Mode Cutoff Research Articles

Liquid surface tension and refractive index sensor based on a tilted fiber Bragg grating

A refractive index (RI) and liquid surface tension (ST) (at the level of 10−3 N) measurement system has been proposed by using a 1.80-cm-long, 8°-tilted fiber Bragg grating (TFBG). When the TFBG is pulled up from the liquid into the air at a fixed height (corresponding to a fixed contact angle between the fiber and the liquid), the ST acting upon the TFBG depends on the length of the TFBG covered with the liquid film along the fiber axis direction. The liquid film covering the grating results in the shifts of the resonant cladding modes of the TFBG. For the liquid with an RI in the range from 1.3341 to 1.4415, its RI and ST can be obtained through the measurements of shifts in the resonant wavelengths of the cutoff mode and changes in the intensities of the resonant wavelength dips in the TFBG spectrum by using the known ST and RI of water as a reference.

Dynamics of coupled mode solitons in bursting neural networks.

Using an electrically coupled chain of Hindmarsh-Rose neural models, we analytically derived the nonlinearly coupled complex Ginzburg-Landau equations. This is realized by superimposing the lower and upper cutoff modes of wave propagation and by employing the multiple scale expansions in the semidiscrete approximation. We explore the modified Hirota method to analytically obtain the bright-bright pulse soliton solutions of our nonlinearly coupled equations. With these bright solitons as initial conditions of our numerical scheme, and knowing that electrical signals are the basis of information transfer in the nervous system, it is found that prior to collisions at the boundaries of the network, neural information is purely conveyed by bisolitons at lower cutoff mode. After collision, the bisolitons are completely annihilated and neural information is now relayed by the upper cutoff mode via the propagation of plane waves. It is also shown that the linear gain of the system is inextricably linked to the complex physiological mechanisms of ion mobility, since the speeds and spatial profiles of the coupled nerve impulses vary with the gain. A linear stability analysis performed on the coupled system mainly confirms the instability of plane waves in the neural network, with a glaring example of the transition of weak plane waves into a dark soliton and then static kinks. Numerical simulations have confirmed the annihilation phenomenon subsequent to collision in neural systems. They equally showed that the symmetry breaking of the pulse solution of the system leaves in the network static internal modes, sometime referred to as Goldstone modes.

Overdense microwave plasma heating in the CNT stellarator

Overdense plasmas have been attained with 2.45 GHz microwave heating in the low-field, low-aspect-ratio CNT stellarator. Densities higher than four times the ordinary (O) mode cutoff density were measured with 8 kW of power injected in the O-mode and, alternatively, with 6.5 kW in the extraordinary (X) mode. The temperature profiles peak at the plasma edge. This was ascribed to collisional damping of the X-mode at the upper hybrid resonant layer. The X-mode reaches that location by tunneling, mode-conversions or after polarization-scrambling reflections off the wall and in-vessel coils, regardless of the initial launch being in O- or X-mode. This interpretation was confirmed by full-wave numerical simulations. Also, as the CNT plasma is not completely ionized at these low microwave power levels, electron density was shown to increase with power. A dependence on magnetic field strength was also observed, for O-mode launch.

The Efficiency of the Pumping of the Lasers Based on Self-Terminating Atomic Transitions Operating in the Energy Input Cut-Off Mode

The analysis of the electro-physical processes in the discharge circuit of the lasers based on the self-terminating transitions of metal atoms (LSTM) and the electrodes placed in the cold buffer zones of the gas discharge tube (GDT) is occurred. That design of the GDT can provide the efficient lasing at the reduction of the current flowing through the switch to zero after the charging of the capacitive components of the circuit from the storage capacitor. Under the circumstances the pumping of the active medium is determined by the energy input from the peaking capacitor and, consequently, the efficiency of the pumping can be increased by an order of magnitude, if (using a managed switch) the energy input into the active medium from the storage capacitor is “cut-off” after charging the capacitive components of the circuit. It was shown that the efficiency values of ∼ 9-11 % and of ∼ 5-6 % for the copper and gold vapor, lasers could be achieved.

Temperature-calibrated high-precision refractometer using a tilted fiber Bragg grating.

We present a refractometer with main- and vernier-scale to measure the refractive index (RI) of liquids with high precision by using the fine spectrum structure of a tilted fiber Bragg grating (TFBG). The absolute RI values are determined by the accurate wavelength of cut-off mode resonances. The main- and vernier-scale are calibrated by measuring large groups of fine spectra at different cut-off mode resonances in a small RI range, and the use of vernier-scale certainly reduces the RI measurement uncertainty resulted from the discrete cladding mode resonances. The performance of the TFBG-based vernier refractometer is experimentally verified by exploring the temperature dependence of RI of anhydrous ethanol in a near infrared region, showing an enhanced accuracy to the order of 10-4, high repeatability and temperature self-calibration capability.

Interactions between the first mode and the second Bragg gap in a cylindrical waveguide with undulated walls

Bragg resonances caused by the same transverse modes can always play a major role in periodic waveguides when the period is larger than the average radius. Because of higher-order mode cutoffs, the related Bragg gaps can be identified as interactions between different spatial harmonics of the fundamental mode, and the first Bragg gaps are more intensive than the higher ones. When we alter the parameters of the periodic waveguide, especially, decrease the period, the first transverse mode can be involved in Bragg gaps. Here, we demonstrate a direct mode-stopband interaction between the first mode and the second Bragg gap, that an extraordinary passband arises in the original second Bragg gap and splits the bandgap into two. Furthermore, the extraordinary passband is mainly composed of a pure first mode, which effectively suppresses the transmission of the fundamental one. We have also investigated the influence of wall profiles on the transmission and mode purity, and have found that the defined shape factor of wall profiles is proportionally related to the width of both pass and stop bands. The results could benefit not only the understanding of wave phenomena but also the applications in mode generators, filters, and so on.

Photonic bandgaps in selectively filled photonic crystal fibers

Simulations of selectively filled photonic crystal fibers using finite elements method were performed. Different patterns of filling were modeled and compared to an empty and fully filled fiber. Dependence of effective refractive indices of guided modes, phase birefringence and confinement losses on guided wavelength was investigated. A comparison of width of photonic bandgaps in different structures was made. Full Text: PDF ReferencesPh. St. J. Russell, "Photonic-Crystal Fibers", J. Lightwave Technol. 24, 4729 (2006) CrossRef Y. Han, S. Tan, M. K. K. Oo, D. Pristinski, S. Sukhishvili, and H. Du, "Towards Full-Length Accumulative Surface-Enhanced Raman Scattering-Active Photonic Crystal Fibers", Adv. Mat. 22, 2647 (2010) CrossRef S. Ertman, A. H. Rodríguez, M. M. Tefelska, M. S. Chychłowski, D. Pysz, R. Buczyński, E. Nowinowski-Kruszelnicki, R. Dąbrowski, and T. R. Woliński, "Index Guiding Photonic Liquid Crystal Fibers for Practical Applications", J. Lightwave Technol. 30, 1208 (2012) CrossRef K. Mileńko, S. Ertman, T. R. Woliński, "Numerical Analysis of the Phase Birefringence of the Photonic Crystal Fibers Selectively Filled with Liquid Crystal", Mol. Cryst. Liq. Cryst. 596, 4 (2014) CrossRef Y. Wang, C. Liao, X. Zhong, Z. Li, Y. Liu, J. Zhou, and K. Yang, "Selective-fluid-filled photonic crystal fibers and applications", Proc. SPIE 8914, 89140J-1 (2013) CrossRef F. Wang, W. Yuan, O. Hansen, and O. Bang, "Selective filling of photonic crystal fibers using focused ion beam milled microchannels", Opt. Express 19, 17585 (2011) CrossRef T. Martynkien, G. Statkiewicz-Barabach, J. Olszewski et al., "Highly birefringent microstructured fibers with enhanced sensitivity to hydrostatic pressure", Opt. Express 18, 15113 (2010) CrossRef B. T. Kuhlmey, R.C. McPhedran, C. M. de Sterke, "Modal cutoff in microstructured optical fibers", Opt. Lett. 27, 1684 (2002) CrossRef

Intensity-based readout of resonant-waveguide grating biosensors: Systems and nanostructures

Resonant waveguide gratings (RWG) − also called photonic crystal slabs (PCS) − have been established as reliable optical transducers for label-free biochemical assays as well as for cell-based assays. Current readout systems are based on mechanical scanning and spectrometric measurements with system sizes suitable for laboratory equipment. Here, we review recent progress in compact intensity-based readout systems for point-of-care (POC) applications. We briefly introduce PCSs as sensitive optical transducers and introduce different approaches for intensity-based readout systems. Photometric measurements have been realized with a simple combination of a light source and a photodetector. Recently a 96-channel, intensity-based readout system for both biochemical interaction analyses as well as cellular assays was presented employing the intensity change of a near cut-off mode. As an alternative for multiparametric detection, a camera system for imaging detection has been implemented. A portable, camera-based system of size 13cm×4.9cm×3.5cm with six detection areas on an RWG surface area of 11mm×7mm has been demonstrated for the parallel detection of six protein binding kinetics. The signal-to-noise ratio of this system corresponds to a limit of detection of 168M (24ng/ml). To further improve the signal-to-noise ratio advanced nanostructure designs are investigated for RWGs. Here, results on multiperiodic and deterministic aperiodic nanostructures are presented. These advanced nanostructures allow for the design of the number and wavelengths of the RWG resonances. In the context of intensity-based readout systems they are particularly interesting for the realization of multi-LED systems. These recent trends suggest that compact point-of-care systems employing disposable test chips with RWG functional areas may reach market in the near future.

Beam Diffraction Effects in the Backward Wave Regions of Viscoelastic Leaky Lamb Modes for Plate Transmission at Normal Incidence.

Plane-wave theory for fluid-embedded isotropic plates is often used in ultrasonic guided-wave applications, and to estimate wall thickness, corrosion, or sound velocities in plates and pipes. In such structures, measured ultrasonic transmission through the solid material is affected by acoustic beam diffraction effects, and the results may deviate from plane-wave descriptions, which are insufficient to describe the complex effects that occur. When exciting a fluid-embedded steel plate with a pulsed ultrasonic beam at normal incidence, resonance frequency downshift, axial sound pressure level increase, and beam narrowing have been observed, for measured resonance peaks in the frequency regions of certain leaky Lamb mode branches of the plate. In the ranges of other leaky Lamb mode branches, the observed effects are different. Measurements, finite element, and angular spectrum modeling are used to indicate a close connection between these beam diffraction phenomena and the backward wave characteristics of certain leaky Lamb mode pairs, in the frequency and Poisson's ratio regions around coincidence of two Lamb mode cutoff frequencies of similar symmetry. In particular, such observations made for the steel plate's fundamental thickness-extensional (TE) mode appear to be caused by acoustic beam excitation of the backward wave regions of the S-2vl and S2vl leaky Lamb modes.

Electron density variability of nighttime D region ionosphere in Vietnamese and Japanese sectors

AbstractRecording tweek atmospherics on geomagnetically quiet days in 2014 at Tay Nguyen University (TNU) (12.65°N, 108.02°E), Vietnam, and at Kagoshima (KAG) (31.48°N, 130.72°E), Japan, we investigated the nighttime electron density variability of the D region ionosphere between the equatorial‐low‐latitude Vietnamese and the low‐ to middle‐latitude Japanese sectors. We estimated the reflection height and electron density of the D region ionosphere using the first‐order mode cutoff frequency of tweek atmospherics. The results observed at both stations show that the mean electron density at the reflection height during winter season was higher than that during summer and equinox seasons. The electron density observed at TNU gradually decreased from 20:15 to 4:15 LT from winter to equinox and to summer. The electron density observed at KAG increased from 20:20 to 4:20 LT during summer and winter seasons. The mean electron density during 2014 observed at TNU (25.0 cm−3) was higher by 2.1 cm−3 than that observed at KAG (22.9 cm−3). During 2014, the nighttime electron density variations show a moderate positive correlation with the sunspot number but show weak to no correlation with the galactic cosmic rays. We suggest that the seasonal variations in the nighttime electron density could be significantly caused by the enhancement of geocoronal hydrogen Lyman α intensity and seasonal variation of nitric oxide density in the lower ionosphere.

Analog signal processing in the terahertz communication links using waveguide Bragg gratings: example of dispersion compensation.

We study the possibility of analog signal processing for the upcoming terahertz (THz) high-bitrate communications using as an example the problem of dispersion compensation in the THz communication links. In particular, two Waveguide Bragg Grating devices (WBGs) operating in the transmission mode are detailed. WBGs are designed by introducing periodic corrugation onto the inner surface of the metalized tubes. The resultant devices operate in a single mode regime either in the vicinity of the modal cutoff or in the vicinity of a bandgap edge, featuring large negative group velocity dispersions (GVD). We fabricate the proposed WBGs using 3D stereolithography, and metallize them using wet chemistry. Optical properties of the fabricated WBGs are investigated both theoretically and experimentally. The results confirm single mode guidance, relatively high coupling efficiency, as well as large negative group velocity dispersions in the range of several -100's ps/(THz · cm) in the vicinity of 0.14THz. This makes the short sections of proposed WBGs suitable for compensating positive dispersion incurred in the THz wireless links or fiber-assisted THz interconnects for signals of several-GHz bandwidth. Finally, we comment on the challenges associated with the analog signal processing in the THz spectral range.

A novel method for cement placement diagnosis behind multiple strings based on sonic dipole cutoff mode processing

Acoustic measurements are widely used to diagnose the condition and placement of cement in cased oil and gas wells, and its bond to interfaces in contact with it. However current methods, encompassing high frequency sonic CBL-VDL and ultrasonic measurements, are designed for single steel casings and insufficient to probe behind more than one casing, and so cannot address the diagnosis of the placement and bond of cement behind a second casing that have become critical in the oil and gas industry. We therefore look at the use of lower frequency sonic measurements with deeper radial probing capability, to identify features appropriate for such a diagnosis. In particular, in this work we look at the modeling of sonic monopole and dipole modes as generated by existing tools and identify a set of cutoff modes that are indicative of annular fill behind a second casing when the annulus behind the first is known. Therefore the acquisition and processing of such modes in conjunction with the use of traditional cement evaluation techniques could become a viable avenue for the acoustic diagnosis of cement placement in multiple casing string geometries. Modeling results for such scenarios will be presented along with potential application to experimental and field data to indicate the feasibility of such a diagnosis using feature extraction.

Wide Range Refractive Index Measurement Using a Multi-Angle Tilted Fiber Bragg Grating

The conventional single-angle tilted fiber Bragg grating (TFBG) can only excite a certain range of cladding modes, limiting it for refractive index (RI) measurement in a wide range. In this letter, we fabricate and demonstrate a multi-angle TFBG, in which five individual TFBGs with tilt angles ranging from 5° to 25° are sequentially inscribed along the core of a single mode fiber within a length of 20 mm. The multi-angle TFBG excites a continuous spectral comb of narrowband-cladding modes over a much wider wavelength range (>170 nm) than a single-angle TFBG, making it suitable for dynamic RI measurement over a wide range (1.15–1.45). We have experimentally measured aqueous solutions with RI ranging from 1.30 to 1.45 using the uncoated (by monitoring the cut-off mode) and gold-coated (by monitoring the surface Plasmon resonance) multi-angle TFBGs, and both methods show linear responses, with RI sensitivities about 500 nm/RIU.

Emission optimised control and speed limit for isolated intersections

Stopping and accelerating at traffic lights is one of the main contributing factors to vehicular emissions in urban environments. The work in this study demonstrates a generic guideline for minimising CO 2 emissions at traffic lights. This was done using an adaptive control, which uses a cost function for optimisation, rather than network-specific control parameters. A new version of the emission model PHEMlight was used, which added of a fuel cut-off mode during coasting and other improvements compared with the previous version. Using this model, it could be determined that the emission optimal ratio between delay time and stops for the cost function of an adaptive control should be 1:165 at 50 km/h. When the speed limit increases the ratio also increases with 1:296 for 70 km/h. However, it was also found that the optimal free flow travel speed was around 70 km/h. Therefore, with long distances between intersections and a low amount of average stops, the maximum speed should be higher than 50 km/h for emission optimality. Application of the ratio for 50 km/h to the adaptive control algorithm ImFlow resulted in a CO 2 emission reduction of 6.3% compared with a vehicle actuated control.

Neutrophil-to-lymphocyte ratio as prognostic indicator in gastrointestinal cancers: a systematic review and meta-analysis.

An accurate, time efficient, and inexpensive prognostic indicator is needed to reduce cost and assist with clinical decision making for cancer management. The neutrophil-to-lymphocyte ratio (NLR), which is derived from common serum testing, has been explored in a variety of cancers. We sought to determine its prognostic value in gastrointestinal cancers and performed a meta-analysis of published studies using the Meta-analysis Of Observational Studies in Epidemiology guidelines. Included were randomized control trials and observational studies that analyzed humans with gastrointestinal cancers that included NLR and hazard ratios (HR) with overall survival (OS), disease-free survival (DFS), progression-free survival (PFS), and/or cancer-specific survival (CSS).We analyzed 144 studies comprising 45,905 patients, two-thirds of which were published after 2014. The mean, median, and mode cutoffs for NLR reporting OS from multivariate models were 3.4, 3.0, 5.0 (±IQR 2.5-5.0), respectively. Overall, NLR greater than the cutoff was associated with a HR for OS of 1.63 (95% CI, 1.53-1.73; P < 0.001). This association was observed in all subgroups based on tumor site, stage, and geographic region. HR for elevated NLR for DFS, PFS, and CSS were 1.70 (95% CI, 1.52-1.91, P < 0.001), 1.64 (95% CI, 1.36-1.97, P < 0.001), and 1.83 (95% CI, 1.50-2.23, P < 0.001), respectively.Available evidence suggests that NLR greater than the cutoff reduces OS, independent of geographic location, gastrointestinal cancer type, or stage of cancer. Furthermore, DFS, PFS, and CSS also have worse outcomes with elevated NLR.

Cut-off-based dual-taper reflectors in on-chip hollow waveguides.

We describe back-to-back (dual) tapers embedded within hollow Bragg waveguides clad by omnidirectional Si/SiO2-based mirrors, and fabricated using a thin film buckling approach. The back-reflection of light subject to mode cutoff in the narrowed tunnel section results in a short-pass transmission characteristic. Thus, the dual taper can act as a waveguide filter with the upper pass-band edge determined by the lithographically controlled height of the tunnel section. We also report preliminary results on the use of these dual tapers as in-plane reflectors (for operation in the cutoff regime), with potential to enable a novel class of open-access hollow-waveguide microcavities.

Cut-off frequencies and correction factors of equivalent single layer theories

Shear and normal correction factors are used within first-order equivalent single-layer theories for homogeneous and layered structures, e.g. first-order shear deformation plate/shell theories, in order to improve the description of the transverse strains. Dynamic correction factors may be derived, following the original treatment for homogeneous plates (Mindlin, R.D., J. Appl. Phys. 1951), by imposing that certain wave propagation frequencies, e.g. the cut-off frequencies of the lowest cut-off frequency modes, match those of three-dimensional elasticity, which are typically obtained through computational procedures. In this paper we consider multilayered plates with principal material directions parallel to the geometrical axes and propose the use of a multiscale structural theory which allows the accurate closed-form derivation of the frequencies of the first thickness modes associated to plane-strain Rayleigh-Lamb waves. The theory captures the effects of the inhomogeneities on local fields and global behavior through homogenized equilibrium equations which depend on a limited number of variables independent of the number of layers. Explicit expressions are obtained for the lowest cut-off frequencies of multilayered wide plates with an arbitrary number of layers, with arbitrary layup and elastic constants, which are then used to define the dynamic correction factors of classical equivalent single-layer theories. The comparison with predictions obtained by matching exact elasticity solutions for highly-inhomogeneous bilayer media highlights the accuracy and potentials of the proposed approach.

Nonlinear coupled mode excitations in microtubules

The dynamics of coupled nonlinear waves is addressed in the framework of the angular model of microtubules. The semi-discrete approximation is used to write the dynamics of the lower and upper cutoff modes in the form of coupled nonlinear Schrödinger equations. The linear stability analysis of modulational instability is used to confirm the existence of soliton solutions, and the growth-rate of instability is shown to be importantly influenced by the dipolar energy. Single mode solutions are found as breathers and resonant kink, while the coupled mode introduces a kink envelope solution, whose characteristics are discussed with respect to the dipolar energy. The found solution is shown to be robust, which is important for energy transport in the Polymerization/depolymerization mechanism of protofilaments.

Design of PANDA ring-core fiber with 10 polarization-maintaining modes

We present a polarization-maintaining PANDA ring-core fiber (PM-PRCF) characterized by the combination of a ring-core structure with two stress-applying rods. This special fiber design separates the adjacent modes and avoids the cutoff of the higher-order modes, which is a common problem in elliptical core polarization-maintaining few-mode fibers. Using a high-contrast index ring and stress-induced birefringence, the PM-PRCF features support for 10 vector modes, with effective refractive index separations from their adjacent modes >10−4. Broadband performance is investigated subsequently over a wide wavelength range from 1500 to 1630 nm. The proposed fiber is targeted at applications in space-division multiplexing while eliminating the complex multiple-input multiple-output signal processing.

Coupling of Cutoff Modes in a Chain of Nonlinear Metallic Nanorods**Supported by the National Basic Research Program of China under Grant No 2012CB921502, the National Natural Science Foundation of China under Grant Nos 11374150, 11074120, 11274163 and 11274164, and the Priority Academic Program Development of Jiangsu Higher Education Institutions of China.

We study the coupling of cutoff modes in a chain of metallic nanorods embedded in a Kerr nonlinear optical medium with strong near-field interactions analytically. Based on a quasidiscreteness approach, we derive a system of two coupled nonlinear Schrödinger equations governing the evolution of the envelopes of these modes. It is shown that this system supports a variety of subwavelength plasmonic lattice vector solitons of the bright-bright, bright-dark, dark-bright, and dark-dark type through a cross-phase modulation. It is also shown that the existence of different solitons depends strongly on the gap width scaled for the rod radius and the type of nonlinearity of the embedded medium.