Diabetic foot ulcers (DFU) are open sores or wounds that develop on the feet of people with diabetes. They are a serious complication and often occur on the bottom of the foot. DFU treatment in the field of medical sciences is an advanced field of study. Patients with DFU have a five-year death rate of approximately 40%. Age, gender, medical history, vascular diseases, and renal illness are major risk factors for mortality. While 90% of people with diabetes worldwide have type 2 diabetes mellitus, accounting for 463 million cases of the disease. DFU diagnosis and treatment has been performed with Laser Speckle Contrast Imaging (LSCI) which is a non-invasive imaging technology. LSCI is becoming widely recognized as a vital technique for evaluating the impacts and implications of this disease. Major types of LSCI has been studied for the application of laser speckle technology in medical diagnosis. Region of Interest (ROI) and Multi exposure based LSCI applications and implementations has been reviewed in this study. Along with the application of conventional LSCI, Artificial Intelligence (AI) tools has been studied for robust results to combat issues associated with diabetes.
AR and VR technologies are advancing rapidly, offering immersive experiences in the digital world. Researchers are exploring new ways to improve visual quality and user immersion. One promising solution is combining Metalens Arrays and Color Filters, which can enhance AR/VR experiences by manipulating light at a tiny scale. These technologies, integrated into AR/VR glasses, promise to revolutionize various fields by improving image resolution, color accuracy, and brightness. Users can expect more lifelike virtual environments, allowing deeper exploration and engagement in simulations and applications. Overall, the integration of Metalens Arrays and Color Filters represents a significant advancement in immersive experiences, opening up new possibilities in entertainment, education, and professional fields. In our research, we create a reflective Color Filter (CF) using a metasurface for RGB color filtering intended for AR/VR displays. This CF reflects light of specific wavelengths for desired colors while absorbing the rest. We assess color purity and accuracy using linear plots in Ansys Lumerical FDTD and chromaticity diagrams. Additionally, to focus this filtered light at various spots on the same plane, we design a metalens array in Ansys Lumerical FDTD and analyze its focusing profile.
Augmented Reality (AR) and Virtual Reality (VR) display for STEM education integrate advanced optical technology with immersive learning experiences. Optical Ray Tracing software serves as the primary platform for designing these educational tools. These softwares help to assess system performance and correct optical distortions, enabling the creation of diverse STEM educational modules. Microlens Array (MLA) based AR/VR displays provide immersive, hands-on learning opportunities and foster deeper understanding. The precise selection of MLA parameters influences critical aspects such as image clarity and field of view. In this study, we have designed an MLA in Zemax Opticstudio for the sake of using in AR/VR displays. We have studied the physical properties like 2D and 3D layouts and surface profile of MLA. We have also analyzed the optical properties, including ray propagation, spot diagram, and illumination. Furthermore, a comparative analysis of the optical performance of 7 × 7 and 11 × 11 MLA arrays in a 5 × 5 mm2 area is also incorporated.
Nanophotonics employ chiro-optical effects for a variety of applications, including advanced imaging and molecular detection and separation. Due to their outstanding qualities in light-matter interactions, planar metasurfaces comprised of subwavelength meta-atoms have attracted a lot of attention. Despite of the vast potential of metasurfaces, achievement of large chiro-optical effects compactly on-chip at the visible wavelengths is still hindered by its complex design and optimization procedure. Deep-learning (DL) based modelling techniques have been put out as an alternative to the time-consuming and computationally demanding traditional design and optimization procedure of metasurfaces during the past few years. In this work, we have employed deep-learning based forward and inverse models to design and optimize achiral nano-fins to achieve giant chiro-optical affects at the visible wavelengths. A regression based forward neural network is proposed, that takes all the structural dimensions of the achiral nano-fins as input and trained separately to predict three different types of asymmetric transmissions i.e., TLL, TLR and TRL and circular dichroism. An inverse design model is also demonstrated that simultaneously considers all the three target transmissions and optimizes the dimensions of the achiral nano-fins in such a way that they experience constructive and destructive interference, resulting in an average circular dichroism of more than 60% and 70% asymmetric transmission. With potential applications in chiral polarizers for optical displays, flat integrated polarization shifter’s exhibiting high efficiency, chiral-metasurface sensors and chiral beam splitters, the suggested DL-enabled design techniques ease the realization of op-chip giant chiro-optical response through planar metasurface.
The ultraviolet (UV) and visible regions of the electromagnetic spectrum incorporate many exciting applications, including high-resolution imaging, optical communication, lithography, sensing, and many more. The classic ways of manipulating electromagnetic waves through bulky, large, and expensive components stand between the new technologies like on-chip systems. The advancement of nanofabrication technologies enables the advent of optical metasurfaces that can manipulate approximately the whole electromagnetic spectrum. However, the availability of a suitable and lossless material for the UV and Visible region hinders the creation of metasurfaces and their integration for practical applications. Herein, we exploit the bandgap-engineered silicon nitride (Si3N4) material, which is transparent in most parts of the UV spectrum and can perform efficiently in both regimes. For proof of the concept, we design and numerically simulate different metasurfaces to generate the perfect vortex beam with different topological charges and a numerical aperture of 0.6. Each metasurface is functional for both UV and visible regions and efficiently manipulates the incident light. The independence of phase profile from topological charge helps perfect the vortex beam, to control the shortcomings of the optical vortex beam. The cross-polarization efficiency of the metasurface is also up to the mark. This work may find potential applications in different fields like on-chip communication, lithography, quantum processing, and optical communication.
Due to the recent advancement in metamaterials for bio-sensing applications, metasurfaces are designed to enhance the chirality of the incident CP light by creating chiral hotspots formed by the interaction of electric and magnetic fields. Most of the reported works focus on induced chirality in plasmonic structures operated by shifting the molecules' circular dichroism (CD) signal to plasmonic resonance frequencies, which results in a decrease in efficiency. Moreover, chiral structures like gammadions were also reported, which can enhance the chirality. Still, the inherent chirality of the structure is much larger than the chirality of the molecules and thus overshadows it. Therefore, highly efficient planar nanomaterials with broadband uniform chirality are needed to sort and detect natural and artificially-made chiral molecules. This work presents an aluminum-based dimer structure that confines the central gap's chiral field, leading to highly uniform volumetric chirality enhancement. The proposed achiral dimer structure enhances the chirality of the incident circularly polarized light without interfering with the circular dichroism (CD) of the molecules. As a result, we report high volumetric chirality and dissymmetry factor compared to the state-of-the-art, which is the figures of merit for CD spectroscopy and separation of enantiomers, respectively. This work can be applied to distinguish molecules with CD bands in the ultraviolet and visible wavelengths.
Here in this paper, we proposed a metasurface, which consists of silicon nitride as dielectric material possessing a high transparent window in the ultraviolet regime. We designed a single-layer dual-band metasurface instead of stacking and interleaved technique to overcome noise and low resolution, which gives broadband response for UV wavelengths. The proposed spin multiplexed metasurface is capable of generating two independent holographic images for right circularly polarized (RCP) and left circularly polarized (LCP) light. We achieved maximum cross-polarization efficiency on the designed wavelength i.e. 350nm and negligible zero-order efficiency. The unit cell and the proposed metasurface are simulated using Finite Difference Time Domain-based FDTD Solution from Lumerical Inc. for the specific wavelength while it gives broadband response for the wavelength band almost covering 290nm to 390nm.
In this paper, we present electrically tunable metasurfaces that exhibit multifunctional characteristics in the visible domain by exploiting electro-optic effect (EO). The metasurfaces consist of an array of Barium Titanate (BTO) meta-atoms on an Indium Titanium oxide (ITO) coated substrate. The resonance wavelength of the metasurface can be tuned by varying the electric field that eventually alters the refractive index of material. The tunability of resonance wavelength is evaluated by a hologram that appears at the desired wavelength by changing its voltage. Furthermore, a zoom metalens is presented with focal length shift by applying different electric fields at the wavelengths of 488, 532 and 633 in nm. The proposed idea can be useful for realizing tunable integrated systems.
The chiroptical effects are omnipresent throughout the universe and play a vital role in the sorting and detecting enantiomers in numerous applications like life sciences, pharmaceuticals, agrochemicals, food industry, etc. These chiroptical effects, along with polarization retention and full phase modulation, can have a significant potential for applications such as chiral imaging, anti-counterfeiting, and security. For strong chiroptical effects, all-dielectric metadevices offer a compact and efficient substitute to three-dimensional (3D) chiral metamaterials and flat plasmonic metadevices, which are prone to complex fabrication and ohmic losses, respectively. Here, we propose a unique metasurface based on the combination of achiral structures to achieve chiroptical effect with polarization retention and wavefront shaping. The proposed structure reflects the left hand circularly polarized (LHCP) light while preserving its handedness with complete absorption of the right hand circularly polarized (RHCP) and vice versa. Meanwhile, the structure provides full 2π phase modulation designed by hydrogenated amorphous silicon (a-Si:H), which is a low-loss, CMOS (complementary metal-oxide-semiconductor) compatible material with fabrication ease. The spin-selective reflection with circular dichroism and full phase modulation of designed structure find application in integrated optics, quantum optics, detection, and chiral imaging.
Metasurfaces have gained considerable attention due to their control over light properties like phase, amplitude, and polarization, which benefitted the industry for their applications in digital displays and multimedia related applications. Miniaturization of the devices has always been an interesting domain for researchers that can be accomplished by enabling a device to perform multifunctional behavior. Here, we propose a meta-atom by breaking symmetry of spin orbit interactions resulting in polarization sensitive device that transmits and reflects simultaneously under different circular polarizations. A z-shaped silicon-based meta-atom is designed, which provides asymmetric transmission of 80 % and 74 % in reflection and transmission, respectively. We demonstrated polarization multiplexed holograms in transmission and reflection for proof of concept that reflects its potential in spin-controlled imaging and sensing devices.
The simultaneous conversion circular dichroism and wavefront shaping play a vital role in light-matter interactions. The conversion circular dichroism achieved either by intrinsic chirality of nano-antennas or by using multilayer structures which have fabrication complexities. We propose a unique single-layered all-dielectric metasurface for circular asymmetric transmission in the visible regime. We introduce the combination of achiral structures as the building block of metasurface for the simultaneous conversion circular dichroism and wavefront modulation by utilizing hydrogenated amorphous silicon (a-Si:H). The proposed material is a low-loss and a CMOS compatible solution for realizing efficient all-dielectric metasurfaces for the visible domain. The demonstrated methodology exhibits highly efficient transmittance under right circularly polarized (RCP) illumination while completely blocking the light for the opposite spin of the incident light. The multifunctionality of the proposed metasurface can provide a promising route for chiral imaging, CD spectroscopy and spin-selective optical systems.
Artificially engineered light-matter interactions provide a unique degree of freedom to tailor wavefront of the incident waves, through pixelated engineering of its phase, amplitude, and polarization. Such dynamic control introduces various intriguing functionalities. Here, we propose a highly efficient metamirror with circular dichroism, which enables selective reflection with preserved handedness and complete absorption of other polarization. The building block of circular dichroism metamirror working on the principle of Jones calculus. For such a phenomenon, it is necessary to break the nfold rotational (n < 2) symmetry and mirror symmetry simultaneously. The proposed highly efficient metamirror with circular dichroism designed in the microwave regime for wavefront engineering. The demonstrated methodology exhibits full reflection for left circularly polarized EM waves without reversing its handedness and completely absorbing the other handedness. Multifunctionality and fabrication simplicity makes the proposed light-matter interaction a promising route for detection and manipulation of circularly polarized light, encryption, and chiral imaging.
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