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.