Short, broadband, and polarization-insensitive adiabatic Y-junction power splitters

Adiabatic Y-junction power splitters have low loss, large bandwidth, high polarization insensitivity, and high tolerance to fabrication errors. However, the adiabatic transition lengths required are generally much longer than other power splitters. Using a nonlinear taper profile can considerably shorten the device length. Here, we introduce a taper profile optimization algorithm based on polynomial functions, which significantly reduces the lengths of the adiabatic power splitters without increasing losses. We experimentally demonstrate the performance of the adiabatic power splitters for minimum feature sizes of 80 nm, 120 nm, and 160 nm on the 220 nm silicon-on-insulator (SOI) platform. Our best device has a minimum feature size of 120 nm and a length of 14 µm, with measured losses of 0.25 dB and 0.23 dB for the transverse electric (TE) and transverse magnetic (TM) modes, respectively, in the 1500-1600 nm region. This device has an average transmission of -3 ± 0.5 dB in the 1500-1600 nm region, indicating highly balanced splitting over a large spectral range.