P. Susthitha Menon

Electro-optics interaction imaging in active plasmonic devices

During surface plasmon polariton (SPP) excitation, the imaging of the interaction between the DC current and the Transverse Mode (TM) optical field is reported for the first time. Using an optical microscope, we have successfully captured images of electro-optic interaction during plasmonic demodulation phenomena. A significant response is observed when images of the transmitted light – which represents SPP excitation – become less bright in the presence of an electric field when the thin-film metal thickness is approximately equivalent to the skin depth of gold (30 nm). The synchronization achieved between the optical reflectance analysis and the SPP imaging shows that maximum interaction is achieved when the optical reflectance change, ΔR is 0.0530.

Angle Shifting in Surface Plasmon Resonance: Experimental and Theoretical Verification

This paper discussed a sensing property of the SPR sensor to detect changes in refractive index of the dielectric medium. The resonant angle shifting was observed as the dielectrics medium was changed from air to SiO2 thin film. The effect of a free space wavelength to the excitation of SPP was investigated by employing laser sources with wavelengths transmission of 545nm and 632.8nm. In comparison with 545nm of wavelength transmission, we revealed that He-Ne laser source with wavelength of 632.8nm is suitable to produce a strong SPR signal due to its high Q-factor. To avoid misinterpretation between the destructive interference and SPR phenomenon, we proposed a simple theoretical approach using momentum conservation principle which concerning the wavevector values to validate the experimental results. By ignoring the imaginary part of the dielectric function of gold, we proved that this theoretical approach is still acceptable due to the excellent agreement between the theoretical and simulation approaches.

Recent Advances in Shape-Controlled Synthesis of Noble Metal Nanoparticles by Radiolysis Route

This paper focuses on the recent advances on radiolysis-assisted shape-controlled synthesis of noble metal nanostructures. The techniques and protocols for producing desirable shapes of noble metal nanoparticles are discussed through introducing the critical parameters which can influence the nucleation and growth mechanisms. Nucleation rate plays a vital role on the crystallinity of seeds while growth rate of different seeds’ facets determines the final shape of resultant nanoparticles. Nucleation and growth rate both can be altered with factors such as absorbed dose, capping agents, and experimental environment condition to control the final shape. Remarkable physical and chemical properties of synthesized noble metal nanoparticles by controlled morphology have been systematically evaluated to fully explore their applications.

An assessment study of absorption effect: LED vs tungsten halogen lamp for noninvasive glucose detection

Noninvasive glucose monitoring development is critical for diabetic patient continuous monitoring. However, almost all the available devices are invasive and painful. Noninvasive methods such as using spectroscopy have shown some good results. Unfortunately, the drawback was that the tungsten halogen lamps usage that is impractical if applied on human skin. This paper compared the light emitting diode (LED) to traditional tungsten halogen lamps as light source for glucose detection where the type of light source plays an important role in achieving a good spectrum quality. Glucose concentration measurement has been developed as part of noninvasive technique using optical spectroscopy. Small change and overlapping in tungsten halogen results need to replace it with a more convenient light source such as LED. Based on the result obtained, the performance of LED for absorbance spectrum gives a significantly different and is directly proportional to the glucose concentration. The result shows a linear trend and successfully detects lowest at 60 to 160 mg/dL glucose concentration.

12-channel tapered SOI-based AWG for CWDM system

A 12-channel Silicon-on-Insulator (SOI)-based Arrayed Waveguide Grating (AWG) with different core width sizes of 1.2 μm and 1.0 μm was designed and characterized for Coarse Wavelength Division Multiplexing (CWDM) System. Beam Propagation Method (BPM) was used to simulate the propagation of light in this device at operating wavelength of 1.491 μm which producing the peak transmission wavelengths ranging from 1391 to 1611 nm. The output spectrum peaks that were obtained from both core widths are close to the CWDM wavelength grid. The core width of 1.2 μm produced the lowest insertion loss and adjacent crosstalk with the values of 4.03 dB and -15.02 dB respectively. Meanwhile, insertion loss of 5.03 dB and adjacent crosstalk of -15.96 dB was obtained from the 1.0 μm core width device where the losses are higher. Hence, the A WG device with larger core width size produced a better insertion loss and adjacent crosstalk.

FDTD Analysis on Geometrical Parameters of Bimetallic Localized Surface Plasmon Resonance-Based Sensor

The localized surface plasmon resonance (LSPR) properties are numerically analyzed using finite-difference time domain (FDTD) method, which is a reliable technique in solving Maxwells equations in dispersive medium. Optical properties and LSPR characteristics were analyzed with Titanium Nitride (TiN) as an adhesion layer at gold(Au)/silver(Ag) interface. The reflection spectra of bimetallic layer nano-holes was compared with various metallic layer thicknesses of Au and Ag, hole radii and lattice period. When compared between single and bimetallic Ag/TiN/Au nano-hole layers, it showed that the layer with 70nm-thick Ag/5nm-thick TiN/50nm-thick Au (Ag70/TiN5/Au50) gave greater LSPR-based sensor performance with narrower plasmonic line width and better full width at half maximum (FWHM). Change in geometrical parameters such as lattice period and hole radii was affected the sensitivity and detection accuracy of Ag70/TiN5/Au50 nano-hole layer, which maximum of 90.9% reflection intensity and minimum of 18nm FWHM were obtained.

FDTD analysis of structured metallic nanohole films for LSPR-based biosensor

We numerically investigated 3-dimensional (3D) sub-wavelength structured metallic nanohole films with various thicknesses using wavelength interrogation technique. The reflectivity and full-width at half maximum (FWHM) of the localized surface plasmon resonance (LSPR) spectra was calculated using finite-difference time domain (FDTD) method. Results showed that a 100nm-thick silver nanohole gave higher reflectivity of 92% at the resonance wavelength of 644nm. Silver, copper and aluminum structured thin films showed only a small difference in the reflectivity spectra for various metallic film thicknesses whereas gold thin films showed a reflectivity decrease as the film thickness was increased. However, all four types of metallic nanohole films exhibited increment in FWHM (broader curve) and the resonance wavelength was red-shifted as the film thicknesses were decreased.

Optical loss analysis in 13-channel SOI-based AWG for CWDM network

In this paper, we report the insertion loss and adjacent crosstalk for tapered and conventional configuration of double S-shaped design of arrayed waveguide grating (AWG) using 1.2 μm and 1.0 μm core width. The 13-channel AWG on silicon-on-insulator (SOI) was simulated using beam propagation method (BPM) at central wavelength of 1.49 μm, producing a transmission spectrum ranging from 1310–1620 nm. Tapered AWG for both core widths gave the lowest insertion loss of < 7 dB while only the AWG with the 1.2 μm core width produced the lowest crosstalk at < -19 dB compared to the other configurations. A 13-channel transmission spectrum of the AWG device has been produced which fits closely the standard ITU-T CWDM wavelength grid.

Performance of 18 channel CWDM system with inline Semiconductor Optical Amplifier

Semiconductor Optical Amplifier (SOA) is used for a 2.5Gbps Coarse Wavelength Division Multiplexing (CWDM) transmission in O to L-band (1271-1611 nm). Analysis of the proposed topology is conducted using Optisystem software. In this paper, discussions on the gain spectrum and the quality of signal of an optically amplified 18 channel system are provided. A wideband travelling wave SOA which operates as an inline amplifier resulted in wide 3 dB bandwidth of 200 nm. The overall quality of signal at the receiver is evaluated with the Q factor value. Better performance based on Q factor analysis is obtained at larger lengths of the first fiber span and a flat gain over 11 CWDM channels is obtained.

A new analytical model for lateral breakdown voltage of double-gate power MOSFETs

A simple analytical model for the surface potential, surface field distribution and lateral breakdown voltage of double-gate power MOSFETs has been proposed. The model is based on the analytical solution for the two-dimensional Poisson equation. From this solution, the reliance of breakdown voltage on the device parameters is also investigated. The validity of this model is demonstrated by comparison with numerical simulation and experimental values.