Adjustable unidirectional beam splitters in two dimensional photonic crystals
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Adjustable unidirectional beam splitters in two dimensional photonic crystals Cheng Ren1 · Longpan Wang1 · Feng Kang2 Received: 30 April 2020 / Accepted: 12 October 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract The splitting properties are investigated in two dimensional silicon photonic crystals by adjusting the interface of the structure. Introducing elliptical air holes with optimized parameters on the heterointerface, the forward transmittance is significantly improved in a wide frequency range. Correspondingly, the unidirectional two-beam splitter is realized and the relative light intensities of each beam can be continuously adjusted by modulating the area ratio (AR) of elliptical air holes. Furthermore, the output beams can be changed into three and five beams by alternately introducing elliptical air holes on the monolayer output interface. Not only the forward light intensities of each beam can be continuously adjusted, but also the reverse can be tuned simultaneously by modulating the shape of elliptical air holes. Particularly, the light transmission behaviors along two opposite directions are significantly different. Moreover, the elliptical-shaped air holes have more structural freedoms and increase the design flexibility of the devices. The performance of the splitter is found to be very encouraging in the complex photonic integrated circuits. Keywords Beam splitter · Photonic crystal · Unidirectional transmission · Photonic integrated circuits
1 Introduction Photonic crystals (PCs) (Yablonovitch 1987; John 1987) are artificial periodic nanostructures having versatile controllable photonic band structures and great efforts have been devoted to this area of research in the past few decades. Many functional devices based on PCs, such as couplers (Koshiba 2001; Mori et al. 2007), cavities (Sekoguchi et al. 2014; Minkov et al. 2017; Kuramochi et al. 2006), filters (Qiu and Jaskorzynska 2003; Takano et al. 2006; Ren et al. 2006) and splitters (Sugimoto et al. 2002; Park et al. 2004; Yu and Fan 2003), have been proposed and are expected to play an important role in optical circuits. Among the functional devices mentioned above, a power splitter is one of the most indispensable components in * Cheng Ren [email protected] 1
School of Opto‑Electronic Information Science and Technology, Yantai University, Yantai 264005, China
2
Wenjing College, Yantai University, Yantai 264005, China
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all-optical integration and remains the research hotspot in recent years. As the typical structure of power beam splitters, PC Y-branch waveguides, having poor transmittance without structural tuning and optimization for zero reflection, are needed to connect with other waveguide structures to realize multi-channel beam splitting function (Sugimoto et al. 2002; Frandsen et al. 2004; Zhou et al. 2014). Considering the practical design for circumventing complex problems involved in Y-branch waveguides, the efficient power-spli
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