Sakoolkan Boonruang

Multiwavelength guided mode resonance sensor array

A multiwavelength guided mode resonance (GMR) sensor array is proposed to minimize the need of complex detection systems. Using a chirped grating in the GMR sensor, a single spectrometer is needed to simultaneously receive the signal from each array without modulating or mechanical scanning techniques. The array elements placed along the direction of the grating chirp can form the GMR structure, and each array element shows a different average period. Thus, the resonance condition for each array element differs from the next. A multiline resonance spectrum can be detected without time delay concerns in each array. A two-channel sensor array is experimentally demonstrated in this study.

Design of electric-field assisted surface plasmon resonance system for the detection of heavy metal ions in water

Surface Plasmon Resonance (SPR) sensors are widely used in diverse applications. For detecting heavy metal ions in water, surface functionalization of the metal surface is typically used to adsorb target molecules, where the ionic concentration is detected via a resonance shift (resonance angle, resonance wavelength or intensity). This paper studies the potential of a possible alternative approach that could eliminate the need of using surface functionalization by the application of an external electric field in the flow channel. The exerted electrical force on the ions pushes them against the surface for enhanced adsorption; hence it is referred to as “Electric-Field assisted SPR system”. High system sensitivity is achieved by monitoring the time dynamics of the signal shift. The ion deposition dynamics are discussed using a derived theoretical model based on ion mobility in water. On the application of an appropriate force, the target ions stack onto the sensor surface depending on the ionic concentration of target solution, ion mass, and flow rate. In the experimental part, a broad detection range of target cadmium ions (Cd 2+) in water from several parts per million (ppm) down to a few parts per billion (ppb) can be detected.

Characterization of polymer nanowires fabricated using the nanoimprint method

In this paper, an ormocomp polymer nanowire with possible use in integrated-optics sensing applications is presented. We discuss the structure design, the fabrication process and present results of the simulation and characterization of the optical field profile. Since the nanowires are designed and intended to be used as integrated optics devices, they are attached to tapered and feed waveguides at their ends. The fabrication process in this work is based mainly on the nanoimprint technique. The method assumes a silicon nanowire as an original pattern, and polydimethylsiloxane (PDMS) as thesoft mold. The PDMS mold is directly imprinted on the ormocomp layer and then cured by UV light to form the polymer based nanowire. The ormocomp nanowires are fabricated to have various dimensions of width and length at a fixed 500nm thickness. The length of the nanowires is varied from 250 µm to 2 mm, whereas the width of the structures is varied between 500nm and 1µm. The possible optical mode field profile that occurs in the proposed polymer nanowire design is studied using the H-field finite element method (FEM). In the characterization part, the optical field profile and the intensity at the device output are the main focus of this paper. The various lengths of the nanowires show different characteristics in term of output intensity. An image processing is used to process the image to obtain the intensity of the output signal. A comparison of the optical field and output intensity for each polymer nanowire is also discussed.

Polarization-independent on-axis light coupler for surface plasmon resonance using a concentric chirped grating

A novel on-axis one-element polarization-independent light in- and out-coupling mechanism for surface plasmon resonance (SPR) is proposed. The system utilizes an integrated high-NA concentric chirped grating to both focus the incident light on the metallic film and collimate the reflected beam onto a CCD array to extract the SPR signal. With NA up to 1.47, a broad sensing dynamic range from n=1 to 1.35 can be achieved. An analytical model is implemented to demonstrate the dependency of the radial location of the resonances on the detecting substance and its sensitivity to the change of the refractive index. The model shows a trend similar to rigorous ray-tracing calculations.

A study of thin profile solar concentrators using wedge prism with diffractive grating

Solar concentrators using wedge prism with diffractive grating or sawtooth profile mirror are proposed and studied. The concentrator length-to-thickness ratio can exceed 7 and the maximum concentration ratios exceed 3.5 for these designs.

Label-free guided mode resonance sensor for detection of glycated hemoglobin

This paper demonstrates the use of Guided Mode Resonance (GMR) optical sensor platform for detection of Glycated Hemoglobin (HbA1c) in human blood. HbA1c is an importance biomarker for monitoring a long-term glucose level in diabetes patients. Here, the sensing approach utilizes boronate affinity by modification of the GMR surface with 3-Aminophenylboronic acid (PBA). The sensing signal is then measured via a resonance shift in a reflection spectrum as the change of the refractive index on the sensor surface. In preliminary experiment, standard HbA1c samples with concentration covering the detection range (5% and 10 %) are used. The results show a good trend of resonance shift corresponding to amount of HbA1c.

Development of Nanohole Array Patterned by Laser Interference Lithography Technique

Periodic nanohole pattern was created in spin-coated photoresist S1805 on Si substrates by Laser Interference Lithography (LIL). Wavelength of a laser source used in the optical system is 442 nm with the photon energy 2.80 eV. The system was set up to employ two laser beams from a beam splitter to generate interference pattern and expose to the photoresist. There are two parameters (incident angle and exposure time) which are determined due to affecting the ordering and feature of nanohole array. Therefore, the relation of these two parameters and actual dose were investigated and theoretically analyzed to optimize the resolution of LIL technique for nanoholes. The prepared samples after developing in the M26A for 5 sec were analyzed by field-emission scanning electron microscopy (FE-SEM). The results show that the pitch of the pattern is 440 nm and the smallest hole size is 190 nm The best feature is found for a laser fluence of 140 mJ/cm2. This nanohole array patterned by LIL consists of periodic nanostructures for high density storage to fabricate various nanodevices.

Design and fabrication of diffractive phase element for minimizing the focusing spot size beyond diffraction limit

This paper proposes a fabrication apparatus of high numerical aperture (NA) diffractive lens (Concentric Chirped Grating, CCG). The fabrication scheme is based on photolithography incorporating with Double Patterning (DP) technique and Litho-Etch-Litho-Etch (LELE) process. The CCG element having NA up to 1.4 in a glass substrate (n=1.5) at 940 nm wavelength and feature size down to 320 nm is successfully fabricated. The fabricated element can be very useful in integrated Surface Plasmon sensors and beam shaping applications. When controlling the shift between the odd and even rings during the second exposure, the novel phase element that can minimize the optical beam spot size beyond the diffraction limit is generated.

Integrated on-axis light coupler for surface plasmon resonance using a concentric chirp grating

A novel on-axis one-element polarization independent light in/out-coupling mechanism in a surface plasmon resonance (SPR) is proposed. The system with broad dynamic range (Δn >0.35) utilizes an integrated high numerical aperture — concentric chirp grating.

Thermal Effects of Volume Bragg Grating as Laser Mirrors Due to Minute Self-Absorption

A simulation using T-matrix and finite element analysis confirm the experimental results and suggest VBG laser wavelength and reflectivity change caused by the volume Bragg grating absorption induced thermal effects.