Browsing by Author "P. P. Yupapin"

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    All-optical switches based-on GaAs/AlAs quantum dots vertical cavities
    (Elsevier Ltd, 2012) C. Teeka; R. Jomtarak; P. P. Yupapin; C. Teeka; Scientific Equipment Center, Faculty of Science and Technology, Suan Dusit Rajabhat University, Bangkok, 10700, Thailand; email: chat_tee@dusit.ac.th
    In this paper, we present an all-optical switch based on self-assembled GaAs/AlAs quantum dots (QDs) within a vertical cavity. Two essential aspects of this novel device have been investigated, which includes the QD/cavity nonlinearity with appropriately designed mirrors and the intersubband carrier dynamics inside QDs. Verticalreflection- type switches have been investigated with an asymmetric cavity that consists of 12 periods of GaAs/Al0.8Ga0.2As for the front mirror and 25 periods for the back mirror. The thicknesses of the GaAs and AlGaAs layers are chosen to be 89 and 102 nm, respectively. To give a dot-in-a-well (DWELL) structure, 65nm dimension of Si was deposited within an 20nm AlAs QW. All-optical switching via the QD excited states has been achieved with a time constant down to 750 fs, wavelength tunability over 29.5 nm. These results demonstrate that QDs within a vertical cavity have great advantages to realize low-power consumption polarization-insensitive micrometer-sized switching devices for the future optical communication and signal processing systems. © 2010 Published by Elsevier Ltd.
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    Geometrically distributed 1D photonic crystals for light-reflection in all angles
    (Elsevier Ltd, 2012) R. Jomtarak; C. Teeka; P. P. Yupapin; R. Jomtarak; Nanoscale Science and Engineering Research Alliance (n'Sera), Faculty of Science, King Mongkut's Institute of Technology Ladkrabang, Bangkok 10520, Thailand; email: rangsan_jom@dusit.ac.th
    In this paper, we presented the general formulation of light reflection using a series of 1D PCs with different periods, made of non-absorptive materials of any refractive indices. In order to have a large bandgap - the spectral range of reflection, the periods of 1D PCs must be distributed in a geometrical progression with a common ratio, r, smaller than a maximum value of rc. The paper have presented exact expressions for rc, bandgap to mid gap ratio of the PC hetero-structure, and the minimum number of PCs to achieve the desired range of bandgap in single and all angles of incidence. The proposed method can be used to design filters for vast range of applications such as UV filters (i.e., sunglasses, eye safety glasses, UV photography filters) and visible light filters. © 2010 Published by Elsevier Ltd.