Compact high-resolution FBG strain interrogator based on laser-written 3D scattering structure in flat optical fiber

Area of Science:

• Photonics and Optical Engineering
• Materials Science
• Sensor Technology

Background:

• Speckle patterns generated by scattering media are wavelength-dependent, enabling applications like wavemeters.
• Instability in traditional scattering-based devices hinders practical realization.
• Femtosecond laser-written scatterers offer a path to improved mechanical stability and compactness.

Purpose of the Study:

• To develop a stable and compact fiber Bragg grating (FBG) strain interrogator.
• To leverage laser-written scatterers for deterministic speckle pattern generation.
• To explore the device's capabilities as both a high-resolution wavemeter and an FBG interrogator.

Main Methods:

• Inscribing 3D arrays of nanovoids within flat optical fiber using a femtosecond laser.
• Utilizing the wavelength-dependency of generated speckle patterns for measurement.
• Calibrating speckle patterns against applied tensile strain for FBG interrogation.

Main Results:

• The device demonstrated stable operation as a wavemeter for over 60 hours with 45 pm resolution (1040-1056 nm).
• As an FBG interrogator, it detected microstrain changes (0-200 µε) with a standard error of 4 µε.
• The femtosecond laser-written scatterers significantly improved the device's mechanical stability and compactness.

Conclusions:

• The developed FBG strain interrogator offers a promising low-cost, high-resolution solution.
• The technology provides an excellent trade-off between resolution, compactness, price, and stability.
• This approach enhances the practical viability of scattering-based optical measurement devices.