Modeling of a Single-Notch Microfiber Coupler for High-Sensitivity and Low Detection-Limit Refractive Index Sensing

Abstract

A highly sensitive refractive index sensor with low detection limit based on an asymmetric optical microfiber coupler is proposed. It is composed of a silica optical microfiber and an As2Se3 optical microfiber. Due to the asymmetry of the microfiber materials, a single-notch transmission spectrum is demonstrated by the large refractive index difference between the two optical microfibers. Compared with the symmetric coupler, the bandwidth of the asymmetric structure is over one order of magnitude narrower than that of the former. Therefore, the asymmetric optical microfiber coupler based sensor can reach over one order of magnitude smaller detection limit, which is defined as the minimal detectable refractive index change caused by the surrounding analyte. With the advantage of large evanescent field, the results also show that a sensitivity of up to 3212 nm per refractive index unit with a bandwidth of 12 nm is achieved with the asymmetric optical microfiber coupler. Furthermore, a maximum sensitivity of 4549 nm per refractive index unit can be reached while the radii of the silica optical microfiber and As2Se3 optical microfiber are 0.5 μm and a 0.128 μm, respectively. This sensor component may have important potential for low detection-limit physical and biochemical sensing applications.

An Integrated-Plasmonic Chip of Bragg Reflection and Mach-Zehnder Interference Based on Metal-Insulator-Metal Waveguide

“…For further investigating the sensing performance of the integrated structure, we change the insulator of air to be the one with the index range from 1.33 -1.36. Certainly, the Q factor, sensitivity S, detection limit (DL), and the figure of merit (FOM) are the significant factors of sensors to evaluate the performances, and they are defined as [7,42,43] FWHM…”

High Sensitivity Refractive Index Sensor Based on Highly Overcoupled Tapered Fiber-Optic Couplers

“…In recent years, optical sensors based on microfiber directional couplers have been proposed and demonstrated to perform high sensitivity measurements in many practical applications [16][17][18][19][20][21][22][23]. For the specific case of fiber coupler based RI sensors, these include fused biconical fibers [24]- [26], microfibers [16], [18], [27]- [30], photonic crystal fibers (PCF) [31]- [33], and specially designed two-core optical fibers [34], [35]. Most of these sensors are presented as wavelength codified and the achieved sensitivities are in the range from 1,125 to 30,100 nanometer (nm) per refractive index unit (RIU), with a detection limit in a range from 4×10 −4 to 5×10 −7 RIU, respectively.…”