Browsing by Author "Pei, Ting-Hang"

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A Continuous-Wave THz Imaging System
(2013)
Pei, Ting-Hang
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Huang, Yang-Tung
;
Wang, Yu-Jiu
;
Chen, Wei-Zen
;
Kuo, Chien-Nan
We develop a continuous wave terehertz (THz) imaging system operating at 288 GHz. This imaging system simply consitutes three parts including the source, two optical lenses, and the detector. The entire size is smaller than the tranditional pulsed THz imaging system. In this developed system, the THz wave is generated by a horn attenna which concentrates the wave in an azimuth angle of 3 degrees similar to 5 degrees. The source originates from a singnal generator, and then the frequency increases to 288 GHz after passing through an 8X multiplier. Next, THz wave is focused by a THz lens on the test sample. By controling the sample position in the x-z plane, we can scan it pixel-by-pixel in which each step along the x- or z- axes is 0.1 mm. After penetrating the test sample, another lens collects the transmitted THz wave and focuses them into the thermal detector. This detector can disply the collected THz power. Finally, by drawing the detected power of each pixel, a transmitted-intensity figure for all pixels is obtained. The resolution of this THz imaging system is about 1 similar to 2 mm at present. We have measured human molar tooth and obtained its transmitted figures. Besides, we also develop a technology to adjust the positions of the source and detector by a system containing one laser, one beamsplitter, and two mirrors. The relative positions between the source and detector is very important. The input of the source and the output of the detector are small so that they have to aim at each other very accurately in order to collect maximum transmitted power in the detector.
A temperature modulation photonic crystal Mach-Zehnder interferometer composed of copper oxide high-temperature superconductor
(2007-04-15)
Pei, Ting-Hang
;
Huang, Yang-Tung
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
A tunable Mach-Zehnder interferometer with a two-dimensional photonic crystal structure using copper oxide high-temperature superconductor is proposed. This photonic crystal is composed of rods of which axes are perpendicular to the two-dimensional anisotropic copper oxide plane. By tuning the temperature of the superconductor, the refractive index of the superconductor as well as the photonic band gap can be changed. The photonic band structures of two-dimensional photonic crystals composed of the superconductor are calculated by using the plane-wave expansion method, and interference properties are investigated by using the finite-difference time-domain method. For our designed photonic crystal Mach-Zehnder interferometer, the simulation results show that the light transmission can be modulated from 92.7% to 1.4% with different temperature distributions.
Analyzing the propagating waves in the two-dimensional photonic crystal by the decoupled internal-field expansion method
(2012-03-01)
Pei, Ting-Hang
;
Huang, Yang-Tung
;
電子工程學系及電子研究所
;
友訊交大聯合研發中心
;
Department of Electronics Engineering and Institute of Electronics
We propose the decoupled internal-field expansion (IFE) method to discuss refractions in the photonic crystal (PhC). This method decouples the full wave in the PhC and classifies them into two categories including the forward-propagating and backward-propagating waves denoted by the index n. A triangular-PhC case is demonstrated and both positive and negative refractions are discussed by this method. The incident angle of 10 degrees results in the positive refracted wave with the refracted angle about 8 degrees, which approximately corresponds to the forward wave of n = 0 order. The negative refracted waves, which exist in the left and right edge regions, propagate almost parallel to the interfaces between the PhC and outside media. Meanwhile, due to the interaction between the negative refracted wave and the nearest few rows of air cylinders, the reflected wave and another weaker negative refracted wave are created. Finally, the weaker negative refracted waves from both edge regions interfere with each other in the middle region. It is found out that the negative refracted waves in edge regions as well as the interfered wave in the middle region can be constructed by two n=-1 forward and backward waves. On the other hand, the positive refracted wave is composed of the n=0 forward wave dressed other n not equal 0 forward waves, the propagation angle is affected by these dressed waves, especially near the edge region. Finally, another case proves this point of view explicitly. Copyright 2012 Author(s). This article is distributed under a Creative Commons Attribution 3.0 Unported License. [http://dx.doi.org/10.1063/1.3700236]
Comparisons of the transmission and resonant tunneling between the superlattice composed of two alternating photonic crystals and its effective structure
(2013-01-01)
Pei, Ting-Hang
;
Huang, Yang-Tung
;
電子工程學系及電子研究所
;
友訊交大聯合研發中心
;
Department of Electronics Engineering and Institute of Electronics
Transmissions and resonant tunneling of superlattices composed of two alternating triangular photonic crystals (PhCs) and their corresponding effective one-dimensional (1D) superlattices are discussed. In the first case, below 0.40 (c/a), the transmissions of effective 1D superlattices calculated by the effective medium theory (EMT) match those of two-alternating-PhC superlattices calculated by the internal-field expansion method. No matter whether the propagating direction is along the symmetric (along Gamma K or Gamma M directions) or nonsymmetric axes (incident angle theta = 45 degrees), the results hold very well. In the second case, resonant-tunneling phenomena and transmissions of the two-period superlattice composed of two alternating PhCs (the resonant-tunneling superlattice) can also be predicted by EMT below 0.20 (c/a). However, due to the evanescent waves at oblique incidence, the interface effect between two PhCs becomes explicit in the higher-frequency region and results in the deviations of resonant-tunneling frequencies in EMT calculations. By modifying the effective refractive indices of both PhCs, deviations are corrected and EMT calculations can exhibit resonant tunneling at right frequencies. Furthermore, the resonant-tunneling superlattice with larger background dielectric constant displays fewer modifications on the effective refractive indices. (C) 2012 Optical Society of America
Effective refractive index of the photonic crystal deduced from the oscillation model of the membrane
(2012-09-01)
Pei, Ting-Hang
;
Huang, Yang-Tung
;
電子工程學系及電子研究所
;
友訊交大聯合研發中心
;
Department of Electronics Engineering and Institute of Electronics
The oscillation model of the circular membrane is used to calculate the effective refractive index of the two-dimensional triangular photonic crystal at normal incidence within the second photonic band. Negatively effective refractive indices deduced from this model match those calculated by equifrequency surfaces very well. The result reveals that the field distribution has relation with the effective refractive index at certain frequency regions. Besides, the field distribution described by the Bessel function is more compact than the Fourier series expansion. (c) 2012 Optical Society of America
Rotational Invariance of the Effective Refractive Index in Photonic Crystals
(2012-11-15)
Pei, Ting-Hang
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Huang, Yang-Tung
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材料科學與工程學系
;
電子工程學系及電子研究所
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Department of Materials Science and Engineering
The rotational invariance of the effective refractive index in the 2-D photonic crystal is discussed. It is proven that, in the case of the n-fold symmetrical omega-k equifrequency surface (EFS), there are two solutions that show the invariance of the effective refractive index after rotating a multiple of the basic repeated angle 2 pi/n within the first Brillouin zone. For the noncircular solution, the behavior of the effective refractive index N-eff(theta) at normal incidence shows that N-eff(0 degrees) has an additional constant of two in the very high symmetric EFS, higher than in the low symmetric case.
Temperature modulation of the superprism effect in photonic crystals composed of the copper oxide high-temperature superconductor
(2007-06-01)
Pei, Ting-Hang
;
Huang, Yang-Tung
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
We have designed a two-dimensional triangular photonic crystal using a copper oxide high-temperature superconductor that can control the superprism effect. The refractive direction of light in the photonic crystal is determined by calculating the direction of the group velocity of the light in the photonic crystal. By tuning the temperature of the superconductor, the photonic band structure as well as the equifrequency surface is changed. When the incident angle is fixed, the refractive angle can be changed by varying the temperature. We choose an operation frequency of omega = 0.83(2 pi c/a) and a fixed incident angle of theta = 13 degrees for discussion. The refractive angle of light in the photonic crystal changes about 28 degrees when the temperature is increased from T = 5 to 101) K. All the equifrequency surfaces of the photonic crystal are calculated by the plane-wave expansion method. and simulations on the propagation of light are investigated by the finite-difference time-domain method.
The Application of the Sawtooth Photonic Crystal on Producing Polarized Light
(2011-09-15)
Pei, Ting-Hang
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Chen, Wei-Chou
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Yang, Kei-Hsiung
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光電學院
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College of Photonics
We have proposed a sawtooth photonic crystal formed by Si-SiO(2) periodic layers designed on a planar medium as a polarizer. The polarizer can produce H-polarized light very efficiently because the frequency of E-polarized light is chosen at the photonic band gap but that of H-polarized light at the photonic conduction band. The best polarization ratio is as high as 2.56 x 10(5) : 1 when the normalized frequency a/lambda is 0.24 and the incident angle is about 13 degrees. Highly polarized light can be produced in a normalized frequency range from 0.23 to 0.25, and this can possibly be applied to an LED with a certain bandwidth.
The equivalent structure and some optical properties of the periodic-defect photonic crystal
(2011-04-01)
Pei, Ting-Hang
;
Huang, Yang-Tung
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
The concept of the effective medium is used to deal with problems of defects in photonic crystals (PhCs) throughout this paper. First, scattering phenomena in PhCs with defects are investigated and can be very well replaced by those in an effective medium with effective defects in interesting frequency region. It is based on the fact that the Bloch wave in the defect-free PhC very approximates to the wave in the effective medium. Then a periodic-defect PhC created by adding periodic defects into the defect-free PhC is proposed. It can be replaced with an effective PhC by utilizing the concept of effective periodic defects embedded into an effective medium. We verify the equivalence between the periodic-defect PhC and the effective PhC by comparing their photonic band structure (PBS) and photonic band gaps (PBGs) as well as transmissions. Next, the effective PhCs instead of the periodic-defect PhCs are used to investigate the variance of the PBGs by applying different periodic defects. The substitution allows us successfully predicting the negative refraction in the periodic-defect PhC through the PBS of the effective PhC. Finally, the field distributions and Fourier coefficients of waveguide modes in the effective PhC and the periodic-defect PhC are equivalent by the supercell method confirmations. (C) 2011 American Institute of Physics. [doi:10.1063/1.3567296]
The Heterostructure Photonic Crystal Waveguide Splitter
(2011-08-15)
Pei, Ting-Hang
;
Huang, Yang-Tung
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
We propose a two-dimensional heterostructure photonic crystal (PhC) waveguide splitter composed of different air-hole radii in the core and claddings. Two PhCs in the core and claddings are treated as two effective homogeneous media in the first photonic band. By using a triangular coupler in the input port, light can be efficiently coupled from the conventional waveguide into the PhC waveguide splitter. Total internal reflections take place at outer interfaces and confine light in the PhC waveguide very well. Finally, incident light is divided into three parts, and each of them couples to output waveguides with total transmission more than 90%.
The high-transmission photonic crystal heterostructure Y-branch waveguide operating at photonic band region
(2011-02-01)
Pei, Ting-Hang
;
Huang, Yang-Tung
;
電子工程學系及電子研究所
;
Department of Electronics Engineering and Institute of Electronics
We design a high-efficiency two-dimensional photonic crystal (PhC) Y-branch waveguide formed as a heterostructure with two different triangular PhCs composed of air holes. At photonic-band frequency regions corresponding to circular equifrequency surfaces, the two PhCs could be taken as effective homogeneous media with effective refractive indices. A triangular coupler composed of the PhC is designed at the input port in order to divide the incident beam into two parts. The two parts finally propagate into different channels. A case demonstrated here shows that the total transmission of light passing through the Y-branch waveguide is about 91.2%. The propagation phenomena can be explained by the mechanism of total internal reflection very well. (C) 2011 American Institute of Physics. [doi:10.1063/1.3532048]
Ultra high-density silicon nanowires for extremely low reflection in visible regime
(2011-10-10)
Pei, Ting-Hang
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Thiyagu, Subramani
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Pei, Zingway
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友訊交大聯合研發中心
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D Link NCTU Joint Res Ctr
We fabricated large-area, vertically aligned silicon nanowire (SiNW) arrays on Si substrates employing catalytic etching on a polystyrene nanosphere template. The density of SiNWs was as high as 10(10)/cm(2), and the bottom radii of SiNWs ranged between 30 and 60 nm. The reflection from the SiNW layer was approximately 0.1% over the spectral range of 300-800nm for SiNWs longer than 750 am. Effective medium theory was applied to explain this extremely low reflection, and it was confirmed that the incident light scatters randomly inside cone-like SiNWs, which lengthens the actual traveling path of light. (C) 2011 American Institute of Physics. [doi10.1063/1.3650266]