Broadband dual-mode 2  ×  2 3  dB multimode interference couplers with a shallowly etched multimode section.

Area of Science:

• Photonics and Optical Engineering
• Integrated Optics
• Semiconductor Devices

Background:

• Multimode interference (MMI) couplers are essential components in photonic integrated circuits.
• Achieving broadband operation and low loss in MMI-based power splitters, especially for higher-order modes, remains a challenge.

Purpose of the Study:

• To propose and simulate a novel broadband dual-mode 2x3dB power splitter on silicon.
• To enhance MMI coupler performance by reducing phase errors for higher-order modes.

Main Methods:

• Utilizing multimode interference (MMI) couplers with a shallowly etched multimode region.
• Optimally engineering the refractive-index profile to minimize phase errors for excited higher-order modes.
• Simulating device performance for TE0 and TE1 input modes across the C-band.

Main Results:

• The proposed MMI coupler demonstrates broadband operation for TE0 and TE1 modes over the C-band.
• For TE0 mode: <0.4 dB excess loss (EL) and <0.12 dB imbalance (IB) from 1.5-1.6 µm.
• For TE1 mode: <0.5 dB EL and <0.2 dB IB from 1.53-1.58 µm; intermode crosstalk < -22 dB from 1.5-1.6 µm.

Conclusions:

• The shallowly etched MMI coupler effectively reduces phase errors, enabling high-performance dual-mode power splitting on silicon.
• The design shows excellent broadband performance with low loss and imbalance for both TE0 and TE1 modes.
• The proposed MMI coupler design can be extended for applications requiring more than two input modes.