Browsing by Author "Chen, Ching-Wei"

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Coherent multiple-stage optical rectification terahertz wave generator
(2010-08-26)
Pan, Ci-Ling
;
Huang, Jung Y.
;
Chang, Chen-Shiung
;
Chen, Ching-Wei
;
Lin, Yu-Shian
The present invention coherent multiple-stage optical rectification terahertz wave generator discloses the generation of single-cycle terahertz radiation with two-stage optical rectification in GaSe crystals. By adjusting the time delay between the pump pulses employed to excite the two stages, the terahertz radiation from the second GaSe crystal can constructively superpose with the seeding terahertz field from the first stage. The high mutual coherence between the two terahertz radiation fields is ensured with the coherent optical rectification process and can be further used to synthesize a desired spectral profile of output coherent THz radiation. The technique is also useful for generating high amplitude single-cycle terahertz pulses, not limited by the pulse walk-off effect from group velocity mismatch in the nonlinear optical crystal used.
Frequency-Dependent Complex Conductivities and Dielectric Responses of Indium Tin Oxide Thin Films from the Visible to the Far-Infrared
(2010-12-01)
Chen, Ching-Wei
;
Lin, Yen-Cheng
;
Chang, Chia-Hua
;
Yu, Peichen
;
Shieh, Jia-Min
Transparent and conducting indium tin oxide (ITO) thin films form an integral part for various optoelectronic devices. In this paper, we report the frequency-dependent complex conductivities and dielectric responses of several sputtered ITO thin films with thicknesses in the range of 189-962 nm by using terahertz time domain spectroscopy (THz-TDS), optical reflectance spectroscopy, and electrical measurements. The plasma frequencies are verified to be from 1590 to 1930 rad.THz, while the scattering times are in the range 6-7 fs based on the Drude free-electron model. The mobilities of the above ITO thin films are calculated to be 32.7-34.2 cm(2) V(-1) s(-1), whereas the carrier concentrations lie in the range 2.79-4.10 x 10(20) cm(-3). The electrical properties derived from the THz-TDS technique agree well with those determined by Hall measurement. Parameters for the complex dielectric function suitable for ITO in the range 0.2-2 and 4-450 THz are also determined.
Generation and spectral manipulation of coherent terahertz radiation with two-stage optical rectification
(2008-09-01)
Chen, Ching-Wei
;
Lin, Yu-Shian
;
Huang, Jung Y.
;
Chang, Chen-Shiung
;
Pan, Ci-Ling
We propose and experimentally demonstrate the generation of single-cycle terahertz radiation with two-stage optical rectification in GaSe crystals. By adjusting the time delay between the pump pulses employed to excite the two stages, the terahertz radiation from the second GaSe crystal can constructively superpose with the terahertz field injected from the first stage. The high mutual coherence between the two terahertz radiation fields is ensured with the coherent optical rectification process and can be further used to synthesize a desired spectral profile of coherent THz radiation. The technique is also potentially useful for generating high-power single-cycle terahertz pulses, usually limited by the pulse walk-off effect of the nonlinear optical crystal used. (c) 2008 Optical Society of America.
Generation properties of coherent infrared radiation in the optical absorption region of GaSe crystal
(2006-10-30)
Chen, Ching-Wei
;
Hsu, Yu-Kuei
;
Huang, Jung Y.
;
Chang, Chen-Shiung
;
Zhang, Jing-Yuan
We report a study of the effect of optical absorption on generation of coherent infrared radiation from mid-IR to THz region from GaSe crystal. The infrared-active modes of epsilon-GaSe crystal at 236 cm(-1) and 214 cm(-1) were found to be responsible for the observed optical dispersion and infrared absorption edge. Based upon phase matching characteristics of GaSe for difference-frequency generation (DFG), new Sellmeier equations of GaSe were proposed. The output THz power variation with wavelength can be properly explained with a decrease of parametric gain and the spectral profile of absorption coefficient of GaSe. The adverse effect of infrared absorption on (DFG) process can partially be compensated by doping GaSe crystal with erbium ions. (c) 2006 Optical Society of America.
New Constructions of Zero-Correlation Zone Sequences
(2013-08-01)
Liu, Yen-Cheng
;
Chen, Ching-Wei
;
Su, Yu T.
;
傳播研究所
;
Institute of Communication Studies
In this paper, we propose three classes of systematic approaches for constructing zero-correlation zone (ZCZ) sequence families. In most cases, these approaches are capable of generating sequence families that achieve the upper bounds on the family size (K )and the ZCZ width (T) for a given sequence period (N). Our approaches can produce various binary and polyphase ZCZ families with desired parameters (N, K, T) and alphabet size. They also provide additional tradeoffs amongst the above four system parameters and are less constrained by the alphabet size. Furthermore, the constructed families have nested-like property that can be either decomposed or combined to constitute smaller or larger ZCZ sequence sets. We make detailed comparisons with related works and present some extended properties. For each approach, we provide examples to numerically illustrate the proposed construction procedure.
Nonvolatile memory with switching interfacial polar structures of nano Si-in-mesoporous silica
(2009-10-05)
Shieh, Jia-Min
;
Huang, Jung Y.
;
Yu, Wen-Chien
;
Huang, Jian-Da
;
Wang, Yi-Chao
We show an artificially engineered electret with Si nanocrystals embedded in mesoporous silica for nonvolatile memory. We attribute the polarization to from polar layers lying at the interfaces between one-side bonded Si nanocrystals and mesoporous silica matrix. Under external field, the Si nanocrystals could be displaced in the porechannels causing displaced charge distributions and therefore a field-controllable electric polarization. Nonvolatile memory is demonstrated with a metal-oxide-semiconductor field-effect transistor. (C) 2009 American Institute of Physics. [doi:10.1063/1.3240888]
Optical properties and potential applications of epsilon-GaSe at terahertz frequencies
(2009-09-01)
Chen, Ching-Wei
;
Tang, Tsung-Ta
;
Lin, Sung-Hui
;
Huang, Jung Y.
;
Chang, Chen-Shiung
Ordinary and extraordinary refractive indices of an epsilon-GaSe crystal at terahertz (THz) frequencies are experimentally determined in this study. Fitting experimental data by THz time-domain spectroscopy (THz-TDS) and a Fourier transform infrared spectrometer (FTIR), we proposed revised complex dielectric functions and Sellmeier equations of GaSe for both ordinary and extraordinary waves from 0.2 to 100 THz. Phonon vibrational modes and overtones in the THz frequency range are examined in detail. The high magnitude of the figure of merit (FOM similar to 10(3) at 1 THz), the large birefringence (Delta n similar to 0.76 at 1 THz). and the low absorption coefficient (alpha similar to 0.2 cm(-1) at 1 THz) of GaSe are also identified. Potential applications to practical photonic devices such as phase shifters at THz frequencies are proposed. (C) 2009 Optical Society of America
Optical sum-frequency generation and Ferroelectric-like Switching in Si-O Polar Structures
(2009-01-01)
Shieh, Jia-Min
;
Yu, Wen-Chien
;
Huang, Jung Y.
;
Wang, Yi-Chao
;
Chen, Ching-Wei
Optical sum-frequency generation and ferroelectric-like switching in Si-O polar structures comprised of Si nanocrystals (nc-Si) in mesoporous silica was reported and attributed to polar layers lying at the interfaces between one-side bonded nc-Si and host. (C) 2009 Optical Society of America
Pulse retrieval from interferometric autocorrelation measurement by use of the population-split genetic algorithm
(2006-10-30)
Chen, Ching-Wei
;
Huang, Jung Y.
;
Pan, Ci-Ling
;
光電工程學系
;
Department of Photonics
The population-split genetic algorithm ( PSGA) was successfully applied to retrieve femtosecond optical fields from interferometric autocorrelation traces. PSGA strikes a balance between diversity and the size of population in the genetic algorithm. As a result, PSGA is less likely prematurely converging to sub-optimal solutions. Theoretical and experimental studies indicate that the PSGA can yield more accurate results in shorter time compared with conventional genetic algorithm and the iterative method. (c) 2006 Optical Society of America.
Systematic Constructions of Zero-Correlation Zone Sequences
(2009)
Chen, Ching-Wei
;
Liu, Yen-Cheng
;
Su, Yu T.
;
電信工程研究所
;
Institute of Communications Engineering
Sequences with desired autocorrelation (AC) and cross-correlation (CC) properties are often needed in many communication and radar system applications. In a multipath fading channel with a known delay spread bound, one needs a family of sequences that meets these desired correlation requirements only for those correlation lags that lie within a window called zero-correlation zone. This paper presents two classes of new systematic approaches a transform domain method and a direct (time domain) synthesis method for generating zero-correlation zone (ZCZ) sequences. The former approach generates sequence families that achieve the upper bounds on the family size and the zero-correlation zone width for a given sequence period. The latter unifies many existing construction methods and both provide more flexibilities in producing new families of sequences. We also suggest a modulation operation that is capable of transforming nonconstant modulus sequences into polyphase sequences.