Tapered-fiber-based refractive index sensor at an air/solution interface

Area of Science:

• Photonics
• Optical Sensing
• Interferometry

Background:

• Refractive index sensing is crucial for chemical and biological analysis.
• Microfiber Mach-Zehnder interferometers (MFMZIs) offer high sensitivity for sensing applications.
• Interface sensing presents unique challenges due to mode coupling effects.

Purpose of the Study:

• To propose and demonstrate a tapered-fiber-based MFMZI for refractive index sensing at an air/aqueous solution interface.
• To investigate the reduced spectral interference visibility at the interface and its relation to sensing performance.
• To utilize the MFMZI as an evanescent wave sensor for measuring glycerol solution concentrations.

Main Methods:

• Fabrication of a tapered-fiber-based MFMZI.
• Experimental setup for interface refractive index sensing.
• Monitoring average power attenuation of the tapered fiber to determine glycerol concentrations.

Main Results:

• Significantly reduced spectral interference visibility at the air/solution interface was observed.
• This reduction is attributed to weak coupling between fundamental and high-order asymmetric cladding modes.
• The MFMZI successfully measured glycerol solution concentrations via power attenuation.

Conclusions:

• The tapered-fiber MFMZI is a viable platform for refractive index sensing at interfaces.
• Evanescent wave sensing using MFMZI provides a sensitive method for concentration measurements.
• The observed mode coupling phenomenon is key to the sensor's high sensitivity to refractive index changes.