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

Mode Division Multiplexing (MDM) technology stands as a cornerstone for enhancing transmission capacity in fiber-optic communication systems. However, in few-mode fibers, the group velocity differences between modes can induce differential mode group delays (DMGD), which increases the complexity of Multiple-Input Multiple-Output Digital Signal Processing (MIMO-DSP) and consequently limits system performance. Conventional fiber compensation methods struggle to achieve high integration. To address this, researchers have developed a photonic chip-based DMGD control device (Fig. 1) in this study.

Researchers designed a DMGD-controlled multilayer waveguide by incorporating a low refractive index difference material as an inner cladding between the core and cladding. Characteristic measurements of the multilayer waveguide revealed precise DMGD control functionality at approximately 10 ps/m (1550 nm). Through dimensional adjustments of the waveguide's core and inner cladding, researchers achieved precise control over the DMGD characteristics.

The device was fabricated using polymer materials through micro/nano processing technology. The fabricated devices were recorded during the preparation process, and near-field patterns and transmission spectra were obtained through an optical testing platform. Experimental measurements of the device's critical wavelength λ₁ showed good agreement with simulation results, demonstrating polarization insensitivity.

This study proposes a 3D waveguide-based on-chip DMGD control scheme, achieving delay regulation from 10 ps/m to ns/m through low/high refractive index difference materials. The introduction of high refractive index materials further enhances the device's integration density and dynamic control capabilities, providing crucial technical support for future on-chip integration of MDM systems.