A hybrid LPG/CFBG for highly sensitive refractive index measurements

Area of Science:

• Photonics and Optical Sensing
• Materials Science
• Analytical Chemistry

Background:

• Refractive index (RI) sensing is crucial in various scientific fields.
• Existing methods often face limitations in sensitivity or complexity.
• Fiber optic sensors offer potential for high-performance RI measurements.

Purpose of the Study:

• To propose and experimentally validate a simple, high-sensitivity fiber optic sensor for RI measurements.
• To investigate the sensing mechanism based on hybrid gratings.
• To demonstrate the effectiveness of the proposed sensor design.

Main Methods:

• Fabrication of a hybrid sensor combining a long period grating (LPG) and a chirped fiber Bragg grating (CFBG).
• Excitation of backward cladding modes through coupling and recoupling between LPG and CFBG.
• Measurement of reflected intensity changes of recoupled cladding modes and core mode.

Main Results:

• The hybrid LPG/CFBG structure successfully excites a wide wavelength range of backward cladding modes.
• The recoupled cladding modes and core mode are modulated by the surrounding RI.
• High sensitivity RI measurements were achieved by monitoring intensity variations.

Conclusions:

• The hybrid LPG/CFBG fiber optic sensor provides a simple and highly sensitive platform for RI measurements.
• The intensity-based detection of cladding modes offers a practical approach for RI sensing.
• This method holds promise for applications requiring precise RI monitoring.