Photonic Devices Research Articles

Polymer-based cascaded waveguide Bragg grating for blood glucose sensing.

Waveguide Bragg grating (WBG) blood glucose sensing, as a biological sensing technology with broad application prospects, plays an important role in the fields of health management and medical treatment. In this work, a polymer-based cascaded WBG is applied to glucose detection. We investigated photonic devices with two different grating structures cascaded-a crossed grating and a bilateral grating-and analyzed the effects of the crossed grating period, bilateral grating period, and number of grating periods on the sensing performance of the glucose sensor. Finally, the spectral reflectance characteristics, response time, and sensing specificity of the cascaded WBG were evaluated. The experimental results showed that the glucose sensor has a sensitivity of 175 nm/RIU in a glucose concentration range of 0-2 mg/ml and has the advantages of high integration, a narrow bandwidth, and low cost.

Magnetically controllable multimode interference in topological photonic crystals

Topological photonic insulators show promise for applications in compact integrated photonic circuits due to their ability to transport light robustly through sharp bendings. The number of topological edge states relies on the difference between the bulk Chern numbers across the boundary, as dictated by the bulk edge correspondence. The interference among multiple topological edge modes in topological photonics systems may allow for controllable functionalities that are particularly desirable for constructing reconfigurable photonic devices. In this work, we demonstrate magnetically controllable multimode interference based on gyromagnetic topological photonic insulators that support two unidirectional edge modes with different dispersions. We successfully achieve controllable power splitting in experiments by engineering multimode interference with the magnetic field intensity or the frequency of wave. Our work demonstrates that manipulating the interference among multiple chiral edge modes can facilitate the advancement of highly efficient and adaptable microwave devices.

Effect of Carbon dots in tuning molecular alignment, dielectric and electrical properties of a smectogenic cyanobiphenyl-based liquid crystal material

Abstract We demonstrate here the effect of dispersing organosoluble carbon dots (CDs, ∼7-8 nm) on tuning the molecular alignment, dielectric and electrical properties of smectic A (SmA) and nematic (N) mesophases of a thermotropic smectogenic LC material, 4-octyl-4′-cyanobiphenyl (8CB) in a planar anchored ITO sample cell using polarized optical microscopy and dielectric spectroscopic techniques. The cross-polarised optical textures clearly show that the doping of CDs (concentration ≥0.25wt%) in planar anchored 8CB, LC led to change its alignment from planar to vertical. Intrestingly, such induced vertical alignment remains stable throughout SmA and N phases of the 8CB, LC material. Moreover, the magnitude of real dielectric permittivity is found to increase with increasing concentration of CDs and exhibited vertical alignment values for composites (≥0.25wt%). The observance of short axis molecular relaxation for composites (≥0.25wt%) without the application of bias field affirmed again the induced vertical alignment. The accumulation of CDs at the substrate surface and their interaction with alignment and ITO layers could be attributed as an important factor for such induced vertical alignment. Electrical conductivity of 8CB is observed to increase significantly with the addition of CDs (i.e., an increment of up to two orders of magnitude in composites as compared to pure 8CB) and attributed to the lowering of viscosity and change in molecular alignment. We certainly believe that such tunable molecular alignment throughout SmA and N phases of thermotropic smectogenic liquid crystal material (8CB) by dopant CDs could pave the way forward for their applications in the flexible displays, biosensors, electro-optical memory, and other tunable photonic devices.

Fundamentals and emerging optical applications of hexagonal boron nitride: a tutorial

Hexagonal boron nitride (hBN), also known as white graphite, is a transparent layered crystal with a wide bandgap. Its crystal structure resembles graphite, featuring layers composed of honeycomb lattices held together through van der Waals forces. The layered crystal structure of hBN facilitates exfoliation into thinner flakes and makes it highly anisotropic in in-plane and out-of-plane directions. Unlike graphite, hBN is both insulating and transparent, making it an ideal material for isolating devices from the environment and acting as a waveguide. As a result, hBN has found extensive applications in optical devices, electronic devices, and quantum photonic devices. This comprehensive tutorial aims to provide readers with a thorough understanding of hBN, covering its synthesis, lattice and spectroscopic characterization, and various applications in optoelectronic and quantum photonic devices. This tutorial is designed for both readers without prior experience in hBN and those with expertise in specific fields seeking to understand its relevance and connections to others.

Multitask Learning Deep Neural Networks Enable Embedded Design of Active Metamaterials.

In this study, we propose and implement a deep neural network framework based on multitask learning aimed at simplifying the forward modeling and inverse design process of photonic devices integrating active metasurfaces. We demonstrate and validate our approach by constructing a continuously tunable bandpass filter that is effective in the midwave infrared region. The key to this filter is the combination of a metasurface and Fabry-Perot (F-P) cavity structure of the tunable phase-change material Ge2Sb2Se4Te (GSST) and the precise control of the crystallinity of the GSST by a silicon-based heater. With the help of a deep learning framework, we are able to independently model the crystallinity and geometric parameters of the filter to maximize the use of GSST tuning for bandpass filtering. Our model discusses the self-attention mechanism and the effect of noise and compares several existing popular algorithms, and the results show that a multitask deep learning strategy can better assist the on-demand reverse design of photonic structures with phase change materials. This opens up new possibilities for personalization and functional extension of optical devices.

Phase Composition of HiVac-VPE Lithium Niobate Optical Waveguides Identified by Spectroscopic Investigations

High-index contrast lithium niobate waveguides, fabricated by the High Vacuum Vapor-phase Proton Exchange (HiVac-VPE) technique, are very promising for increasing both the optical nonlinear and electro-optical efficiencies of photonic integrated devices. So as to play this role effectively, it is mandatory to know the crystallographic phase composition of waveguides and the position of protonated layers for appropriate tailoring and optimization based on the intended applications. In addition, the estimation of structural disorder and electro-optical properties of the waveguides are also of high interest. Benefiting from Raman spectroscopy, IR reflection, IR absorption, and UV-VIS absorption, the HxLi1−xNbO3 phase compositions, as well as the structural disorder in waveguides, were determined. Based on experimental data on the shift of the fundamental absorption edge, we have quantitatively estimated the electro-optic coefficient r13 in as-exchanged waveguides. The electro-optical properties of the waveguides have been found to be depending on the phase composition. The obtained results allow for reconsidering the proton exchange fabricating process of photonic nonlinear devices and electro-optic modulators based on high-index contrast channel waveguides on the LiNbO3 platform.

The role of annealing in optimizing the electrical, linear, and nonlinear optical properties ZIf-8@TiO2 films for possible use in photonic and optoelectronic devices

Abstract Here, we fabricate zeolitic imidazolate framework-8 (ZIF-8)–doped 5 wt. % nanosized TiO2 (ZIf-8@TiO2) thin films using a vapor coating unit. The effects of annealing up to 473 K on the physical characteristics of fabricated ZIf-8@TiO2 thin films were studied. XRD, FTIR, and UV-Vis spectroscopy were utilized to investigate the structural properties of the as-deposited and annealed samples. An increase of approximately 18% was observed in the electrical conductivity. As the annealing temperature increased, the light transmission decreased. This could be due to the growth or aggregation of TiO2 particles during annealing. Raising the annealing temperature by 100 K enhanced the refractive index (n) and energy gap (Eg) by approximately 33% and 8%, respectively. The decrease in ε1 and ε2 in response to the annealing temperature increase was due to the evaporation of MOF organic linkers. The nonlinear optical results indicated a dependence on the annealing temperatures that improved charge carrier mobility and coherent light-matter interactions. Our thesis findings can improve the overall performance and efficiency of optoelectronic devices.

A Critical Review on Recent Progress of Solution‐Processed Monolayer Assembly of Nanomaterials and Applications

AbstractThe rapid development in nanotechnology has necessitated accurate and efficient assembly strategies for nanomaterials. Monolayer assembly of nanomaterials (MAN) represents a challenging and important architecture to manufacture and is critical in understanding interactions among nanomaterials, solvents, and substrates. MAN enables highly tunable performance in electronic and photonic devices. This review summarizes the recent progress on the methods to achieve MAN and discusses important control factors. Moreover, the importance of MAN is elaborated by a broad range of applications in electronics and photonics. In the end, the opportunities as well as challenges in manufacturing and new applications are outlooked.

Leveraging statistical-spectral correlations of random metasurfaces for steganography and multi-wavelength cryptography

The ability to tailor the spectral response of photonic devices is paramount to the advancement of a broad range of applications. The vast design space offered by disordered optical media provides enhanced functionality for spectral tailoring while also making it challenging to map the spectral properties of such complex systems to their structural attributes. In this work, we investigate correlations between the configuration statistics of random metasurfaces and their spectral transmissivity in the visible, and leverage those to develop a reduced phase space. In the latter part of the manuscript, we use this reduced phase space to design a pixelated color filter that hides visual data within a preselected cover image for steganography. Furthermore, we design a pair of color filters that can collectively encrypt a given grayscale image in their spectral transmissivities. We envision such devices to create opportunities for the development of compact, next-generation cryptographic systems. More broadly, the results presented in this manuscript provide new, to the best of our knowledge, avenues for optimizing large-scale random metasurfaces to achieve enhanced optical functionalities for a wide variety of applications.

Bulk α-alumina embedded tapered fiber as Q-switcher in an erbium-doped fiber laser

We present bulk α-alumina (Al2O3) in a polydimethylsiloxane matrix decorated tapered fiber as a Q-switcher for microsecond pulse generation. The integration of α-Al2O3-saturable absorber (SA) in an erbium-doped fiber laser yielded a Q-switched operating regime within 62.0–308.6 mW pump power. The shortest pulse width was 7 μs, whereas the repetition rate was tunable from 19.17 to 43.24 kHz. This work reveals a substantial improvement over previously reported Al2O3-SA works with a recorded pulse energy of 150.32 nJ and an estimated damage threshold of beyond 6.75 GW cm−2 incident intensity. Our findings suggest that α-Al2O3-SA has enormous potential as a next generation light-absorbing material for high-energy photonic devices.

Optical non-linearities and applications of ZnS phosphors

Optical non-linearities play a crucial role in enabling efficient and ultrafast switching applications that are essential for next-generation photonic devices. ZnS phosphor material produces the best results in terms of increased luminescence quantum yield when doped with certain impurities. Nevertheless, the investigation of the third-order non-linear optical susceptibility of the phosphor materials can be exploited for various switching applications. In this regard, we review the recent advancements in the investigation of non-linear optical properties of ZnS phosphors, where the knowledge of absorption and refraction is utilized in various optical and detector applications. Furthermore, the review highlights strategies employed to enhance the non-linear optical response of phosphor materials as well as a general discussion of an attosecond optical switching scheme which can be used to fabricate devices with petahertz speeds. Consequently, we provide a solution to the unsolved problem of the significant extension of optical limiting applications to switching applications by developing design strategies to manipulate conventional ZnS phosphor material. The potential challenges and future prospects of utilizing phosphor materials for switching applications are also addressed. The strategies for manipulating ZnS phosphor can be generalized for a broad range of other materials by minimizing linear and non-linear losses, while enhancing the values of the non-linear refractive index coefficient. We propose that the figure-of-merit of ZnS material can be enhanced by using a suitable combination of pump and probe wavelength values, which can be useful for optical switching applications.

Ultrafast Laser Direct Writing Nanogratings and their Engineering in Transparent Materials

AbstractFemtosecond laser direct writing is a powerful technique for fabricating micro‐nano devices as it can modify the interior of transparent optical materials in a spatially selective manner through nonlinear multi‐photon absorption. In this context, laser‐induced nanogratings, i.e., a sub‐wavelength assembly of nanolayers (≈20 nm in width, ≈200 nm period), are ultrashort self‐organized structures created by light in the bulk of transparent materials. These have been intensively explored over the last two decades opening a novel era of micro photonic devices due to their unique physicochemical properties, like orientable form birefringence, anisotropic light scattering, highly selective chemical etching, optical chirality, and extraordinary thermal stability. This review provides a throughout overview of the advances in this field, specifically focused on the formation of nanogratings, optical properties that can be exploited in various transparent solids, and the related main applications. Also, the fundamental characteristics, formation mechanism, tuning methods of nanogratings are reviewed.

Graphene-integrated microring cavity for electronically controlled molecular fingerprinting

Microring cavities supporting whispering-gallery modes (WGMs) have an exceptionally high quality factor (Q) and a small mode volume, greatly improving the interaction between light and matter, which has attracted great attention in various microscale/nanoscale photonic devices and potential applications. Recently, two-dimensional van der Waals (vdW) materials such as graphene have emerged as a potential platform for next-generation biosensing by enabling the confinement of light fields at the nanoscale. Here, we propose what we believe to be a novel approach to achieve molecular fingerprint retrieval by integrating graphene into a microring cavity and conducting numerical simulations using the finite-difference time-domain (FDTD) method. The hybrid cavity exhibits high-quality WGMs with a high Q factor of up to 800. Moreover, the resonant wavelength can be electronically controlled through modulation of graphene’s Fermi level, enabling coverage of the entire free spectral range at infrared frequencies. By depositing a thin layer of biomolecular material (e.g., CBP) onto the surface of our hybrid cavity, we are able to accurately read out the absorption spectrum at multiple spectral points, thereby achieving broadband fingerprint retrieval for the targeted biomolecule. Our results pave the way for highly sensitive, chip-integrated, miniaturized, and electrically modulated infrared spectroscopy biosensing.

Mitigating waveguide loss in Ge–Sb–Se chalcogenide glass photonics

Minimizing propagation loss within waveguides remains a central objective across diverse photonic platforms, impacting both linear lightwave transmission and nonlinear wavelength conversion efficiencies. Here, we present a method to mitigate waveguide loss in Ge28Sb12Se60 chalcogenide glass, a material known for its high nonlinearity, broad mid-infrared transparency, and significant potential for mid-IR photonics applications. By applying a sacrifical oxide layer to eliminate etching residues and a subsequent waveguide thermal reflow to smooth lithography-induced line edge roughness, we successfully reduced the waveguide loss down to 0.8 dB cm−1 at 1550 nm wavelength. This represents the best result in small-core and high-index-contrast Ge28Sb12Se60 channel waveguides. Our approach paves the way for low-loss, on-chip chalcogenide photonic devices.

Characterization and the physical properties of nano-sized Bi2O3/polymer for energy and high-refractive index applications

The present work focuses on developing nanocomposites for optoelectronics and energy storage devices leveraging the unique physicochemical features of bismuth (III) oxide (Bi2O3) using a polyvinyl pyrrolidone/polyvinyl alcohol matrix (PV(A/P)). Bi2O3 nanofillers (NF) and Bi2O3/PV(A/P) nanocomposite (NC) films were prepared by facile chemical solution approaches. The X-ray (XRD) data and a transmission electron image revealed that the NF exhibits a monoclinic phase, resembling slightly deformed agglomerated spheres. In the FTIR spectrum, different stretching vibrations of Bi-O-Bi bonds were found, along with their complexation and interaction with the reactive groups in the matrix. The SEM revealed a uniform distribution of Bi2O3 NF loading up to 1.5 wt% on the sample’s surface. Thermal analyses (TGA and DSC thermograms) were used to study the thermal stability, melting, and decomposition temperatures of the NC films. The dielectric features were studied under frequencies between 2 × 103 and 8 × 106 Hz and heating from 293 to 393 K. The dielectric constant and energy density were increased with Bi2O3 NF content. This implies that we can utilize the prepared NC for the fabrication of energy storage devices. The influences of the Bi2O3 NF doping level on the transmittance, band gap, Urbach energy, refractive index, conductivity, and other physical parameters were discussed. The modifications induced in the dielectric/optical parameters make the prepared NC films the best candidates for applications requiring a high refractive index, such as optical coatings and integrated photonic devices.

Exciton Localization Modulated by Ultradeep Moiré Potential in Twisted Bilayer γ-Graphdiyne.

Twisted moiré superlattice is featured with its moiré potential energy, the depth of which renders an effective approach to strengthening the exciton-exciton interaction and exciton localization toward high-performance quantum photonic devices. However, it remains as a long-standing challenge to further push the limit of moiré potential depth. Herein, owing to the pz orbital induced band edge states enabled by the unique sp-C in bilayer γ-graphdiyne (GDY), an ultradeep moiré potential of ∼289 meV is yielded. After being twisted into the hole-to-hole layer stacking configuration, the interlayer coupling is substantially intensified to augment the lattice potential of bilayer GDY up to 475%. The presence of lateral constrained moiré potential shifts the spatial distribution of electrons and holes in excitons from the regular alternating mode to their respective separated and localized mode. According to the well-established wave function distribution of electrons contained in excitons, the AA-stacked site is identified to serve for exciton localization. This work extends the materials systems available for moiré superlattice design further to serial carbon allotropes featured with benzene ring-alkyne chain coupling, unlocking tremendous potential for twistronic-based quantum device applications.

Bi-functional dynamic tunable absorber and highly robust polarisation converter for graphene-based metasurface

In this study, a graphene-based metasurface structure with bi-functional dynamically tunable absorber and highly robust polarisation converter is proposed. The device primarily consists of two functional tiers. The top tier of cyclically patterned graphene and the back of a fully reflective gold mirror, which are separated by an intermediate tier of SiO2 dielectric to form a typical sandwich structure. The proposed device is numerically calculated by finite element method (FEM), and the equivalent R-L-C circuit model is built to validate the calculated results. The proposed reflective-type circularly to circularly polarisation converter (RCCPC) has a wide operating band of 0.8 THz (2.12 THz to 2.92 THz) and can obtain near unity polarisation conversion rate (χPCR). It is worth noting that the device is also immune to structural parameter deviations. In addition, due to the excited charge of monolayer graphene has the cyclotron property in a static magnetic field, the cross-polarised component of the polarisation converter can be increased by applying a vertical magnetic field, which provides a feasible method to improve the energy conversion rate of the device. At the same time, the device can also serve as a narrowband dual channel absorber, with 95 % absorption effect. In addition, the tunability of graphene is based on the correlation between conductivity and Fermi energy. As the Fermi energy changes, the working frequency of the device is shifted, realizing the dynamic tunable absorber and polarisation converter. It is believed that these findings provide a way to implement a variety of novel multifunctional photonic device, including polarisation imaging, electromagnetic energy absorption, and integrated photonic devices.

Tunable Unexplored Luminescence in Waveguides Based on D-A-D Benzoselenadiazoles Nanofibers

A set of novel Donor-Acceptor-Donor (D-A-D) benzoselenadiazole derivatives has been synthesized and crystallized in nanocrystals in order to explore the correlation between their chemical structure and the waveguided luminescent properties. The findings reveal that all crystals exhibit luminescence and active optical waveguiding, demonstrating the ability to adjust their luminescence within a broad spectral range of 550–700 nm depending on the donor group attached to the benzoselenadiazole core. Notably, a clear relationship exists between the HOMO-LUMO energy gaps of each compound and the color emission of the corresponding optical waveguides. These outcomes affirm the feasibility of modifying the color emission of organic waveguides through suitable chemical functionalization. Importantly, this study marks the first utilization of benzoseleniadiazole derivatives for such purposes, underscoring the originality of this research. In addition, the obtention of nanocrystals is a key tool for the implementation of miniaturized photonic devices.

Luminescence and two-photon absorption assisted optical limiting properties of Ag-doped CdWO4 nanorods

The emerging demand for the fabrication of nonlinear optical materials with high limits of optical power is obvious in nonlinear optics due to their wide application in photonic devices. We report the linear and third-order nonlinear optical properties of Ag-doped CdWO4 nanorods and their dependence on Ag-doping concentration. CdWO4 nanorods with different Ag concentrations were synthesized by the chemical precipitation method and characterized by UV–Vis absorption, X-ray diffraction (XRD), Raman, Photoluminescence and its lifetime studies, X-ray Photoelectron spectroscopy and Transmission Electron Microscopy (TEM). The introduction of Ag ions has led to an increased redshift in the CdWO4 absorption spectra extended into longer wavelength bands, thus enhancing optical absorption within the visible range. The XRD pattern showed that the nanorods crystallized in a monoclinic wolframite structure. The incorporation of Ag in CdWO4 decreases the luminescence emission intensity due to surface quenching effect. Luminescence lifetime measurement reveals the longer decay lifetime for Ag-doped CdWO4 nanorods due to the reduction of density of defects and deep trap state. The nonlinear optical behaviour of the nanorods was investigated by an Open aperture Z-scan technique at 532 nm using pulsed wave Nd: YAG laser. Experimental results showed that reverse saturable absorption is responsible for the observed nonlinearity in the nanorods. The addition of Ag can significantly improve the nonlinear absorption coefficient and optical limiting effects of CdWO4 which can be used as a potential material in nonlinear optical devices.

Symmetry-Reduction Enhanced Polarization-Sensitive Photoresponse Based on One-Dimensional van der Waals Materials.

Designing high-performance polarization-sensitive photodetectors is essential for photonic device applications. Anisotropic one-dimensional (1D) van der Waals (vdW) materials have provided a promising platform to that end. Despite significant advances in 1D vdW photonic devices, their performance is still far from delivering practical potential. Herein, we propose the design of high-performance polarization-sensitive photodetectors using unique 1D vdW materials. By leveraging the chemical vapor transport technique, we successfully fabricate high-quality 1D vdW Nb2Pd1-xSe5 (x = 0.29) nanowires. The 1D vdW Nb2Pd1-xSe5 photodetector exhibits a high mobility of ∼56 cm2/(V s) and superior photoresponse performance, including a high responsivity of 1A/W and an ultrafast response time of ∼8 μs under 638 nm illumination. Moreover, the 1D vdW Nb2Pd1-xSe5 photodetector demonstrates excellent polarization-sensitive photoresponse with a degree of linear polarization (DOLP) up to 0.85 and can be modulated by adjusting the gate voltage, laser power density, and wavelength. Those exceptional performance are believed to be relevant to the symmetry-reduction induced by the partial occupation of Pd sites. This study offers feasible approaches to enhance the anisotropy of 1D vdW materials and the modulation of their polarization-sensitive photoresponse, which may provide deep insights into the physical origin of anisotropic properties of 1D vdW materials.