News Release

Complete photonic bandgap comes to silicon nitride slabs

Peer-Reviewed Publication

Higher Education Press

Complete photonic bandgap comes to silicon nitride slabs

image: Dual polarization silicon nitride microcavity view more 

Credit: Can Ma, Jin Hou, Chunyong Yang, Ming Shi, Shaoping Chen;

Silicon nitride (SixNy) is a very promising platform for CMOS-compatible integrated photonics, owing to significantly lower nonlinear losses, a broader transparency range, and a much smaller thermo-optic coefficient. To better enhancement nonlinearity, naturally, photonic bandgap (PBG) that could confine light within a small mode volume is frequently introduced into SixNy slabs. However, almost all the PBG in SixNy slabs demonstrated currently only could work for one single-polarization state. In such situation, the asymmetry of the structure or imperfect fabrication would cause polarization mode conversion loss, which will reduce the efficiency of nonlinearity. If complete photonic bandgap (CPBG) could be applied in SixNy slabs, such leaky loss would be restricted, and the nonlinear efficiency could be furtherly enhanced. Moreover, demonstration of CPBG in SixNy slab, also means the ability of polarization multiplexing, polarization management could be benefit from the unique features of CPBG. So CPBG in SixNy slabs is attractive.

Recently, in a photonic crystal (PC) slab with the SixNy refractive index of 2.5, a research group led by Prof. Jin Hou at South-Central MinZu University, achieved the largest normalized CPBG of 5.62%. Previous investigations show that, in two dimensional PCs, TM PBG could be obtained with a lower refractive index contrast than the TE PBG. Meanwhile, in a sandwiched slab structure like SixNy on silica, the slab effective index for TM polarization is also usually lower than that for TE polarization. So the group thinks that, making use of the slab effective index difference between the polarizations, it should be possible to achieve CPBGs in a SixNy slab with lower refractive index. And also, there would be a suitable effective index pair of TE and TM polarizations, with which the coincident frequency range in the TE PBGs and TM PBGs for the same structure parameters could be easily engineered. Through adjusting the effective index pair by changing the thickness of the SixNy core layer or changing the center wavelength, and also optimizing the structure parameters within the PC plane, the largest CPBG of 5.62% was theoretically obtained in their investigation. Moreover, using the same principle, the lowest refractive index of SixNy for a CPBG could be extended to as low as 2. The value, to the best of our knowledge, is also the lowest record refractive index for a PC slab that could support CPBG. Breakthrough of CPBG in SixNy slabs not only enhances nonlinearity, but also indicates that development of various high-performance CPBG devices in SixNy slab would be possible. The work entitled “Complete photonic bandgap in silicon nitride slab assisted by effective index difference between polarizations” was published on Frontiers of Optoelectronics (May 6 2022).


Reference: Can Ma, Jin Hou, Chunyong Yang, Ming Shi, Shaoping Chen. Complete photonic bandgap in silicon nitride slab assisted by effective index difference between polarizations. Front. Optoelectron. 15, 20 (2022).


About Higher Education Press

Founded in May 1954, Higher Education Press Limited Company (HEP), affiliated with the Ministry of Education, is one of the earliest institutions committed to educational publishing after the establishment of P. R. China in 1949. After striving for six decades, HEP has developed into a major comprehensive publisher, with products in various forms and at different levels. Both for import and export, HEP has been striving to fill in the gap of domestic and foreign markets and meet the demand of global customers by collaborating with more than 200 partners throughout the world and selling products and services in 32 languages globally. Now, HEP ranks among China's top publishers in terms of copyright export volume and the world's top 50 largest publishing enterprises in terms of comprehensive strength.

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About Frontiers of Optoelectronics

Frontiers of Optoelectronics (FOE) aims at introducing the most recent research results and the cutting edge improvements in the area of photonics and optoelectronics. It is dedicated to be an important information platform for rapid communication and exchange between researchers in the related areas. The journal publishes review articles, research articles, letters, comments, special issues, and so on. The Editors-in-Chief are Academician Qihuang Gong from Peking University and Prof. Xinliang Zhang from Huazhong University of Science and Technology. FOE has been indexed by ESCI, Ei, SCOPUS, CSCD, Source Journals for Chinese Scientific and Technical Papers and Citations, etc. FOE is fully open access since 2022.

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