Cladding Medium Research Articles

Boundary Feedback Fiber Random Microcavity Laser Based on Disordered Cladding Structures

The cavity form of complex microcavity lasers predominantly relies on disordered structures, whether found in nature or artificially prepared. These structures, characterized by disorder, facilitate random lasing through the feedback effect of the cavity boundary and the internal scattering medium via various mechanisms. In this paper, we report on a random fiber laser employing a disordered scattering cladding medium affixed to the inner cladding of a hollow-core fiber. The internal flowing liquid gain establishes a stable liquid-core waveguide environment, enabling long-term directional coupling output for random laser emission. Through theoretical analysis and experimental validation, we demonstrate that controlling the disorder at the cavity boundary allows liquid-core fiber random microcavities to exhibit random lasing output with different mechanisms. This provides a broad platform for in-depth research into the generation and control of complex microcavity lasers, as well as the detection of scattered matter within micro- and nanostructures.

Alternative Approach to Design and Optimization of High-Q Ring Resonators for Membrane-Free Acoustic Sensors.

Membrane-free acoustic sensors based on new principle and structure are becoming a research hotspot, because of many advantages, e.g., their wide bandwidth and high sensitivity. It is proposed that a membrane-free acoustic sensor employs a semi-buried optical waveguide ring resonator (SOWRR) as a sensing element. Using air as the upper cladding medium, the excited evanescent field in the air cladding medium would be modulated by acoustic wave. On this basis, the acoustic sensing model is established. Taking high Q factor and resonance depth as design criteria, the optimal design parameters are given. The optimal values of the air/SiO2: Ge/SiO2 waveguide resonator length and coupling spacing are obtained as 50 mm and 5.6 μm, respectively. The Q factor of the waveguide resonator of this size is as high as 8.33 × 106. The theoretical simulation indicates that the frequency response ranges from 1 Hz to 1.58 MHz and that the minimum detectable sound pressure is 7.48 µPa using a laser with linewidth of 1 kHz. Because of its advantages of wide bandwidth and high sensitivity, the membrane-free sensor is expected to become one of the most promising candidates for the next-generation acoustic sensor.

Preparation and characterization of polyacrylonitrile/nitrocellulose engineering blend

AbstractPolyacrylonitrile (PAN) polymer blends were more in demand due to their wide range of applications. We overcome the restricted low thermal stability and poor strength for deployable blend. In the present study, we prepared PAN and nitrocellulose (NC) polymer blends by solution casting method to overcome the low loss, low dielectric properties as alternative blend for cladding purpose in communication domain. C≡N bond exclusively demonstrated the impact on blending was confirmed by Fourier‐transform infrared spectrophotometer (FTIR) and Raman microscopy measurement. Semicrystalline nature of polymer blends as a function of NC loading was determined by X‐ray diffraction (XRD). Optical polarizing microscopy (OPM) and scanning electron microscopy (SEM) analysis illustrated an appearance of micro flocculated spherulites. Blending ratio of PAN/NC demonstrated the decreased direct band gap identified by Ultraviolet spectroscopy (UV). PAN/NC proved excellent alternative as low dielectric constant and low loss as cladding medium. Blending of NC with PAN exhibited an increased hydrophilicity was confirmed by surface goniometer. Increased thermal stability of polymer blends was mapped by thermogravimetric analysis (TGA). Blend melting temperature and glass transition temperature was increased from 322°C to 334°C and 88°C to 102°C confirmed by Differential scanning calorimetry (DSC) analysis. Thermal conductivity was increased from ~0.13 to ~0.34 W/m. k for PAN/NC determined by Lee's disc probe method. Mechanical properties of blends were measured using universal testing machine (UTM). Tensile strength and Young's modulus was increased up to ~23%, and ~ 56%, whereas elongation break was decreased up to ~71% for PAN/NC blends compared to host PAN system. PAN/NC may suit promising candidate as cladding blend for communication engineering due to low loss and low dielectric constant.

Reconfigurable Guided‐Mode Conversion Using Cladding Medium Switching Strategy in Subwavelength Grating Waveguide

AbstractIn a waveguide‐based coupled‐mode system, various mode conversions are achieved by designing mode evolution procedures. However, the differences of refractive indices among modes exceed the capability of conventional tuning mechanism, so most reported mode manipulation devices can only realize fixed mode conversions. This paper introduces the cladding medium switching strategy to the subwavelength grating waveguide‐based coupled‐mode system, and proposes a reconfigurable mode converter on silicon nitride platform. This work systematically analyzes the phase matching conditions on a coupled‐mode system. Results show that for both whole and partial upper‐cladding switchable, it is possible to achieve reconfigurable mode conversions. For whole cladding switchable case, this work demonstrates a double‐state mode converter, which converts the input mode to TE2 and TE1 modes under cladding refractive indices of 1 and 1.7. This work expands it to triple‐state mode conversion with window‐style cladding, which converts the input to TE2, TE1, and TE0 modes under cladding of 1, 1.54, and 1.7. The optical bandwidths are relatively large, and the conversion efficiencies exceed 56% for all cases. The mechanism provides a non‐volatile and energy‐efficient way for tunable mode conversions, which is promising for applications in optical networks, communications, and sensors, etc.

Surface-wettable nonenzymatic fiber-optic sensor for selective detection of hydrogen peroxide.

A micro-nanostructure-based surface-modified fiber-optic sensor has been developed herein to selectively detect hydrogen peroxide (H2O2). In our design, phenylboronic ester-modified polymers were used as a modified cladding medium that allows chemo-optic transduction. Sensing is mechanistically based on oxidation and subsequent hydrolysis of the phenylboronic ester-modified polymer, which modulates hydrophobic properties of fiber-optic devices, which was confirmed during characterization of the chemical functional group and hydrophobicity of the active sensing material. This work illustrates a useful strategy of exploiting principles of chemical modifications to design surface-wettable fiber-optic sensing devices for detecting reactive species of broad relevance to biological and environmental analyses.

Selectively excited bimodal interferometer for highly sensitive refractive index sensing

A selectively excited bimodal interferometer was developed for highly sensitive detection of refractive index changes. Numerical simulation revealed that multimode waveguides with tall, narrow cross-sections are suitable for realizing a highly sensitive bimodal (fundamental and lateral first-order modes) interferometer, owing to deeper penetration of the lateral first-order mode through its side surfaces into the cladding medium. A device with an optimum design was determined by simulation and fabricated by electron-beam lithography using a negative photoresist as the material for the waveguide core. The detection of glucose was demonstrated, and the sensitivity and detection limit was found to be 2547 rad / RIU (RIU—refractive index unit) and 9.8 × 10 − 6 RIU, respectively.

Effect of medium entropy alloy powder-core wire on friction wear and corrosion resistance of arc cladding additive layer

AbstrastLow carbon steel was suitable for industrial fields due to its low price, wide application range and excellent comprehensive performance. However, there were still shortcomings such as poor wear resistance and corrosion resistance in special occasions. In hence, this paper carried out a study on the strengthening process of low-carbon steel parts surface deposition. The TIG welding arc welding method was used to study the strengthening performance of the arc-enhanced medium entropy alloy additive layer. To analyze the elements and microstructure of the medium entropy alloy additive layer by x-ray diffractometer(XRD), scanning electron microscope (SEM), energy dispersive spectrometer (EDS) and other modern analysis methods. The micro-hardness, friction and wear and electrochemical corrosion detection methods were used to study the friction and wear and corrosion resistance of the medium entropy alloy additive layer. The results show that the microstructure of the medium entropy alloy additive layer is a typical lamellar pearlite, which is wrapped with face-centered cubic solid solution (FCC) and unevenly distributed in the additive layer. The microhardness of the medium entropy alloy additive layer is significantly higher than that of the substrate. As the friction and wear load increases, the friction coefficient of the medium entropy alloy additive layer gradually decreases. The wear rate of the additive layer is much lower than that of the substrate and the wear resistance is doubled compared to the substrate. The form of wear is mainly abrasive wear and fatigue spalling wear. The medium entropy alloy additive layer has excellent corrosion resistance. Its corrosion rate is about one tenth of the substrate. The arc cladding medium entropy alloy powder core wire can meet the surface strengthening requirements of low-carbon steel parts and provide engineering basis for the low-carbon steel large-scale, multi-domain, high-level application.

Mode Sensitivity Analysis of Subwavelength Grating Slot Waveguides

In this paper, we investigate the mode sensitivity (S mode ) of subwavelength grating slot (SWGS) waveguides. S mode is an important parameter in various waveguide-based photonic circuits such as sensors, modulators, and thermally-controlled devices. It is a measure of the sensitivity of the waveguide effective index towards the refractive index perturbations in the cladding medium. The SWGS waveguide exhibits high mode sensitivity, as it combines sensitivity enhancement features of both slot and subwavelength grating waveguides. Finite-difference time-domain simulations are performed for the analysis, design, and optimization of the hybrid structure. The SWGS waveguide is incorporated into a Mach-Zehnder interferometer and fabricated on a silicon-on-insulator platform for the experimental estimation of S mode . The measured S mode value of 79% is consistent with the theoretical prediction of 83%.

LSPR Excitation on Au Nanorings From Integrated Hybrid Plasmonic Aperture Waveguide and Its Application in Methanol Detection in the IR-Band

The presented work deals with an infra-red (IR)-band methanol sensor, which has been realized in an integrated device having hybrid plasmonic aperture waveguide and Au-nanoring array over broad wall of it covered by porous silicon clad. Through modeling and numerical simulations, we have shown that suitable synthesized aperture in the waveguide can excite localized surface plasmon resonance (LSPR) on the nanorings of suitable diameter via radiative field coupling, whereas LSPR can be tuned with the received methanol by the porous silicon clad. Thus, by contrasting the power available at the sense port of the waveguide with null and finite methanol doses, we have determined sensitivity (STM) and figure of merit (FOM) of the sensor, and our further analyses suggest that the sensor response can be tailored by diameter of aperture and ring, and by the porosity of the silicon cladding medium. In this respect, we have found that, for 20%-45% clad porosity, S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">TM</sub> = 77.95-66.66 nm/RIU and FOM = 17.51-7.66/RIU can be achieved during methanol detection.

Polarizing properties of a 2D photonic crystal slab for simultaneous in-plane and out-of-plane light incidence

We study a 2D photonic crystal slab for its properties of polarizing light propagating in the plane of periodicity and for light incident from outside the plane of the slab as well. We identify the frequency ranges that can yield polarized light for both cases. The analysis is done for triangular and square lattice configurations in both symmetric and asymmetric background media. The 2D photonic crystal slab can behave as both reflection-type and transmission-type polarizer for in-plane and out-of-plane incidence of light. The structure in an asymmetric background, which is more favorable for practical applications, yields orthogonally polarized out-of-plane transmitted states which ultimately radiate to the cladding medium within certain frequency interval of the incident light.

Dispersion properties of plasma cladded annular optical fiber

One of the considerable problems in a conventional image transferring fiber optic system is the two-fold coupling of propagating hybrid modes. In this paper, using a simple and practical analytical approach based on exact modal vectorial analysis together with Maxwell's equations, we show that applying plasma as a cladding medium of an annular optical fiber can remove this defect of conventional fiber optic automatically without any external instrument as the polarization beam splitter. Moreover, the analysis indicates that the presence of plasma in the proposed optical fiber could extend the possibilities for controlling the propagation property. The proposed structure presents itself as a promising route to advanced optical processing and opens new avenues in applied optics and photonics.

Guiding characteristics of guided waves in slab waveguide with hexagonal boron nitride

Due to the non-overlapping Reststrahlen bands, both type I and type II hyperbolic responses are available in hexagonal boron nitride (hBN), which can be used as the guiding medium or the cladding medium in the slab waveguide. The characteristics of guided waves in the slab waveguide with hBN are theoretically investigated, and the existence conditions of the guided and surface modes of waveguides in the two types of hyperbolic responses are analyzed by using the graphic method. It is shown that, in the type-Ι hyperbolicity of the hBN waveguide, both TE and TM guided modes are existent. In the type-ΙΙ hyperbolicity, both the guided and surface modes are existent for TM guided waves; however, the guided and surface modes of TE polarization are absent. In addition, the propagation constant and the normalized power versus the thickness of waveguide are showed and the cutoff thickness and the power localization are discussed.

Square fractal-like nanoapertures for SEIRA spectroscopy: An analytical, numerical and experimental study

Due to the sensitivity limitations, infrared (IR) spectroscopy systems, in which conventional sensing platforms are used, have some problems with detecting the small quantities of molecules. By the advantages coming from their aperture based nature, nanoaperture arrays increase the light-matter interaction and can be useful to overcome some of these limitations. In this work, we propose an analytical, numerical and experimental study for a novel nanoaperture array which has enhanced transmission and reflection characteristics with high surface enhanced IR absorption (SEIRA) distributions. We numerically analyze the square fractal-like nanoapertures through the finite difference time domain method. Thus, we present a fine tuning mechanism for adjusting the resonance frequency which is highly desirable for SEIRA applications. We then propose analytical formulas for the resonance frequencies of the structures. Moreover, we experimentally realize the structure by using a high-precision and lift-off free nanofabrication method based on electron-beam lithography. Correspondingly, refractive index sensitivity analyses are performed by embedding our structure into different cladding media with several refractive index values. Finally, in order to show the SEIRA performance of the proposed nanoaperture array, we analyze the sensing characteristic of carbonyl ν(CO) stretching mode in a thin poly(methyl methacrylate) (PMMA) film for a set of different film thicknesses. Due to the enhanced transmission and reflection behaviors with easily accessible ultra-high-field localization characteristics, the proposed sensing platform can be a good candidate for SEIRA spectroscopy and label-free bio sensing applications.

Polarization insensitive plasmonic perfect absorber with coupled antisymmetric nanorod array

Plasmonic perfect absorbers have a large potential for biomolecular sensing applications such as refractometric biosensing and surface enhanced spectroscopy due to their high near-field enhancement and near-unity absorption capabilities. Despite these properties, novel plasmonic perfect absorbers with additional features are highly needed for real-world sensing applications. In this context, we present the design, characterization and experimental realization of a subwavelength plasmonic perfect absorber array with crucial properties including the dual-band absorption, high near-field enhancement with a large number of hot-spots, mass-production compatible design, high sensitivity, and polarization independency for both narrow and wide resonance bands. In order to investigate the spectral characteristics and to obtain a fine-tuning mechanism, we perform several numerical analyses by using finite difference time domain method. We also investigate the charge and current density distributions at the corresponding resonances. It is observed that the physical origin of the dual-band behavior is based on the dipolar plasmonic resonance of the horizontal nanorods and the plasmonic coupling mechanism of the structure. Furthermore, we investigate the sensing performance of the proposed device by calculating the refractive index sensitivity and figure-of-merit for the resonant modes by embedding it into different cladding media with various refractive indices. Finally, in order to demonstrate the potential of the proposed plasmonic perfect absorber for surface enhanced infrared absorption spectroscopy, we simulate the detection of carbonyl v(CO) stretching mode of a conformal poly(methyl methacrylate) layer. Due to its highly desired properties, the proposed device can be a good candidate for biomolecular sensing applications and also the results of our investigation can be useful for the further designs of plasmonic based sensors.

Refractive index sensing characteristics of dual resonances in rectangular fractal nano-apertures

Aperture based sensing platforms can be useful for both gas and bio-sensing applications. In this study, we investigate the refractive index sensing characteristics of dual resonances in rectangular fractal nanoapertures. By taking the advantages coming from its aperture based nature and dual band resonant behavior, one can use this platform to detect two different chemical/bio-molecules simultaneously. For the numerical analysis, we study the rectangular fractal nanoantenna array through the finite difference time domain (FDTD) method. We also introduce a fine tuning mechanism for adjusting the resonance frequencies which is important for the sensing applications. Then, we demonstrate the results of refractive index sensitivity tests in order to show the behavior of the structure against the refractive index changes. In these tests, we embed our sensing platform into different cladding media and obtain the refractive index sensing characteristics of dual resonances. Due to the dual-resonant behavior with easily accessible ultra-high-field localization characteristics, the proposed sensing platform can be a good candidate for ultra-sensitive chemical- and bio-sensing applications.

Realization of a polymer nanowire optical transducer by using the nanoimprint technique.

An optical transducer using an integrated optics polymer nanowire is proposed. The nanoimprint technique is used to fabricate an OrmoComp nanowire with 1.0μm width and 0.5μm height, but the resulting sidewalls are not perfectly vertical. Maximum sensitivity is achieved by enhancing the evanescent field in the cladding region. The possible mode fields and power confinement of the nanowire are studied with respect to their structural dimensions, the operating wavelength, and the cladding material by using the H-field finite element method. The attenuation coefficient is extracted and calculated over the different cladding media, specifically air, water, and glycerol solution. It is observed that the scattering caused due to the surface roughness is the dominant effect that provides a larger attenuation coefficient.

Optimizing terahertz surface plasmons of a monolayer graphene and a graphene parallel plate waveguide using one-dimensional photonic crystal

Through analytical calculations, the transverse magnetic surface plasmon (SP) dispersion relations for a monolayer graphene and a graphene parallel-plate waveguide (PPWG) in the presence of a one-dimensional photonic crystal (1D PC) as a substrate and a symmetric/asymmetric cladding medium are obtained. For the monolayer graphene case, we show that the presence of the 1D PC leads to significant modification in propagation length (PL) and localization length (LL) of THz SPs, as compared with the SPs of monolayer graphene on SiO2 substrate. And the SPs with largest PL and small LL, named as optimized SPs, could be supported when the 1D PC is used only as a substrate. For the graphene PPWG case with the plate separation “D” (here, 10 nm≤D≤1 μm), in addition to support of typical upper and lower branches of coupled THz SPs, presence of the 1D PC leads to support of an extra branch when 10 nm≪D≤1 μm. Moreover, as far as supporting optimized 0–2 THz SPs are concerned, the case in which the graphene PPWG with D = 1 μm is sandwiched between two symmetric 1D PC could be the best candidate. Whereas the graphene PPWG on the 1D PC, with D = 10 nm, supports optimized SPs in a frequency range from 2 to 4.5 THz. Therefore, using 1D PC improves the capability of monolayer graphene and also graphene PPWG for sensing and waveguide applications in THz frequencies.

Nanoparticle-Based Metamaterials as Multiband Plasmonic Resonator Antennas

Plasmonic metamaterials based on metal-dielectric nanostructures exhibit unique optical properties such as high near-field enhancement, negative refractive indexing, and optical cloaking. In this paper, we present a plasmonic multiband metamaterial based on UT shaped nanoparticles. In order to understand the multispectral response, we analyze the near-field distributions at the corresponding resonance frequencies. In addition, we both numerically and experimentally, show the dependence of the spectral response on the geometrical parameters of the structure. By embedding the system in a dielectric cladding medium, we show strong sensitivities of the resonant behavior to the refractive index and thickness of the dielectric load. Due to its tunable multiband spectral characteristics, the proposed metamaterial antenna can be used for wide range of applications, such as wavelength-tunable active filters, optical modulators, ultrafast switching devices, and biosensing.

Optical coupling between a self-assembled microsphere grating and a rib waveguide

We report the fabrication of a linear array of self-assembled polystyrene microspheres side coupled to a rib waveguide. The optical coupling between the lateral evanescent field and the periodically perturbed effective refractive index alongside the waveguide results in a transmission stopband at the Bragg wavelength. The observed transmission spectrum shows a notch centered at λ≈1590 nm, which is in close agreement with theory. The coupling coefficient, κ, and the spectral response are derived for variable cladding medium index using perturbation theory. Structures of this type are expected to find application in wavelength selection, optical sensing, and optical delays.

Calculation of nonlinear waves guided by optical fibers with an inhomogeneous nonlinear core

A circular optical fiber consisting of an inhomogeneous nonlinear core bounded by a linear cladding medium is considered here. In this case, the calculation of the nonlinear modes is of practical importance because of the joint effects of nonlinearity and inhomogeneity on the field concentration and the achievable optical confinement. Numerical results indicate that the combination of this type of inhomogeneity along with the characteristics of nonlinearity may play a significant role towards the optical confinement in the core.