Complex photosensitivity observed in germanosilica planar waveguides.

Area of Science:

• Materials Science
• Optical Engineering
• Photonics

Background:

• Optical fibers and waveguides are crucial for telecommunications and sensing.
• Photosensitivity in silica-based materials allows for waveguide fabrication and modification.
• Germanosilica offers tunable properties compared to pure silica.

Purpose of the Study:

• To investigate and characterize photosensitive effects in germanosilica waveguides.
• To compare these effects with those in standard optical fibers.
• To understand the underlying mechanisms and thermal stability of induced refractive index changes.

Main Methods:

• Deposition of germanosilica waveguides using hollow-cathode plasma-enhanced chemical-vapor deposition (HC-PECVD).
• Exposure of waveguides to 193-nm ultraviolet (UV) light.
• Measurement of refractive index changes using interferometric techniques.
• Thermal annealing experiments to determine stability.

Main Results:

• Observed pronounced type I and type IIA photosensitive effects in germanosilica waveguides.
• Induced positive refractive index changes (> 2 x 10(-3)) attributed to increased polarizability.
• Induced negative refractive index changes (> -5 x 10(-3)) linked to reduced material density.
• Negative index changes exhibited higher thermal stability, annealing at 900°C, compared to positive changes annealing at 500°C.

Conclusions:

• Germanosilica waveguides fabricated via HC-PECVD show significant, tunable photosensitivity.
• The observed index changes are governed by distinct physical mechanisms (polarizability vs. density).
• The enhanced thermal stability of negative index changes is advantageous for robust photonic device applications.