On-chip differential mode group delay manipulation based on 3D waveguides

Mode-division multiplexing based on few-mode optical fiber is a promising technology to increase the transmission capacity of optical communication systems, where multi-input multi-output (MIMO) digital signal processing (DSP) is employed to (de)multiplex the signals from different mode channels. Since the group velocity of each mode is different, the signals are separated in the time domain when they reach the receivers. Therefore, it is necessary to compensate for the mode-group-velocity delay of the interval modes to reduce the complexity of the MIMO-DSP algorithm. In this work, we demonstrated an on-chip differential-mode group delay (DMGD) manipulating device based on 3D multilayer cladding waveguides. The proposed device supports compensating the DMGD of about 10.0 ps/m with a device formed with a low refractive index difference. In the meanwhile, the value of DMGD can be greatly improved to be 1878.6 ps/m by forming the device with high refractive index difference material such as thin-film lithium niobate with silicon dioxide cladding. The proposed device provides a feasible design for on-chip DMGD manipulation, which can find various applications in the mode division multiplexing system.