Optimization of long-period grating-based refractive index sensor by bent-fiber interference

Area of Science:

• Photonics and Optical Sensing
• Fiber Optic Sensors
• Interferometry

Background:

• Long-period gratings (LPGs) are widely used for sensing applications.
• Temperature cross-sensitivity remains a challenge in LPG-based refractive index (RI) sensors.
• Existing RI sensing methods often lack sufficient sensitivity or require complex structures.

Purpose of the Study:

• To develop a novel hybrid fiber optic sensor for enhanced refractive index (RI) sensing.
• To eliminate the temperature cross-sensitivity in RI measurements.
• To achieve higher sensitivity through the combined use of two resonance dips.

Main Methods:

• A hybrid structure integrating an LPG with a bent-fiber intermodal interferometer was fabricated.
• The bent-fiber intermodal interferometer featured a semi-circular bending region with a 5 mm radius.
• The spectral responses of both LPG and the interferometer were analyzed under varying RI and temperature conditions.

Main Results:

• The LPG resonance wavelength shifted to shorter wavelengths with increasing RI.
• The bent-fiber intermodal interferometer resonance wavelength shifted to longer wavelengths with increasing RI.
• The separation between the two resonance dips increased with RI, enhancing sensitivity.
• The separation of the two resonance dips remained constant with temperature variations, confirming temperature independence.

Conclusions:

• The proposed hybrid sensor effectively enhances RI sensitivity.
• The novel approach successfully eliminates temperature cross-sensitivity.
• This technology offers a promising solution for accurate and robust RI sensing in various applications.