Muhammad Mahmood Ali

Bio: Muhammad Mahmood Ali is an academic researcher from University of Limerick. The author has contributed to research in topics: Fiber Bragg grating & Metamaterial. The author has an hindex of 11, co-authored 52 publications receiving 629 citations. Previous affiliations of Muhammad Mahmood Ali include Institute of Technology, Sligo & Ghulam Ishaq Khan Institute of Engineering Sciences and Technology.

Chronology of Fabry-Perot interferometer fiber-optic sensors and their applications: a review.

Abstract: Optical fibers have been involved in the area of sensing applications for more than four decades. Moreover, interferometric optical fiber sensors have attracted broad interest for their prospective applications in sensing temperature, refractive index, strain measurement, pressure, acoustic wave, vibration, magnetic field, and voltage. During this time, numerous types of interferometers have been developed such as Fabry-Perot, Michelson, Mach-Zehnder, Sagnac Fiber, and Common-path interferometers. Fabry-Perot interferometer (FPI) fiber-optic sensors have been extensively investigated for their exceedingly effective, simple fabrication as well as low cost aspects. In this study, a wide variety of FPI sensors are reviewed in terms of fabrication methods, principle of operation and their sensing applications. The chronology of the development of FPI sensors and their implementation in various applications are discussed.

Cladless few mode fiber grating sensor for simultaneous refractive index and temperature measurement

Abstract: In this work, we have demonstrated a cladless few-mode fiber grating sensor for simultaneous measurement of refractive index (RI) and temperature. The proposed sensor is fabricated from an etched few-mode Fiber Bragg Grating (FMFBG) that can support two Bragg wavelengths, in which the sensitivities for each Bragg wavelength to the changes of RI and temperature are different. A mode coupling theory is used to describe the sensing principle of the proposed sensor and the simulation result finding that an etched diameter of 14.1 μm can get the better performance for optimal the power confinement of etched FMFBG. Experimental results show that the proposed sensor has the RI sensitivities for both λ 01 and λ 11 are estimated to be 1.183 nm/RIU and 4.816 nm/RIU respectively, and temperature sensitivities for λ 01 and λ 11 are 9.62 ± 0.08 pm/°C and 9.52 ± 0.13 pm/°C respectively. With the assistance of 3 × 3 characteristic matrix, discrimination measurements of temperature and RI has been demonstrated and the deviations in RI and temperature measurements are ±8 × 10 −4 RIU and ±1 °C respectively.

Elliptical metallic rings-shaped fractal metamaterial absorber in the visible regime

Abstract: Achieving the broadband response of metamaterial absorbers has been quite challenging due to the inherent bandwidth limitations. Herein, the investigation was made of a unique kind of visible light metamaterial absorber comprising elliptical rings-shaped fractal metasurface using tungsten metal. It was found that the proposed absorber exhibits average absorption of over 90% in the visible wavelength span of 400–750 nm. The features of perfect absorption could be observed because of the localized surface plasmon resonance that causes impedance matching. Moreover, in the context of optoelectronic applications, the absorber yields absorbance up to ~ 70% even with the incidence obliquity in the range of 0°–60° for transverse electric polarization. The theory of multiple reflections was employed to further verify the performance of the absorber. The obtained theoretical results were found to be in close agreement with the simulation results. In order to optimize the results, the performance was analyzed in terms of the figure of merit and operating bandwidth. Significant amount of absorption in the entire visible span, wide-angle stability, and utilization of low-cost metal make the proposed absorber suitable in varieties of photonics applications, in particular photovoltaics, thermal emitters and sensors.

Design of a wideband terahertz metamaterial absorber based on Pythagorean-tree fractal geometry

Abstract: Broadband absorption in the terahertz regime is a challenge and onerous to realize with a single layer metasurface. Self-similarity in fractal structures are exploiting metamaterial characteristics that offer a promising platform to design wideband microwave and optical devices. This paper presents a metamaterial absorber that consists of fractal geometry of Pythagorean-tree. The proposed metamaterial absorber demonstrates the wideband absorptivity in a terahertz spectrum ranging from 7.5–10 THz. Both transverse electric (TE)–and transverse magnetic(TM)–mode are taken up under different obliquity incidence angles to deeply study the angular dependence on absorption features of the Pythagorean-tree fractal meta-absorber (PTFMA). A numerical approach of interference theory is employed to verify the simulation results of the designed PTFMA. Further, the performance of the PTFMA was analyzed in terms of the figure of merit (FOM) and operational bandwidth (OBW) for different geometric parameters. Furthermore, surface electric field patterns and current distributions were studied to understand the absorption mechanism of the suggested PTFMA. The designed absorber would be a promising contender for bolometers, THz detection, and communication.

Characterization of Mode Coupling in Few-Mode FBG With Selective Mode Excitation

Abstract: We present the results on fabrication and the characterization of few-mode fiber Bragg gratings (FM-FBGs) inscribed in two mode and four mode step-index fibers. Under the conditions of selective input mode launching, coupling between specific modes of interest can be selectively excited and the self-coupling and cross-coupling properties at the associated resonant wavelengths can be clearly identified and verified by observing the reflected mode intensity profiles. Such FM-FBGs can potentially be used as reflective mode-converters for mode division multiplexed data transmission systems.

Hazards of Postoperative Atrial Arrhythmias

Abstract: Between January 1, 1986, and December 31, 1991, 4,507 adult patients underwent cardiac surgical procedures requiring cardiopulmonary bypass. Of these patients, 3,983 patients who did not undergo operation for supraventricular tachycardia and who were in normal sinus rhythm preoperatively form the study group for the present study. Postoperatively, all patients were monitored continuously for the development of arrhythmias until the time of hospital discharge. The incidence of atrial arrhythmias requiring treatment for the most commonly performed operative procedures were as follows: coronary artery bypass grafting, 31.9%; coronary artery bypass grafting and mitral valve replacement, 63.6%; coronary artery bypass grafting and aortic valve replacement, 48.8%; and heart transplantation, 11.1%. For all patients considered collectively, the risk factors associated with an increased incidence of postoperative atrial arrhythmias (p < 0.05 by multivariate logistic regression) included increasing patient age, preoperative use of digoxin, history of rheumatic heart disease, chronic obstructive pulmonary disease, and increasing aortic cross-clamp time. Postoperative atrial fibrillation was associated with an increased incidence of postoperative stroke (3.3% versus 1.4%; p < 0.0005), increased length of hospitalization in the intensive care unit (5.7 versus 3.4 days; p = 0.001) and postoperative nursing ward (10.9 versus 7.5 days; p = 0.0001), increased incidence of postoperative ventricular tachycardia or fibrillation (9.2% versus 4.0%; p < 0.0005), and an increased need for placement of a permanent pacemaker (3.7% versus 1.6%; p < 0.0005). These data provide a basis for targeting specific patient subgroups for prospective, randomized trials of therapeutic modalities designed to decrease the incidence of postoperative atrial arrhythmias.

Fiber-Optic Chemical Sensors and Biosensors (2013-2015).

Abstract: Xu-dong Wang*,† and Otto S. Wolfbeis*,‡ †Department of Chemistry, Fudan University, 200433 Shanghai, P. R. China ‡Institute of Analytical Chemistry, Chemoand Biosensors, University of Regensburg, D-93040 Regensburg, Germany ■ CONTENTS Books, Reviews, and Articles of General Interest 204 Sensors for (Dissolved) Gases and Vapors 204 Hydrogen 204 Hydrocarbons 206 Oxygen 206 Carbon Dioxide 208 Nitrogen Oxides 208 Other Gases 208 Ammonia 209 Ethanol 209 Other Volatile Organic Compounds (VOC)s 210 Sensors for Humidity, Water Fractions, Hydrogen Peroxide, and Hydrazine 211 Humidity 211 Water Fractions in Organic Solvents 212 Hydrogen Peroxide 213 Sensors for pH Values, Ions, and Salinity 213 pH Values 213 Ions 214 Salinity and Ionic Strength 215 Sensors for Organic Species 216 Glucose Sensing 216 Sucrose 217 Oils 217 Other Organics 217 Biosensors 218 Nucleic Acid-Based Biosensors (DNAand Aptamer-Based) 218 Immunosensors 218 Enzymatic Biosensors 219 Other Biosensors 220 New Schemes and Materials 220 New Sensing Schemes 220 Molecularly Imprinted Polymer (MIP)-Based Sensors 221 Photonic Crystals 223 Author Information 223 Corresponding Authors 223 Notes 223 Biographies 223 Acknowledgments 223 References 223

Optical Refractive Index Sensors with Plasmonic and Photonic Structures: Promising and Inconvenient Truth

Abstract: DOI: 10.1002/adom.201801433 Scientific American selects plasmonic sensing as the top 10 emerging technologies of 2018.[15] Almost every single new plasmonic or photonic structure would be explored to test its sensing ability.[16–29] These works tend to report the sensing performance of their own structure. Some declare that their sensitivity breaks the world record. However, there is still a missing literature on what the world record really is, the gap between the experiments and the theoretical limit, as well as the differences between metal-based plasmonic sensors and dielectric-based photonic sensors. To push plasmonic and photonic sensors into industrial applications, an optical sensing technology map is absolutely necessary. This review aims to cover a wide range of most representative plasmonic and photonic sensors, and place them into a single map. The sensor performances of different structures will be distinctly illustrated. Future researchers could plot the sensing ability of their new sensors into this technology map and gauge their performances in this field. In this review, we focus on optical refractive index (RI) sensors with no fluorescent labeling required. We will utilize two parameters to characterize and compare the performance of optical RI sensors: sensitivity to RI change (denoted by symbol SRI) and figure of merit (in short, FoM). For simplicity, we restrict our discussions to bulk RI change, where the change in RI occurs within the whole sample. There is another case where the RI variation occurs only within a very small volume close to the sensor surface. This surface RI sensitivity is proportional to the bulk RI sensitivity, the ratio of the thickness of the layer within which the surface RI variation occurs, and the penetration depth of the optical mode.[6] The bulk RI sensitivity defines the ratio of the change in sensor output (e.g., resonance angle, intensity, or resonant wavelength) to the bulk RI variations. Here, we limit our discussions to the spectral interrogations and the bulk RI sensitivity SRI is given by[3,5–7,30]