Two-port multimode interference reflectors based on aluminium mirrors in a thick SOI platform

Area of Science:

• Photonics
• Integrated Optics
• Materials Science

Background:

• Multimode interference reflectors (MIRs) are novel photonic integrated devices for on-chip broadband light reflection.
• Previous MIR designs utilized total internal reflection mirrors, limiting field pattern shapes and MIR types.

Purpose of the Study:

• To propose and demonstrate aluminium-based mirrors for designing 2-port MIRs with variable reflectivity.
• To overcome the design limitations imposed by total internal reflection mirrors.

Main Methods:

• Fabrication of devices with varying reflectivities (0-0.5) on a 3 µm thick silicon-on-insulator (SOI) platform.
• Experimental characterization of multiple dies to gather statistical performance data.
• Development of a theoretical model using the effective index method and Fresnel equations for multilayer thin films.

Main Results:

• Aluminium-based mirrors provide greater design flexibility without restricting incident field patterns.
• Fabricated devices achieved reflectivities within the target range, with average performance at 79% of the target value due to losses.
• Characterization showed standard deviations below ±5% across a 20 nm wavelength range (1540-1560 nm).
• Theoretical model showed good agreement with Finite-Difference Time-Domain (FDTD) simulations.

Conclusions:

• Aluminium-based mirrors are a viable and flexible alternative for constructing 2-port MIRs.
• The proposed design and theoretical model enable precise control over reflectivity for on-chip photonic applications.
• This work expands the design space for MIRs, facilitating advanced integrated photonic devices.