Search

In this paper, a unique one-dimensional double anti-PT-symmetric ring optical waveguide network (1D DAPTSROWN) is designed whose refractive index satisfies n ( x ) = − n ∗ ( − x ) . The extraordinary optical characteristics of the network are studied by means of the generalized Floquet-Bloch theorem, three-material network equation and generalized eigenfunction method. Due to the physical difference between the anti-PT-symmetric and PT-symmetric optical waveguide networks, the previous methond of the PT-symmetric optical waveguide network is not applicable to the anti-PT-symmetric optical waveguide network designed in this paper. Thus, based on the previous method and the network equation, we propose a connection function to identify the extremum mode points in the anti-PT-symmetric optical waveguide network. At the extremum mode point, the optical waveguide network can produce extraordinary ultra-strong transmission, ultra-strong reflection, and ultra-strong photonic localizations. The corresponding calculated values in this paper arrives at 1 0 28 , which is much larger than 1 0 12 (the best result reported previously). This shows that the anti-PT-symmetric network may have potential in applications in designing optical filters, optical amplifiers and so on.

PurposeTo compare axial length (AL) measurements in long eyes by two swept-source optical coherence tomography (SS-OCT) biometers, one based on the group refractive index (IOLMaster 700, Zeiss) and the other based on sum of segments (Argos, Movu), and compare these measurements to previously published methods to optimize AL.SettingI.R.C.C.S. - G.B. Bietti Foundation, Rome, ItalyDesignProspective case seriesMethodsAL was measured with both optical biometers in myopic patients (AL > 24.00 mm) and compared to the values obtained with Wang-Koch adjustment, polynomial equations for the Holladay 1 and 2 formulas and Cooke modified AL (CMAL).ResultsIn 102 eyes of 55 subjects, a statistically significant difference (p

Owing to the unique electromagnetic response ability, artificial electromagnetic metasurfaces have potential applications in medical, imaging, sensing, and other fields. In this paper, a novel composite THz metasurface integrated by carbon nanotubes (CNTs) resonant metasurface and silicon microfluidic channel has been proposed, which combines the advantages of semiconductor and carbon nanotubes film materials. The absorption characteristics and the refractive index sensing capabilities are investigated comprehensively. Calculation results show that two obvious resonant absorption peaks located at 1.20 THz and 1.85 THz and the absorption is nearly 99.6% and 89.8%, respectively; the device performs a good linear relationship between the position of resonant absorption peaks and the refractive index, and the frequency sensitivity can achieve 492 GHz/RIU. The influence of structural parameters and the offset of the center of the CNTs metasurface on the absorption spectrum demonstrate that the novel composite metasurface has a good reliability and stability and can be used for sensing various materials in other frequency regions range from radio frequency through THz and to the infrared regime. This novel composite metasurface has good biocompatibility and low cost, which widens the application range of terahertz functional devices.

The optical Bloch oscillation (OBO) is an optical-quantum analogy effect that is significant for light field manipulations, such as light beam localization, oscillation and tunneling. As an intra-band oscillation, OBO was important for optical investigations in photonic lattices and atomic vapors over an extended period of time. However, OBO in reconfigurable platforms is still an open topic, even though tunability is highly desired in developing modern photonic techniques. Here we theoretically establish and experimentally demonstrate OBO in an electromagnetically induced photonic lattice with a ramping refractive index, established in a coherently-prepared three-level 85Rb atomic vapor under the electromagnetically induced transparency condition. This is achieved by interfering two coupling beams with Gaussian profiles and launching a probe beam that exhibits OBO within the resulting lattice. The induced reconfigurable photonic lattice possesses a transverse gradient, due to the innate edges of Gaussian beams, and sets a new stage for guiding the flow of light in periodic photonic environments. Our results should motivate better understanding of peculiar physical properties of an intriguing quantum-optical analogy in an atomic setting.

The traditional ways of tuning a silicon photonic network are mainly based on the thermo-optic effect or the free carrier dispersion. The drawbacks of these methods are the volatile nature and the extremely small change in the complex refractive index (Δn

The present work exhibits a novel design of surface plasmon resonance (SPR) biosensor, which comprises CaF2 prism, TiO2, metal (Ag/Au), PtSe2, 2D materials (graphene/ transition metal dichalcogenides (MoS2/WS2)) and sensing medium, for point-of-care detection of various stages of malaria diseases. The transfer matrix method (TMM) is employed to examine the angular reflectivity of the proposed structure after judiciously optimizing the layer thicknesses and layer numbers. Phase interrogation technique is utilised to validate the position of occurrence of resonance angles. Additionally, the proposed SPR structure is designed using COMSOL Multiphysics, to assay the electric field intensity and electric field enhancement factor near the edge of 2D material-sensing layer interface. Simulation upshots revealed that the use of new class of 2D materials catapult the sensor performance to a new height compared to the traditional SPR configuration. A maximum sensitivity of 240.10°/RIU, quality factor of 78.46 RIU-1 and detection accuracy of 1.99 is attained for Ag-based SPR configuration with bilayer of WS2. Sensing parameters are compared with previously reported works to prove the superiority of the present research. Moreover, the real-time and label-free detection of malaria diseases makes the suggested sensor worth to fabricate as a SPR chip with the recent nanofabrication technologies.

The Terahertz (THz)-based thickness measurement of thermal barrier coatings (TBCs) demands smart determination of THz peaks instead of human intervention for efficiency and accuracy, especially in the case of uneven microstructure due to imperfect spraying conditions. To this end, a long short-term memory (LSTM) framework driven by a theoretical model of THz signals is proposed to locate peaks automatically and location errors are eliminated by finding the maximum around the originally located results. Then, the local extrema are used to extract peaks for calculating refractive index online to remove the influence of the change in refractive index on thickness measurement. Finally, the simulations and experiments were carried out to verify the proposed method. The results show that our method generated identical results with those from the manual intervention, while the efficiency is significantly improved.

Thin film of WO3 has been deposited on conductive fluorine tin oxide substrate using the hydrothermal technique. The film's microstructural, morphological and optical properties have been identified using X-ray diffraction, atomic force microscope, and spectrophotometer. The obtained results have confirmed the nanocrystalline structure of the as-received WO3 thin film with crystallite size ≈63.4 nm. Analysis of the absorption coefficient using Tauc's model shows the possibility of direct and/or indirect allowed transition with energy gaps 3.95 and/or 3.45 eV, respectively. The refractive index has been determined by different methods showing the average value (2.2 and 2.3 corresponding to the direct and indirect transitions, respectively). The nonlinear refractive index and third-order nonlinear optical susceptibility have been determined, showing the high polarizability of WO3/FTO with radiation to be promising for different optical devices and applications.

The polypyrrole is a conducting polymer prepared by chemical route. The diffuse reflectance measured in the wavelength range (300–2500 nm) permitted the calculation of the refractive index (n), extinction coefficient (k), dissipation factor (tan δ) and relaxation time (τ). The optical band gap (E g) was evaluated from the dielectric and conductivity properties, and its value (1.01 eV) was confirmed by using the Tauc relation.

Bolometer sensors are prominent and excellent choice in technology because they do not need cooling. The trade-off between high sensitivity, fast response time, and strong light absorption is a key important challenge in bolometer sensors. Here, the bolometric effect for a high resistance sensitivity plasmonic sensing of total and profile infusion of radiation is studied for the proposed bolometer sensor based on plasmonic multilayer structure at 26° C. In the present study, by generating strong coupling condition between incident wave and surface plasmon polaritons (SPPs), a very narrow absorption spectra with high figure of merit (FoM) is achieved. The analytical model and numerical simulation are fulfilled based on the transfer matrix method (TMM) and 3-D finite-difference time-domain (FDTD), respectively. The narrow absorption spectra that generate by strong coupling with SPPs heats the silver thin film that leads to variation in temperature and supports TE surface mode. This temperature change rectifies the resistance of the metal thin film by the bolometric effect. So, optical characteristics of the proposed metasurface bolometer sensor, including quality factor (Q), sensitivity, and figure of merit (FoM) are calculated that Max sensitivity, FoM, and Q are 17.2 RIU-1, 530 and 434.5, respectively. Finally, we analytically simulate the temperature coefficient of resistance (TCR) in terms of wavelength and refractive index of analyte (na) that this resistance change can be monitored by an external electric model. The proposed plasmonic multilayer configuration is a very compact footprint structure that achieved high resistance sensitivity and FoM in comparison with any previous reports. This proposed thermal, optical, and electric plasmonic metasurface bolometer sensor can be used in different applications such as biophysics, biology, and environmental science.

In this paper, we propose and theoretically design a highly sensitive refractive index (RI) sensor based on Vernier effect in three coupled micro-ring resonators (CMRR) with identical geometries. When the whispering gallery mode phases of different microresonators match with each other, transmittance of the CMRR increases and the envelope peak wavelength shift of the modulated spectrum could be exploited for wavelength-interrogated RI sensing based on Vernier effect. Further simulation results indicate that RI sensing could be achieved within a wide RI range of 1.33 to 1.43 by adjusting RI of the liquid kept inside the control cavity, and limitless sensitivity could be achieved for some specific RI ranges which are mainly determined by geometric parameters of the resonators and the order of selected envelope peak for sensing, making the sensor available for different sensing requirements. The proposed CMRR provides a compact, flexible and low-cost solution for biochemical sensing applications. And moreover, the proposed RI sensing range extension method as well as limitless sensitivity mechanism pave a new way toward the development of dynamic RI sensing and tunable optoelectronic devices.

We propose and demonstrate a single fiber optical tweezer for particle multi-dimensional arrangement based on a high-order Bessel-like beam produced by concatenating a few-mode fiber and a step-index multimode fiber. We use the mode division multiplexing technology to produce the high-order Bessel-like beam with uneven energy distribution. The LP11 and LP21 mode beams are excited by docking a 980 nm single-mode fiber at the outlet of the light source to a few-mode fiber with a defined offset. The few-mode fiber allows LP01, LP11, and LP21 mode beams to be spread in. The high-order Bessel-like beam is focused by a high refractive index glass microsphere integrated on the fiber end facet. The LP01 mode beam is used to trap particles and array them in a one-dimension space (linear arrangement), the LP01 and LP11 mode beams are used to trap and array particles in a two-dimension space (planar arrangement), and the LP01, LP11, and LP21 mode beams are used to trap and array particles in a three-dimension space (solid arrangement). The proposed fiber optical tweezer is simple in structure and will allow us to examine the interaction between the cells when held in close proximity.

We present the structural design and polarization-maintaining performance of solid-core anti-resonant fiber with two nested circular tubes in 3 m wavelength for the first time, to the best of our knowledge. Numerical simulation results indicated that laser fundamental mode could be obtained by filling the specially designed fiber model with materials of different refractive indices to form the completely solid configuration. We calculated the bend loss of fiber to demonstrate the preferable birefringence performance and outstanding light-confining ability. With the structural deformations from resonant tubes, the birefringence coefficient was enhanced significantly from 210-5 to 6.9310-5, which was of great importance in the polarization sensitive systems. In particular, when nested circular tubes were moved to introduce deformations, the confined loss difference in two orthogonal polarizations was calculated more than two orders of magnitude, which was the desirable result to promote the fabrication of the linear polarizer in 3 m wavelength.

Optical tunneling is an effect extremely sensitive to wavelength changes. In this article, we use this effect to design a new type of biosensor. The tunneling effect is excited by long range surface plasmon resonance, the energy is concentrated in the sensing medium in the form of standing waves, which lead a very high wavelength sensitivity and quality factor. By using COMSOL for finite element analysis, for the sensor structure of BK7/Cytop /Al2O3/Ag/Al2O3/sensing media/air, a quality factor of 10296 RIU-1 is achieved under angle modulation, a sensitivity of 170,000 nm/ RIU and a quality factor of 11333 RIU-1 are obtained under wavelength modulation. At the same time, the advantage of this structure is that there is no excessive requirement on the refractive index of the material, and a good sensing effect can be achieved even if the material is cheap and easy to prepare. After optimization, this structure is suitable for sensing media with a refractive index of 1.335-1.375, which can be applied to most liquid solutions.

In this paper, a new method for pesticide detection based on porous silicon microcavities was proposed. First, the aptamer of acetamiprid was fixed in the functionalized porous silicon microcavity. Then, the complementary strand of the aptamer modified with graphene quantum dots was hybridized with the aptamer, and the effective refractive index of the porous silicon microcavity increased. When acetamiprid was added, it bound to the aptamer due to its stronger specificity. The aptamer separated from the complementary strand of the coupled graphene quantum dots and bound to acetamiprid, resulting in a decrease in the effective refractive index, and its central wavelength of reflection spectrum was blue shifted, and the blueshift increased with the increase of acetamiprid concentration. The relationship between the change in central wavelength and the concentration of acetamiprid was analysed, and the detection limit of acetamiprid was 151 nm.

To better utilize the infrared (IR) region in sunlight for photovoltaic devices (PVs), upconversion nanoparticles (UCNPs) have been proposed to improve power conversion efficiency (PCE). However, researchers recently have found that the upconversion (UC) effect is negligible in PVs performance improvement for their ultra-low UC photoluminescence quantum yields of UCNPs solid film, while the real mechanism of UCNPs in PVs has not been clearly studied. Herein, based on the material inorganic perovskites γ-CsPbI3, NaYF4:20%Yb3+,2%Er3+ UCNPs were integrated into different transport layer to optimize device performance. Compared with reference device, the short-circuit current density and PCE of optimized device reached 20.87 mA/cm2 (20.39 mA/cm2) and 18.34% (17.72%), respectively, without sacrificing open-circuit voltage and filling factor. Further experimental characterizations verified that the improved performance was attributable to enhanced visible light absorption instead of IR. To theoretically explain the statement, the light field distribution in device was simulated and the absorption in different layers was calculated. The results revealed that the introduction of UCNPs with different refractive index from other layers caused light field disturbance, and improved visible light captured by γ-CsPbI3. Importantly, through experiments and theoretical calculation, the research deeply explored the potential mechanism of UCNPs in optimizing PVs performance..

In this paper, we demonstrate the transmission spectral and surrounding refractive index (SRI) sensing performance of long-period fiber gratings (LPFGs) at 2 m waveband. The cladding modes operating at 2 m waveband show higher SRI sensitivity than 1.55 m waveband. The influence of a little off resonance region of grating period, refractive index modulation and duty cycle of gratings are analyzed theoretically. Additionally, the LPFGs of LP08 mode near dispersion turning point operating at 2 m waveband are investigated theoretically and experimentally. Mode splitting brings out with the increasing SRI. After the resonant dip splitting into two dips (dip A and dip A), the SRI sensitivity of dip A are measured to be as high as -8495.2 nm/RIU in the SRI region of 1.445-1.457. The proposed 2-m-waveband LPFG makes it a potential in biochemical and environmental monitoring.

This letter presents a novel hybrid design approach for the Fresnel zone lenses (FZL). The method combines the two conventional design approaches: grooved and perforated methods. Perforated lenses minimize the shadow blockage that grooved lenses suffer from, and therefore provide improved antenna gain. However, the fabrication of the low refractive index regions in the perforated lenses is challenging due to the limited manufacturing resolution, which means low refractive index dielectrics cannot be realized. The proposed hybrid FZL design utilizes the perforated method for the inner regions and applies the grooved method for the outer regions. This paper describes the equations used to optimize the design and gives the general design guidelines. A hybrid FZL antenna that operates at the center frequency of 33 GHz is presented. Measurement results show that the hybrid FZL improved the realized gain by up to 3.2 dB and the -3 dB gain bandwidth by up to 2 GHz when compared with the equivalent grooved FZL.

To use optical modeling to compare a 6.0 mm and 7.0 mm intraocular lens (IOL) optic diameters on peripheral retinal illumination with implications for negative dysphotopsia.Mayo Clinic, Rochester, Minnesota, and Simpson Optics LLC, Arlington, Texas.Model eye.Ray-tracing software was used to simulate retinal illumination from an extended light source for a pseudophakic eye with in-the-bag biconvex IOLs (refractive index [n] = 1.46 and 1.55) and a 2.5 mm pupil. Ray-tracing diagrams and simulated retina illumination profiles were compared using the 6.0 mm and 7.0 mm optic diameter IOLs. Retinal locations were scaled to relative visual angles from 70 to 110 degrees horizontally.A 7.0 mm optic (n = 1.46) expands the image field by 2.8 degrees compared with a 6.0 mm optic. High-angle input light misses a 7.0 mm optic at a larger visual angle than a 6.0 mm optic, shifting illumination of the peripheral retina by this light anteriorly by 5.6 degrees. Consequently, a region of nonilluminated peripheral nasal retina is enlarged and shifted peripherally using a 7.0 mm optic (visual angle, 86.3 to 96.3 degrees) compared with a 6.0 mm optic (visual angle, 83.5 to 90.7 degrees). Similar illumination changes were seen modeling a 1.55 n IOL.A narrow dark region in the nasal retina when using a 6.0 mm optic is changed to a broader, more peripheral dark region when using a 7.0 mm optic. An extended, more peripheral dark nasal region may make a temporal shadow less bothersome and explain lower negative dysphotopsia rates using a 7.0 mm optic.

This study uses silicon wafer as the substrate, on which a multi-layered structure is formed. This structure includes a 50-nm indium tin oxide (ITO) film, ZnO films with variable thickness and ZnO nanorods of various radii and height on the top. This kind of coating can enhance solar cell productivity at omnidirectional angles because there is a gradual declination of the refractive index. The multi-layered structure were designed and tested using Finite-difference time-domain (FDTD) simulations, and this reduced it reflectance to

In this paper, a new architecture for developing plasmonic bio-sensors is proposed in which sensing is achieved through optical beam steering. The proposed structure consists of an array of nano-antennas that generate an outcoming optical beam whose direction varies when the material under test or its volume changes. This mechanism of sensing eliminates the requirement for complex instruments such as optical spectrum analyzers. For realization of the proposed bio-sensor, both 1-D and 2-D configurations for the nano-antenna array are designed and numerically studied. The full wave numerical simulation results show that the designed bio-sensor provides a very high sensitivity of per unit refractive index, and also the output light has an enough intensity to be observed by a naked eye. The final results show that although both versions have the same sensitivity, the 2-D structure can project the results with much higher intensity. It is also theoretically shown that the performance of the biosensor will be subject to the size of the array, and therefore, a practical large-scale version of the numerically studied structure would significantly outperform the simulated structure.

Highly sensitive, simple and multiplex detection capabilities are key criteria of point-of-care (POC) diagnosis in clinical samples. Here, a simple and highly sensitive multi-analyte detection technique is proposed by using photonic crystal fiber (PCF) based surface plasmon resonance (SPR) sensor that employs both internal and external sensing approaches. The proposed sensor can detect two different analytes simultaneously by the internal and external plasmonic micro-channels. The light propagation through the sensor is controlled by the scaled-down air-holes to excite the free electrons of the plasmonic metal layers. The light-guiding and sensing properties of the sensor is numerically analyzed by using the Finite Element Method (FEM). The proposed sensor shows the maximum wavelength sensitivities (WS) of 12,000 nm/refractive index unit (RIU), and 10,000 nm/RIU, for the internal and external sensing approaches, respectively, and corresponding resolution of 8.33×10-6 RIU and 1.0×10-5 RIU. Moreover, the hybrid sensor is applicable to detect unknown analyte refractive index (RI) in the range of 1.33 to 1.40 which covers extensively investigating analytes such as viruses, different cancer cells, glucose, proteins and DNA/RNA. Due to high sensing performance with multi-analyte detection capability, the proposed sensor can play a significant role to detect bio targets at the POC platform.

Coherently coupled microcavity lasers have desirable properties for emerging applications. We use 2-dimensional complex refractive index waveguide modeling of 2-element photonic crystal vertical cavity surface emitting laser arrays to analyze their supermodes. The complex modal effective indices are used in turn to calculate the complex coupling coefficient between the laser array elements. An analysis of the effects of array design parameters, such as photonic crystal period, fill-factor, or confinement, to engineer the coupling coefficient for the desired properties is given and example designs for 850 nm arrays are presented.

The study of refractive index provides the complete picture of material bodies with reference to their major properties like physical, chemical, optical, etc., and hence decides the behavior of the material body at macro level. Measurement of refractive index in small volume samples using a U-shaped extrinsic fiber optic sensor based on the principle of direct contact evanescent wave absorption can be employed to detect such information. In order to obtain such measurements, a U-shaped glass probe connected between a light transmitter and an optical detector using two PCS multimode optical fibers of the same diameters (200/230 μm) was developed and investigated in the present study. Liquid mixtures prepared using Toluene and Acetic acid taking at different proportions making total volume equivalent to 20 ml employing a two burette system. When the liquid mixtures are applied on the U-shaped probe the light reaching the detector from the source was shown varying depending upon the refractive index of the mixture. The changes in the transmitted power spectra were measured as a function of absorption of higher order evanescent wave modes at various refractive index values at different temperature levels ranging from 20 °C to 60 °C of the mixture and by repeating the experiment with various operating wavelengths (630 nm, 660 nm, 820 nm & 850 nm). The calibrated curves were plotted, which can be used to determine the refractive index of liquids at various temperatures with high degree of accuracy, precision and sensitivity measurements, exploiting all the benefits offered by the optical fiber communication systems.

We present a numerical analysis of noise performance improvement of the erbium-doped fiber amplifier by flatting the mode field intensity distribution within the interaction region of erbium ions. Three different refractive index types of erbium-doped fiber were used to study the effect of the pump mode intensity distribution on noise performance. The results show that taking advantage of the depressed refractive index erbium-doped fiber which has a flat mode distribution in the fiber core, the maximum reduction of nearly 0.53 dB for noise figure was achieved across the full C-band. Based on the center depressed refractive index profile, the noise figure was further decreased by about 0.1 dB by reducing the doping radius to 0.71 μm. Finally, maintaining the same gain level of ∼38.3 dB, a NF reduction of ∼0.63 dB was realized by introducing the center depressed refractive index profile and narrowing the erbium doping region. It is suggested that our investigation shows great potential for improving the noise performance of the erbium-doped fiber amplifier.

We present a microfluidic device compatible with high resolution light sheet and super-resolution microscopy. The device is a 150 μm thick chamber with a transparent fluorinated ethylene propylene (FEP) cover that has a similar refractive index (1.34) to water (1.33), making it compatible with top-down imaging used in light sheet microscopy. We provide a detailed fabrication protocol and characterize the optical performance of the device. We demonstrate that the device supports long-term imaging of cell growth and differentiation as well as the rapid addition and removal of reagents while simultaneously maintaining sterile culture conditions by physically isolating the sample from the dipping lenses used for imaging. Finally, we demonstrate that the device can be used for super-resolution imaging using lattice light sheet structured illumination microscopy (LLS-SIM) and DNA PAINT. We anticipate that FEP-based microfluidics, as shown here, will be broadly useful to researchers using light sheet microscopy due to the ability to switch reagents, image weakly adherent cells, maintain sterility, and physically isolate the specimen from the optics of the instruments.

Experimental studies into the beam parameter product ( BPP ) of 940–980 nm GaAs-based high-power diode lasers are presented. Such lasers exhibit broadening far field and narrowing near field with increasing bias, with BPP increasing tenfold over the diffraction limit. First, spectrally-resolved beam profile measurements of lasers with monolithically-integrated gratings are presented, showing that a reproducible series of spatially-extended optical modes makes up the optical field. Then, changes to the device construction are presented, enabling effects limiting BPP to be inferred and addressed. Process- and package-induced effects can be minimized by design, while the effects of carrier, gain and temperature profiles dominate. Self-heating within the laser stripe raises the refractive index, forming a thermal lens, and the variation in curvature of this lens with bias and device construction directly affects BPP . Temperature non-uniformity along the resonator is also shown to strongly degrade BPP . Moreover, current spreading and the resulting lateral carrier accumulation (LCA) amplify high-order, high- BPP modes, thus degrading BPP for any given thermal lens. This LCA-induced degradation is shown to be suppressed by regrown lateral current-blocking structures. Finally, a flatter thermal lens and lower BPP can be achieved using thermal engineering, via changes to the epitaxial design or device layout.

The study of refractive index of liquids becoming increasingly popular in diverse areas to monitor chemical, pharmaceutical, food, scientific, biochemical, medical, etc. processes and procedures. In the present paper a low cost, simple, compact, reliable, robust, miniaturized and sturdy Refractive Index sensor is reported. It is configured by using a set of two multimode PCS fiber of 50 cm length in each, connected one to the source of wavelength 660 nm and other to a light detector. A glass rod drawn in the form of ‘U’, of compatible dimensions to that of two multimode fibers, was connected between source and detector by jointing to the remaining ends of the fibers, thus creating a sensing zone. Maintaining the binary liquids of Toluene and t-Butanol at the sensing zone at various temperatures, the light launched from source was monitored in the detector at the detector end. By forming relationship between index of refraction and power output at the temperature range of 10 °C to 60 °C, the sensor expected to be used to detect the index of refraction of liquids with maximum resolution of the order of 10-5 in the operating range from 1.36312nD to 1.50915nD.

Summary Ferroelectrics with switchable spontaneous polarization have taken a dominant position as the nonlinear optical candidates, of which birefringence is an essential merit to optical devices. Despite the increasing advance of hybrid perovskite ferroelectrics, it remains a great challenge to control and tune their birefringence, thus hindering their practical optical applications. Here, we present a 2D trilayered hybrid perovskite-type ferroelectric obtained by 3D-to-2D dimensional tailoring, [(CH3)2CH(CH2)2NH3]2(CH3NH3)2Pb3Cl10, showing biaxial polarizations of ∼5 μC/cm2 and a relatively wide optical band gap. The intrinsic 2D architecture results in highly anisotropic principal refractive indices, namely, the optical birefringence. Interestingly, its birefringence can be reversibly switched through ferroelectric-to-paraelectric symmetry breaking. The birefringence tuning is further established by virtue of pretransitional modulation of ferroelectricity, exhibiting unusual polarization-dependent behaviors. In our judgment, this study on the polarization-dependent birefringence of hybrid perovskite ferroelectrics will provide a new pathway toward modulating nonlinear optical properties for smart devices.

A terahertz metamaterial refractive index/thickness sensor with flexible substrate, exhibiting low-frequency Fano resonance and high-frequency electromagnetically induced transparent (EIT) resonance, is proposed. The physical formation mechanisms of Fano and EIT resonances are investigated by calculating the electromagnetic field. Simulated results demonstrate that the refractive index sensing sensitivity based these two resonances are up to 60 and 100 GHz/RIU, and the thickness sensing sensitivity are up to 1 and 1.7 GHz/μm, respectively. Furthermore, the proposed sensor was fabricated using femtosecond laser etching technology, and its sensing performance was verified by the experimental results that it can distinguish different liquids and detect the polyimide film with different thicknesses less than 180 μm. The remarkable performances make the proposed metamaterial sensor has feasible capability for biological and chemical sensing in terahertz range.

In this work we present the first application of software-defined optoelectronics (SDO) for bidimensional optoacoustic tomography (OAT). The SDO concept refers to optoelectronic systems where the functionality associated with the conditioning and processing of optical and electrical signals are digitally implemented and controlled by software. This paradigm takes advantage of the flexibility of software-defined hardware platforms to develop adaptive instrumentation systems. We implement an OAT system based on a heterodyne interferometer in a Mach-Zehnder configuration and a commercial software-defined radio platform (SDR). Here the SDR serves as a function generator and oscilloscope at the same time providing perfect carrier synchronization between its transmitter and receiver in a coherent baseband modulator scheme. Therefore, the carrier synchronization enables us to have a much better phase recovery. We study the performance of the OAT SDO system by means of different bidimensional phantoms and the analysis of the reconstructed images., Comment: Published in Applied Optics

Nonlinear optical materials, whose optical properties such as refractive index can be changed by light, are essential for advanced light functionalities such as all optical switching. In this chapter, the fundamentals of nonlinear optics have been described and the second- and third-order nonlinear optical materials based on both organic and inorganic molecules have been reviewed. In particular, the nonlinear optically active subwavelength scale architectures have been highlighted.

A single-polarization fiber is an important device in many applications ranging from communications to sensors. However, most of the single-polarization fibers focus on linear polarization, and the single-polarization fiber supporting a circular polarization remains a challenge. Here, we propose a novel wavelength-tunable single-circular-polarization (SCP) twisted photonic crystal fiber (PCF). The single left-circular polarization and single right-circular polarization operate around $1.665 ~\mu \text{m}$ and $1.700 ~\mu \text{m}$ , respectively. The resonance can be tuned by adjusting the twist rate of PCF and the refractive index filling. The SCP bandwidth is up to 20 nm, and the polarization extinction ratio is as high as 1.3 dB/cm. This design not only extends the single-polarization fiber to circular polarization but also provides a twisting PCF application.

In this work, we propose a simple yet highly sensitive multi-channel hexagonal photonic crystal fiber (PCF) based surface plasmon resonance (SPR) refractive index (RI) sensor for detecting multiple analytes. The target analytes and the plasmonic materials, such as, gold (Au), Au with Tantalum Pentoxide (Ta2O5) and Au with Titanium Dioxide (TiO2) are employed around the exterior of the sensor for the feasibility of the operation. Twelve circular air-holes in two layers constitute the fiber structure which makes the fabrication process easy and realizable. Numerical investigations are carried out employing a full-vector finite element method (FEM) to obtain the sensing performance of the PCF-SPR structure. After optimizing the structural parameters, the sensor achieves maximum wavelength sensitivity (WS) of 38100 and 21600 nm/RIU, for channels-1 and -2, respectively. For channel-3, the sensor achieves a maximum WS of 45800 nm/RIU. To the best of our knowledge, the proposed sensor achieves better performance in terms of wavelength sensitivity, wavelength resolution, amplitude sensitivity, amplitude resolution, figure of merit, etc., compared to the existing literature. In the case of cancerous cell detection, the proposed sensor achieves maximum WS and amplitude sensitivity of 12000 nm/RIU and -2440.30 RIU-1, respectively, for HeLa cells. We envisage that the proposed sensor has a high potential to detect unknown RI for different chemical and biomedical applications due to its superior performance, simple design, and multi-analyte detection ability.

We propose a new type of self-referencing and multiplexed refractive index (RI) sensor based on a compound optical microresonator structure consisting of Fabry-Pérot (FP) resonators coupled with microring resonators. The transmission spectra shows resonant features that are superimposed on a background defined by FP oscillations. The resonances have asymmetric Fano-like non-Lorentzian shapes, which are used as sensing peaks, while the FP oscillations are used as reference peaks for internal self-referencing. The sensing peaks shift linearly with the increased RI of the cladding in the microring resonator, while FP peaks stay constant. When the temperature is increased, both the FP peaks and the Fano resonances shift linearly at the same rate, which eliminates the temperature effect on RI measurements. We theoretically analyzed that the two-mirror FP resonator coupled with a single microring resonator and optimized its sensing performance through finite-difference time-domain simulations. A sensitivity value of 220 nm/RIU and a maximum figure of merit of 4400 RIU-1 were achieved. We also proposed two possible multiplexing schemes consisting of two-mirror and three-mirror FP resonators coupled with two microring resonators of different radii. The proposed sensor concept is simple, easy-to-fabricate, self-calibrating and can be used for simultaneous measurements of different samples.

This work presents a study of the resistive switching behavior of ZnO thin films deposited via DC magnetron sputtering. Thin films were deposited on soda-lime glass and Ti foils, varying ZnO target power, between 80 W and 120 W, and substrate temperature, between 293 K and 423 K. All samples were submitted to annealing processes in situ at 473 K for 2 h. XRD measurements allowed identifying the ZnO wurtzite phase, while AFM micrographs showed the surface formation characterized by small, elongated grains of approximately 80 nm wide. Optical properties were determined by the Swanepoel method using transmittance spectra in the range of 300 nm to 1100 nm. The band-gap obtained was about 3.28 eV for the ZnO thin film, and the refractive index and extinction coefficient were calculated. Modification of the transport mechanism was associated with high defect concentration in the samples and contributed to resistive changes. I-V curves were performed in the -1 V–1 V range and showed a bipolar switching behavior in all samples. A correlation between the variation of synthesis parameters, structural characterization, and shape of bipolar switching effect was evidenced through a change in the resistance states and thickness of thin films. This research provides an insight into the fabrication and control of the resistive switching behavior for resistive random access memories.

One of the key elements for early diagnosis of acute and severe diseases is the development of ultra-sensitive detection methods, which are required to analyze the pathological state of the human body from trace amounts of substances in blood or urine. Surface plasmon resonance (SPR) optical fiber biosensors, particularly those based on tilted fiber Bragg gratings (TFBG), have emerged in recent years as a novel solution for in-situ biomedical detection. TFBGs can sensitively detect the physical and chemical interactions between biomolecules in real-time by sensing minute changes in refractive index, even in vivo. The TFBG-based SPR method can achieve rapid and accurate analysis of biological samples by demodulating the wavelength, intensity, phase and polarization state of the optical spectrum. In addition, TFBG-based SPR fiber optic sensors are capable of simultaneously detecting the absolute or relative values of multiple parameters. This effectively eliminates the interference from the ambient environment and ensures the stability and reliability of the sensor.

This study successfully developed a semiconductor metal oxide-based ammonia gas sensor that was powered by an Ultraviolet–Visible-near-IR optical light source. However, optical fibre gas sensors using single metal oxide nanomaterial are limited. To address this situation, a h-MoO3 nanorod was grown on a tapered region of optical fibre glass using a simple chemical bath deposition to form a unique sensing element. An additional annealing treatment was then performed to modify the oxidation state of h-MoO3. The property changes of the samples were characterised using different techniques, such as FESEM, TEM, XRD, XPS, TGA and UV–Vis. Overall, the annealing treatment improved the sensitivity performance, response and recovery time of the sensor towards NH3. h-MoO3 that was annealed at 150 °C in air showed stable room temperature absorbance responses of 0.05, 0.18, 0.22, 0.28 and 0.35, a fast response time of 210 s towards 500 ppm of NH3 and strong stability and repeatability. The optical NH3 gas-sensing behaviour was significantly correlated with the non-stoichiometric Mo5+ content. The chemisorbed oxygen species and physiosorbed NH3 altered the refractive index and its absorption coefficient on the nanorod, which manipulated the optical signal and acts as a sensing mechanism. These results verify that a chemical bath deposition growth of the h-MoO3 nanorod exhibits a promising optical sensing characteristic, which paves a path for emerging gas-sensing technology.

This letter presents an end-fire fan-beam radiation antenna by utilizing a gradient refractive index metamaterial lens. The lens includes one core and two impedance matching layers which are both based on the proposed metamaterial unit cells with a large refractive index variation range. An incident wave is excited from the antenna source and propagates to the lateral side of the lens. Two parallel plates set for the TE1 mode condition are utilized such that E-plane radiating beam can be controlled. To validate our proposed design, a prototype working at 10 GHz is fabricated and measured. Measured results are in good agreement with the simulation. The height and thickness of the metamaterial lens are about 0.44 0 and 0.36 0, where 0 is the wavelength of the center frequency in free space. The measured E- and H- planes 3-dB beamwidths are 25o and 82o at the center frequency, respectively. The measured peak gain of the antenna is about 11.1 dBi, which implies a 5.4 dB gain enhancement compared with initial radiation source. Furthermore, this lens offers a high aperture efficiency of 72.4%.

Surface plasmon resonance (SPR) is used to infer information about a sample that is in contact with an Au-coated glass slide coupled to the SPR prism. Shifts in the angle of the "SPR minimum reflection" can be related to changes in the refractive index (and/or thickness) of the sample that is in contact with the Au film, which can then be used to determine the concentration of an analyte in that sample. Here, we show that by depositing a layer of poly(N-isopropylacrylamide-co-acrylic acid) [p(NIPAm-co-AAc)] microgel on the SPR's Au film, with a subsequent layer of Au deposited on top of the microgels, the sensitivity of SPR to changes in solution properties can be enhanced. We investigated the sensitivity of the SPR to changes in the temperature of water in contact with the SPR's Au film as a function of the microgel immobilization density and the thickness of the Au layer deposited on the microgel layer. The data revealed that the SPR's Au film densely coated with microgels, with 5 nm of Au deposited, exhibited the maximal enhancement. The plasmon coupling effect between the additional Au film on the microgels and the SPR's Au film was further confirmed by 3D finite difference time domain simulations.

This article introduced a double guided ring-based spiral photonic crystal fiber (S-PCF) supporting both the orbital angular momentum (OAM) and linear polarization (LP) mode simultaneously with the efficient transmission. The outcomes exhibition that the designed S-PCF have good optical features such as less confinement loss (4.05342 × 10−12 dB/m for the EH9,1 mode), better mode quality and ISO (up to 98.87% and 126 dB, respectively), supported a decent amount of modes which is numerically 64 OAM and 6 LP modes, maintaining the large refractive index differences (> 10 - 4 ) of all the eigenmodes, and a relatively flat dispersion variation (0.0743 ps/km-nm for the EH1,1 mode). Also, we obtained the crosstalk less than −12 dB and the power fraction is approximately 93%-99% of the S-PCF. All the optimizing properties are obtained using the full-vector finite element method (FEM) and also the perfectly matched layer (PML) as a boundary condition. Thus, the above mentioned optimizing propagation characteristic based S-PCF has effective applications like reliable long-distance communication into the space division multiplexing (SDM) process of the large-capacity fiber communication systems.

Chalcogenide materials are ideal for IR applications because of their wide transmission window, variable bandgap, and high nonlinearity. In this regard, optical characteristics of (Dy) doped (GeTe2)80(In2Te3)20 thin films have been measured and investigated. The influence of annealing on the optical characteristics of thin films has been reported. The reflectance and transmittance spectra were used to calculate the refractive index (n) and extinction coefficient (k) of thin films. With the annealing of as-prepared film, the penetration depth (Δ) measured at a wavelength of 1.1 μm and bandgap (Eg) decrease. The relaxation process has been realized using electric modulus (M) determination, and the dielectric loss has been estimated in terms of loss tangent (tan δ). Wemple Di-Domenico (WDD) model has been employed to calculate dispersion energy (Ed) and average energy gap (E0). Using the values of E0 and Ed, the static refractive index (n0) and the moments (M-1, M-3) of the optical spectra have been determined. Sellmeier oscillator parameter (λ0) increases while So decreases with a rise in the annealing temperature.

Lithium niobate LiNbO3 (LN) on insulator wafers (LNOI) representing a submicron-thick LN film bonded to a SiO2 layer deposited on a thick LN substrate have been manufactured recently by ion slicing. Today, LNOI is one of the most promising materials for fabrication of various integrated optical devices, including waveguides, electro-optical modulators, and wavelength convertors, due to their high drop in refractive index at the interface between the film and the SiO2 layer. Creation of the stable domain structures with submicron periods in LNOI will improve the properties of nonlinear optical devices. Periodically poled LN with periods below 300 nm can be used to implement an optical parametric oscillator in the backward configuration. We have studied experimentally the ways to create the stripe domains and periodical domain structures in LNOI with a dielectric layer under the film by local switching. The identified scenarios of the domain evolution were attributed to the ineffective screening of depolarization field. We have shown that stripe domains and periodic domain structures can be produced by scanning with a biased tip only at temperatures above 80 °C. Periodical stable domain structures with periods down to 300 nm have been created.

A method for the construction of a tiny in-line coupler tip is presented. An in-line coupler tip was manufactured by tapering a dual-core PCF and cleaving half of the waist region. Even and odd supermodes with different propagation constants are produced in the tapered region, which results in the inter-mode interference. The interferometric spectrum depends on both the length of the tapered region and the refractive index. Due to the thermo-optics coefficient and thermal expansion coefficient of the pure silica, the temperature of the external environment can be measured by interrogating the optical reflection spectrum. Therefore, the in-line coupler can be constructed for the measurement of temperature. The experimental results show that the temperature sensitivity of 0.024nm/°0 and operation range of 1425°C are achieved. Compared with other expensive methods, the proposed method possesses wide operation range and tiny size. Thus the microstructured fibre sensor technique appears to have potential applications in industry, medicine, biology, and chemistry.

An idea of a colored glaze is presented in this study to hide and dispose all the obstacles of using solar systems as facades integrated with buildings. This aim is achieved by designing multilayer optical interference filters by using Mat lab program . Appropriate dielectric materials, namely NdF3 of high refractive index (nH =1.6) and ThF4 of low refractive index (nL =1.5143) were employed. Quarter wave thicknesses of high (H) and low (L) refractive index were deposited on a microscopic slide substrate with n=1.513 and 550 nm design wavelength (l°). Two optical models were designed, which are Air//HL//glass and Air//LH//glass, for even numbers of layers (2-32 layers). The challenge in this study is to find the most efficient design which has lower solar reflectance (Rsol.) and higher solar transmittance (Tsol.) to raise the efficiency of the solar systems and, in parallel, obtain the colored reflection to achieve the esthetic appearance of the buildings integrated with the solar system facades. The Tsol. value was high (94-95 %), whereas the Rsol. was very low (4-5 %). Hence, the efficiency of the solar system was increased. The two optical models exhibited green color reflectance in the visible region. The first design, i.e. Air/HL/glass, showed higher values of Rvis. and the merit factor (M) than the second model, resulting in a higher potential of coloration. The first design requires fewer materials and layers, thus, it is more cost-effective as compared to the second one.

A method to determine the optimum laser parameters for maximizing laser induced refractive index change (LIRIC) while avoiding exceeding the damage threshold for different materials with high water content (in particular, polymers such as hydrogels or the human cornea) is proposed. The model is based upon two previous independent models for LIRIC and for laser induced optical breakdown (LIOB) threshold combined in a simple manner. This work provides qualitative and quantitative estimates for the parameters leading to a maximum LIRIC effect below the threshold of LIOB.

Compositional dependence of the linear and nonlinear optical characteristics of dye–polymer composite (DPC) films based on methylcellulose-methylene blue (MC-MB) were studied. The absorbance spectra were used to estimate absorption edge, optical density, skin depth, optical band gap energy, and Urbach's parameters for all DPC films. The direct allowed optical band gap energy decreased from 6.29 eV for pure MC to 5.95 eV when doped with 2.5 wt.% of MB. The dispersion of the refractive index is discussed in terms of both the single-oscillator Wemple–DiDomenico and single Sellmeier oscillator models. The nonlinear optical characteristics such as the third-order nonlinear optical susceptibility and nonlinear refractive index were calculated using the dispersive oscillator parameters obtained from the single-oscillator model. The observed improvements in the linear and nonlinear optical characteristics of MC upon incorporating MB make the present DPC a potential candidate for multifunctional applications like optoelectronic and photonic devices.