Inverse design of asymmetric Y-junctions for ultra-compact, broadband, and low crosstalk mode (de)multiplexers

• Published in: Optics express 2023-10, Vol.31 (22), p.37284-37301
• Main Authors: Wang, Qi, Wang, Wenkang, Sun, Ronglei, Yu, Ping, Qiu, Huiye, Cheng, Rui
• Format: Article
• Language: English
• ISSN: 1094-4087; 1094-4087
• DOI: 10.1364/OE.502168

Asymmetric Y-junctions, compared with mode coupling-based devices, possess considerably smaller wavelength dependence and thus are more promising for ultra-broadband mode (de)multiplexing in integrated optics. However, these devices also feature relatively high mode crosstalk and insertion loss. Here, we show that the mode crosstalk and loss of an asymmetric Y-junction can be significantly reduced by optimizing the waveguide shape of the Y-junction using an adjoint-based inverse design. Based on such inverse-designed asymmetric Y-junctions, we realize ultra-compact, broadband, and low crosstalk silicon photonic TE0 0 & TE 1 and TE 0 & TE 2 mode (de)multiplexers with sizes of only 4.5 × 1.2 µm 2 and 6 × 1.4 µm 2 , respectively. From simulations it is shown that the TE 0 & TE 1 and TE 0 & TE 2 mode (de)multiplexers contain wide bandwidths of 160 nm (1460-1620 nm) and 140 nm (1460-1600 nm), respectively, over which the mode crosstalks are below about −20 dB, and the losses are