We present the design of a high birefringence hollow core with nested anti-resonance nodeless fiber (HC-NANF). This model is designed for terahertz guidance made by TOPAS copolymer. The finite element method is used to study the properties of the proposed fiber: effective material loss, confinement loss, and birefringence. In this model, the cladding consists of four circular anti-resonant tubes: two tubes aligning in the horizontal axis and two tubes aligning in the vertical axis. Each circular anti-resonant tube consists of two circular nested tubes. First, we optimize the thickness of circular nested tubes due to anti-resonance reflecting guidance mechanism to achieve the lowest loss. The simulation results show that the thickness of 0.09 mm is suitable for operating at 1 THz. To achieve the birefringence, we attempted to rotate the inner circular nested tube with two patterns: symmetric and asymmetric rotations. The simulation results show that only the asymmetric rotation can provide the birefringence in the structure. It also shows that the birefringence can be adjusted by rotating the inner circular nested tube with respect to the core radius. Finally, the orthogonal birefringence of the proposed design from HC-NANF is found to be higher than 10-4. This study offers an alternative model to provide the birefringence in THz regime, which might be relevant for future polarization related applications.
Malaria is a disease generally found in a tropical area including Thailand. It is widely known that the biological technique such as PCR normally used for an accurate detection of malaria-infected blood requiring a considerable period to repeat the process. Raman spectroscopy is considered to be an alternative method for the malaria infected blood detection. Theoretically, Raman spectroscopy is based on the scattering process that is less likely in a normal situation. Therefore, an enhancing technique known as “surface-enhanced Raman scattering (SERS)” is required for the signal augmentation. The SERS provides the enhancement of the electric field near the surface of the substrate. With the application of the technique, the main target of this research focuses on the comparison of the SER Raman spectra of the normal red blood cell and malaria infected red blood cell. However, only a single spectrum cannot provide a clear difference between the normal and the infected blood. An additional tool for even more effective discrimination was provided by using PCA analysis. In the sample preparation stage, the spin coating process was applied to spread the red blood cells uniformly on the surface. In addition, the spectra of the red blood cells including media were collected in various conditions in terms of the excitation wavelengths and the types of substrate. This additional information can be used as references for any red blood cell related investigation using Raman spectroscopy.
KEYWORDS: Sensing systems, Single mode fibers, Cladding, Sensors, Optical fibers, Signal attenuation, 3D printing, Calibration, Optical design, Refractive index
We demonstrate an application of the mechanically induced long period fiber grating system for a foot plantar measurement. The system is designed as a fixed fiber grating platform that can be utilized for monitoring a subject’s foot plantar pressure distribution in static and dynamic activities. The pressure information obtained from the foot loading characteristics can be used for various application such as disease diagnosis of foot problem, foot ware design, sport biomechanics and injury prevention. The system is composed of a strand of a single mode fibers with 800 nm cut off wavelength and circular plastic grooved plates with the grating period of 0.8 and 1.0 mm made by 3 D printing. The sensing units are fixed at biomechanically significant positions; fore-foot, mid-foot and hind-foot of the foot platform for monitoring the foot plantar pressure distribution. The sensing locations are chosen appropriately to contact with sensitive areas of foot and can initially provide enough foot plantar pressure characteristics of a subject. The fiber sensing units with grating having different periods provides different sets of transmission spectra which separately respond to individual perturbed points. Preliminary result shows that the system can be used to classify different types of foot. With some advantageous properties of the optical fiber such as structural flexibility and light weight, the system can successfully be used to monitor the static and dynamic perturbations such as the movement of the body center of mass and foot actions in the stance phase. The study has demonstrated that the proposed fiber-optic sensing systems has a feasibility of being used as an alternative for insole plantar pressure detection systems.
Metamaterials (MMs) are the artificially engineered materials that can exhibit particular electromagnetic properties such as negative refractive index, left-handed behavior, extraordinary transmission, etc. These fascinating properties of MMs are of great and increasing interest to be used in various applications in the terahertz regime (0.1-10 THz). In this study, the electromagnetic property of metamaterial that we are interested is an extraordinary transmission for creating a “Metamaterial Absorber (MMA)”. Over the past decade, there has been a number of designed patterns of metamaterial absorbers having high absorptivity and also multi-absorption characteristics such as split-ring resonator, square, U-shape, T-shape and Hexagon. Most of the Hexagons are designed to have the absorption characteristics in GHz frequency. We intend to investigate the effects of the parameters regarding the absorption in the terahertz regime, especially in 0.3-5.0 THz for various applications such as security and medicine. The proposed absorber structure in this study consists of 3 layers which are a periodically arranged metallic hexagonal pattern layer, a dielectric layer, and a continuous metallic layer. Length, width, number of gaps, gap size, the position of a gap of the hexagon in the first layer are the studied parameters. The proposed hexagon metamaterial absorber of the first design having 5 gaps with gap size 5 μm each located at the corner of the hexagon provide 4 absorption bands with high absorptivity. For the other design having 6 gaps with gap size of 5 μm each located at hexagon side show not only 3 narrow bands of perfect absorption but also a broadband absorbance for the terahertz regime around 3 THz.
A fiber in-line Mach-Zehnder interferometer based on an inner air-cavity is presented for high-pressure measurement.
The inner air-cavity is fabricated by use of femtosecond laser micromachining together with fusion splicing technique.
A micro-channel is created on the top of the inner air-cavity to allow the high pressure gas to flow in. The fiber in-line
device is featured with miniature size, good robustness and excellent operation stability while exhibiting a high pressure
sensitivity of 8,239 pm/MPa.
This paper presents the polarizing triangular cyclic interferometer (pTCi) for characterizing optical samples with birefringent properties such as half- and quarter-wave plates. The interferometric system was set up to analyze the phase retardation of wave retarders in both qualitative and quantitative aspects. For the qualitative aspect, the distinct signal outputs from the inspected birefringent components oriented at particular angles are employed to distinguish different types of optical devices. For the quantitative aspect, the same arrangement could determine the phase difference γ of unknown retarders, so that it could be used to characterize types of samples. The experimental results showed the corresponding results obtained from both mentioned aspects where γ were measured to be 89.62° and 177.17° for half- and quarter-wave plates, respectively. The pTCi has been proved to be a proper scheme to characterize optical samples with birefringent properties.
The optical fiber filter can be used to reject the noise or unwanted spectrum in the optical communication system. In this study, the performance of the optical fiber filter in visible and near-infrared wavelengths is studied. The working principle of the filter is based on the cladding mode coupling to the high order mode introduced by perturbation on a short section of single-mode (SM) fiber with a specific cut-off wavelength. In the previous study, the filtered wavelengths from the SM-fibers with the cut-off wavelength of 600 nm are 547 nm and near IR range (980-1,100 nm). The filtered wavelength from the SM-fiber with the cut-off wavelength of 800 nm is 666 nm. Also, the magnitude of the filtered wavelengths can be controlled by the magnitude of the applied perturbation force. In this study, the green solid state laser with the wavelength of 532 nm (2nd harmonic component), 808 nm (pump wavelength), and 1,064 nm (fundamental component) and the red diode laser with the wavelength of 668 nm are launched into the SM-fiber with the cut-off wavelength of 600 and 800 nm, respectively. The experimental results clearly show that the harmonic wavelength of 1,064 nm of green laser can be filtered out by the fiber with cut-off wavelength of 600 nm up to 66% with the perturbation force 60 N. The fiber with cut-off wavelength of 800 nm can reject the red laser spectrum up to 50% with the perturbation force 80 N.
Numerical results using transfer matrix method (TMM) of omnidirectional photonic band gap (omni-PBG) for both TE and TM polarizations from 0º to 89º for THz responses are presented. Such omni-PBG design is based on one-dimensional photonic crystal (1D-PC) containing thin slices of 10 pairs of high-resistivity silicon and magnesium fluoride (MgF2) as the high and low refractive index components respectively, in the (HL)10 structure. With a quarter-wavelength thickness of layer, the thickness increase of either high or low index layer increases this PBG redshift for TE as well as TM polarizations. Conversely, decreasing the thickness causes the PBG of both TE and TM polarizations to become blueshift. This also gives rise to the spectral shift for the omni-PBG. High reflectivity omni-PBG within a certain wavelength is found in the range of 390-515 μm. This suggests a practical way of controlling the thickness of layer to achieve a suitable omni-PBG. This structural design shows the potential of omnidirectional mirror as a key element in THz communication system. In addition, the proposed structure shows a probable application based on the polarization sensitivity of the structure. At an angle of incidence greater than 60º, the TM polarized mode is highly transmitted whereas the transmittance of the TE polarized mode become nearly zero. The TM mode filter is therefore realized.
This research purpose is to investigate the changing of teeth color and to study the surface of teeth after treatment by
laser diode at different power densities for tooth whitening treatment. In the experiment, human-extracted teeth samples
were divided into 7 groups of 6 teeth each. After that laser diode was irradiated to teeth, which were coated by 38%
concentration of hydrogen peroxide, during for 20, 30 and 60 seconds at power densities of 10.9 and 52.1 W/cm2. The
results of teeth color change were described by the CIEL*a*b* systems and the damage of teeth
surface were investigated by scanning electron microscopy (SEM). The results showed that the power density of the laser
diode could affect the whiteness of teeth. The high power density caused more luminous teeth than the low power
density did, but on the other hand the high power density also caused damage to the teeth surface. Therefore, the laser
diode at the low power densities has high efficiency for tooth whitening treatment and it has a potential for other clinical
applications.
This research is based on the Fresnel's equations and the ellipsometric technique that investigate the sample of SiO2 thinfilm
on Si substrate. The investigation is made by a probing beam which is in the form of a rotating linearly polarized
light generated by the polarizing Mach-Zehnder interferometer (pMZi). The detection of the changed polarization states
of the incident light due to reflection on the sample surfaces led to a set of unique characteristics describing a thin-film
substrate system in terms of ellipsometric parameters ψ and Δ. SiO2 thin-films were chosen to study because of their
well known characteristics. The accuracy of measurements was confirmed by comparisons to calculated values derived
from Fresnel's equations and a standard instrument. The results clearly reveal a feasibility of using the rotating linearly
polarized light produced by pMZi for a non-destructive characterization of the thin-film system.
A surface mount typed multi-coloured Light-Emitting Diode (LED) is used as a light source for the hands-on coloured light mixer. The LED consists of red, green and blue tiny sources but the mixer is designed to have four switches corresponding to red, green, blue and yellow light. These colours correspond to students’ misconceptions of primary coloured lights; they realize that the primary colours and the rules for lights mixing are the same as those of paints. To generate a yellow light, a microcontroller placed between four input switches and the LED operates both a red and green tiny sources. In addition, the microcontroller is employed to eliminate some combinations of coloured light mixing to simplify the experiment (basic mode) for non advanced students. If the mixer is used with more advanced students, a number of combinations will increase and students need more analytical skills to find out the primary coloured lights (the coloured lights that can not be produced by the mixing of any other coloured lights). Therefore, the mixer is able to use with more advanced and non advanced students depending on the program in the microcontroller and some modifications of the circuit. Furthermore, to introduce students an idea that other hues or shades can be generated by mixing of these three primary coloured lights of different intensities, a tuning circuit is integrated to vary an intensity of the green light source.
The application of a highly birefringent fiber polarization modulation technique for ellipsometric measurements on sol-gel thin films is described. The ability of the system to determine the ellipsometric parameters of thin films is demonstrated. The system is then used to monitor the ellipsometric parameters of thin films on exposure to a perturbing environment of humidity and pressure. The potential of the system for application in chemical sensor systems is indicated and discussed.
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