Lossy waveguide design considering polarization dependency to reduce back reflection in 2 × 1 MMI combiners

Area of Science:

• Photonics and Optical Engineering
• Integrated Optics
• Waveguide Design

Background:

• Multimode Interference (MMI) combiners are crucial optical components.
• Back reflection in MMI devices can degrade performance.
• Existing methods for reducing back reflection may be complex or impact MMI operation.

Purpose of the Study:

• To propose and analyze a novel, compact lossy waveguide structure.
• To effectively reduce back reflection in MMI combiners.
• To ensure the proposed structure does not negatively affect MMI design or performance.

Main Methods:

• Theoretical calculations.
• Two-dimensional Finite-Difference Time-Domain (2D FDTD) analysis.
• Optimization of waveguide parameters (bend radius, taper dimensions).

Main Results:

• A lossy waveguide structure comprising a bend and taper section was proposed.
• For Transverse Electric (TE) modes, an optimal bend radius of approximately 7.5 µm was identified, with back reflectance dependent on taper end width.
• For Transverse Magnetic (TM) modes, a taper length of 30 µm achieved back reflection below -30 dB, independent of bend radius.
• The lossy waveguide introduction did not alter MMI design or operation.

Conclusions:

• The proposed compact, simply structured lossy waveguide effectively reduces back reflection in MMI combiners.
• The design offers mode-specific optimization strategies for TE and TM modes.
• This solution provides a non-disruptive method for enhancing MMI performance.