Large increase in photosensitivity through massive hydroxyl formation.

Area of Science:

• Materials Science
• Optical Engineering
• Photonics

Background:

• Photosensitivity in optical fibers is crucial for fabricating fiber Bragg gratings (FBGs).
• Germanium doping is a common method to increase photosensitivity, but alternative techniques are explored.
• Hydrogen loading enhances photosensitivity but can introduce hydroxyl absorption losses.

Purpose of the Study:

• To investigate a novel method for significantly increasing the photosensitivity of germanium-doped silicate fibers.
• To analyze the trade-off between enhanced photosensitivity and thermally induced absorption.
• To demonstrate the applicability of this technique to germanium-free phosphorous-doped fibers.

Main Methods:

• Rapid heat treatment at 1000°C of hydrogen-loaded germanium-doped silicate fibers prior to 242-nm UV exposure.
• Measurement of photosensitivity enhancement and induced absorption losses.
• Fabrication of FBGs in germanium-free phosphorous-doped fibers using the same technique.

Main Results:

• A large increase in photosensitivity was achieved in germanium-doped silicate fibers.
• Thermally induced absorption due to hydroxyl species was quantified (0.02 dB/cm mol.% OH at 1.55 µm).
• Strong gratings (Δn > 1 x 10⁻⁴) were successfully fabricated in germanium-free phosphorous-doped fibers.

Conclusions:

• Rapid high-temperature heat treatment is an effective method to dramatically enhance fiber photosensitivity.
• This technique offers a viable route for FBG fabrication with controlled absorption losses.
• The method is versatile, enabling strong grating inscription in both germanium-doped and germanium-free phosphorous-doped fibers.