Surasak Chiangga

Analytical and simulation results of a triple micro whispering gallery mode probe system for a 3D blood flow rate sensor.

The whispering gallery mode (WGM) is generated by light propagating within a nonlinear micro-ring resonator, which is modeled and made by an InGaAsP/InP material, and called a Panda ring resonator. An imaging probe can also be formed by the micro-conjugate mirror function for the appropriate Panda ring parameter control. The 3D WGM probe can be generated and used for a 3D sensor head and imaging probe. The analytical details and simulation results are given, in which the simulation results are obtained by using the MATLAB and Optiwave programs. From the obtained results, such a design system can be configured to be a thin-film sensor system that can contact the sample surface for the required measurements The outputs of the system are in the form of a WGM beam, in which the 3D WGM probe is also available with the micro-conjugate mirror function. Such a 3D probe can penetrate into the blood vessel and content, from which the time delay among those probes can be detected and measured, and where finally the blood flow rate can be calculated and the blood content 3D image can also be seen and used for medical diagnosis. The tested results have shown that the blood flow rate of 0.72-1.11  μs-1, with the blood density of 1060  kgm-3, can be obtained.

Nonlinear switching in silicon-based ring resonators

In this paper, we analyzed and investigated the nonlinear switching characteristics of an optical device using a double-coupler silicon ring resonator in the presence of the linear losses, the Kerr nonlinearity, two-photon absorption, thermo-optic effects, free-carrier-induced absorption, and dispersion. Results obtained have shown that the general features of the nonlinear switching of the throughput and drop port signals are similar to a single-couple ring and nonlinear Fabry-Perot resonators, respectively. The interesting results of the double-coupler silicon ring resonator are the low switching power conditions and the linear amplification gain. The various applications can be provided by controlling the input-output of silicon-based resonators, for instance, by controlling the coupling ratio, free-carrier lifetime, and input wavelength, in which the multiple applications for optical switches, logic gates, and memories can be provided.

Synthesis of cobalt oxides thin films fractal structures by laser chemical vapor deposition.

Thin films of cobalt oxides (CoO and Co3O4) fractal structures have been synthesized by using laser chemical vapor deposition at room temperature and atmospheric pressure. Various factors which affect the density and crystallization of cobalt oxides fractal shapes have been examined. We show that the fractal structures can be described by diffusion-limited aggregation model and discuss a new possibility to control the fractal structures.

Optical Bistability Investigation in a Nonlinear Silicon Microring Circuit

We describe the optical bistability phenomenon in a silicon-on-insulator microring resonators device by using an analytical theory, which includes both linear and nonlinear effects such as two-photon absorption, Kerr effect, free carrier and thermo-optic effect (TOE). We show that the bistable switching threshold and the hysteresis loop width can be tuned by geometrical parameters of the device and by the nonlinear parameters. The accuracy of the analytical approach is verified by comparing the spectrum responds with the predicting data from a commercial finite-difference time-domain software tool, and a very close agreement is found between the two when TOE is incorporated in analytical theory. In addition, our analysis reveals that a new type of hysteresis loop occurs at low input intensity. The mode suppression of the designed device by Vernier effect for tunable filter applications is also briefly discussed.

Fast, Slow, Stopping and Storing Light Simultaneously using a PANDA Ring On-Chip

Past and slow light behaviors are the interesting aspects of light which can be useful for many fundamental and applied researches. Pornsuwancharoen and Yupapin et al. [1] have proposed the use of a simple device called “microring resonator” to perform such behaviors. In this research work, the four different behaviors of light i.e., fast, slow, stopping and storing of light where investigated using a ring resonator. Nowadays, stopping or cooling light beam has become the promising technique for atom/molecule trapping investigations (using static or dynamic tweezers), especially, after the announcement of Nobel Prize 2012 in Physics on the whispering gallery modes [2, 3]. There are two more kinds of devices that can be used to trap light beams, the use of microcavity arrays performed by Yanik and Fan [4], and nonlinear microring resonator by Yupapin and Pornsuwancharoen [5] for stopping light (laser beam). Nanyang Technological University scientists have also done experiment to slowing the light in microresonators using a microring system recently [6]. This concept is a concrete backbone for many applications.

On a Fitzhugh-Nagumo type model for the pulse-like jasmonate defense response in plants.

A mechanistic model of the Fitzhugh-Nagumo type is proposed for the pulse-like jasmonate response in plants. The model is composed of a bistable signaling pathway coupled to a negative feedback loop. The bistable signaling pathway describes a recently discovered positive feedback loop involving jasmonate and the MYC2 transcription factor regulating promoter activity during plant defense. The negative feedback loop is assumed to reflect a second jasmonate-dependent signaling pathway that is also used for ethylene signaling. The impact of the negative feedback loop is to destroy the high-level jasmonate fixed-point of the bistable jasmonate/MYC2 module. As a result, the high-level state becomes a ghost attractor and the jasmonate defense response becomes pulse-like.

Mid-infrared supercontinuum in a Ge11:5As24Se64:5 chalcogenide waveguide

We present results of numerical simulations of a supercontinuum generation (SCG) in a Ge11:5As24Se64:5 chalcogenide rectangular waveguide with air as an upper cladding and the lower cladding is magnesium fluoride. A broadband infrared 1.3-3.0 μm SCG could be achieved by pumping with femtosecond pulses in the two zero dispersion wavelengths. The effect of chirp on SCG spectrum has been also investigated. The simulation shows a significant SCG spectral flatness in the mid-infrared range with positive frequency chirp input pulses.

TUNABLE ASYMMETRIC FANO LINESHAPES IN SILICON-BASED MICRORING RESONATORS WITH FEEDBACK

We theoretically examine the Fano lineshapes of silicon-based compound microring resonators consisting of a single resonator channel dropping filter linked to a loop as a feedback structure. All possible optical effects for the continuous-wave operating regime, such as linear absorption or scattering, two-photon absorption, free-carrier absorption and dispersion, thermo-optics, are simultaneously considered. We show that sharp Fano resonances can be tuned by variation in the coupling coefficients, length of feedback loop, effective free carrier lifetime and the temperature inside the device. Tunable Fano lineshapes open up opportunities for applications in sensing, computing, and communications.

High-contrast optical vortex detection using the Talbot effect

We apply the near-field Talbot effect to distinguish, characterize, and detect optical vortices. We perform experiments with single-, double-, multiple-slit, and grating diffraction. High-contrast image detection is achieved with the Talbot effect of a grating, even for higher than l=±1 orbital angular momentum states. Furthermore, we manipulate the vortex beam with different vortex states and use the Talbot effect for detecting. The experimental results are supported by theoretical simulations and demonstrate that the Talbot effect provides an excellent tool for optical vortex detection.

Growth of MWCNTs on Flexible Stainless Steels without Additional Catalysts

Multiwalled carbon nanotubes (MWCNTs) were synthesized on austenitic stainless steel foils (Type 304) using a home-built thermal chemical vapor deposition (CVD) under atmospheric pressure of hydrogen (H2) and acetylene (C2H2). During the growth, the stainless steel substrates were heated at different temperatures of 600, 700, 800, and 900°C. It was found that MWCNTs were grown on the stainless steel substrates heated at 600, 700, and 800°C while amorphous carbon film was grown at 900°C. The diameters of MWCNTs, as identified by scanning electron microscope (SEM) images together with ImageJ software program, were found to be 67.7, 43.0, and 33.1 nm, respectively. The crystallinity of MWCNTs was investigated by an X-ray diffractometer. The number of graphitic walled layers and the inner diameter of MWCNTs were investigated using a transmission electron microscope (TEM). The occurrence of Fe3O4 nanoparticles associated with carbon element can be used to reveal the behavior of Fe in stainless steel as catalyst. Raman spectroscopy was used to confirm the growth and quality of MWCNTs. The results obtained in this work showed that the optimum heated stainless steel substrate temperature for the growth of effective MWCNTs is 700°C. Chemical states of MWCNTs were investigated by X-ray photoelectron spectroscopy (XPS) using synchrotron light.