Temperature-insensitive refractive index sensor based on a spindle-shaped few-mode fiber modal interferometer.

Area of Science:

• Optoelectronics
• Fiber Optics Sensing
• Nanophotonics

Background:

• Refractive index (RI) sensing is crucial for real-time monitoring in chemical and environmental applications.
• Conventional RI sensors often suffer from temperature cross-talk, limiting their accuracy and applicability.
• Few-mode fiber (FMF) based interferometers offer potential for enhanced sensitivity in RI sensing.

Purpose of the Study:

• To propose and demonstrate a temperature-insensitive modal interferometer for accurate refractive index measurement.
• To investigate the sensing performance of a spindle-shaped FMF based interferometer.
• To address the challenge of temperature cross-talk in optical fiber sensors.

Main Methods:

• Designing a modal interferometer by fusing a specific length of FMF between single-mode fibers.
• Fabricating a spindle shape by bending and flame-treating the FMF to enhance mode coupling.
• Interferometric analysis of light propagating through core and cladding modes for RI detection.

Main Results:

• The spindle-shaped FMF interferometer exhibited high sensitivity to surrounding refractive index, reaching 237.3 nm/RIU in the range of 1.333 to 1.365.
• The sensor demonstrated excellent temperature insensitivity, effectively eliminating temperature cross-talk.
• The fabricated sensor showed advantages including small size, simple fabrication, low insertion loss, and good mechanical strength.

Conclusions:

• The developed spindle-shaped FMF modal interferometer is a robust and sensitive platform for refractive index measurement.
• The temperature-insensitive nature of the sensor broadens its applicability in dynamic environments.
• The sensor's practical advantages suggest significant potential for industrial and environmental monitoring systems.