http://hdl.handle.net/10397/266 Search the Channel search http://repository.lib.polyu.edu.hk/jspui/simple-search http://hdl.handle.net/10397/5655 Title: Study of optical Tamm states based on the phase properties of one-dimensional photonic crystals<br/><br/>Authors: Chen, Zefeng; Han, Peng; Leung, C. W.; Wang, Yu; Hu, Mingzhe; Chen, Yihang<br/><br/>Abstract: We demonstrate the physical mechanism of optical Tamm states using the phase properties of the photonic crystals. Based on such mechanism, we propose an efficient way that can precisely produce optical Tamm states at specific frequencies. Moreover, we show that dielectric photonic crystals and single-negative materials can be effectively connected through their reflection phase. Two kinds of one-dimensional dielectric photonic crystals with different single-negative characteristics are designed and repeated alternately to construct a superlattice structure. The band structures and the transmission spectra of this superlattice show that multiple optical Tamm states arise and these Tamm states are coupled with each other to form transmission bands. A special zero-effective-phase gap can also be observed in such superlattice.<br/><br/>Description: DOI: 10.1364/OE.20.021618 http://hdl.handle.net/10397/5654 Title: Superbroadband near-infrared emission and energy transfer in Pr³⁺-Er³⁺ codoped fluorotellurite glasses<br/><br/>Authors: Zhou, Bo; Tao, Lili; Tsang, Yuen Hong; Jin, Wei; Pun, Edwin Yue-Bun<br/><br/>Abstract: We report the first demonstration of superbroadband emission extending from 1.30 to 1.68 μm in praseodymium(Pr³⁺)-erbium(Er³⁺) codoped fluorotellurite glasses under 488 nm excitation. This superbroad near-infrared emission is contributed by the Pr³⁺: ¹D₂→ ¹G₄ and Er³⁺: ⁴I ₁₃ ̷ ₂→ ⁴I ₁₅ ̷ ₂ transitions which lead to emissions located at 1.48 and 1.53 μm, respectively. The quenching of the Pr³⁺ emission resulted from the cross relaxation [ ¹D₂, ³H₄]→[ ¹G₄, ³F₃,₄] was effectively compensated by the codoping of Er³⁺. The results suggest that, other than the heavy-metal and transition-metal elements of active bismuth (Bi), nickel (Ni), chromium (Cr), etc., Pr³⁺-Er³⁺ codoped system is a promising alternative for the broadband near-infrared emission covering the expanded low-loss window.<br/><br/>Description: DOI: 10.1364/OE.20.012205 http://hdl.handle.net/10397/5653 Title: Superbroadband near-IR photoluminescence from Pr³⁺-doped fluorotellurite glasses<br/><br/>Authors: Zhou, Bo; Tao, Lili; Tsang, Yuen Hong; Jin, Wei; Pun, Edwin Yue-Bun<br/><br/>Abstract: Praseodymium(Pr³⁺)-doped fluorotellurite glasses were synthesized and broadband photoluminescence (PL) covering a wavelength range from 1.30 to 1.67 μm was observed under both 488 and 590 nm wavelength excitations. The broadband PL emission is mainly due to the radiative transition from the manifolds Pr³⁺: ¹D₂to ¹G₄. The PL line-shape, band width, and lifetime were modified by the Pr³⁺ dopant concentration, and a quantum efficiency as high as 73.7% was achieved with Pr³⁺ dopant in a low concentration of 0.05 mol%. The good spectroscopic properties were also predicted by the Judd-Ofelt analysis, which indicates a stronger asymmetry and covalent bonding between the Pr³⁺ sites and the matrix lifgand field. The large stimulated emission cross-section, long measured lifetime, and broad emission bandwidth confirm the potential of the Pr³⁺- singly doped fluorotellurite glass as broadband luminescence sources for the broadband near-infrared optical amplifications and tunable lasers.<br/><br/>Description: DOI: 10.1364/OE.20.003803 http://hdl.handle.net/10397/5652 Title: Time-variant 1D photonic crystals using flowing microdroplets<br/><br/>Authors: Chen, Zefeng; Yong, Zehui; Leung, C. W.; Zhang, Xuming; Chen, Yihang; Chan, Helen L. W.; Wang, Yu<br/><br/>Abstract: In this paper we propose a time-variant photonic crystal, which can be formed by a stream of wave-length-scale microdroplets flowing through a microfluidic channel. The functionality stems from the photonic bandgap generated from the 1D periodic perturbation of refractive index. The periodicity, volume fraction and composition of both the dispersed and the continuous phases can be conveniently tuned in real time by hydrodynamic or pneumatic methods. By simulation, it is found that the timevariant nature of the proposed structure can induce an abnormal energy evolution, which is distinct from any existing photonic crystal structures. As a basic component for optofluidic systems, the droplet-based photonic crystal may find potential applications in light modulation and light confinement, and could be an ideal model for pursuing physical insights into time-variant optofluidic systems.<br/><br/>Description: DOI: 10.1364/OE.20.024330