Multimode interference-based fiber optic sensors using single mode/no-core/single mode (SNS) configuration

Fiber optic sensors show many advantages as compared to other alternatives for a wide range of energy applications spanning electrical grid, pipelines, and civil infrastructure monitoring amongst others. Multimode interference-based fiber optic sensor configuration is one device architecture that is being explored for a range of different analytes, and which is fabricated by sandwiching a section of multimode fiber between two single mode fibers. Fiber optic devices based on multimode interference (MMI) are easy to fabricate and offer attractive prospects for applications in the areas of optical communication and fiber lasers as well as sensing. When light is coupled from a single mode fiber to a multimode fiber (MMF), multiple modes supported by the MMF are excited and interfere with each other, giving rise to an interference pattern along the MMF length. At specific positions along the axis of the MMF, light is concentrated and forms replicas of the input field which are known as self-images, with the self-imaging condition providing a narrow-band interference feature as a function of wavelength that is also affected by a wide range of analytes for sensing purposes. The self-images formed are simulated here using commercial software COMSOL Multiphysics. Sensitivity to a range of different analytes including refractive index, strain and hydrogen gas is explored. Optical fiber sensors based upon multimode interferometer sensors are investigated as attractive sensing options for infrastructure monitoring applications.