Temperature-insensitive optical fiber refractometer based on multimode interference in two cascaded no-core square...

Area of Science:

• Photonics and Optical Sensing
• Fiber Optic Sensors
• Refractometry

Background:

• Optical fiber sensors offer advantages like remote sensing and immunity to electromagnetic interference.
• Refractometers are crucial for measuring liquid concentrations and identifying substances.
• Existing refractometer designs often face challenges with temperature sensitivity and complex structures.

Purpose of the Study:

• To propose and experimentally demonstrate a temperature-insensitive optical fiber refractometer.
• To investigate the performance of a novel refractometer based on multimode interference in no-core square fibers.
• To evaluate the refractive index (RI) and temperature sensing characteristics of the proposed device.

Main Methods:

• Fabrication of the refractometer by fusion splicing a single-mode fiber between two segments of no-core square fibers.
• Utilizing multimode interference (MMI) within the no-core square fiber structure.
• Experimental measurement of transmission spectra to determine RI and temperature sensitivity.

Main Results:

• A significant redshift of approximately 25 nm in transmission dip was observed with an increase in ambient RI from 1.3424 to 1.4334.
• High RI sensitivity of 474.8189 nm/RIU was achieved in the RI range of 1.4033 to 1.4334.
• Low temperature sensitivity of 0.00639 nm/°C and minimal temperature cross-sensitivity (1.35×10⁻⁵ RIU/°C) were experimentally verified.

Conclusions:

• The proposed optical fiber refractometer exhibits excellent RI sensitivity and low temperature dependence.
• The device's simple structure, low cost, and compact size make it highly practical.
• The refractometer is a promising candidate for chemical sensing and multi-parameter measurement applications.