Polarization effects in polymer FBGs: study and use for transverse force sensing

Area of Science:

• Photonics and Optical Engineering
• Materials Science
• Fiber Optic Sensors

Background:

• Polymer optical fiber Bragg gratings (POFBGs) offer enhanced sensitivity to temperature and pressure compared to silica-based gratings.
• POFBGs are typically fabricated using poly(methylmethacrylate) (PMMA) and a 325 nm HeCd laser.
• Birefringence effects in POFBGs are critical for understanding their sensing capabilities.

Purpose of the Study:

• To investigate and quantify birefringence effects in POFBGs manufactured from different fiber types.
• To analyze the impact of photo-induced and externally applied forces on POFBG birefringence.
• To assess the temperature-insensitivity of POFBG response to lateral forces.

Main Methods:

• Fabrication of highly reflective (>90%) POFBGs using the phase mask technique.
• Monitoring spectral response with polarized light and computing Polarization Dependent Loss (PDL) and Differential Group Delay (DGD) via Jones matrix eigenanalysis.
• Utilizing an inverse scattering technique to estimate photo-induced birefringence and investigating lateral force response using PDL.

Main Results:

• Maximum PDL exceeding several dB and DGD reaching a few picoseconds were observed.
• An estimation of photo-induced birefringence was obtained from experimental data.
• A force-dependent evolution of PDL maximum was observed when lateral force was applied, showing good temperature-insensitivity.

Conclusions:

• POFBGs exhibit significant birefringence, influenced by both fabrication and external forces.
• The study provides quantitative insights into PDL and DGD in POFBGs.
• POFBGs demonstrate potential for force sensing applications due to their predictable and temperature-insensitive response to lateral forces.