Effects of Post-Etch Microstructures on the Optical Transmittance of Silica Ridge Waveguides

Area of Science:

• Materials Science
• Optical Engineering
• Nanofabrication

Background:

• Silica waveguides are critical components in optical communication and integrated photonics.
• Reactive Ion Etching (RIE) is a common fabrication method for silica waveguides.
• Surface topography resulting from RIE can significantly increase optical loss.

Purpose of the Study:

• To investigate the relationship between optical loss and different RIE process parameters in silica waveguides.
• To evaluate the impact of a subsequent wet etch step using hydrofluoric acid (HF) on optical loss.
• To identify an optimal RIE process for fabricating low-loss silica waveguides.

Main Methods:

• Fabrication of ridge waveguides using three distinct RIE processes with varied gas composition, pressure, and power.
• Application of a hydrofluoric acid (HF) wet etch to half of the fabricated waveguides.
• Optical transmission measurements using the cutback method to determine optical loss.
• Data analysis involving exponential curve fitting to transmission versus waveguide length measurements.

Main Results:

• Significant variations in optical loss were observed among the different RIE processes.
• The HF treatment demonstrated a notable effect, reducing optical loss for two RIE processes and increasing it for one.
• One specific RIE process yielded the lowest optical loss among all tested conditions.

Conclusions:

• The choice of RIE process critically impacts the optical loss of silica waveguides.
• Hydrofluoric acid (HF) treatment can be beneficial but its effect is process-dependent.
• A specific RIE process is recommended for silica waveguide fabrication due to its lowest optical loss and highest etch rate.