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A refractive index sensor is proposed comprising one-dimensional photonic bandgap geometry in conjunction with a thin metal film. The refractive index sensor is based on the cavity mode formed in a thin cavity layer sandwiched between multilayers of SiO2/Ta2O5 and a metal film. The cavity structure traps light through excitation of the cavity mode and hence sharp resonance minima (maxima) are obtained in the reflection (transmission) spectrum. Our theoretical model investigates the impact of cavity thickness, nature of plasmon-active metal, the angle of incidence, and polarization of light on the sensitivity. It is found that the resonance wavelength increases linearly as the analyte refractive index increases. Additionally, the enhancement in the interaction between the analyte medium and micro-cavity mode-field further enhances the sensitivity of the proposed sensor. It is observed that as the cavity thickness increases from 200 nm to 900 nm, the sensitivity increases from 200 nm/RIU to 350 nm/RIU. The performance of the proposed photonic crystal based sensor exhibits strong polarization and angular dependences. Also, the sharp micro-cavity resonance results in improved detection accuracy as compared to surface plasmon resonance based schemes. The proposed structure advantage is an alternative to the conventional surface plasmon refractive index sensor. [ABSTRACT FROM AUTHOR]

Complex aperiodic 1D dielectric distributions offer intriguing optical propagation features. For example, Thue–Morse (TM) sequence-based 1D photonic crystals (PCs) exhibit transmission spectra that are characterized by fractal band structure, i.e. they comprise traditional photonic band gaps (TPBGs) and fractal PBGs along with non-intuitive local resonances. These arise out of not-so-apparent positional correlations in the dielectric distribution. We identify inter-cell and intra-cell interaction between hidden dimer-like units in a TM-PC and present a relationship between the topological phase of lowest-order pass bands with reflection phase (φ) in the TPBGs. The analysis reveals that the dielectric filling factor (σ) of a TM-PC could serve as a parameter that determines the topological invariants for the geometry and could be tuned optimally in TM-PC-based heterostructures for exciting optical edge modes, which are disorder resistant (or topologically protected). We also discuss the robustness of optical edge modes. [ABSTRACT FROM AUTHOR]

In this study, we analyze the combined effect of TMD/Perovskite/2D Material on the performance of SPR biosensor using Kretschman configuration. In order to optimize the parameters, we compare the results of each material falls in the family of TMD/Perovskite/2D respectively and finally applied in the proposed sensor. It is observed that the combined structure based on black phosphorus, a 2D material, Barium Titanate (BaTiO3) as a Perovskite material and Tungsten disulfide (WS2) as a TMD material respectively shows excellent performance in terms of a performance parameter of the sensor. Incident light wavelength is fixed of 633 nm and radiative properties of a multi‐layered structure are calculated by transfer Metrix method. Essential performance parameters like Figure of Merit (FOM), Sensitivity, Detection Accuracy obtained by using the standard formula given in the paper. The reported figure of merit (FoM) and sensitivity are 62.51/RIU and 370. respectively. The results obtained in this paper expect to prove a significant role in the biosensing field like DNA hybridization as well as for the application of Perovskite materials in biosensing. [ABSTRACT FROM AUTHOR]

We present a novel scheme for generation of broadband mid-infrared (mid-IR) radiation using a quasiphase-matched difference-frequency-generation (DFG) process in a planar high index core symmetric Bragg reflection waveguide (BRW) geometry based on GaN/AlxGa1-xN system. By suitably tailoring the dispersion properties of the BRW so as to maintain the phase-matching condition over a broad range of pump wavelengths, we show that the pump acceptance bandwidth could be enhanced by nine to ten times for a DFG process. This manifests into a broadband mid-IR difference-frequency idler with greater than 280 nm bandwidth close to 4.35 μm wavelength. Since the design presented here exploits the dispersive features of the BRW; we can shift the broadband characteristics to any desired region of the mid-IR spectrum within the constraints imposed by transparency and nonlinearity of the constituent materials. The design also facilitates pumping by standard high-power solid-state laser sources. [ABSTRACT FROM AUTHOR]

We present a detailed design principle and propagation characteristics of a channel plasmon-photonic-crystal-coupled-waveguide (PPCCW) for realizing terahertz (THz) waveguides and waveguide-based devices. The avoided-crossing behavior exhibited by dispersion curves of the supermodes due to modal interference leads to a sharp change in group velocity close to the phase-matching wavelength. As a consequence, the group-velocity dispersion (GVD) peaks to a maxima (~1.40 × 10 ps/km·μm) and dips to a minima (~−1.60 × 10 ps/km·μm), thus exhibiting extremely large GVD. The propagation length is obtained in the order of a few centimeters. The analysis is substantiated by the frequency dependence of mode field distribution and propagation loss suffered by the supermodes of PPCCW geometry. Also, the obtained result is in good agreement with FEM-based study. The proposed waveguide is aimed at facilitating enhanced performance THz-waveguide sensors and GVD compensation modules. [ABSTRACT FROM AUTHOR]

Hybrid modes formed as a consequence of coupling between Tamm-plasmon polariton (TPP) mode and surface plasmon polariton (SPP) mode in a metallo-dielectric heterostructure geometry exhibit interesting dispersive features which can be employed for realizing highly sensitive and accurate surface-plasmon-resonance (SPR) sensor. The transverse magnetically (TM) polarized TPP modes (TM-TPP), formed at the interface of distributed-Bragg reflector (DBR) and metal, are strongly dispersive as compared to SPP modes at optical frequencies that forms the basis of narrow interaction bandwidth which, in turn, results in improved accuracy of sensing. By deploying a nano/micro-fabrication compatible TiO 2 /SiO 2 -based DBR architecture in combination with different plasmon-active metals such as gold (Au), silver (Ag) and aluminum (Al), we propose a TM-TPP and SPP hybrid-mode sensor which exhibit high sensitivity ≥ 900 nm/RIU for analyte refractive indices varying between 1.330 and 1.345. The investigation also revealed that the hybrid-mode sensor is most accurate in case of Al-based configuration amongst Au, Ag and Al which is primarily due to weaker dispersion characteristics exhibited by Al at visible frequencies. Since, the dispersive behavior of TM-TPP modes could be tailored appropriately in any spectral band, the sensing configuration could be immensely useful for designing sensors at those wavelength where optical sources are readily available. [ABSTRACT FROM AUTHOR]

The article reports on the tailoring of the spectral features of extraordinary transmission (EOT) through sub-wavelength periodic hole array using a distributed-Bragg-reflector (DBR). Topics discussed include the new EOT created by the photonic stop-bands and high transmission regions in the DBR spectrum, and full-vectorial two-dimensional finite difference time domain (2D-FDTD) technique.

We present an experimental study on measurement of nonlinear refractive index ( n) of organic liquids when the thermo-optic effects manifest into large nonlinear phase shifts (Δ ϕ) in an open-aperture Z-scan configuration. Although we do not obtain the familiar peak-valley normalized transmittance curve as in the case of closed-aperture Z-scan technique, we use a theoretical model using Gaussian beam decomposition (GD) technique to estimate the value of n. Using this recipe, we obtain the nonlinear refractive index n = −(4.90 ± 1.20) × 10 cm/W for toluene (organic solvent) and n = −(10.60 ± 2.10) × 10 cm/W for an organic polymer solution (10 M in toluene). By carrying out absorption measurements directly with an unfocussed Gaussian beam, we found nonlinear absorptions β = (2.42 ± 0.20) × 10 m/W and β = (2.79 ± 0.24) × 10 m/W which are close to the expected results. [ABSTRACT FROM AUTHOR]

We propose a highly sensitive temperature sensor based on photonic crystal surface plasmon waveguides comprising different plasmonic active metals such as gold, silver, and aluminum, utilizing surface plasmon resonance phenomenon. We found that the resonance wavelength can be easily and substantially tuned over a broad spectral range by changing the temperature and also by judiciously choosing the different plasmonic metals. Employing coupled mode theory, we found that the proposed sensor can be used in harsh environment with sensitivity as high as ∼70 pm/K around telecommunication window. [ABSTRACT FROM AUTHOR]

Abstract: A highly sensitive surface plasmon resonance (SPR) sensor based on channel photonic crystal waveguide (PCW) is proposed. The PCW is based on widely used lithographic and nano-fabrication compatible materials like TiO2 and SiO2. Gold has been used as a SPR active metal. By rigorously optimizing the different waveguide parameters, we have shown that there is significant transfer of modal power around phase-matching or resonance wavelength which has been utilized to design a compact and highly sensitive sensor for lab on chip. The ultra narrow width (∼765pm for an interaction length of 10mm) of surface plasmon resonance curve and sensitivity as high as 7500nm-RIU−1 will open a new window for bio-chemical sensing applications. [Copyright &y& Elsevier]

A novel scheme for enhancing the bandwidth of optical parametric amplification using asymmetric Bragg reflection waveguides is presented. The unique dispersion characteristics exhibited by the Bragg reflection waveguides are exploited for countering the rapidly falling signal gain as one moves away from the phase-matching wavelength. The role of the periodic cladding on the gain and bandwidth of optical parametric amplification in a lithium niobate based Bragg reflection waveguide is analysed. Such an idea could be used in any nonlinear up conversion or down conversion process for enhancing the bandwidth significantly and for easing fabrication tolerances. [ABSTRACT FROM AUTHOR]

Abstract: A novel asymmetric Bragg reflection waveguide (BRW) showing anomalous dispersion characteristic is presented. The abnormal behaviour of increase of modal effective index with wavelength is primarily caused by the changes taking place in the imaginary part of the Bloch wavevector, in the periodic stratified cladding. The phase velocity and the group velocity dispersion characteristics for the waveguide have also been analyzed. Such an anomalous behaviour can find applications in the design of integrated optical devices. [Copyright &y& Elsevier]

Abstract: A novel scheme for second harmonic generation in asymmetric Bragg reflection waveguides is presented for enhancing the bandwidth of non-linear interaction. The strong dispersion exhibited by the Bragg reflection waveguide is exploited for countering the rapidly falling efficiency as one moves away from the phase-matching wavelength. The role of the periodic cladding on the efficiency and bandwidth of second harmonic generation in a lithium niobate based Bragg reflection waveguide is analyzed. Such an idea could be used in other parametric processes for enhancing the bandwidth and for easing fabrication tolerances. [Copyright &y& Elsevier]

We present a detailed design principle and propagation characteristics of channel Bragg-plasmon-coupled-waveguide. We have found that there is a significant change in the slope of the phase-velocity dispersion curve leading to an ultranarrow interaction bandwidth (∼765 pm) and group-velocity dispersion (GVD∼±4.5×104 ps/km-nm) that is an appreciably large GVD using a waveguide mode-coupling geometry in any region of the optical spectrum. The effect of waveguide parameters such as channel width, number of bilayers, etc. on a mode-coupling mechanism is also studied with significant emphasis on the propagation loss suffered by the supermodes of the structure. The proposed waveguide exhibits sensitivity as high as 7500 nm/RIU, thereby opening a route for biochemical sensing. [ABSTRACT FROM AUTHOR]

We present an experimental investigation on third-order nonlinear optical properties of RF-sputtered WSe 2 thin films using a single-beam Z -scan technique around the optical communication window in a near-infrared spectral band. The nonlinear absorption coefficient was obtained from the open-aperture Z -scan transmission using ultrashort pulses centered at 1520 nm excitation wavelength. The results show a reverse saturable absorption signature for all the WSe 2 films due to two-photon absorption (TPA) mediated electronic transitions. The dependency of the TPA coefficient on film thickness is analyzed through the modification in an electronic band structure essentially caused due to defects induced in the samples. In addition, we also explored the impact of high laser intensity on the TPA process, which essentially pointed toward a significant contribution of free-carrier absorption at small laser intensities in WSe 2 thin films. This investigation provides a basis for optimally tailoring the nonlinear optical properties of transition-metal-dichalcogenides via bandgap engineering for improving photonic device functionality. [ABSTRACT FROM AUTHOR]

A self-referenced sensor based on coupled hybrid mode Tamm-plasmon-polariton (TPP) is proposed for detection of different blood group components. The geometry which has been investigated theoretically, is comprised of blood components sandwiched between two ‘metal-distributed Bragg reflectors (DBRs)’ exhibiting two distinguishable absorption peaks within the photonic band-gap (PBG) of DBR. The two absorption maxima are essentially due to excitation of one symmetric (Mode-I) and one anti-symmetric mode (Mode-II) within the PBG. Mode-I remains invariant for a change of blood constituents whereas Mode-II exhibits strong dispersive properties by virtue of significant presence within the sensing region. This gives rise to a hybrid self-reference scheme where the longer wavelength arm (Mode-II) varies significantly providing proper signature of a particular blood component. A straight line fit to the resonance wavelength shift gives rise to a sensitivity of ≈200 nm/RIU with the proposed architecture. The polarization dependence of the spectral shift of hybrid-mode resonance wavelengths for oblique incidence is also investigated and analyzed theoretically. The sharp absorption maxima facilitate precise detection with an improved detection accuracy of a particular blood component. A brief analysis to optimize the sensor design for enhanced sensitivity, as well as detection accuracy, has also been discussed. [ABSTRACT FROM AUTHOR]

We demonstrate a Tamm-plasmon-polariton (TPP) based sensor for accurate determination of temperature. The sensing architecture is comprised of thin silver (Ag) film on a distributed-Bragg-reflector (DBR) structure made of periodically stratified multilayers of Ta 2 O 5 and SiO 2 . TPP mode is excited using direct incidence of white-light-source at normal incidence as well as oblique incidence. The mode excitation is characterized by a sharp reflectivity minimum within the photonic bandgap (PBG) of DBR. It was observed that the depth of TPP resonance reduces uniformly as a function of temperature without affecting its sharpness. Defining temperature sensitivity in terms of change in reflectivity from the composite structure, a sensitivity of 7.8 × 10 −4 /°C is estimated for the sensing geometry. Also, the metallo-dielectric geometry supporting TPP modes is modeled using transfer-matrix-method for ascertaining the salient features of TPP modes which have a direct impact on sensing properties. [ABSTRACT FROM AUTHOR]

In this work high density ZnO nanorods were grown on glass substrate by using a two-step method. In the first step, drop-casting method was used for growth of seed layer by taking Zinc Acetate Dihydrate as precursor. In the second step, ZnO nanorods were prepared through Chemical Bath Deposition process on this seed layer by taking Zinc Nitrate as precursor. Field Emission Scanning Electron Microscope study was done to study the morphology of grown ZnO nanorods. From this study the average diameter and length of nanorods were found to be 33 nm and 270 nm respectively. These nanorods are successfully used for second harmonic generation (SHG) of femtosecond laser pulses of central wavelengths like 1000 nm, 1100 nm and 1300 nm. Discussion is given on the significance of this result along with its potential application. [ABSTRACT FROM AUTHOR]

We report here a set of triaryl pyrazole based B−N coordinated boron compounds (11‐17) synthesized by electrophilic aromatic borylation strategy. All the pyrazole boron compounds were thoroughly characterized using multinuclear NMR spectroscopy, LC–MS, and single crystal X‐ray diffraction analysis (for 12–17). The photoluminescence measurements of 11–17 revealed that the emission peak maxima were tuned based on the substitution on N‐phenyl. The photophysical and electrochemical properties were further supported by theoretical calculations. Z‐scan based investigations at 515 nm pump wavelength showed that B−N coordination led to enhancement of nonlinear absorption (two‐photon absorption (TPA)) in these compounds if an electron deficient moiety is attached. It has also been observed that an appropriate choice of moiety allows to optimally maneuver the molecular polarizability of the π‐system and consequently, assists in controlling the third‐order nonlinear optical response. [ABSTRACT FROM AUTHOR]

The objective of the proposed work is to design a biosensor that monitors hemoglobin (Hb) concentration using the combination of nanolayer, i.e., barium titanate (BaTiO3) and antimonene based on surface plasmon resonance (SPR) technique. Antimonene is used here as bio-recognition element (BRE) layer to attach the Hb analyte through physical adsorption due to its hydrophilic nature, higher adsorption energy and larger active surface area. The use of BaTiO3 adlayer (7 nm) just before antimonene is to enhance the refractive index (RI) sensitivity up to 1.90 times for the proposed SPR biosensor. The reason behind sensitivity enhancement is its high dielectric constant which enhances the electromagnetic field with in analyte medium. The performance of the biosensor is demonstrated with performance parameters namely sensitivity, detection accuracy (DA), figure of merit (FOM) and resolution. The proposed biosensor has potential to achieve much higher performance in terms of RI sensitivity of 303.83°/RIU, FOM of 50.39 RIU−1 and resolution of 0.021 g/l in comparison with reported biosensors in the literature for detection of Hb concentration. Thus, based on the obtained results one can say that the proposed work unlocks a reliable sensing in the field of medical science to detect hemoglobin-related diseases in human being. [ABSTRACT FROM AUTHOR]

We present a comprehensive study on the impact of phase transformations of metallophthalocyanine thin films on their third-order nonlinear optical (NLO) properties. The metallophthalocyanine thin films are prepared by thermally evaporating the commercially available Copper(II)2,9,16,23-Tetra-tert-butyl-29H, 31H-phthalocyanine (CuPc) and Zinc(II) 2,9,16,23-Tetra-tert-butyl-29H, 31Hphthalocyanine (ZnPc) powder on glass substrate. Thermal annealing causes a phase transformation which has a distinct signature in powder X-ray diffraction and UV-Vis-NIR spectroscopy. The NLO characteristics which include nonlinear refractive index n2, as well as nonlinear absorption coefficient (βeff), were measured by using a single beam Z-scan technique. An ultrashort pulsed fiber laser emitting femtosecond pulses (▵ ι≈250 fs) at 1064nm central wavelength is used as a source for the Z-scan experiment. The βeff values in as prepared thin films were ascertained to be smaller as compared to the annealed one due to the smaller value of saturation intensity (Is) which, in turn, is a consequence of ground-state bleaching in the thermally unstable amorphous state of the molecule. Interestingly, the nonlinear refractive indices bear opposite sign for CuPc and ZnPc. The variations in the third-order nonlinearity in CuPc and ZnPc are discussed in terms of molecular packing and geometries of metallophthalocyanine molecules. [ABSTRACT FROM AUTHOR]

Three-coordinated organoboron fluorophores bearing 3,5-diphenyl pyrazoles have been synthesized. The pyrazole anchored boron fluorophores show selective fluorescence quenching response to trinitrophenol (or) picric acid (PA) and have the ability to discriminate picric acid over other analytes. We investigated nonlinear optical (NLO) properties of these three-coordinated organoboron compounds (in solutions) in the presence and absence of PA. In absence of PA, the two-photon-absorption coefficient (β) of organoboron fluorophores exhibits a variation from 2 × 10−12 cm W−1 to 4 × 10−12 cm W−1. The results also reveal that the NLO characteristics of organoboron fluorophores exhibit a discernible variation with PA addition which has correlations with quenching observed in fluorescence measurements. [ABSTRACT FROM AUTHOR]

An experimental design of high resolution non-intrusive displacement sensor working on the principle of basic LDV is being presented. Resolution enhancement has been achieved through phase multiplication using multiple reflections within a high-Q cavity created by a vibrating surface and a high reflection mirror placed parallel to each other. Displacement of 72 nm has been measured with an error range of ± 14 nm through direct counting of characteristic peaks in "half cycle" of a interferogram. A linear relationship between displacement and number of reflections has been obtained which offers a straightforward route to measure displacements up to sub-nanometer scale and the resolution is essentially dictated by the reflectivity and physical dimension of moving source. [ABSTRACT FROM AUTHOR]

• An SPR sensor proposed using Ti 3 C 2 T x MXene nanomaterial. • High sensitivity 190.22 (°/ RIU) is obtained using a single layer of Ti 3 C 2 T x MXene. • The penetration depth of the sensor is 1.52 times larger compared to a conventional sensor. The aim of the paper is to see the effect of new nanomaterial, i.e., MXene on sensing application. A surface plasmon resonance biosensor comprising of BK7 prism, MXene, transition metal dichalcogenides (TMDCs), black phosphorus (BP), and gold (Au) as a plasmonic material is proposed for sensing application in visible region. We have investigated and carried out detailed analysis to design the high-performance biosensor by exploiting the unique properties of Ti 3 C 2 T x MXene and black phosphorus. The performance of the biosensor is quantified in terms of sensitivity. The highest sensitivity 190.22 (° / R I U) is obtained using single layer of each nanomaterials. Proposed sensor offered penetration depth i.e., 1.52 times larger in compared to conventional sensor. Our contribution reveals potential application of combination of Black Phosphorus, Ti 3 C 2 T x MXene and TMDCs as a new type of biosensor providing promising applications in SPR biosensors. [ABSTRACT FROM AUTHOR]

Intramolecular B ← N coordinated fluorophores have shown potential applications in optoelectronics and as sensors due to their unique photophysical properties. In this work, we report the synthesis and characterization of π-conjugated boron doped phenanthroimidazole dimers. All the π-conjugated B ← N coordinated phenanthroimidazole dimers exhibited high quantum yields in solution (up to 99%) and moderate quantum yields in the solid state (up to 51%). We investigated the nonlinear optical properties of phenanthroimidazole dimers and found that the measurement of two-photon-absorption cross-section is correlated with the conjugation length. [ABSTRACT FROM AUTHOR]

We present a detailed investigation on the impact of thermal annealing on the third-order nonlinear optical (NLO) properties of sputtered W S e 2 thin films. The process of annealing results in an appreciable change in morphology and texture of W S e 2 films that is governed by the annealing temperature and duration of annealing. These modifications are apparent from the electron micrographs as well as X-ray diffraction and Raman spectrum. The visible absorption spectroscopy point towards a gradual shrinkage of electronic bandgap which motivated us to explore the impact of NLO properties of the annealed W S e 2 films. The NLO measurements were carried out using a single-beam Z-scan technique using ultrashort pulses centered at 1030 nm excitation wavelength. The investigations reveal a distinct two-photon absorption (TPA) signature for the annealed W S e 2 films along with a self-focusing effect. The observations indicate the strengthening of optical limiting behavior exhibited by W S e 2 films when they are annealed for a longer duration. The outcomes suggest that the process of annealing in W S e 2 films allows controlling the NLO properties and renders them more suitable candidates as optical limiters for high-power applications. • We study a layered transition metal dichalcogenide (TMD), known as WSe 2 and explore the impact of annealing on its nonlinear optical properties. • The process of annealing the WSe 2 thin film results in removal of defects that gets reflected in the electronic bandgap. • This is accompanied by lowering of stress associated with the annealed thin films. • We experimentally show that the improvement in stoichiometry of WSe 2 films leads to a discernible strengthening of nonlinear optical response. • The annealed films shows improved optical limiting characteristics at ultrashort time scales in the infrared spectral band. [ABSTRACT FROM AUTHOR]

We present a detailed investigation on thickness-dependent third-order (χ (3)) nonlinear optical properties of RF-sputtered WSe 2 thin-films using ultrashort pulses centered at different excitation wavelengths. The single-beam Z-scan based investigation in the visible spectrum reveals a predominant Pauli-blocking effect led saturable absorption or optical limiting in WSe 2 thin-films. The study also explores the dispersion in third-order nonlinear susceptibility (χ (3)) in WSe 2 thin films. Interestingly, WSe 2 thin-films of any thickness exhibit a self-focusing effect depicting a positive nonlinear refractive index (n 2 > 0). The frequency-dependent nonlinear absorption (β) bear distinct correlations with the bandgap of the films which is also investigated through density-functional-theory (DFT) based simulations. The alteration in bandstructure is primarily due to the Se -deficiency induced defect bands in WSe 2 thin-films which has discernible impact on the optical limiting characteristics. • The third-order nonlinear optical properties of RF sputtered WSe 2 thin films are investigated. • The thin films exhibit strong Pauli-blocking induced saturable absorption effect which is strongy affected by the defect states/bands emanating from Se-deficiency in the films. • The density-functional-theory (DFT) simulations predict the defect state(s) which closely match with the experimental observations. [ABSTRACT FROM AUTHOR]