Islam Ashry - Profile on Academia.edu (original) (raw)

Papers by Islam Ashry

Optics express, Jan 25, 2014

We report a non-contact method that utilizes fluorescence lifetime (FL) to characterize morpholog... more We report a non-contact method that utilizes fluorescence lifetime (FL) to characterize morphological changes of a tunable plasmonic nanostructure with nanoscale accuracy. The key component of the plasmonic nanostructure is pH-responsive polyelectrolyte multilayers (PEMs), which serve as a dynamically tunable "spacer" layer that separates the plasmonic structure and the fluorescent materials. The validity of our method is confirmed through direct comparison with ellipsometry and atomic force microscopy (AFM) measurements. Applying the FL-based approach, we find that a monolayer polycation film responds to pH changes with significantly less hysteresis than a thicker multilayer film with polyelectrolytes of both charges. Additionally, we characterize an active and tunable plasmonic nanostructure composed of self-assembled fluorescent dye (Texas Red), pH-sensitive PEMs, and gold nanospheres adsorbed on the PEM surface. Our results point towards the possibility of using stimul...

Optics Express, 2015

We develop and characterize a UV ablation technique that can be used to pattern soft materials su... more We develop and characterize a UV ablation technique that can be used to pattern soft materials such as polymers and nonlinear molecules self-assembled over silica microstructures. Using this method, we fabricate a spatially periodic coating of nonlinear film over a thin silica fiber taper for second harmonic generation (SHG). Experimentally, we find that the second harmonic signal produced by the taper with periodic nonlinear coating is 15 times stronger than the same taper with uniform nonlinear coating, which suggests that quasi-phase-matching is at least partially achieved in the patterned nonlinear silica taper. The same technique can also be used to spatially pattern other types of functional nanomaterials over silica microstructures with curved surfaces, as demonstrated by deposition of gold nanoparticles in patterned structures.

Optics Express, 2014

Micro-and nano-patterned fluorescent materials are important for many photonic devices and applic... more Micro-and nano-patterned fluorescent materials are important for many photonic devices and applications. In this paper, we investigate the impact of three common lithographical techniques, deposition and removal of sacrificial masks, ultraviolet ablation, and focused ion beam milling, on self-assembled fluorophores. We find that different patterning techniques can dramatically change the fluorescence lifetime of the fluorophores and that the degree of modification depends on the patterning techniques.

Self-assembled nanomaterials for nonlinear fiber optics and tunable plasmonics

Ultrafast Imaging and Spectroscopy, 2013

ABSTRACT As an amorphous material with full inversion symmetry, silica-based microstructures cann... more ABSTRACT As an amorphous material with full inversion symmetry, silica-based microstructures cannot possess significant secondorder nonlinearity. We recently developed a method that can potentially overcome this deficiency by coating a silica fiber taper with layers of radially aligned nonlinear molecules. The coating process can be accomplished through layerby- layer self-assembly, where the alignment of the nonlinear molecules is maintained through electrostatic interaction. As a result, the nonlinear fiber structures are thermodynamically stable and can generate significant second-order nonlinear responses despite their full rotational symmetry. This prediction has been experimentally confirmed through SHG measurements. To further enhance the overall second-order nonlinearity, we have developed an UV-ablation-based approach that can generate second-order nonlinearity that is spatially periodic along the fiber taper. Our preliminary experiments suggest that SHG intensity can be enhanced by such quasi-phase-matching configurations. We can also use the self-assembly approach to construct tunable plasmonic systems. As a proof-of-concept study, we assembled swellable polymer films over a planar Au substrate through layer-by-layer assembly and covered the swellable polymer with a monolayer of quantum dots. After immersing the swellable plasmonic structure in solution and adjusting its pH value, we used a fluorescence lifetime based approach to demonstrate that the thickness of the swellable polymers can be modified by almost 400%. The fluorescence lifetime measurements also confirmed that the plasmonic resonance can be significantly modified by the swellable polymers.

Lecture Notes in Electrical Engineering, 2014

Curvature has a great effect on fringing field of a microstrip antenna. Consequently, the fringin... more Curvature has a great effect on fringing field of a microstrip antenna. Consequently, the fringing field affects the effective dielectric constant and then all antenna parameters. A new mathematical model for return loss mutual coupling coefficient as a function of curvature for two element array antenna is introduced in this paper. These parameters are given for TM10 mode and using three different substrate materials RT/duroid-5880 PTFE, K-6098 Teflon/Glass and Epsilam-10 ceramic-filled Teflon.

In this paper, we propose a new architecture for tunable Fabry-Perot (FP) interferometer using fi... more In this paper, we propose a new architecture for tunable Fabry-Perot (FP) interferometer using fiber Bragg gratings (FBGs). The main feature of the architecture is its ability to increase the finesse using a potentially low cost technique. Furthermore, it decreases the power loss of the filtered channel and can be implemented easily in practice.

All-optical variable delay buffer for next generation optical networks

A novel all-optical delay buffer based on fiber Bragg gratings (FBGs) is proposed. This buffer ha... more A novel all-optical delay buffer based on fiber Bragg gratings (FBGs) is proposed. This buffer has the ability to provide variable delay times and can store the contenting packets for a relatively long time.

Proceedings of the 2014 Zone 1 Conference of the American Society for Engineering Education, 2014

In this paper, we introduce a full fiber-to-the-home system architecture. The introduced system i... more In this paper, we introduce a full fiber-to-the-home system architecture. The introduced system is used to obtain a system bit rate of 10 Gbps and 20 Gbps downstream and 5 Gbps and 10 Gbps upstream. Wavelength division multiplexing passive optical network technique is used to share the overall bandwidth between 32 users with 0.8 nm spacing between each user. To reduce the overall cost of the proposed system, the bidirectional subcarrier multiplexed technique is used at the optical network unit to avoid using any optical laser sources at the receiver side for upstream data transmission. Quality factor, bit error rate, and eye diagrams are derived for different pulse shapes then used to compare the results in order to select the best pulse shape that gives the best performance. The pulse shapes used in this paper are non-return to zero, return to zero, saw-up, triangle, raised cosine, and hyperbolic-secant pulses. The results demonstrates that the non-return to zero pulse shape at bit rate of 20 Gbps at both downstream and upstream data transmission leads a high quality factor. Furthermore, at 10 Gbps return to zero is selected at the transmission side and hyperbolic-secant at the optical network unit.

Proceedings of the 2014 Zone 1 Conference of the American Society for Engineering Education, 2014

Fiber Bragg gratings (FBGs) technology has demonstrated its suitability for many applications in ... more Fiber Bragg gratings (FBGs) technology has demonstrated its suitability for many applications in recent fiber technologies. Sensing application is one of the main applications of FBGs. In this work, we present a comprehensive investigation for using apodized FBGs in sensing applications. Different evaluation parameters such as, reflectivity, sidelobes, and fullwidth-half-maximum (FWHM) are tested in order to determine the most proper apodization profile for sensors. According to our study, the Blackman apodization gives the best profile that can be used in sensing applications. The reflectivity of Blackman apodization is nearly unity with minimum sidelobes level, -60.3 dB, and narrow FWHM. The length of Blackman apodized FBG is 0.33 cm and Δn = 14.4 x 10 -4 and maximum reflectivity is 99.44%.

Optics Letters, 2012

The process of spontaneous emission can be dramatically modified by optical microstructures and n... more The process of spontaneous emission can be dramatically modified by optical microstructures and nanostructures. We have studied the modification of fluorescence dynamics using a variable thickness polymer spacer layer fabricated using layer-by-layer self-assembly with nanometer accuracy. The change in fluorescence lifetime with spacer layer thickness agrees well with theoretical predictions based on the modified photonic density of states (PDOS), and yields consistent values for the fluorophores' intrinsic fluorescence lifetime and quantum yield near a dielectric as well as a plasmonic interface. Based on this observation, we further demonstrate that self-assembled fluorophores can be used to probe the modified PDOS near optical microstructures and nanostructures.

Optics Express, 2013

With extremely low material absorption and exceptional surface smoothness, silica-based optical r... more With extremely low material absorption and exceptional surface smoothness, silica-based optical resonators can achieve extremely high cavity quality (Q) factors. However, the intrinsic material limitations of silica (e.g., lack of second order nonlinearity) may limit the potential applications of silica-based high Q resonators. Here we report some results in utilizing layer-by-layer self-assembly to functionalize silica microspheres with nonlinear and plasmonic nanomaterials while maintaining Q factors as high as 10 7 . We compare experimentally measured Q factors with theoretical estimates, and find good agreement.

Measurement of chromophores density using high Q -factor silica microspheres

Journal of Nanophotonics, 2016

Mode-division-multiplexing of absorption-based fiber optical sensors

Optics Express, 2016

_ A novel tunable multi-wavelength laser using an erbium doped fiber (EDF) as a gain medium is pr... more _ A novel tunable multi-wavelength laser using an erbium doped fiber (EDF) as a gain medium is proposed theoretically. The laser source is terminated by a chirped fiber Bragg grating (CFBG) on one side and cascaded apodized FBGs on the other side. Three and five-wavelength tunable EDF laser (EDFL) are demonstrated using applied strains and temperature variations to tune the lasing wavelengths.

Investigating the characteristics of TM-pass/TE-stop polarizer designed using plasmonic nanostructures

Applied Optics, 2015

Plasmonics-based polarizers are important for many photonic devices and applications. In this pap... more Plasmonics-based polarizers are important for many photonic devices and applications. In this paper, we design and investigate the characteristics of a new TM-pass/TE-stop polarizer using silver nanograting of exponentially tapered slit sidewalls. Performance of the designed polarizer is determined through monitoring the modification of its insertion loss, return loss, extinction ratio, and far-field transform due to changing its structural parameters. We find that the structural parameters of the reported polarizer such as a slit sidewall tapering coefficient and slit opening widths have a significant impact on tuning the polarizer characteristics.

Detection of coating fluorophores’ densities in improved Q-factor cavities

Nanoengineering: Fabrication, Properties, Optics, and Devices XII, 2015

Optics express, Jan 25, 2014

We report a non-contact method that utilizes fluorescence lifetime (FL) to characterize morpholog... more We report a non-contact method that utilizes fluorescence lifetime (FL) to characterize morphological changes of a tunable plasmonic nanostructure with nanoscale accuracy. The key component of the plasmonic nanostructure is pH-responsive polyelectrolyte multilayers (PEMs), which serve as a dynamically tunable "spacer" layer that separates the plasmonic structure and the fluorescent materials. The validity of our method is confirmed through direct comparison with ellipsometry and atomic force microscopy (AFM) measurements. Applying the FL-based approach, we find that a monolayer polycation film responds to pH changes with significantly less hysteresis than a thicker multilayer film with polyelectrolytes of both charges. Additionally, we characterize an active and tunable plasmonic nanostructure composed of self-assembled fluorescent dye (Texas Red), pH-sensitive PEMs, and gold nanospheres adsorbed on the PEM surface. Our results point towards the possibility of using stimul...

Optics Express, 2015

We develop and characterize a UV ablation technique that can be used to pattern soft materials su... more We develop and characterize a UV ablation technique that can be used to pattern soft materials such as polymers and nonlinear molecules self-assembled over silica microstructures. Using this method, we fabricate a spatially periodic coating of nonlinear film over a thin silica fiber taper for second harmonic generation (SHG). Experimentally, we find that the second harmonic signal produced by the taper with periodic nonlinear coating is 15 times stronger than the same taper with uniform nonlinear coating, which suggests that quasi-phase-matching is at least partially achieved in the patterned nonlinear silica taper. The same technique can also be used to spatially pattern other types of functional nanomaterials over silica microstructures with curved surfaces, as demonstrated by deposition of gold nanoparticles in patterned structures.

Tunable Multi-wavelength Erbium Doped Laser Using Cascaded Apodized Fiber Bragg Gratings

Optics Express, 2014

Micro-and nano-patterned fluorescent materials are important for many photonic devices and applic... more Micro-and nano-patterned fluorescent materials are important for many photonic devices and applications. In this paper, we investigate the impact of three common lithographical techniques, deposition and removal of sacrificial masks, ultraviolet ablation, and focused ion beam milling, on self-assembled fluorophores. We find that different patterning techniques can dramatically change the fluorescence lifetime of the fluorophores and that the degree of modification depends on the patterning techniques.

Optics express, Jan 25, 2014

We report a non-contact method that utilizes fluorescence lifetime (FL) to characterize morpholog... more We report a non-contact method that utilizes fluorescence lifetime (FL) to characterize morphological changes of a tunable plasmonic nanostructure with nanoscale accuracy. The key component of the plasmonic nanostructure is pH-responsive polyelectrolyte multilayers (PEMs), which serve as a dynamically tunable "spacer" layer that separates the plasmonic structure and the fluorescent materials. The validity of our method is confirmed through direct comparison with ellipsometry and atomic force microscopy (AFM) measurements. Applying the FL-based approach, we find that a monolayer polycation film responds to pH changes with significantly less hysteresis than a thicker multilayer film with polyelectrolytes of both charges. Additionally, we characterize an active and tunable plasmonic nanostructure composed of self-assembled fluorescent dye (Texas Red), pH-sensitive PEMs, and gold nanospheres adsorbed on the PEM surface. Our results point towards the possibility of using stimul...

Optics Express, 2015

We develop and characterize a UV ablation technique that can be used to pattern soft materials su... more We develop and characterize a UV ablation technique that can be used to pattern soft materials such as polymers and nonlinear molecules self-assembled over silica microstructures. Using this method, we fabricate a spatially periodic coating of nonlinear film over a thin silica fiber taper for second harmonic generation (SHG). Experimentally, we find that the second harmonic signal produced by the taper with periodic nonlinear coating is 15 times stronger than the same taper with uniform nonlinear coating, which suggests that quasi-phase-matching is at least partially achieved in the patterned nonlinear silica taper. The same technique can also be used to spatially pattern other types of functional nanomaterials over silica microstructures with curved surfaces, as demonstrated by deposition of gold nanoparticles in patterned structures.

Optics Express, 2014

Micro-and nano-patterned fluorescent materials are important for many photonic devices and applic... more Micro-and nano-patterned fluorescent materials are important for many photonic devices and applications. In this paper, we investigate the impact of three common lithographical techniques, deposition and removal of sacrificial masks, ultraviolet ablation, and focused ion beam milling, on self-assembled fluorophores. We find that different patterning techniques can dramatically change the fluorescence lifetime of the fluorophores and that the degree of modification depends on the patterning techniques.

Self-assembled nanomaterials for nonlinear fiber optics and tunable plasmonics

Ultrafast Imaging and Spectroscopy, 2013

ABSTRACT As an amorphous material with full inversion symmetry, silica-based microstructures cann... more ABSTRACT As an amorphous material with full inversion symmetry, silica-based microstructures cannot possess significant secondorder nonlinearity. We recently developed a method that can potentially overcome this deficiency by coating a silica fiber taper with layers of radially aligned nonlinear molecules. The coating process can be accomplished through layerby- layer self-assembly, where the alignment of the nonlinear molecules is maintained through electrostatic interaction. As a result, the nonlinear fiber structures are thermodynamically stable and can generate significant second-order nonlinear responses despite their full rotational symmetry. This prediction has been experimentally confirmed through SHG measurements. To further enhance the overall second-order nonlinearity, we have developed an UV-ablation-based approach that can generate second-order nonlinearity that is spatially periodic along the fiber taper. Our preliminary experiments suggest that SHG intensity can be enhanced by such quasi-phase-matching configurations. We can also use the self-assembly approach to construct tunable plasmonic systems. As a proof-of-concept study, we assembled swellable polymer films over a planar Au substrate through layer-by-layer assembly and covered the swellable polymer with a monolayer of quantum dots. After immersing the swellable plasmonic structure in solution and adjusting its pH value, we used a fluorescence lifetime based approach to demonstrate that the thickness of the swellable polymers can be modified by almost 400%. The fluorescence lifetime measurements also confirmed that the plasmonic resonance can be significantly modified by the swellable polymers.

Lecture Notes in Electrical Engineering, 2014

Curvature has a great effect on fringing field of a microstrip antenna. Consequently, the fringin... more Curvature has a great effect on fringing field of a microstrip antenna. Consequently, the fringing field affects the effective dielectric constant and then all antenna parameters. A new mathematical model for return loss mutual coupling coefficient as a function of curvature for two element array antenna is introduced in this paper. These parameters are given for TM10 mode and using three different substrate materials RT/duroid-5880 PTFE, K-6098 Teflon/Glass and Epsilam-10 ceramic-filled Teflon.

In this paper, we propose a new architecture for tunable Fabry-Perot (FP) interferometer using fi... more In this paper, we propose a new architecture for tunable Fabry-Perot (FP) interferometer using fiber Bragg gratings (FBGs). The main feature of the architecture is its ability to increase the finesse using a potentially low cost technique. Furthermore, it decreases the power loss of the filtered channel and can be implemented easily in practice.

All-optical variable delay buffer for next generation optical networks

A novel all-optical delay buffer based on fiber Bragg gratings (FBGs) is proposed. This buffer ha... more A novel all-optical delay buffer based on fiber Bragg gratings (FBGs) is proposed. This buffer has the ability to provide variable delay times and can store the contenting packets for a relatively long time.

Proceedings of the 2014 Zone 1 Conference of the American Society for Engineering Education, 2014

In this paper, we introduce a full fiber-to-the-home system architecture. The introduced system i... more In this paper, we introduce a full fiber-to-the-home system architecture. The introduced system is used to obtain a system bit rate of 10 Gbps and 20 Gbps downstream and 5 Gbps and 10 Gbps upstream. Wavelength division multiplexing passive optical network technique is used to share the overall bandwidth between 32 users with 0.8 nm spacing between each user. To reduce the overall cost of the proposed system, the bidirectional subcarrier multiplexed technique is used at the optical network unit to avoid using any optical laser sources at the receiver side for upstream data transmission. Quality factor, bit error rate, and eye diagrams are derived for different pulse shapes then used to compare the results in order to select the best pulse shape that gives the best performance. The pulse shapes used in this paper are non-return to zero, return to zero, saw-up, triangle, raised cosine, and hyperbolic-secant pulses. The results demonstrates that the non-return to zero pulse shape at bit rate of 20 Gbps at both downstream and upstream data transmission leads a high quality factor. Furthermore, at 10 Gbps return to zero is selected at the transmission side and hyperbolic-secant at the optical network unit.

Proceedings of the 2014 Zone 1 Conference of the American Society for Engineering Education, 2014

Fiber Bragg gratings (FBGs) technology has demonstrated its suitability for many applications in ... more Fiber Bragg gratings (FBGs) technology has demonstrated its suitability for many applications in recent fiber technologies. Sensing application is one of the main applications of FBGs. In this work, we present a comprehensive investigation for using apodized FBGs in sensing applications. Different evaluation parameters such as, reflectivity, sidelobes, and fullwidth-half-maximum (FWHM) are tested in order to determine the most proper apodization profile for sensors. According to our study, the Blackman apodization gives the best profile that can be used in sensing applications. The reflectivity of Blackman apodization is nearly unity with minimum sidelobes level, -60.3 dB, and narrow FWHM. The length of Blackman apodized FBG is 0.33 cm and Δn = 14.4 x 10 -4 and maximum reflectivity is 99.44%.

Optics Letters, 2012

The process of spontaneous emission can be dramatically modified by optical microstructures and n... more The process of spontaneous emission can be dramatically modified by optical microstructures and nanostructures. We have studied the modification of fluorescence dynamics using a variable thickness polymer spacer layer fabricated using layer-by-layer self-assembly with nanometer accuracy. The change in fluorescence lifetime with spacer layer thickness agrees well with theoretical predictions based on the modified photonic density of states (PDOS), and yields consistent values for the fluorophores' intrinsic fluorescence lifetime and quantum yield near a dielectric as well as a plasmonic interface. Based on this observation, we further demonstrate that self-assembled fluorophores can be used to probe the modified PDOS near optical microstructures and nanostructures.

Optics Express, 2013

With extremely low material absorption and exceptional surface smoothness, silica-based optical r... more With extremely low material absorption and exceptional surface smoothness, silica-based optical resonators can achieve extremely high cavity quality (Q) factors. However, the intrinsic material limitations of silica (e.g., lack of second order nonlinearity) may limit the potential applications of silica-based high Q resonators. Here we report some results in utilizing layer-by-layer self-assembly to functionalize silica microspheres with nonlinear and plasmonic nanomaterials while maintaining Q factors as high as 10 7 . We compare experimentally measured Q factors with theoretical estimates, and find good agreement.

Measurement of chromophores density using high Q -factor silica microspheres

Journal of Nanophotonics, 2016

Mode-division-multiplexing of absorption-based fiber optical sensors

Optics Express, 2016

_ A novel tunable multi-wavelength laser using an erbium doped fiber (EDF) as a gain medium is pr... more _ A novel tunable multi-wavelength laser using an erbium doped fiber (EDF) as a gain medium is proposed theoretically. The laser source is terminated by a chirped fiber Bragg grating (CFBG) on one side and cascaded apodized FBGs on the other side. Three and five-wavelength tunable EDF laser (EDFL) are demonstrated using applied strains and temperature variations to tune the lasing wavelengths.

Investigating the characteristics of TM-pass/TE-stop polarizer designed using plasmonic nanostructures

Applied Optics, 2015

Plasmonics-based polarizers are important for many photonic devices and applications. In this pap... more Plasmonics-based polarizers are important for many photonic devices and applications. In this paper, we design and investigate the characteristics of a new TM-pass/TE-stop polarizer using silver nanograting of exponentially tapered slit sidewalls. Performance of the designed polarizer is determined through monitoring the modification of its insertion loss, return loss, extinction ratio, and far-field transform due to changing its structural parameters. We find that the structural parameters of the reported polarizer such as a slit sidewall tapering coefficient and slit opening widths have a significant impact on tuning the polarizer characteristics.

Detection of coating fluorophores’ densities in improved Q-factor cavities

Nanoengineering: Fabrication, Properties, Optics, and Devices XII, 2015

Optics express, Jan 25, 2014

We report a non-contact method that utilizes fluorescence lifetime (FL) to characterize morpholog... more We report a non-contact method that utilizes fluorescence lifetime (FL) to characterize morphological changes of a tunable plasmonic nanostructure with nanoscale accuracy. The key component of the plasmonic nanostructure is pH-responsive polyelectrolyte multilayers (PEMs), which serve as a dynamically tunable "spacer" layer that separates the plasmonic structure and the fluorescent materials. The validity of our method is confirmed through direct comparison with ellipsometry and atomic force microscopy (AFM) measurements. Applying the FL-based approach, we find that a monolayer polycation film responds to pH changes with significantly less hysteresis than a thicker multilayer film with polyelectrolytes of both charges. Additionally, we characterize an active and tunable plasmonic nanostructure composed of self-assembled fluorescent dye (Texas Red), pH-sensitive PEMs, and gold nanospheres adsorbed on the PEM surface. Our results point towards the possibility of using stimul...

Optics Express, 2015

We develop and characterize a UV ablation technique that can be used to pattern soft materials su... more We develop and characterize a UV ablation technique that can be used to pattern soft materials such as polymers and nonlinear molecules self-assembled over silica microstructures. Using this method, we fabricate a spatially periodic coating of nonlinear film over a thin silica fiber taper for second harmonic generation (SHG). Experimentally, we find that the second harmonic signal produced by the taper with periodic nonlinear coating is 15 times stronger than the same taper with uniform nonlinear coating, which suggests that quasi-phase-matching is at least partially achieved in the patterned nonlinear silica taper. The same technique can also be used to spatially pattern other types of functional nanomaterials over silica microstructures with curved surfaces, as demonstrated by deposition of gold nanoparticles in patterned structures.

Tunable Multi-wavelength Erbium Doped Laser Using Cascaded Apodized Fiber Bragg Gratings

Optics Express, 2014

Micro-and nano-patterned fluorescent materials are important for many photonic devices and applic... more Micro-and nano-patterned fluorescent materials are important for many photonic devices and applications. In this paper, we investigate the impact of three common lithographical techniques, deposition and removal of sacrificial masks, ultraviolet ablation, and focused ion beam milling, on self-assembled fluorophores. We find that different patterning techniques can dramatically change the fluorescence lifetime of the fluorophores and that the degree of modification depends on the patterning techniques.