Browsing by Author "Chiang, Chih-Kai"

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Coupled nanowire-based hybrid plasmonic nanocavities on thin substrates
(2014-11-28)
Cheng, Pi-Ju
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Chiang, Chih-Kai
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Chung, Yi-Cheng
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Tien, Chung-Hao
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Lin, Tzy-Rong
We theoretically analyze nanowire-based hybrid plasmonic nanocavities on thin substrates at visible wavelengths. In the presence of thin suspended substrates, the hybrid plasmonic modes, formed by the coupling between a metal nanowire and a dielectric nanowire with optical gain, exhibit negligible substrate-mediated characteristics and overlap better with the gain region. Consequently, the confinement factor of the guided hybrid modes is enhanced by more than 42%. However, the presence of significant mirror loss remains the main challenge to lasing. By adding silver coatings with a sufficient thickness range on the two end facets, we show that the reflectivity is substantially enhanced to above 50%. For a coating thickness of 50 nm and cavity length of about 4 mu m, the quality factor is above 100.
High Q/V-m hybrid photonic-plasmonic crystal nanowire cavity at telecommunication wavelengths
(2015-01-01)
Chiang, Chih-Kai
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Chung, Yi-Cheng
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Cheng, Pi-Ju
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Wu, Chien-Wei
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Chang, Shu-Wei
We haw analyzed a hybrid photonic-plasmonic crystal nanocavity consisting of a silicon grating nanowire adjacent to a metal surface with a gain gap between. The hybrid plasmonic cavity modes are highly confined in the gap due to the coupling of photonic crystal cavity modes and surface plasmonic gap modes. Using the finite-element method, we numerically solve guided modes of the hybrid plasmonic waveguide at a wavelength of 1.55 jim. The modal characteristics such as wave guide confinement factors and modal losses of the fundamental hybrid plasmonic modes are explored as a function of the groove depth at various gap heights. After that, we show the band structure of the hybrid crystal modes, corresponding to a wide band gap of 17.8 THz. To effectively trap the optical modes, we introduce a single defect into the hybrid crystal. At a deep sub-wavelength defect length as small as 180 nm, the resonant mode exhibits a high quality factor of 566.5 and an ultrasmall mode volume of 0.00186 (ln)3 at the resonance wavelength of 1.55 gm. In comparison to the conventional photonic crystal nanowire cavity in the absence of metal surface, the figure of merit QIVm is enormously enhanced around 15 times. The proposed nanocavities open up the opportunities for various applications with strong light-matter interaction such as nanolasers and bio sensors.
Realization of UV Plasmonic Nanolasers With Extremely Small Mode Volume
(2015-11-01)
Chou, Bo-Tsun
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Chou, Yu-Hsun
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Chiang, Chih-Kai
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Wu, Yen-Mo
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Lin, Tzy-Rong
It is difficult to operate plasmonic nanolasers on silver films in the ultraviolet regime owing to the bending-back effect of surface plasmon dispersion. In this paper, we report on plasmonic lasers comprised of a ZnO nanowire lying on a single-crystalline silver film with a SiO2 spacer layer. The silver can strongly shrink the mode volume, thereby boosting the Purcell factor. Meanwhile, the SiO2 spacer thickness is optimized to adjust the surface plasmon dispersion curve so that the lasing wavelength can be located at a large dispersion region, thereby achieving a large group index of 55, an ultra-small effective mode volume of 3.5 x 10(-3)lambda(3), and low-threshold of 11 MW/cm(2).
Ultrastrong Mode Confinement in ZnO Surface Plasmon Nanolasers
(2015-04-01)
Chou, Yu-Hsun
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Chou, Bo-Tsun
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Chiang, Chih-Kai
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Lai, Ying-Yu
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Yang, Chun-Ting
Nano lasers with an ultracompact footprint can provide high-intensity coherent light, which can be potentially applied to high-capacity signal processing, biosensing, and subwavelength imaging. Among various nanolasers, those with cavities surrounded by metals have been shown to have superior light emission properties because of the surface plasmon effect that provides enhanced field confinement capability and enables exotic light matter interaction. In this study, we demonstrated a robust ultraviolet ZnO nanolaser that can operate at room temperature by using silver to dramatically shrink the mode volume. The nanolaser shows several distinct features including an extremely small mode volume, a large Purcell factor, and a slow group velocity, which ensures strong interaction with the exciton in the nanowire.
Ultraviolet Lasing in a ZnO Plasmonic Nanolaser
(2014)
Chou, Yu-Hsun
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Chou, Bo-Tsun
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Lai, Ying-Yu
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Yang, Chun-Ting
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Chiang, Chih-Kai
We report on the demonstration of a sub-diffraction-limited plasmonic laser at UV region by using the ZnO nanowire based on the semiconductor-insulator-metal (SIM) structure. At 77K, the laser with a threshold power of about 76MW/cm(2) and the wavelength of 373 nm with an extremely small mode area below lambda(2)/1000 was realized.