Browsing by Author "Lin, Yuan-Yao"

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Chirped-pulse manipulated carrier dynamics in low-temperature molecular-beam-epitaxy grown GaAs
(2014-04-28)
Lee, Chao-Kuei
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Lin, Yuan-Yao
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Lin, Sung-Hui
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Lin, Gong-Ru
;
Pan, Ci-Ling
Chirped pulse controlled carrier dynamics in low-temperature molecular-beam-epitaxy grown GaAs are investigated by degenerate pump-probe technique. Varying the chirped condition of excited pulse from negative to positive increases the carrier relaxation time so as to modify the dispersion and reshape current pulse in time domain. The spectral dependence of carrier dynamics is analytically derived and explained by Shockley-Read Hall model. This observation enables the new feasibility of controlling carrier dynamics in ultrafast optical devices via the chirped pulse excitations. (C) 2014 AIP Publishing LLC.
Efficient wavelength conversion with low operation power in a Ta2O5-based micro-ring resonator
(2017-12-01)
Wu, Chung-Lun
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Huang, Jen-Yang
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Ou, Ding-Hsin
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Liao, Ting-Wei
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Chiu, Yi-Jen
The Ta2O5-based micro-ring resonator with an unloaded quality factor of 182,000 has been demonstrated to realize efficient nonlinear wavelength generation. The propagation loss of the resonator is 0.5 cm(-1), and the buildup factor of the ring resonator is estimated to be similar to 50. With a high buildup factor of the ring structure, the four-wave-mixing (FWM) conversion efficiency of -30 dB is achieved in the resonator with a pump power of 6 mW. Based on power-dependent FWM results, the nonlinear refractive index of Ta2O5 is estimated to be 1.4x10-14 cm(2)/W at a wavelength of similar to 1550 nm. The demonstration of an enhanced FWM process in the Ta(2)O(5-)based micro-ring cavity implies the possibility of realizing FWM-based optical parametric oscillation in a Ta2O5-based micro-ring resonator. (C) 2017 Optical Society of America
Pre-Chirped Pulse Excitation Enhanced Terahertz Radiation
(2016-03)
Lee, Chao-Kuei
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Lin, Yuan-Yao
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Lin, Gong-Ru
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Wu, Chung-Lun
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Wu, Tsung-Han
The enhanced broadband THz radiation excited by pre-chirping the femtosecond pumping laser pulse is explored from a photoconductive antenna made by the low-temperature molecular-beam-epitaxy (LT-MBE) grown Gallium Arsenide (GaAs). Nearly 3-dB enlargement on peak amplitude of THz radiation accompanied with broadened bandwidth is achieved with positively chirped pulse excitation. The laser with short pulsewidth assists the broadening of THz bandwidth, whereas the peak intensity of THz relies strictly on lengthened carrier lifetime. The enhancement of high-frequency radiation components at low pumping intensity also indicates the nature of power dependence in such a coherently controlled process. When photocurrent saturation occurs in the LT-MBE-grown GaAs under high-power pumping condition, the clipping effect on peak amplitude of current pulse lengthens the duration of current surge effect. Both the peak intensity and the frequency spectrum of the generated THz pulse concurrently declines. The physical mechanism related to pre-chirped pulse excitation dependent carrier dynamics is proposed to elucidate the spectral response as well as the power dependence in such a coherently controlled THz radiation process.
Tens of GHz Tantalum pentoxide-based micro-ring all-optical modulator for Si photonics
(2017-03-01)
Wu, Chung-Lun
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Hsieh, Cheng-Hsuan
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Lin, Gong-Ru
;
Chi, Wen-Chun
;
Chiu, Yi-Jen
A tantalum pentoxide-based (Ta2O5-based) micro-ring alloptical modulator was fabricated. The refractive index inside the micro-ring cavity was modified using the Kerr effect by injecting a pumped pulse. The transmittance of the ring resonator was controlled to achieve all-optical modulation at the wavelength of the injected probe. When 12 GHz pulses with a peak power of 1.2 W were coupled in the ring cavity, the transmission spectrum of the Ta2O5 resonator was redshifted by 0.04 nm because of the Kerr effect. The relationship between the modulation depth and gap of the Ta2O5 directional coupler is discussed. An optimized gap of 1100 nm was obtained, and a maximum buildup factor of 11.7 with 84% modulation depth was achieved. The nonlinear refractive index of Ta2O5 at 1.55 mu m was estimated as 3.4 x 10(-14) cm(2)/W based on the Kerr effect, which is almost an order of magnitude higher than that of Si3N4. All results indicate that Ta2O5 has potential for use in nonlinear waveguide applications with modulation speeds as high as tens of GHz.