Kosom Chaitavon

A highly sensitive optofluidics-based refractometer in a Young interferometer design

This paper proposes a highly sensitive and compact optofluidics-based refractometer. Our key idea is based on the use of a two-channel microfluidic chip in a free-space Young interferometer structure that provides an inherent advantage in cancelling the unwanted optical phase noise induced from the surrounding environment during optical beam propagation. By using a 655-nm monochromatic light that travels in free space for 57.5 cm and a microfluidic chip designed to have two fluidic channels in parallel with a distance between channels of 900 μm and a channel depth of 100 μm, our simulation indicates that analysis of the movement of the interference fringe offers a sensitivity of better than 1.31×10-4 in measuring the change of the refractive index. A better than thousand-fold improvement can also be accomplished by investigating the amplitude change of the interference fringe via a > 10-bit digitalization. Our experiment in analyzing the change of the refractive index of the sucrose solution will be discussed. Polarization insensitivity and simplicity in design and implementation are also additional key advantages.

Surface plasmon resonance-based highly sensitive optical touch sensor with a hybrid noise rejection scheme

A surface plasmon resonance (SPR)-based optical touch sensor structure is proposed that provides high switch sensitivity and requires a weak activating force. Our proposed SPR-based optical touch sensor is arranged in a compact Kretschmann-Raether configuration in which the prism acting as our sensor head is coated with a metal nanofilm. Our optical-based noise rejection scheme relies on wavelength filtering, spatial filtering, and high reflectivity of the metal nanofilm, whereas our electrical-based noise reduction is obtained by means of an electrical signal filtering process. In our experimental proof of concept, a visible laser diode at a 655 nm centered wavelength and a prism made from BK7 with a 50 nm thick gold layer on the touching surface are used, showing a 7.85 dB optical contrast ratio for the first touch. An estimated weak mechanical force of <0.1 N is also observed that sufficiently activates the desired electrical load. It is tested for 51 operations without sensor malfunction under typical and very high illumination of 342 and 3000 lx, respectively. In this case, a measured average optical contrast of 0.80 dB is obtained with a +/-0.47 dB fluctuation, implying that the refractive index change in a small 3.2% of the overall active area is enough for our SPR-based optical touch sensor to function properly. Increasing optical contrast in our SPR-based optical touch sensor can be accomplished by using a higher polarization-extinction ratio and a narrower-bandwidth optical beam. A controlled environment and gold-coated surface using the thin-film sputtering technique can help improve the reliability and the durability of our SPR-based optical touch sensor. Other key features include ease of implementation, prevention of a light beam becoming incident on the user, and the ability to accept both strong and weak activating forces.

Scalable highly-sensitive optical touch keyboards

Due to the need of a highly sensitive touch keyboard for the disabled, we propose no-moving-parts optical touch keyboard architectures based on the use of light splitting and blocking concepts. Light splitting via a fiber optic splitter is also introduced to reduce the precise optical alignment technique required in our free-space-based optical touch keyboard. Several key features are accomplished, including high switch sensitivity, scalability, ease of implementation, and low electrical power consumption. Our free-space-based 5×4 optical touch keyboard prototype shows a key activating time of 19 ms for a keyboard scanning rate of 180 ms per 20 keys. Our optical touch keyboard prototype is also tested in more than 4000 key operations under environmental illuminations from a typical 400 lux to a high 3000 lux without keyboard failure, thus promising good use in practice.

High-dynamic-range high-optical-isolation wavelength-sensitive thin film filter-based variable fiber optic attenuator

A wavelength-sensitive variable fiber optic attenuator (VFOA) is introduced by incorporating the movable optical mirror with a fixed desired thin film filter (TF) in a compact in-line reflective architecture. Our TF-based wavelength-sensitive VFOA features low component count, high attenuation dynamic range, and high optical isolation. Experimental proof of concept using an off-the-shelf measured 1545.71-nm TF and a mechanically movable mirror shows a 4.64-dB optical loss, and a low polarization-dependent loss of 0.12 dB at the output port. A high optical attenuation dynamic range of >43 dB with a better than 30-dB optical isolation is obtained. Several proposed reflective wavelength-sensitive TF-based VFOAs can also be cascaded to form a low-cost, compact, multiwavelength amplitude controller.

Far-field diffraction analysis of submillimeter-thick bars for edge quality assessment

Parameters such as dimensions, edge parallelism, and edge defect are important in separating good rectangular bars from bad ones. This work proposes a Fourier-optics-based noninvasive quality assessment tool for a rectangular bar ranging from a few micrometers to submillimeters thick. Our design concept relies on a transmissive optical architecture to reduce the effect of an objects angle misalignment that can introduce a significant measurement error. From the far-field diffraction pattern of the bar, the thickness of the bar can be determined from the distance between the two adjacent diffracted order beams. In addition, because all diffracted order beams are aligned, we use the resulting slope to determine edge parallelism. The amount of edge defect on the sample can be investigated by evaluating the distribution of the optical intensity inside diffracted order beams. Our experiment using a 635-nm wavelength laser diode, a 150-mm focal length lens, and an image sensor with 8.4-µm pixel pitch for 22 sample bars with an average thickness of 238 µm shows that our approach can simultaneously evaluate the thickness and the edge parallelism of the bar samples, as well as distinguish nicely edged bars from poorly edged bars. Other key features include low cost, ease of implementation, robustness, and low component counts.

A Fourier-optics-based non-invasive and vibration-insensitive micron-size object analyzer for quality control assessment

This paper proposes a Fourier-Optics-based non-invasive quality assessment tool for a micron-thick bar. Our design concept relies on a transmissive optical architecture to reduce the effect of an objects angle misalignment that can introduce a significant measurement error. From the far-field diffraction pattern of the micron-thick bar, we determine its thickness from the distance either between the two adjacent diffracted order beams or between a high order diffracted beam and the zero order beam. In addition, because all diffracted order beams are aligned, we use the resulting slope to determine the edge parallelism. The amount of edge defect on the sample can be investigated by evaluating the distribution of the optical intensity inside diffracted order beams. Our theoretical analysis indicates that for a 238-μm thick bar, our proposed concept provides better than 1 μm and 0.1° resolutions in thickness and edge parallelism measurements. Our experiment using a 635-nm wavelength laser diode and 22 sample bars with an average thickness of 238-μm shows that our approach can simultaneously evaluate the thickness and the edge parallelism of the bar samples as well as distinguish nicely edged bars from poorly edged bars. Key features include low cost, ease of implementation, robustness, and low component counts.

A noninvasive human temperature screening system with multiple detection points

This paper introduces a non-invasive human temperature screening system for use in a large public area. Our key idea is to combine an image filtering process, an image morphology algorithm, and a particle analysis process in such a way that an individuals face in live thermal image can be located so that the skin temperature can be monitored and displayed. From our experiment, we find that the temperature measurement depends on each individuals response to the ambient temperature and on the contrast of the thermal image against the black body radiation source. This indicates that using the blackbody radiation source as our temperature reference does not totally compensate the fluctuation in human skin temperature. Our field test study at the triage section of Rajavithi Hospital, Thailand, shows that the maximum skin temperatures from peoples faces can be simultaneously monitored and displayed in real time. In addition, the temperature value obtained from the thermal imaging camera has less fluctuation with respect to the true core body temperature once the disturbance from the surrounding environment is compensated. Hyperthermic patients can be identified with 100% sensitivity when the temperature threshold level and the offset temperature value are appropriately chosen.

Built-in-mask microfluidic chip for highly-sensitive Young interferometry-based refractometer structure

In this article, we propose a built-in-mask two-flow-channel microfluidic chip for use in our highly-sensitive Young interferometry-based refractometer structure. Our key idea is to make the area surrounding the two flow channels opaque by using a black material (e.g., black silicone). Once the incoming optical beam passes through the two flow channels, it is automatically divided into two optical beams that will interfere with each other at the two-dimensional detection plane, eliminating a highly precise alignment technique previously required between an external mask and the microfluidic chip. Experimental proof of concept using a two-flow-channel microfluidic chip with a channel spacing and depth ratio of 3, a 635-nm wavelength laser diode, and a 1600×1200-pixel image sensor shows a measured high 4.28×10-5 RIU/pixel sensitivity with a measured resolution of 8.11×10-6 RIU.

Highly-sensitive optofluidics-based single-flow-channel refractometer structure

This paper shows how only a single-channel microfluidic chip when deployed in our interferometric optofluidics-based refractometer can offer a very high sensitivity of 6.16×10−6 RIU/pixel suitable for sensitive bio and chemical sensing applications.

An optically non-destructive, non-contact, and vibration-insensitive edge quality assessment system for semiconductor and harddisk drive industries

This paper proposes an edge quality assessment system for a sub-millimeter thick wafer bar suitable for semiconductor and harddisk drive industries. Our key approach is based on Fourier optics analysis in a retro-reflective optical architecture featuring nondestructive and non-contact measurement. In our proposed design, a collimated optical beam is incident on a sub-millimeter thick wafer bar from its side. In this way, part of the optical beam is reflected back and is then Fourier transformed on a two-dimensional image sensor. By investigating the far-field diffraction pattern, important parameters of the wafer bar such as thickness, surface parallelism, edge parallelism, and surface defect can simultaneously be analyzed. To our knowledge, this is the first time that these important parameters are analyzed by only one system. Other key features include low cost and vibration insensitivity. Our field test study using a 635-nm wavelength laser and a 15-cm plano-convex lens for specified 246-μm thick rectangular wafer bars are discussed.