Modal interference discrepancy and its application to a modified fiber Mach-Zehnder Vernier interferometer

Area of Science:

• Optics and Photonics
• Fiber Optic Sensing
• Interferometry

Background:

• Modal interference in fiber optic Mach-Zehnder Interferometers (MZIs) presents distinct responses to ambient refractive index (RI) and temperature.
• Understanding these differential responses is crucial for developing advanced optical sensors.

Purpose of the Study:

• To theoretically analyze and experimentally verify the modal interference discrepancy in all-fiber MZIs.
• To leverage this discrepancy for fabricating an improved Vernier sensor with enhanced RI sensitivity and restrained temperature cross-talk.
• To explore potential applications in biochemical sensing.

Main Methods:

• Theoretical analysis of core-cladding and cladding-cladding modal interference in all-fiber MZIs.
• Experimental verification of theoretical predictions.
• Fabrication of a cascaded Vernier sensor using two unit MZIs with different core-offset fusions.
• Measurement of ambient RI and temperature responses of individual MZIs and the cascaded sensor.

Main Results:

• Core-cladding modal interference shows a blue-shift RI response, while cladding-cladding interference shows a red-shift RI response.
• Both interference types exhibit a red-shift temperature response.
• The cascaded Vernier sensor achieved a significantly enhanced ambient RI sensitivity of -1788.160 nm/RIU.
• The sensor demonstrated low temperature sensitivity (0.167 nm/°C), resulting in minimal RI error.

Conclusions:

• The modal interference discrepancy provides a viable mechanism for improving fiber optic sensor performance.
• The fabricated Vernier sensor offers high RI sensitivity and excellent temperature stability.
• The sensor's simple structure and performance make it suitable for biochemical sensing applications.