Inverse design of zig-zag shaped 1x4 optical power splitters in SOI platform

Abstract

Optical power splitter has become one of the key components in photonic integrated circuits and specifically it is widely used in many silicon photonic devices, such as an optical phased array, multiplexers, de-multiplexers, etc. In the case of a 1xN splitter, it is critical to distribute optical power equally to each port while minimizing its insertion loss. The majority of the previous research efforts dealing with the inverse design have been mainly dedicated to 1x2 power splitter and limited studies have reported results for the case of N=4. To obtain a design satisfying many criteria such as low insertion loss, high uniformity among channels, broadband, and compatible with the standard CMOS process is very challenging. For this reason, we proposed two designs of compact and longitudinally zig-zag shaped 1x4 power splitter using particle swarm optimization algorithm integrated with the finite-difference time-domain method. Different objective functions in the algorithm are tested. One splitter structure has low insertion loss (less than 0.04 dB), and the other is broadband (1.50 - 1.62 mu m). Our designs show the best performance with low insertion loss and high uniformity compared to the existing ones, while it can be fabricated with industry-standard lithography due to its unit cell length of 200 nm or more. This method might be used to inverse design optical power splitters having more channels, such as 1x8 or 1x16 towards implementing large-scale photonic integrated circuits.