Unitary transformation of general nonoverlapping-image multimode interference couplers with any input and output ports  

作　　者：Ze-Zheng Li Wei-Hua Han Zhi-Yong Li 李泽正;韩伟华;李智勇(College of Materials Science and Opto-Electronic Technology,University of Chinese Academy of Sciences,Chinese Academy of Sciences,Beijing 100049,China;State Key Laboratory on Integrated Optoelectronics,Institute of Semiconductors,Chinese Academy of Sciences,Beijing 100083,China)

机构地区：[1]College of Materials Science and Opto-Electronic Technology,University of Chinese Academy of Sciences,Chinese Academy of Sciences,Beijing 100049,China [2]State Key Laboratory on Integrated Optoelectronics,Institute of Semiconductors,Chinese Academy of Sciences,Beijing 100083,China

出　　处：《Chinese Physics B》2020年第1期287-292,共6页中国物理B（英文版）

基　　金：Project supported by the National Key Research and Development Program of China(Grant No.2018YFB2200202);the National Natural Science Foundation of China(Grant No.61804148)

摘　　要：An explanation of optical unitary transformation is presented for general nonoverlapping-image multimode interference(MMI)couplers with any number of input and output ports.The light transformation in the MMI coupler can be considered as an optical field matrix acting on an input light column vector.We investigate the general phase principle of output light image.The complete proof of nonoverlapping-image MMI coupler’s optical unitarity along with the phase analysis of matrix element is provided.Based on a two-dimensional finite-difference time-domain(2 D-FDTD)simulation,the unitary transformation is obtained for a 4×4 nonoverlapping-image MMI coupler within a deviation of 4×10-2 for orthogonal invariance and 8×10-2 for transvection invariance in the C-band spectral range.A compact 1×4 splitter based on cascaded MMI coupler is proposed,showing a phase deviation less than 5.4°while maintaining a low-loss performance in C-band spectra.An explanation of optical unitary transformation is presented for general nonoverlapping-image multimode interference（MMI） couplers with any number of input and output ports. The light transformation in the MMI coupler can be considered as an optical field matrix acting on an input light column vector. We investigate the general phase principle of output light image. The complete proof of nonoverlapping-image MMI coupler’s optical unitarity along with the phase analysis of matrix element is provided. Based on a two-dimensional finite-difference time-domain（2 D-FDTD） simulation,the unitary transformation is obtained for a 4× 4 nonoverlapping-image MMI coupler within a deviation of 4× 10-2 for orthogonal invariance and 8× 10-2 for transvection invariance in the C-band spectral range. A compact 1 × 4 splitter based on cascaded MMI coupler is proposed, showing a phase deviation less than 5.4° while maintaining a low-loss performance in C-band spectra.

关 键 词：multimode interference coupler optical unitary transformation integrated photonics 

分 类 号：TN622[电子电信—电路与系统]