Planar fabrication process of a high-coupling-efficiency interface between optical waveguides of large index...

Area of Science:

• Photonics
• Materials Science
• Optical Engineering

Background:

• Efficiently coupling optical waveguides with large index differences is crucial for integrated photonic circuits.
• Existing methods often suffer from low coupling efficiency due to mode mismatch and Fresnel reflections.

Purpose of the Study:

• To report a high-coupling-efficiency interface for connecting optical waveguides with large index differences.
• To theoretically analyze and experimentally validate the proposed interface design.
• To demonstrate a fabrication process for integrating dissimilar waveguides.

Main Methods:

• Theoretical analysis of mode profile matching and antireflection (AR) section design.
• Experimental implementation using a quadrilevel photomasking and lift-off process.
• Fabrication of a glass-SiO(2) waveguide integrated into an AlGaAs host waveguide.

Main Results:

• Theoretical coupling efficiency of up to 98% predicted between glass-SiO(2) and GaAlAs waveguides with a TiO(2) AR section.
• Achieved a large index difference of 1.8 for the TE(0) mode.
• Experimentally measured 83% coupling efficiency for the TE(0) mode at 1.15 µm wavelength, despite a 1.75 index difference.

Conclusions:

• The developed interface effectively overcomes the challenge of coupling optical waveguides with large index differences.
• The novel fabrication process enables the integration of low- and high-index waveguides on a single substrate.
• This approach facilitates the creation of diverse and advanced photonic devices and modules.