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Published on: August 30, 2012
Refractive index sensing based on higher-order mode reflection of a microfiber Bragg grating
Yu Zhang1, Bo Lin, Swee Chuan Tjin
1Wuhan National Laboratory for Optoelectronics and Institute of Optoelectronics Science and Engineering, Huazhong University of Science and Technology, Wuhan 430074, China.
Optics Express
|December 18, 2010
Summary
We demonstrated microfiber Bragg gratings (MBG) for sensing. Higher-order modes show enhanced sensitivity to surrounding fluid refractive index changes, reaching 102 nm/RIU.
Area of Science:
- Photonics and optical sensing
- Materials science
- Fiber optics
Background:
- Fiber Bragg gratings (FBGs) are widely used in optical sensing.
- Microfiber Bragg gratings (MBGs) offer potential for enhanced sensitivity due to their small mode field diameter.
- Developing novel MBGs with improved sensing capabilities is crucial for advanced applications.
Purpose of the Study:
- To demonstrate the fabrication of Bragg gratings in photosensitive microfibers.
- To investigate the spectral characteristics and sensing performance of MBGs.
- To compare the sensitivity of fundamental and higher-order reflection modes.
Main Methods:
- Fabrication of Bragg gratings in microfibers using a KrF excimer laser and a uniform phase mask.
- Characterization of microfiber Bragg gratings (MBG) using reflection spectroscopy.
- Numerical simulations to analyze the spectral response.
- Experimental measurement of refractive index (RI) sensitivity by exposing MBGs to fluids with varying RI.
Main Results:
- Successfully fabricated two Bragg gratings in microfibers of different diameters.
- Observed two reflection peaks in the MFBG reflection spectrum, consistent with numerical simulations.
- Higher-order reflection modes exhibited greater sensitivity to RI variations than the fundamental mode.
- Achieved a maximum sensitivity of approximately 102 nm/RIU at an RI of 1.378 for a 6 μm diameter MFBG.
Conclusions:
- Microfiber Bragg gratings are effectively fabricated using KrF excimer laser inscription.
- Higher-order modes in MFBGs are more sensitive to surrounding refractive index changes due to their extended evanescent field.
- MBGs demonstrate significant potential for high-sensitivity optical sensing applications, particularly for liquid analyte detection.
