Browsing by Author "Chung, Yi-Cheng"

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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.
High-operation-temperature Aluminum-based SPP Nanolasers
(2016)
Chou, Yu-Hsun
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Hong, Kuo-Bin
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Chou, Bo-Tsun
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Wu, Yen-Mo
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Shih, Jheng-Hong
Metal-insulator-semiconductor structures has widely adopted in plasmonics lasers. However, we found that the insulator is not necessary if permittivity combination of laser structures is properly designed. Single-mode laser operation was demonstrate in devices without artificial insulator layers. Moreover, the operation temperature can achieve to 353 K.
High-Operation-Temperature Plasmonic Nanolasers on Single-Crystalline Aluminum
(2016-05)
Chou, Yu-Hsun
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Wu, Yen-Mo
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Hong, Kuo-Bin
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Chou, Bo-Tsun
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Shih, Jheng-Hong
The recent development of plasmonics has overcome the optical diffraction limit and fostered the development of several important components including nanolasers, low-operation-power modulators, and high-speed detectors. In particular, the advent of surface-plasmon-polariton (SPP) nanolasers has enabled the development of coherent emitters approaching the nanoscale. SPP nanolasers widely adopted metal insulator semiconductor structures because the presence of an insulator can prevent large metal loss. However, the insulator is not necessary if permittivity combination of laser structures is properly designed. Here, we experimentally demonstrate a SPP nanolaser with a ZnO nanowire on the as-grown single-crystalline aluminum. The average lasing threshold of this simple structure is 20 MW/cm(2), which is four-times lower than that of structures with additional insulator layers. Furthermore, single-mode laser operation can be sustained at temperatures up to 353 K. Our study represents a major step toward the practical realization of SPP nanolasers.
Metal for Plasmonic Ultraviolet Laser: Al or Ag?
(2017-11-01)
Chou, Yu-Hsun
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Hong, Kuo-Bin
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Chung, Yi-Cheng
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Chang, Chun-Tse
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Chou, Bo-Tsun
Surface plasmon polariton (SPP) nanolasers have recently emerged as promising candidates for generating a coherent light source in nanophotonic integration circuits. The properties of SPP nanolasers, such as group velocity, mode area, modulation speed, and threshold performance, can be manipulated using a dispersion relation. In this study, we investigated the characteristics of SPP nanolasers operated near and far from the SP frequency. Our results indicated that SPP nanolaser performance can be significantly influenced by manipulating the dispersion relation.
Single-crystalline aluminum film for ultraviolet plasmonic nanolasers
(2016-01-27)
Chou, Bo-Tsun
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Chou, Yu-Hsun
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Wu, Yen-Mo
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Chung, Yi-Cheng
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Hsueh, Wei-Jen
Significant advances have been made in the development of plasmonic devices in the past decade. Plasmonic nanolasers, which display interesting properties, have come to play an important role in biomedicine, chemical sensors, information technology, and optical integrated circuits. However, nanoscale plasmonic devices, particularly those operating in the ultraviolet regime, are extremely sensitive to the metal and interface quality. Thus, these factors have a significant bearing on the development of ultraviolet plasmonic devices. Here, by addressing these material-related issues, we demonstrate a low-threshold, high-characteristic-temperature metal-oxide-semiconductor ZnO nanolaser that operates at room temperature. The template for the ZnO nanowires consists of a flat single-crystalline Al film grown by molecular beam epitaxy and an ultrasmooth Al2O3 spacer layer synthesized by atomic layer deposition. By effectively reducing the surface plasmon scattering and metal intrinsic absorption losses, the high-quality metal film and the sharp interfaces formed between the layers boost the device performance. This work should pave the way for the use of ultraviolet plasmonic nanolasers and related devices in a wider range of applications.
Study of Plasmonic Nanolasers with Graphene-Metal Interaction
(2019-01-01)
Chung, Yi-Cheng
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Li, Heng
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Lu, Tien-Chang
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Chen, Kuo-Ping
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Lin, Tzy-Rong
The charge transfer effect of the graphene-oxide-metal interface on the performance of plasmonic nanolasers was investigated. The results show that the variation of electron densities of metals can influence the characteristics of surface-plasmon-polariton modes and lead to a significant improvement in the performance of plasmonic nanolasers.
Surface roughness effects on aluminium-based ultraviolet plasmonic nanolasers
(2017-01-03)
Chung, Yi-Cheng
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Cheng, Pi-Ju
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Chou, Yu-Hsun
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Chou, Bo-Tsun
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Hong, Kuo-Bin
We systematically investigate the effects of surface roughness on the characteristics of ultraviolet zinc oxide plasmonic nanolasers fabricated on aluminium films with two different degrees of surface roughness. We demonstrate that the effective dielectric functions of aluminium interfaces with distinct roughness can be analysed from reflectivity measurements. By considering the scattering losses, including Rayleigh scattering, electron scattering, and grain boundary scattering, we adopt the modified Drude-Lorentz model to describe the scattering effect caused by surface roughness and obtain the effective dielectric functions of different Al samples. The sample with higher surface roughness induces more electron scattering and light scattering for SPP modes, leading to a higher threshold gain for the plasmonic nanolaser. By considering the pumping efficiency, our theoretical analysis shows that diminishing the detrimental optical losses caused by the roughness of the metallic interface could effectively lower (-33.1%) the pumping threshold of the plasmonic nanolasers, which is consistent with the experimental results.
Tuning the Characteristics of Surface Plasmon Polariton Nanolasers by Tailoring the Dispersion Relation
(2017-01-01)
Lu, Tien-Chang
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Chou, Yu-Hsun
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Hong, Kuo-Bin
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Chung, Yi-Cheng
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Lin, Tzy-Rong
Nanolasers with ultra-compact footprint are able to provide high intensity coherent light, which have various potential applications in high capacity signal processing, biosensing, and sub-wavelength imaging. Among various nanolasers, those lasers with cavities surrounded with metals have shown to have superior light emission properties due to the surface plasmon effect providing better field confinement capability and allowing exotic light-matter interaction. In this talk, we report robust ultraviolet ZnO nanolaser by using silver (Ag) [1] and aluminum (Al) [2] to strongly shrink the mode volume. The nanolasers operated at room temperature and even high temperature (353K) shows several distinct features including an extremely small mode volume, large Purcell factor and group index. Comparison of characteristics between Ag-and Al-based will also be made.