TFBGs in polyimide-coated optical fibers for multi-parameter measurements

Area of Science:

• Optoelectronics
• Fiber optic sensing
• Nanofabrication

Background:

• Tilted fiber Bragg gratings (TFBGs) are versatile sensors for environmental parameters, utilizing core and cladding modes.
• Existing research often uses stripped fibers, limiting applications in harsh environments.
• Preserving the protective coating on fibers is crucial for practical, robust sensing applications.

Purpose of the Study:

• To develop and characterize a polyimide (PI)-coated TFBG using femtosecond laser direct writing.
• To investigate the influence of the PI coating on TFBG performance and sensing capabilities.
• To demonstrate the TFBG's ability to measure temperature, strain, and surrounding refractive index.

Main Methods:

• Femtosecond laser direct writing to inscribe a 12-degree tilted grating into a PI-coated single-mode fiber.
• Utilizing the PI coating as a Fabry-Perot cavity to induce amplitude modulation in cladding modes.
• Experimental measurements of temperature, strain, and surrounding refractive index changes.

Main Results:

• Successful fabrication of a robust PI-coated TFBG using femtosecond laser inscription.
• The PI coating acts as a Fabry-Perot cavity, modulating cladding mode resonances.
• The modulated cladding modes exhibit distinct responses to different measurands (temperature, strain, refractive index).

Conclusions:

• PI-coated TFBGs offer enhanced robustness for sensing in challenging environments.
• The integrated Fabry-Perot cavity effect provides additional sensing mechanisms.
• This approach advances the development of practical and versatile fiber optic sensors.