the cross‐talk of channels 4, 5, and 6, respectively. As a proof‐of‐concept demonstration of high‐capacity polarization multiplexing, an arbitrary‐polarization‐controlled 5‐channel dual‐layer metasurface exhibiting five nanoprintings and five holographic images with reduced cross‐talk under different incident and output polarizations is successfully designed. Thus, the research highlighting the high‐multiplexing‐capacity of dual‐layer metasurfaces can significantly advance multifunctional optical devices with high efficiency, simple integration, and ease of manipulation.

Giant and controllable nonlinear magneto-optical effects in two-dimensional magnets

The interplay of polarization and magnetism in materials with light can create rich nonlinear magneto-optical (NLMO) effects, and the recent discovery of two-dimensional (2D) van der Waals magnets provides remarkable control over NLMO effects due to their superb tunability. Here, based on first-principles calculations, we reported giant NLMO effects in CrI3-based 2D magnets, including a dramatic change of second-harmonics generation (SHG) polarization direction (90°) and intensity (on/off switch) under magnetization reversal and a 100% SHG circular dichroism effect. We further revealed that these effects could not only be used to design ultra-thin multifunctional optical devices but also to detect subtle magnetic orderings. Remarkably, we analytically derived conditions to achieve giant NLMO effects and proposed general strategies to realize them in 2D magnets. Our work not only uncovers a series of intriguing NLMO phenomena but also paves the way for both fundamental research and device applications of ultra-thin NLMO materials.

Metasurfaces enabled dual-channel complex-amplitude hologram designed with neural network

In this work we present a polarization-multiplexing metasurface hologram designed with neural network, which can modulate the amplitude and phase of incident light with four nanopillars comprised unit structures with high efficiency. Then, to improve image quality by minimizing the difference between the complex amplitude field modulated by the structure and that obtained through the network, we developed an end-to-end framework-assisted multifunctional metasurface design method based on the aforementioned neural network, which can directly map geometric parameters of the metasurface to holographic images. The comparative results indicate that for the end-to-end framework, although the optimized distributions of complex amplitudes are limited by the selected finite number of structures, in the simulation results, higher-quality images can still be obtained compared to the forward design method. Full-wave simulation results show our proposed method can obtain higher quality holographic images compared to the GS algorithm. This work may open new possibilities in holographic displays and multifunctional optical devices.

Spin Unlocked Vortex Beam Generation on Nonlinear Chiroptical Metasurfaces.

Optical vortices with spin and orbital angular momentum (SAM and OAM) states offer multiple degrees of freedom for manipulating optical fields and thus enable great potentials in optical information processing. Recently, the optical metasurface has become an important platform for vortex beam generation and steering. However, the strong spin-orbit interaction on such metasurfaces usually leads to spin locked OAM generation, which limits the complete control of the angular momentum state of light. Here, we propose to solve this constraint using geometric phase controlled nonlinear chiroptical metasurfaces. The metasurface consists of two types of plasmonic meta-atoms which have opposite handedness and exhibit a strong spin-dependent circular dichroism effect. By encoding specific phase singularities and phase gradients to different channels, we experimentally demonstrate the spin unlocked second harmonic beam steering. The proposed nonlinear chiroptical metasurfaces may have important applications in developing multifunctional nonlinear optical devices.

Multifunctional optical logic device based on nanoscale rectangular ring resonator

Integrated optical logic devices are essential building blocks for implementing all-optical arithmetic and logic unit. In this paper, an ultra-compact multifunctional optical logic device consisting of a rectangular ring resonator coupled with two parallel metal–insulator–metal waveguides is presented. The transmission characteristics of the structure are analyzed in detail via temporal coupled-mode theory. The finite-difference time-domain simulation results reveal that multiple logic functions can be implemented with the aid of the wavelength division multiplexing technique at different output ports. Specifically, all seven basic types of logic gates, half-adder, half-subtractor, and 2*4 decoder can be implemented by monitoring the transmission of through and drop ports at different wavelengths. More importantly, among these functions, six logic gates (OR, XNOR, NAND, NOR, XOR, and AND) and half-adder functions can be performed simultaneously; the NOT logic operation is performed with controllable output ports and selectable working wavelengths; the half-subtractor and 2*4 decoder functions can be operated simultaneously. The proposed logic device is characterized by a small area overhead, multifunctionality, fast response time, and ultrahigh-speed information processing. It may potentially be applied in on-chip universal and parallel photonic computing units.

Alkaline-earth metal sulfide nanocrystals embedded in oxysulfide glasses

As a wide band gap semiconductor, alkaline-earth metal sulfides (AES) with low phonon energy, high laser damage threshold, and high transmittance in infrared, have wide application prospects in bioimaging, spectral conversion, and solid-state lighting. However, AES nanocrystals (NCs) suffer from the weak chemical-stability and low mechanical-stability, and can be easily oxidized in humidity and oxygen. Incorporation of AES NCs into inorganic glass is expected to overcome those inherent limitations. In this work, a new type of oxysulfide glass-ceramics containing CaS, SrS, BaS, SrxBa1−xS, and CaxSr1−xS NCs is developed, and average diameters of these AES NCs are tuned in the range of 3–18 nm. Precipitation of AES NCs not only improves the mechanical properties of glass, but also maintains high transmittance (˃60%) in the spectral range of 1–4.3 µm. Results reported in this work offer a new pathway for developing novel oxysulfide glass-ceramics for multi-functional optical devices.

Multiple High‐Q Optical Modes in a Polymer‐Lithium Niobate Integrated Metasurface

AbstractWith the development of miniaturization and integration, multifunctional optical devices are necessary. However, its practical realization is a critical challenge due to the lack of simple structures with multiple functionalities. Here, a multimode metasurface is proposed by simply placing polymer nanocubes on the lithium niobate (LN) thin film. The intriguing properties of the integrated structure include high‐quality (Q) factors and different spectral characteristics, associated with quasi‐guide modes (GM) and Mie modes, respectively. The experiment demonstration reveals that Q factors of four modes are larger than 1000 and a second harmonic generation (SHG) enhancement factor of 25.4 is obtained, featuring strong light‐matter interaction. Importantly, the abundant spectral characteristics greatly boost three degrees of freedom, i.e., polarization, incident angle, and slot, to realize multifunctional designs. The results provide a sophisticated platform for developing high‐performance LN metasurfaces with the advantages of simplified fabrication processes and multifunctionality. The strategy can also be extended to other material systems, enabling the flexibility of metasurface‐inspired subwavelength engineering.

Polychromatic Dual-Mode Imaging with Structured Chiral Photonic Crystals.

Optical spatial differentiation is a typical operation of optical analog computing and can single out the edge to accelerate the subsequent image processing, but in some cases, overall information about the object needs to be presented synchronously. Here, we propose a multifunctional optical device based on structured chiral photonic crystals for the simultaneous realization of real-time dual-mode imaging. This optical differentiator is realized by self-organized large-birefringence cholesteric liquid crystals, which are photopatterned to encode with a special integrated geometric phase. Two highly spin-selective modes of second-order spatial differentiation and bright-field imaging are exhibited in the reflected and transmitted directions, respectively. Two-dimensional edges of both amplitude and phase objects have been efficiently enhanced in high contrast and the broadband spectrum. This work extends the ingenious building of hierarchical chiral nanostructures, enriches their applications in the emerging frontiers of optical computing, and boasts considerable potential in machine vision and microscopy.

Opto‐Mechano‐Thermo‐Sensitive Allochroic Luminescence Based on Solution‐Grown Halide Double Perovskite Crystal

AbstractMultimode luminescence generally exhibits tunable photon emission through multidimensional stimuli, demonstrating high‐throughput and facile identification for anticounterfeiting and encryption. Nevertheless, producing multimodal luminescent materials through low‐temperature treatment remains a challenge. Herein, the Mn2+/Er3+ co‐doped Cs2Ag0.8Na0.2InCl6 perovskite material (reaction temperature of 180 °C) achieves long‐persistent luminescence, multicolor luminescence, and upconversion emission by responding to several types of excitations ranging from UV to NIR and mechanical force. The adjustable energy transfer process between self‐trapped excitons (STE) and Mn2+ ions achieves multicolor luminescence with temperatures ranging from 97 to 397 K. Theoretical calculation reveals that the important role of Mn2+ dopants and Na+ dopants in the modulation of local electronic environments and the afterglow emission comes from carriers escaping from the trap center (primarily caused by Cl vacancy and interstitial Na) to the local emission center (Mn2+ ions). This integrated multimodal luminescent material provides a novel direction for the development of multifunctional optical materials and devices.

The realization of the nanoscale bar-codes based on CdS branched nanostructure

The nanostructures with controllable emission colors have shown great attention for achieving high throughput sensing, anti-counterfeiting, and information security. Here, a branched CdS nanostructure with Sn nanoparticles implanted in the junctions is proposed to construct lateral photonic barcodes in a two dimensional domain. Due to the encapsulated Sn nanoparticles, the plasmon enhanced photoluminescence is practically observed. However, with the generation of the high-energy electrons under illumination of the electron beam, the transfer process occurring between the CdS and Sn nanoparticles, result in cathodoluminescence quenching at the junctions. In addition, both temperature coefficients and Debye temperatures of the CdS branched nanostructures are determined to be 5.56 × 10−4 eV/K and 97 K, respectively, based on the temperature dependent photoluminescence spectrum. Also, the emission intensity of the band edge and the defect related emission can be well tuned by the excitation power. As the laser power increases, the emission color changes from red to the green. Therefore, the coding capacity of the CdS branched barcodes can be well modulated by the temperature and pump laser power. Our studies demonstrate the possibility of using these branched nanostructures in multifunctional optical devices.

A Mid-Infrared Multifunctional Optical Device Based on Fiber Integrated Metasurfaces.

A metasurface is a two-dimensional structure with a subwavelength thickness that can be used to control electromagnetic waves. The integration of optical fibers and metasurfaces has received much attention in recent years. This integrated device has high flexibility and versatility. We propose an optical device based on fiber-integrated metasurfaces in the mid-infrared, which uses a hollow core anti-resonant fiber (HC-ARF) to confine light transmission in an air core. The integrated bilayer metasurfaces at the fiber end face can achieve transmissive modulation of the optical field emitted from the HC-ARF, and the Fano resonance excited by the metasurface can also be used to achieve refractive index (RI) sensing with high sensitivity and high figure of merit (FOM) in the mid-infrared band. In addition, we introduce a polydimethylsiloxane (PDMS) layer between the two metasurfaces; thus, we can achieve tunable function through temperature. This provides an integrated fiber multifunctional optical device in the mid-infrared band, which is expected to play an important role in the fields of high-power mid-infrared lasers, mid-infrared laser biomedicine, and gas trace detection.

Greatly Enhanced Resonant Exciton-Trion Conversion in Electrically Modulated Atomically Thin WS2 at Room Temperature.

Excitonic resonance in atomically thin semiconductors offers a favorite platform to study 2D nanophotonics in both classical and quantum regimes and promises potentials for highly tunable and ultra-compact optical devices. The understanding of charge density dependent exciton-trion conversion is the key for revealing the underlaying physics of optical tunability. Nevertheless, the insufficient and inefficient light-matter interactions hinder the observation of trionic phenomenon and the development of excitonic devices for dynamic power-efficient electro-optical applications. Here, by engaging an optical cavity with atomically thin transition metal dichalcogenides (TMDCs), greatly enhanced exciton-trion conversion is demonstrated at room temperature (RT) and achieve electrical modulation of reflectivity of ≈40% at exciton and 7% at trion state, which correspondingly enables a broadband large phase tuning in monolayer tungsten disulfide. Besides the absorptive conversion, ≈100% photoluminescence conversion from excitons to trions is observed at RT, illustrating a clear physical mechanism of an efficient exciton-trion conversion for extraordinary optical performance. The results indicate that both excitons and trions can play significant roles in electrical modulation of the optical parameters of TMDCs at RT. The work shows the real possibility for realizing electrical tunable and multi-functional ultra-thin optical devices using 2D materials.