Ultra-sensitive refractive index sensor based on an extremely simple femtosecond-laser-induced structure

Area of Science:

• Photonics and Optical Sensing
• Fiber Optic Sensors
• Nanofabrication

Background:

• Refractive index (RI) sensors are crucial for various analytical applications.
• Existing intensity-modulated RI sensors often lack sufficient sensitivity and robustness.
• Need for compact, highly sensitive, and easily fabricated RI sensing platforms.

Purpose of the Study:

• To demonstrate a novel, simple, and compact RI probe sensor.
• To achieve ultra-high sensitivity and low temperature cross-sensitivity.
• To explore its potential for biochemical and environmental monitoring.

Main Methods:

• Fabrication of a refractive index-modified dot (RIMD) near a single-mode fiber end face using femtosecond laser.
• Formation of a Fabry-Perot interferometer (FPI) using the RIMD and fiber end face.
• Characterization of the FPI sensor's response to surrounding RI changes.

Main Results:

• The RIMD fabrication is a single-step process completed in approximately 0.1 seconds.
• The sensor exhibits an ultra-high sensitivity of ~2523.2 dB/RIU at RI=1.435.
• Achieved sensitivity is one to two orders of magnitude higher than existing intensity-modulated RI sensors.
• Demonstrated compact size (~50 μm) and no temperature cross-sensitivity.

Conclusions:

• The femtosecond-laser fabricated FPI sensor offers a simple, robust, and highly sensitive RI sensing solution.
• Its compact size, ease of fabrication, and high sensitivity make it suitable for advanced sensing applications.
• The sensor is a promising candidate for biochemical and environmental measurement fields.