High-order LP modes based Sagnac interference for temperature sensing with an enhanced optical Vernier effect

Area of Science:

• Fiber optic sensing
• Optical interferometry
• Photonics

Background:

• Sagnac interferometers are widely used for sensing applications.
• Few-mode fibers (FMFs) enable multiplexing and enhanced sensitivity through higher-order modes.
• Traditional optical sensors face limitations in sensitivity and stability.

Purpose of the Study:

• To propose and theoretically investigate high-order LP modes based Sagnac interference for temperature sensing.
• To design a stress-induced Panda-type FMF supporting multiple LP modes for a highly sensitive temperature sensor.
• To explore an enhanced optical Vernier effect for magnified temperature sensitivity.

Main Methods:

• Excitation of specific high-order LP modes using mode selective couplers (MSCs).
• Construction of a Sagnac interferometer using a Panda-type FMF supporting 4 LP modes.
• Investigation of different LP modes (LP01, LP11, LP21, LP02) performance in single and parallel Sagnac interferometers.
• Implementation of two Sagnac loops in temperature boxes with opposite variation trends for the enhanced optical Vernier effect.

Main Results:

• The LP21 mode exhibits the highest temperature sensitivity, improving by at least 18.2% compared to the fundamental LP01 mode.
• An enhanced optical Vernier effect is proposed, achieving an eightfold magnification of temperature sensitivity, surpassing the traditional fivefold magnification.
• The novel approach demonstrates improved stability and avoids measurement errors in the sensing system.

Conclusions:

• High-order mode interference in Sagnac interferometers offers a pathway to highly sensitive temperature sensing.
• The LP21 mode provides significantly enhanced temperature sensitivity.
• The proposed enhanced optical Vernier effect offers a substantial improvement in sensitivity and system stability, with broad implications for advanced optical sensor development.