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Compact eccentric long period grating with improved sensitivity in low refractive index region
Optics Express
|August 10, 2017
Summary
We developed a compact eccentric long period grating that shows enhanced sensitivity for detecting changes in low refractive index environments. This fiber optic sensor offers improved performance for refractive index sensing applications.
Area of Science:
- Photonics
- Optical Sensing
- Fiber Optics
Background:
- Long period gratings (LPGs) are used in optical sensing.
- High-order cladding modes in LPGs offer potential for enhanced sensitivity.
- Low coupling coefficients of high-order modes limit LPG performance.
Purpose of the Study:
- To demonstrate a compact eccentric LPG with enhanced sensitivity in low refractive index regions.
- To improve the low coupling coefficients of high-order cladding modes.
- To achieve high sensitivity for refractive index sensing.
Main Methods:
- Fabrication of an eccentric long period grating using femtosecond laser inscription.
- Design of a 15 µm grating period for coupling to high-order cladding modes.
- Characterization of the grating's sensitivity to surrounding refractive index changes.
Main Results:
- A compact grating (4.05 mm length) was successfully fabricated.
- Eccentric inscription significantly improved coupling coefficients for high-order modes.
- An average sensitivity of ~505 nm/RIU was achieved in the low refractive index region (1.3328-1.3544).
Conclusions:
- The eccentric LPG demonstrates significantly enhanced sensitivity in low refractive index regions.
- Femtosecond laser inscription is effective in improving coupling efficiency for high-order modes.
- The proposed principle is adaptable for sensing in different refractive index ranges by selecting appropriate resonant cladding modes.
