Employing Higher Order Cladding Modes of Fiber Bragg Grating for Analysis of Refractive Index Change in Volume and at the Surface

Abstract

In this work, a detailed study on volume and surface refractive index (RI) sensitivity of cladding modes for a fiber Bragg grating (FBG) based sensor is presented. Surface RI sensitivity of the cladding mode of FBGs has been illustrated and quantified with the concept of add-layer sensitivity for the first time to the best of our knowledge. A detailed investigation of mode transition of higher-order cladding modes has been revisited and important characteristics of the cladding modes are observed which could open a new designing path of fabrication and innovative way of the use of this family of optical fiber grating-based sensors. The effect of "mode transition" of higher-order cladding modes, higher operating wavelength for respective cladding mode and "mode stretching" effects are combined together to achieve higher volume and surface RI sensitivity of cladding mode of FBG. It has been shown numerically that with proper designing, sub-nanometer (∼0.04 nm) attachment of target analyte could be recognized by cladding mode of FBG which is quite promising for application in optical fiber grating bio-sensors. This critical designing method of FBG based surface refractometer would be very helpful in case of the fabrication of highly sensitive sensors for distinct biochemical applications.

Mode-division and spatial-division optical fiber sensors

“…In such case, the separate measurement tells the user at which temperature the refractive index was measured. This is routinely done with TFBGs where the core mode resonance is inherently insensitive to changes occurring solely outside the core mode field cross section, as long as the group index contribution is taken into account in the measurements of the other resonances [14,[207][208][209][210]. Although temperature sensing is already very well addressed by SMF sensor technologies, it is discussed here for two reasons: applications at higher temperatures than those of common FBG technologies and dealing with the cross-sensitivity to temperature of multimodal sensors for other applications.…”

Building-up and suppression of cladding mode coupling in fiber Bragg gratings

“…Offaxis UV-inscribed FBG was used to detect directional bending via its cladding mode resonance shift [5]. Higher order cladding modes of FBG were employed to analyze the refractive index change [6]. A high temperature (>1000 • C) stable FBG with ultra-strong cladding mode resonance can be achieved through femtosecond laser and phase mask (PM) [7].…”

Strongly coupled multicore fiber with FBGs for multipoint and multiparameter sensing

“…Over the past decades, optical fiber sensors have been widely used in the fields of civil engineering, mechanical manufacturing, robotics and aeronautical engineering due to its unique characteristics such as immunity to electromagnetic interference, resistant to corrosion, high sensitivity and compact size [1,2]. So far, various optical fiber sensors have been developed based on different sensing principles, such as long period gratings, fiber Bragg gratings (FBGs), Fabry-Perot interferometers, Mach-Zehnder interferometers, and so on [3][4][5][6]. Among them, FBG-based sensors are one of the most representative and promising optical fiber sensing technique due to their mature manufacturing process and multiplexing capability.…”