Photonic Structures Research Articles

Enhanced THz emission from photoconductive antennas by integrating photonic structures on a semi-insulating GaAs substrate

Enhanced THz emission from photoconductive antennas by integrating photonic structures on a semi-insulating GaAs substrate

Rewritable ITO Patterning for Nanophotonics

AbstractNanophotonic devices leverage unique interactions between photons and materials at the nanoscale, enabling applications in optical communication, biosensing, and quantum computing. These devices' properties are susceptible to material composition and structural design. Nanofabrication techniques, such as optical lithography, e‐beam lithography, two‐photon polymerization, and direct laser writing, have been widely applied to fabricate nanophotonic devices. Notably, rewritable fabrication stands out due to its low cost, flexibility, efficiency, and multi‐functionality. In this paper, a novel rewritable nanofabrication technique is proposed, which combines electrochemical reactions with direct laser writing, to fabricate nanophotonic devices on low‐cost indium tin oxide (ITO) films. The experimental results have demonstrated that high‐quality and erasable photonic structures such as diffraction gratings and holography masks can be directly fabricated using our technique. Hence, it is believed that this method can be applied in diverse fields such as nanophotonics, optoelectronic devices, biosensors, micro‐electromechanical systems, and nonlinear optics.

Single photon structure model and multi-photon composite monomer

Single photon structure model and multi-photon composite monomer

Thermal emission modulation of fabrication-friendly, free-form metasurfaces via explainable deep-learning Bayesian optimization

Free-form metasurfaces with superimposed transformative meta-atoms provide a versatile platform to realize cross-band thermal emission control. However, design and manufacturing of free-form metasurfaces is extremely challenging, owing to the complex and fractal sub-wavelength topology. Here, we address these two issues by proposing an explainable deep-learning Bayesian optimization (DeepBO) framework to realize a library of fabrication-friendly, free-form metasurfaces with different light–matter interaction bandwidths. The DeepBO requires only 50 training data and is capable of screening high-dimensional design space of 1043 thermal photonic structure candidates with bandwidths from 0.3 to 3.2 eV. We unfold the black-box of deep-learning process by pattern recognition and identify the sub-space key features in the high-dimensional design space, which provides insights for thermal photonic metasurface design. We showcase the design and manufacturing of the broadband solar absorber and the narrowband thermophotovoltaic emitter with record-high spectral efficiency. The spectral selectivity of the fabricated free-form metasurface matches well with the design. The fabrication-friendly, free-form metasurfaces realized in this work can be generalized to thermal emitters for broad-ranges applications in energy and sensing.

Sustainable passive radiation cooling transparent film for mobile phone protective screens

Passive daytime radiative cooling (PDRC) is a promising approach to address energy, environmental, and safety issues caused by global warming, with high emissivity in a transparent atmospheric window and high reflectivity in the solar spectrum. However, most demonstrations of PDRC rely mainly on complex and expensive spectral selective nanophotonic structures, requiring specialized photonic structures that are both expensive and difficult to obtain. The superiorities of low-cost, abundant resources, renewability, and high value-added biomass resources prompt Gleditsia sinensis polysaccharides (GSP) to be used in thermal emission materials to explore further the characteristics of regulating object temperature within a specific range without any external energy consumption. The three-layer thermal emission film (PDMS3PG3/t4) obtained by the scalable scraping method has high transparency, hydrophobicity (114.2°), and super flexibility. The spectral variations of non-selective PDMS3PG3/t4 (1.0 wt% GSP, 800 μm thickness) in the 3–5 μm and 8–13 μm waveband ranges were discussed in detail, and high emissivities of 69.1 % and 92.2 % were obtained, respectively. PDMS3PG3/t4 was appointed a mobile phone screen film and experimented with a 4.9 °C average temperature difference below ambient temperature, materializing prime PDRC and desiring to broaden the passive cooling technology and reduce the global energy burden.

Photonic crystal fibre optic sensor based on a U-shaped detection channel with large air-hole cladding

A photonic crystal fibre-optic sensor based on a U-shaped detection channel with a large aperture cladding has been designed for refractive index sensing and detection, taking advantage of the flexibility of the photonic crystal fibre-optic structure and its superior performance. The results show that the relative intensities and central wavelengths of the directional coupling absorption peaks of the photonic crystal fibre-optic sensor are closely related to the ratio of the long and short semi-axes of the U-shaped detection channel and the thickness of the gold nanofilm. The sensor has a sensitivity of up to 21700 nm/RIU in the refractive index range of 1.33–1.43, a resolution of 4.608 × 10−6 RIU and a maximum quality factor of 126.12 RIU−1. Photonic crystal fibre-optic sensors with large-aperture cladding and U-shaped detection channels are simple in structure, highly sensitive and have significant potential applications in environmental monitoring, medical assays and industrial control.

Bottom-up fabrication of 2D Rydberg exciton arrays in cuprous oxide

Solid-state platforms provide exceptional opportunities for advancing on-chip quantum technologies by enhancing interaction strengths through coupling, scalability, and robustness. Cuprous oxide (Cu2O) has recently emerged as a promising medium for scalable quantum technology due to its high-lying Rydberg excitonic states, akin to those in hydrogen atoms. To harness these nonlinearities for quantum applications, the confinement dimensions must match the Rydberg blockade size, which can reach several microns in Cu2O. Using a CMOS-compatible growth technique, this study demonstrates the bottom-up fabrication of site-selective arrays of Cu2O microparticles. We observed Rydberg excitons up to the principal quantum number n = 5 within these Cu2O arrays on a quartz substrate and analyzed the spatial variation of their spectrum across the array, showing robustness and reproducibility on a large chip. These results lay the groundwork for the deterministic growth of Cu2O around photonic structures, enabling substantial light-matter interaction on integrated photonic platforms and paving the way for scalable, on-chip quantum devices.

Performance analysis of the photonic crystal–based X-OR gate for the terahertz applications

Abstract A key component of high-speed switching networks is an optical logic gate. This study presents the design and analysis of an all-optical XOR gate based on a two-dimensional photonic crystal (2D PC) structure, aiming to enhance high-speed switching in optical networks. The XOR gate, with two input and one output waveguide, is constructed on a hexagonal lattice, optimized for operation at a wavelength of 1,550 nm. The design is evaluated using the Finite Difference Time Domain (FDTD) approach, which simulates the optical performance of the structure. Key performance metrics, including the bit rate, contrast ratio, and delay time, are computed, showing that the proposed logic gate achieves a high contrast ratio of 30.35 dB and a minimal delay time of 0.4 ps. The results confirm the potential of this all-optical XOR gate for integration into high-speed optical circuits, offering low power consumption and high efficiency. This work demonstrates the feasibility of utilizing photonic crystal structures for high-performance optical logic gates in future communication systems. The simplicity of fabrication in a two-dimensional photonic crystal (2D-PC)-based all-optical logic gate can often be attributed to its simple design.

Robust nonlinear isolators based on frozen mode exceptional point degeneracies

We introduce a class of imperfection-protected nonlinear isolators designed to operate at exceptional point degeneracies (EPDs) of the Bloch modes of periodic photonic structures. These Bloch EPDs are responsible for slow light and the emergence of a scattering frozen mode regime (FMR). When a spectral asymmetry is introduced, the group velocity in their proximity varies sharply, boosting the directional nature of the nonlinear interactions and leading to extreme isolation. Published by the American Physical Society 2025

Coupling Bifunctional Scaffolds with Slow Photon Effect for Synergistically Enhanced Photoassisted Lithium-Sulfur Battery Properties.

Photoassisted lithium-sulfur (Li-S) batteries offer a promising approach to enhance the catalytic transformation kinetics of polysulfide. However, the development is greatly hindered by inadequate photo absorption and severe photoexcited carriers recombination. Herein, a photonic crystal sulfide heterojunction structure is designed as a bifunctional electrode scaffold for photoassisted Li-S batteries. Inverse opal (IO) structures utilize a slow photon effect that originates from their adjustable photonic band gaps, giving them distinctive optical response characteristics. The incorporation of a SnS/ZnS heterojunction within these IO frameworks further broadens the light absorption spectrum and enhances the charge transfer process. This efficient IO hybrid bifunctional electrode not only enhances the adsorption and conversion of polysulfides at the cathode but also induces uniform Li nucleation at the anode. These contribute the full batteries to output a high reversible capability of 1072 mAh g-1 and maintain stable cycling for 50 cycles. Additionally, a specific capacity of 698.8 mAh g-1 is still obtained even under a sulfur loading of up to 4 mg cm-2. The present strategy on SnS/ZnS IO to enhance photoassisted Li-S battery properties can be extended to rationally construct other energy storage devices.

Hierarchical Nanocellulose Photonic Design for Synergistic Colored Radiative Cooling.

Daytime radiative cooling (DRC) materials offer a sustainable, pollution-free passive cooling solution. Traditional DRC materials are usually white to maximize solar reflectance, but applications like textiles and buildings need more aesthetic options. Unfortunately, colorizing DRC materials often reduce cooling efficiency due to colorant sunlight absorption. Thus, this study reports a hierarchical photonic structure consisting of photoluminescent scatterer networks and a nanocellulose cholesteric structure. This design effectively addresses the trade-off between cooling efficiency and coloration, achieving enhanced cooling through synergistic all-day coloration. Sustainable nanocellulose with highly ordered cholesteric structures selectively reflects visible wavelengths, generating structural color and high mid-infrared (MIR) emission. The photoluminescent scatterer networks enhance reflectance and convert absorbed light into photoluminescent emission, further promoting cooling. This synergistic photonic interaction results in a significantly enhanced high reflectance of 92%, high MIR emissivity of >90%, stable and tunable structural color appearance, and hours-long afterglow photoluminescence. Consequently, a subambient cooling of up to 11.3 °C under sunlight is attainable, accompanied by the ability to produce programmable structural color and photoluminescent patterns for daytime and nighttime visibility. The enhanced cooling efficiency achieved through the synergistic interplay of four optical mechanisms from the UV to MIR region offers a promising design paradigm for other DRC materials.

Dual-Task Optimization Method for Inverse Design of RGB Micro-LED Light Collimator

Abstract: Miniaturized pixel sizes in near-eye digital displays lead to pixel emission patterns with large divergence angles, necessitating efficient beam collimation solutions to improve the light coupling efficiency. Traditional beam collimation optics, such as lenses and cavities, are wavelength-sensitive and cannot simultaneously collimate red (R), green (G), and blue (B) light. In this work, we employed inverse design optimization and finite-difference time-domain (FDTD) simulation techniques to design a collimator comprised of nano-sized photonic structures. To alleviate the challenges of the spatial incoherence nature of micro-LED emission light, we developed a strategy called dual-task optimization. Specifically, the method models light collimation as a dual task of color routing. By optimizing a color router, which routes incident light within a small angular range to different locations based on its spectrum, we simultaneously obtained a beam collimator, which can restrict the output of the light emitted from the routing destination with a small divergence angle. We further evaluated the collimation performance for spatially incoherent RGB micro-LED light in an FDTD using a multiple-dipole simulation method, and the simulation results demonstrate that our designed collimator can increase the light coupling efficiency from approximately 30% to 60% within a divergence angle of ±20° for all R/G/B light under the spatially incoherent emission.

Deterministic generation and nanophotonic integration of 2D quantum emitters for advanced quantum photonic functionalities

Abstract Quantum emitters (QEs) are essential building blocks for quantum applications, such as quantum communication, quantum computing and metrology. Two-dimensional (2D) materials, such as transition metal dichalcogenides (TMDs) and hexagonal boron nitride (hBN), are promising platforms for scalable QE generation due to their unique properties, including their compatibility with external photonic structures. Advances in defect engineering and strain manipulation enable precise localization of emission sites within these materials, while integration with nanophotonic structures, including cavities and waveguides, enhances photon emission through the Purcell effect. This integration supports quantum functionalities like single-photon routing and spin-photon interactions. Challenges include achieving precise QE placement and emission control, as environmental factors can affect QE purity and indistinguishability. Nonetheless, electrically driven QEs, strain-tunable emission, and the integration of van der Waals magnets present opportunities for compact, scalable quantum devices with on-demand single-photon sources and spin-based quantum memory, positioning 2D QEs as foundational for next-generation quantum devices.

Transverse-Electric Surface Plasmon in Graphene Under Uniform Strain

Abstract Compared to surface plasmon polariton in metals, graphene can support transverse electric (TE) surface modes when the imaginary part of its conductivity is negative. TE graphene plasmons are generally weakly confined in direction perpendicular to the graphene plane, and they cannot be resonantly excited by an external incident wave because their dispersion curve spectrally lies just below the light line. In this work, we investigate theoretically the light reflectance of a graphene layer under uniform strain on the top of a one-dimensional photonic crystal consisting of high and low-index dielectric materials and a material film layer on the graphene sheet. The strain not only changes the electronic band structure but also can be employed to influence the electronic collective excitations and thus the optical reflectance of graphene monolayers. We demonstrate that TE plasmon excitation is based on the observation of a pronounced sharp minimum in the reflection coefficient of the suggested photonic structure upon the incident angle, the wavelength, and refractive index. Therefore, the graphene under uniform strain on the photonic structure is found to be promising in the fabrication of optical sensors devices with TE plasmons.

Design and analysis of optical devices with ultra-high quality factor based on a plasmonic photonic hybrid structure

Abstract In the present paper, the design of a tunable, high transmitting, and optical ultra-narrow band-pass filter using a plasmonic-photonic hybrid structure comprised of a multilayer stack of dielectrics and a thin sheet of silver is proposed. This current design can create more energy coupling, thus having a higher transmission peak in comparison to prior studies. To obtain a filtering operation, two different topologies are designed to achieve better performance specifications. The materials used in the structure include silicon, silicon-dioxide, and silver. The Drude model is employed for the silver. It has been shown that the geometrical parameters are sensitive to choose such that transmission properties and resonance wavelengths are arbitrarily tunable. The structure's design enables a single-mode as well as a multi-mode spectrum for each topology. We have achieved a maximum quality factor of 432.87 with an ultra-small full-width-at-half-maximum bandwidth of 1.43 nm, while the maximum transmission values are greater than 75%. Most of the various advantages include adjustability, high detection resolution, and integration at the nanoscale for optical applications owing to the basic merits of the hybrid structures of plasmonic and photonic crystals.

Optical Transmission Enhancement of MoS2 Nanosheets Doped with Magnetic Materials Ni, Mn, and Cr

In this work, we report both theoretical and experimental study of the influence of some materials with magnetic aspects such as Ni, Mn, or Cr in MoS2 photonic crystal structures. A functional density method technique has been introduced. Indeed, the results indicated that the transmission spectrum is considerably affected by the impact of doping from a photo shape and amplitude. Furthermore, appropriate doping has been shown to change the peak transmission shape of the MoS2 photonic crystal by splitting as an example. In fact, the transmission spectrum remains less identical with Ni and Mn doping and exhibits a doubling peak with Cr attributed to the first and second waveguide propagation modes. The obtained results can give a new degree of freedom in device application of MoS2 nanosheets such as photonic sensors, filter, and reflector. Finally, we can predict that the MoS2 photonic crystal doped with magnetic materials could be used in applications involving plasmonic Fano-resonances. Received: 29 July 2024 | Revised: 4 November 2024 | Accepted: 27 December 2024 Conflicts of Interest The authors declare that they have no conflicts of interest to this work. Data Availability Statement Data sharing is not applicable to this article as no new data were created or analyzed in this study. Author Contribution Statement Sondes Kaddour: Conceptualization, Formal analysis, Writing – original draft. Randa Zaimia: Formal analysis, Investigation. Nouha Mastour: Validation, Investigation. Said Ridene: Methodology, Writing – review & editing, Supervision. Noureddine Raouafi: Resources.

Surfactant-based interface capture towards the development of 2D-printed photonic structures.

This study focuses on fabricating photonic crystals (PCs) by surfactant-based particle capture at the gas-liquid interface of evaporating sessile droplets. The captured particles form interfacial films, resulting in ordered monolayer depositions manifesting iridescent structural colors. The particle dynamics behind the ordered arrangement is delineated. This arrangement is influenced by the alteration in particles' hydrophobicity, charge, and internal flow introduced by the surfactant addition. The influence of surfactant and particle concentrations on the phenomenon is also investigated. The work demonstrates a drop-by-drop technique to scale up the formation of PCs. Furthermore, the work is extended towards demonstrating the utilization of this mechanism to fabricate arbitrary PCs efficiently by direct writing technique. The particle coverage in directly written patterns is influenced by printing speed and particle concentration, which are adjusted to achieve covert photonic patterns. Finally, the replication of colloidal PC onto a flexible polymer with minimal colloid transfer is demonstrated using soft lithography.

Highly Efficient and achromatic mid-infrared silicon nitride meta-lenses

Inverse design with topology optimization considers a promising methodology for discovering new optimized photonic structure that enables to break the limitations of the forward or the traditional design especially for the meta-structure. This work presents a high efficiency mid infra-red imaging photonics element along mid infra-red wavelengths band starts from 2 to 5 µm based on silicon nitride optimized material structures. The first two designs are broadband focusing and reflective meta-lens under very high numerical aperture condition (NA = 0.9). The two designs are modeled by inverse design with topology optimization problem with Kreisselmeier–Steinhauser (k–s) aggregation objective function, while the final design is depended on novel inverse design optimization problem with double aggregation objective function that can target bifocal points along the wavelength band producing high efficiency achromatic broadband multi-focal meta-lens under very high numerical apertures ().

Realization and simulation of silicon-on-sapphire mid-infrared one-dimensional photonic crystal cavities

The mid-infrared (MIR) waveband is significant for chemical and biological sensing since it covers several atmospheric windows and molecular fingerprint regions. On-chip photonic integrated one-dimensional (1D) microcavities have great potential for high-performance mid-IR sensing because of their high sensitivity and compact structure. However, high-performance 1D microcavities based on the promising silicon-on-sapphire (SoS) MIR platform have not yet been designed or realized. Based on the photonic band structure induced by 1D photonic crystals (PhC), a high-performance Bragg reflector, an inward apodized Bragg grating, and a free spectral range (FSR)-free PhC microcavity integrated system operating in the MIR waveband were developed on the SoS platform. By carefully designing the period and penetration depth of the corrugation in the Bragg reflector, a stopband of 45 nm and an extinction ratio of −12 dB were achieved. The inward apodized Bragg grating was optimized by adjusting the apodization depth and the number of periods, resulting in a quality factor of 1043 at a wavelength of 3088.4 nm. Furthermore, introducing a Fabry–Pérot (F-P) cavity between two Bragg reflectors (with side-coupled light) and precisely tuning the stopband of the Bragg reflector and the FSR of the F-P cavity enabled the realization of an FSR-free PhC microcavity. This microcavity exhibited a single deep resonance dip with subnanometer bandwidth across a record-wide operational waveband from 3025 to 3200 nm, achieving a quality factor of approximately 5090. The MIR 1D PhC microcavities on the SoS platform hold great promise for high-performance gas detection and molecular sensing in future applications.

Design and fabrication of photonic devices and a microfluidic channel with a femtosecond laser

This article presents the modeling and fabrication of photonic devices such as a Mach-Zehnder waveguide interferometer (MZWI) and a 1 × 4 optical power splitter (OPS) with a microfluidic channel. The photonic structures were designed using CAD software and BeamPROPTM to have an s-shaped waveguide bend geometry and a total length of 8000 μm, and the devices were then integrated with a 6000 μm microfluidic channel to form configurations based on conical spirals and helices with femtosecond laser radiation. The entire writing process was performed in a single step with a 20X microscope objective to achieve greater accuracy in the manufacturing process. A chemical etching step was performed using the shape-controlled with femtosecond laser irradiation followed by chemical etching (SC-FLICE) technique, forming a uniform cross-section in the central part of the microfluidic channel. The energy doses and translation speeds of the system were varied, resulting in a longer microfluidic channel. However, this work was limited to the design and development of the prototype due to the project objectives and limited resources. In this research, we introduce an optofluidic system which integrates the principles of optics and microfluidics, is suitable for biosensing applications. The compatibility of this system with biosensing applications paves the way for significant progress in various sectors, including medical diagnostics, environmental surveillance, and biochemical studies. The originality and value of this work lie in its unique design and potential for broad application. The present work, it was demonstrated that using ultrafast laser writing, we can fabricate photonic devices and a consistent microfluidic channel on a single step.