Ultra-broadband MMI power splitter from 1.26 to 1.67 μm with photonic bound states in the continuum

Abstract

Photonic bound states in the continuum (BIC) have excellent effects in localizing light fields. Low propagation loss of TM mode has been achieved in different orders of BICs on an etchless lithium niobate (LiNbO3) platform. Herein, we simulatively demonstrate a 1 × 2 MMI (Multimode interference) power splitter based on waveguides constructed by low-refractive-index structure (ZEP-520A) on a high-refractive-index thin membrane (LiNbO3), which can optimize the bandwidth, insertion loss and other performance indicators of optical devices. Simulation results show that the working wavelength cover the entire communication band ranging from 1260 nm to 1675 nm, and the transmission efficiency is more than 48.7%, while the insertion loss is less than 0.01 dB covering a 415 nm bandwidth. The field distribution results verify that the designed MMI demonstrated high mode purity at the output, and the mode field is well localized in the LiNbO3 film, leading to a reduce of the dependence of the transmission efficiency originated from the quality of the sidewall of the device, and the device can evenly distribute the TM0 mode of the ultra-broadband incident light to the two output ports. Furthermore, the fabrication process of the MMI device can be immensely simplified by a one-step exposure method, which reduces the scattering loss and asymmetry caused by the fabrication.