Ultra-Compact Multi-Mode Converter for Optical Delay Line Application

Optical delay lines (ODL) are one of the key components in integrated photonic circuits and systems. We propose a novel optical delay line structure based on multimode conversion. The silicon multi-mode converter is optimized via an inverse design method to simultaneously convert the $\mathbf{TEi}$ modes to $\mathbf{TE}_{\mathrm{i}}+1$ modes $(\mathbf{i}=1,2$, and 3) at the wavelength of 1550 nm. It only occupies an area of 4 $\mu \mathbf{m}\times 3 \mu\mathbf{m}$. Simulation results show that the insertion loss of the mode-order converter is less than 1.6 dB and the crosstalk is lower than −22 dB for all three modes.