Ultra-compact multimode waveguide bend with shallowly etched grooves.

Area of Science:

• Photonics and Optical Engineering
• Integrated Optics
• Waveguide Technology

Background:

• Multimode waveguide bends (MWBs) are essential components in integrated photonic circuits.
• Achieving compact, low-loss, and low-crosstalk MWBs, especially for multiple modes, remains a significant challenge.
• Existing designs often struggle with trade-offs between bending radius and optical performance.

Purpose of the Study:

• To propose and demonstrate a novel ultra-sharp multimode waveguide bend (SMWB).
• To achieve simultaneous low excess loss and low inter-mode crosstalk for the lowest-order TE modes.
• To provide a compact and efficient solution for multimode silicon photonics applications.

Main Methods:

• Design and simulation of an MWB utilizing gradient shallowly etched grooves.
• Fabrication of the proposed shallowly-etched-groove multimode waveguide bend (SMWB).
• Experimental characterization of the fabricated SMWB for optical performance evaluation.

Main Results:

• Simulated excess losses for TE0-TE3 modes below 0.46 dB over 1500-1600 nm for a 90° bend.
• Simulated inter-mode crosstalk below -18 dB for TE0-TE3 modes within the 1500-1600 nm range.
• Measured excess losses below 1 dB and inter-mode crosstalk below -14 dB for TE0-TE3 modes from 1510-1580 nm.

Conclusions:

• The gradient shallowly etched groove design enables ultra-compact MWBs with a bending radius of 5.6 μm.
• The demonstrated SMWB effectively supports low-loss and low-crosstalk propagation for the four lowest-order TE modes.
• This technology presents a promising advancement for miniaturized multimode photonic integrated circuits.