Y-junction beamsplitter engineered through subwavelength metamaterials

Abstract

Efficient power splitting is a fundamental function in silicon photonics integrated circuits and, consequently, compact power splitters with low losses over a broad bandwidth are sought after. Symmetric Y-junctions, consisting of a stem waveguide branching into two diverging arms, are typically used. However, the finite resolution of current photonic fabrication technologies results in a limited minimum feature size (MFS) of the tip between the splitter arms, penalizing fundamental transverse electric mode (TE0) since its intensity maximum coincides with the central region of the splitter. In this work, we propose a novel high-performance power splitter based on a symmetric Y-junction incorporating subwavelength metamaterials. Our device performance was simulated using 3D finite-difference time-domain method, considering two different fabrication resolution limits. In the worst-case resolution scenario (i.e., MFS of 100 nm), the device shows excess loss (EL) as low as 0.5 dB for both the TE0 mode and the first-order transverse electric mode (TE1) in a 300 nm bandwidth (1300 nm - 1600 nm). For the high-resolution fabrication process (i.e., MFS of 50 nm), total EL is further reduced under 0.3 dB over a bandwidth of 250 nm (1350 nm - 1600 nm). A proof-of-concept device was fabricated with electron beam lithography using SOI wafers with a 220-nm-thick Si layer and a SiO2 upper cladding. Preliminary experimental results show negligible losses for the TE0 mode over a broad bandwidth of 180 nm (i.e., 1500 nm - 1680 nm), for both fabrication scenarios (100 nm and 50 nm MFS).