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We present a relative sensitivity of in-fiber inter-cross demodulation of a Mach–Zehnder interferometer (MZI) based on an etched multi-core fiber (eMCF). The sensor can measure the external refractive index (RI) and temperature with a large fringe visibility of 15 dB. It is tuned using a simple technique of slow chemical etching. When the outer cores of MCF will be exposed to the surrounding, a large difference of relative effective RI is observed, which enhances the sensitivity of the sensor. The sensor's wavelength and intensity responses have displayed that it can function with three different inter-cross-demodulation phenomena. A superior RI sensitivity of 178.20 dB/RIU in the range of 1.334 to 1.370, and temperature sensitivity of 66.73 pm/°C in the range of 30 to 80 °C are obtained, with an adequate linear response. Besides, it can readily resolve the issues of cross-sensitivity. Moreover, it has many advantages including easy fabrication, compact size, multiplex, repeatable, stable, and can easily differentiate RI and temperature, which lack others.

Scattering from a grounded chiral slab with rough interface is studied using perturbation theory. A system of equations for zeroth and higher order solution is written, which can be solved to get c...

A design of the highly non-linear and ultra-sensitive modified core of a photonic crystal fiber (PCF) sensor is reported for the detection of various liquid analytes. The sensor design comprises three rings of a hexagonal lattice around the liquid-infiltrated hollow core. A steric-shaped hollow core design in PCF effectively optimizes the sensor’s sensitivity and performance. The design is analyzed numerically by using the full vector finite element method with perfectly matched layers to find a rigorous solution. The proposed PCF sensor exhibits ultra-high relative sensitivity, a high power fraction, high non-linearity coefficient, low confinement loss, ultra-low chromatic dispersion, compact effective mode area, and single-mode operation in a wider wavelength range, i.e., within visible and infrared wavelength regimes. At an operating wavelength of 1.0 µm, optimum relative sensitivities of 96.37%, 97.40%, and 99.82% with high non-linear coefficients of 78.0 W − 1 k m − 1 , 66.09 W − 1 k m − 1 , and 62.57 W − 1 k m − 1 and extremely low confinement loss of ∼ 10 − 10 d B / m are obtained for water, ethanol, and benzene analytes, respectively. Further, waveguiding characteristics of the PCF sensor endorse its usage for a range of liquid analyte detections. It is a simple design and can be fabricated using existing manufacturing technologies.

This study aims at ground based atmosphere monitoring for Islamabad region (33.7167°N and 73.667°E, 508 m altitude) using locally designed dual channels, (Green (550nm) and red (625nm)) LED based handheld sunphotometer. Calibration was done by using improvised transfer of calibration method employing pre-calibrated GLOBE (Global Learning and Observation to Benefit Environment) sunphotometer. Aerosol optical thickness (AOT) of said region for the month of July, August 2017 was calculated using acquired data for red and green channels. Matching trends (correlation up to 95%) were observed for AOT obtained with GLOBE and local sunphotometer. AOT of Islamabad region generated by satellitebased Moderate Resolution Imaging Spectro-radiometer (MODIS) instrument board on AQUA and Terra satellites has also been presented for calibration period (Oct 2016-Feb 2017) to qualify our findings. The inter-comparison of data with MODIS instrument AQUA and Terra from Oct 2016 to Feb. 2017 with the local sunphotometer green channel yielded a correlation coefficients in range of 0.51-0.55 approaching the previously reported range values of (∼0.55-0.60) for similar comparison. Along with AOT, in this study, the average daily Angstrom exponent α, and angstrom turbidity constant ?, have also been reported. The average of angstrom exponent for recorded data is 1.42, this implies moderately polluted urban atmosphere of area under study, while the 19th and 20th July are clearest day for monitoring period with ? = 0.07 and ? = 0.083 respectively.

An extension of the problem of reflection from a flat dielectric-chiral interface is presented. A dielectric-chiral rough interface is assumed and scattered field is calculated using small perturba...

Radiation due to an electric line source placed under a planar dielectric slab of non-integer dimensional space is determined. It has been assumed that the non-integer dimensional dielectric slab is sandwiched between two integer dimensional dielectric mediums. Radiated fields are written in terms of unknown spectrums of propagating waves. The unknown spectrum functions are determined using the boundary conditions. Special cases have also been discussed to verify the derived results. Radiation pattern is given for different parameters related to the geometry.

In this paper, we present an enhanced sensitivity of temperature sensors based on thermo-coupled Multicore Fiber (MCF) structures. The sensors are all fabricated using a controlled arc power of a splicing device. Two different principles of a Mach-Zehnder interferometer (MZI) and Michelson interferometer (MI) have been observed experimentally. The MZI and MI structures exhibit temperature sensitivity as 136.67 pm/°C and 70.61 pm/°C, respectively, and found insensitive to the refractive index (RI). Also, its RI response can readily resolve the issues of cross-sensitivity.

A numerical solution, using the general formulation of the transcendental equation and eigenmode values, is proposed to demonstrate number of strongly guided modes propagating in sapphire crystal fibers (SCF). The SCF is considered to have hexagonal geometry of a single crystal and multimode step-index profile. Several distinguished characteristics are naturally embedded in SCF compared to other ordinary optical fibers. The eigenmodes of the SCF are numerically determined and are a combination of transverse electric, transverse magnetic, and hybrid modes. The numerical solution for wave-guiding in ultra-violet (UV), visible infrared (VIS/IR) spectrum, is investigated by the number of modal propagation under strongly guided approximation. The cross-sectional energy distribution of fundamental mode (FM) and higher order modes (HoM) describe the variation of the effective mode index with respect to the change in the core radius. The proposed waveguide is of ~35micron radius, exhibit −0.077 dB/m confinement loss at 200 nm. The simulations in this study are performed by the COMSOL multi-physics® software.

The investigation of core-shell nanoparticles has been greatly exciting in biomedical applications, as this remains of prime importance in targeted drug delivery, sensing, etc. In the present work, the polarizability and scattering features of nanoparticles comprised of nano-sized dielectric/metallic core-shell structures were investigated in the fractional dimensional (FD) space, which essentially relates to the confinement of charged particles. For this purpose, three different kinds of metals&mdash, namely aluminum, gold and silver&mdash, were considered to form the shell, having a common silicon dioxide (SiO2) nanoparticle as the core. It is noteworthy that the use of noble metal-SiO2 mediums interface remains ideal to realize surface plasmon resonance. The core-shell nanoparticles were considered to have dimensions smaller than the operating wavelength. Under such conditions, the analyses of polarizability and the scattering and absorption cross-sections, and also, the extinction coefficients were taken up under Rayleigh scattering mechanism, emphasizing the effects of a varying FD parameter. Apart from these, the tuning of resonance peaks and the magnitude of surface plasmons due to FD space parameter were also analyzed. It was found that the increase of FD space parameter generally results in blue-shifts in the resonance peaks. Apart from this, the usage of gold and silver shells brings in fairly large shifts in the peak positions of wavelengths, which allows them to be more suitable for a biosensing purpose.

Atmospheric changes in the lower troposphere have been remotely studied using a self-engineered Mie scattering lidar with special emphasis on aerosols and clouds profiling over Islamabad region in Pakistan. The lidar is based on a Nd:YAG laser operating at 1064 nm, with maximal energy of 350 mJ at 20-Hz repetition rate and 5-ns pulse length. A silicon avalanche photodiode (Si-APD, C30950E) module is used as a detector. A higher resolution of the lidar revealed time evolution of thermal transport phenomena in the convective boundary layer. Regions of incessant wind speed, temperature, and particulates concentration have been detected through band-like structures at altitudes above 900 m. Strong backscattering (β) and extinction (α) due to a partially invisible thin cloud layer falling in the field-of-view of the lidar beyond 4 km have been identified.

In this paper, near zone scattering properties of a perturbed perfect electromagnetic conductor (PEMC) cylinder are observed using the perturbation theory (PT). The analytical solution of the scattered field is obtained for both the transverse electric (TE) and transverse magnetic (TM) polarizations of the incident field. The perturbed cross section is generated considering the limits imposed by the PT. The effect of perturbations on the co and cross polarized components of the scattered field from a perturbed PEMC cylinder is observed and compared with the reference scattered field from the circular PEMC cylinder. In particular, the distinctions due to perturbations are observed in the forward and backward scattering. The forward scattering deviates more than the backward scattering. Also, the effect of perturbations for the TE polarization is more evident. The variations in the co and cross polarized scattering are also noted by changing the value of the admittance of the PEMC cylinder.

Two dimensional Green's function for grounded dielectric half space geometry in non-integer dimensional space has been derived. It has been assumed that both half spaces are of non-integer dimension. Radiated fields are written in terms of unknown plane wave spectrum. Unknown spectrum functions are determined using the boundary conditions. Special cases have also been addressed considering one or both the spaces are of integer dimensional space. The solution for both the spaces are of integer dimension is used to make a comparison with previously reported results. Results are reported for different values of physical and geometrical parameters.

An arbitrary shaped scatterer is often modeled as a canonical structure while solving an electromagnetic boundary value problem. This approach approximates the boundary to provide complex analytical solutions. However, most real life structures do not have canonical or regular boundaries. Determining an analytical solution of electromagnetic scattering problem is quite a tedious task, especially for random geometries. This work proposes a method to compute the scattering statistics of a random cylinder. A formulation is developed to determine the probability density function (pdf) of scattering cross section, σ T , from the statistics of random cylinder's radius. This approach eliminates the need to actually solve an electromagnetic scattering problem. The optical theorem is employed to estimate the pdf of σ T from the pdf of lateral width. The proposed results are found in good agreement with the numerically simulated results.

Scattering from a perfect electric conducting cylinder with random radius buried below a half space dielectric homogenous interface is studied. The cylindrical wave scattered by cylinder is expanded in terms of plane wave spectrum. Small perturbation method is used to study the interaction of each plane wave with the interface. The zeroth order term yields solution for a flat interface, whereas scattering from a rough surface is given by first-order term. Results are obtained for both TM and TE polarizations. Analytical expressions of the average scattered field are obtained and verified using numerical evaluation. Different scattering scenarios are simulated by varying the distribution of the radius. It is observed that average scattering cross section of an ensemble with normal/uniform distribution is almost equal to that of a cylinder with mean radius.

A general theoretical formulation is done to calculate the field scattered by perfect electromagnetic conductor (PEMC) cylinder coated with anisotropic plasma material. It is buried below a slightly rough surface. Spectral plane wave representation of fields and small perturbation method are used to calculate multiple reflections between coated cylinder and rough surface. To validate the present formulation, scattered field from a PEMC cylinder coated with double negative (DNG) material is obtained from the present formulation. Scattering pattern of non coated PEC/PEMC cylinder or coated with isotropic material can also be obtained by the proper selection of physical parameters such as anisotropy, admittance of PEMC cylinder and permittivity of hosting medium. Analytical expressions of scattered field for a sinusoidal rough surface are given along with their physical interpretation to get a good insight. Effect of geometrical and physical parameters on scattering pattern is observed.

Scattering from a perfect electromagnetic conductor (PEMC) rough surface has been considered. PEMC does generalize perfect electric conductor (PEC) and perfect magnetic conductor (PMC). In contrast to PEC rough surface, cross-polarized component of the scattered field also exists. Small perturbation method is applied to evaluate co- and cross-polarized scattered fields. The zeroth-order solution corresponds to flat case while first-order term gives the contribution from the surface perturbations. The results reduce to that of the PEC flat/rough surface as , where M is the admittance parameter which characterizes the PEMC. The incoherent bi-static co- and cross-polarized scattering coefficients of a random rough surface are given. As an example, the case of a rough surface with sinusoidal profile is considered and the expressions for co- and cross-polarized filed components are reported.

Spectral plane wave representation of fields (SPRF) is applied to evaluate the scattered-transmitted field from a chiral cylinder buried beneath a flat/rough interface. Small Perturbation Method is used to evaluate rough surface scattering. An effort has been done to validate the results by making a comparison with the previously available results. Effect of surface period, chirality and size of the cylinder on scattered field is observed. It is noted that radar cross section (RCS) is significantly reduced for chiral objects buried beneath the flat interface. The same effect is observed in case of rough interface.

In this paper, near and far zone fields scattered from a perfect electromagnetic conductor (PEMC) cylinder coated with complex conjugate material (CCM) and buried below a sinusoidal rough surface is studied. Multiple reflections between the rough surface and the cylinder are evaluated with the help of perturbation theory applied on the plane wave spectrum representation of the cylindrical scattered field. Scattering from CCM coated cylinder is compared with that of a dielectric coated cylinder. Both the CCM and the dielectric material have same refractive index. Difference between the scattered fields is observed due to different impedance of the coating material. Near zone back scattering and forward scattering patterns are very insightful to pronounce the distinctions between the CCM and dielectric coating. It is also noted that for transverse electric (TE) polarized incident field, the forward scattering for CCM and dielectric coated cylinders differs significantly from each other. It is possible to achieve scattering maximization with CCM coating. Moreover, the effects of roughness and the admittance of the PEMC core are also noted on the scattering.

A numerical solution is presented for electromagnetic scattering from a random cross-section of a cylinder placed inside a dielectric half-space. Assumed that a plane wave of known parameters is incident from the half space. The incident electric field of an electromagnetic plane wave is parallel to the z-axis of the random cylinder. The method of moment is employed to obtain surface currents and Electric field integral solution is used to obtain the scattered field. The problem consists of two regions, the observer located in the free space region above from interface and the second region is an underground region where the random cylinder is placed. In the whole scenario, the medium is considered as homogeneous and lossless. The average scattered field is observed by varying different parameters for realization. To diversify the solution, COMSOL Multiphysics® and Matlab is used for simulations to investigate backscattered field involving transverse electric (TE) and transverse magnetic (TM) polarizations.

The reduction in radar cross section (RCS) of a perfect electric conductor (PEC) cylinder coated with chiral media buried below a sinusoidal surface is investigated. Spectral plane wave representation of field (SPRF) is used to account for the interaction of buried cylinder with the sinusoidal surface. Small perturbation method (SPM) is used to observe scattering from the sinusoidal surface. Different scattering scenarios are simulated by changing chirality and thickness of coating layer. It is observed that co polarized RCS is significantly reduced for some values of chirality. The behavior of the scattering coefficients is very useful to understand the dependence of RCS reduction on chirality.

Scattering of electromagnetic wave from a DNG coated perfect electromagnetic conductor (PEMC) cylinder buried below a slightly rough sinusoidal surface is investigated. This is a generalization of different earlier solved such problems involving PEC/PEMC coated/non-coated cylinder buried below flat/rough surface. The initial reflected and transmitted field from the sinusoidal surface are evaluated using Small Perturbation Method (SPM). All the interactions between the object and the sinusoidal surface have been taken into account using spectral plane wave representation of fields (SPRF). The effect of geometrical and physical parameters on the scattering pattern is observed.

The scattering of left circularly polarized wave from a perfectly electric conducting (PEC) rough surface in isotropic chiral media is investigated. Since a slightly rough interface is assumed, the solution is obtained using perturbation method. Zeroth-order term corresponds to solution for a flat interface which helps in making a comparison with the results reported in the literature. First-order term gives the contribution from the surface perturbations, and it is used to define incoherent bistatic scattering coefficients for a Gaussian rough surface. Higher order solution is obtained in a recursive manner. Numerical results are reported for different values of chirality, correlation length, and rms height of the surface. Diffraction efficiency is defined for a sinusoidal grating.

Electromagnetic scattering from a topological insulator (TI) cylinder buried beneath a rough surface is considered. To account for the interactions of the scattered field and the rough surface, spectral plane wave representation of fields is used along with small perturbation method. Both time-reversal symmetry TI cylinder and time-reversal symmetry broken TI cylinder are considered to evaluate the scattered-transmitted field above the rough surface for different values of the periods of the rough surface and the size of the object. It is observed that co- and cross-polarized field components show a maximum before the time-reversal symmetry is broken. The co-polarized component remains almost constant while the cross-polarized component decreases for time-reversal symmetry broken case.

Total scattering cross section (σT) of a PEC cylindrical scatterer is a function of it's scattering amplitude and is closely related to scatterer's cross section. It is difficult to determine σT analytically for arbitrary cross sections of scatterer, especially for random cross sections. Defining some bounds on the value of σT is therefore very helpful in its estimation. In this paper, σT of canonical shaped objects is used to define bounds on σT of random cylinder. The geometrical parameters of canonical scatterers are obtained from the geometric parameters of the random cylinder. A formulation is also developed to approximate the value of σT from its bounding values. This work therefore, helps to predict the σT of a random cylinder from its geometrical parameters, without solving an electromagnetic boundary value problem.

The problem of electromagnetic scattering of two-dimensional field by a perfect electromagnetic conducting cylinder buried beneath slightly rough surface has been considered. The solution is obtained using the spectral, plane wave representation of the fields together with perturbation method to deal with the rough deviations on the interface. Asymptotic evaluation of the spectral integrals has been done to obtain results for both co- and cross-polarized scattered-transmitted fields. To validate the theory, the case of rough surface with sinusoidal profile is simulated. A rough surface with Gaussian roughness spectrum has also been considered. The illuminated area is limited by the use of Gaussian beam incidence. Different scattering scenarios are implemented, varying the correlation length of the surface and the radius of the cylinder. Studies are done to determine both co- and cross-polarized scattered fields that can be useful in the detection of the material properties of the buried object below the r...

Analytical solution of vector wave equation describing the scattering of electromagnetic plane waves from an infinitely long circular chiral cylinder placed in another chiral metamaterial is presented. Cylindrical vector wave functions are used to express the fields both inside and outside the circular cylinder. The unknown are determined by applying the appropriate boundary conditions at the cylindrical interface. The numeric results are presented taking different combinations of metamaterials for inner and outer mediums of the cylinder. For this purpose chiral and/or chiral nihility cylinder placed in chiral and/or chiral nihility mediums are considered. Extreme cases of permittivity and permeability corresponding to PEC and PMC cylinder are also considered.

For the next generation wireless communication system, Multi carrier Code Division Multiple Access (MC-CDMA) has become very appealing scheme due to due to high data rates and interference limiting factors. In this research work we analyzes the capacity of MC-CDMA system using adaptive power and sub-channel allocation under perfect, imperfect and predicted channel state information (CSI). The transmitter and receiver both have been targeted in this paper. The proposed scheme is a novel idea that divides the sub-channels into small groups. Each group is assigned power according to the Eigen values and gain of the each sub-channel in that specific group. The receiver calculates optimal feedback vector for the transmitter by calculating the bit error rates using the above strategy and selects the optimal feedback vector. The simulations show that the usage of joint power and sub-channel allocation outperforms the capacity of the system. The capacity of the system is highly improved using adaptive power and sub-carriers allocation along with CSI prediction. The simulation results have been carried out for other power allocation schemes available in literature and results have been compared with perfect, imperfect and predicted CSI.

Multi input multi output (MIMO) is a multifarious and captivating technology due to its high data rate and capacity. In this research work, the authors have proposed a novel successive interference scheme for un-coded MIMO spatial multiplexing system with multiple interference cancellation structure. The multi branch multiple feedback successive interference cancellation (MB-MF-SIC) employees multiple SIC in parallel according to ordering of the received signal. The branch which yields best performance is selected which in turn gives higher detection diversity. The arrangement of the layers demolish the propagation of error in the feedback loop and hence enhances the bit error rate performance. Simulation results show that the combination of MB-MF-SIC and the ordering of the layers named Multi Branch Layers Ordered Multiple Feedback SIC (MB-LOMF-SIC) significantly improves the results compared to the existing MF-SIC and conventional SIC schemes.

A mathematical model of random cylinder is given to facilitate realization of a single random cylinder and study its electromagnetic scattering properties. The proposed model is very versatile as cylinders with cross sections varying from circular to rough (noise like) can be easily generated. Statistical properties of the radius of random cylinder are analytically determined. Electromagnetic field scattered from a smooth random cylinder is obtained using Moments Method. Ensemble averages of the scattered field in all directions and total scattering cross section are obtained. The optical theorem test shows that the solution obtained in this paper is better than the earlier proposed solutions.

A power allocation algorithm for projection matrix receiver based MC-CDMA system named Adaptive Threshold SAFNAQ (AT-SAFNAQ), has been proposed. SAFNAQ is a combination of frequency domain (FDPA) and eigenvector based (EBPA) power allocation algorithms. SAFNAQ algorithm does not optimize threshold value and it uses same threshold value over different channel realizations. In AT-SAFNAQ, the receiver has an extra unit compared to the receiver used in SAFNAQ algorithm. This extra unit optimizes threshold level adaptively. In accordance with optimum threshold value and the subcarrier gains, the feedback vector is sent to the transmitter for allocation of power. We have compared our results with no power allocation, FDPA, EBPA and SAFNAQ. Simulation results show that AT-SAFNAQ algorithm provides noticeable improvement in performance compared to the algorithms available in literature. We have generated testing bits at transmitter end, passed through Rayleigh fading channel to calculate BER performance of the system at receiver end to verify the results. Moreover, Variances of BER for different users are explored to show that in our system all the users have equal priority.

For future systems of wireless communication, multi-carrier code division multiple access (MC-CDMA) is becoming much attractive due to its high data rate and multiple access capability. Continuing our research on main issues of MC-CDMA, which mainly include power and channel allocation, here we have considered power allocation following the channel allocation to improve overall performance of the system. In the current work, adaptive sub-channel allocation scheme has been incorporated into SAFNAQ algorithm to improve bit error rate (BER) performance of MC-CDMA system. SAFNAQ is an algorithm for transmission power allocation in MC-CDMA system. A projection matrix receiver based MC-CDMA system has been considered. The Rayleigh fading channel was used for simulations. The SAFNAQ algorithm, cohesion of frequency domain power allocation (FDPA) and eigen vector based power allocation (EBPA) algorithms, allocates available transmission power to adaptively chosen strongest sub-carriers with respect to corresponding coefficients of power balance vector computed using EBPA algorithm. In adaptive sub-channel allocation, different sub-channels are allocation to different users on the base of channel state information (CSI). In sub-channel allocation module, sub-channels were divided into small groups. Number of sub-channels in each group was equal to the length of pseudo random codes used to gain multiple access capability. At most one user can be allocated to each group simultaneously and corresponding user's desired power is allocated to sub-channels of that group in accordance with SAFNAQ algorithm. The system was simulated for different number of users and channel paths. Simulation results showed that usage of adaptive sub-channel allocation along with SAFNAQ algorithm improves the overall system bit error rate (BER) performance.

Scattering by a perfectly conducting strip which is buried in an infinite grounded dielectric layer is considered. It is assumed that the strip is far away from interfaces of the grounded dielectric layer. This assumption is utilized to simplify the work by considering that the scattered field, which is reflected more than once by any interface or reflected by both the interfaces of grounded dielectric layer, has no interaction with the buried strip. Dominant contribution of the reflected scattered field which interacts with the strip is calculated asymptotically, for large separation of the strip from boundaries of the grounded dielectric layer. Far-zone field expression, for region above the grounded dielectric layer, is derived taking into account the effects of interaction of reflected scattered field with the strip. This expression is derived in a general form which can be applied to any arbitrary cylindrical obstacles. Some numerical results are given for the case of perfectly conducting circular cy...