Low-Loss Broadband Silicon-on-Insulator Demultiplexers in the $O$ -Band

A low-loss 1 × 4 channel silicon-on-insulator (SOI) wavelength demultiplexer with a 3.2-nm channel spacing at O-band (1260-1360 nm) is demonstrated. The demultiplexer is based on cascaded asymmetric Mach-Zehnder interferometers with adiabatic splitters on a 340-nm-thick SOI platform. In this letter, we introduce adiabatic splitters here to replace the traditional 2 × 2 directional couplers in the optical filters. The adiabatic splitters can achieve a splitting ratio of ~50%:50% over a broadband. The demonstrated wavelength demultiplexer shows an excess loss of ~2 dB, and a crosstalk less than -25 dB at a large wavelength range of ~100 nm.