Self-Reference Refractive Index Sensor Based on Independently Controlled Double Resonances in Side-Coupled U-Shaped Resonators

Abstract

A plasmonic, refractive, index nanosensor is investigated theoretically and numerically in two U-shaped cavities side-coupled to a metal–dielectric–metal (MDM) waveguide. A transparency window between two transmission dips is observed. The physical origin of the transmission phenomenon is revealed by mapping the magnetic field distribution. Independent double resonances are realized through the proposed design. Double resonances showed diverse responses to the variations of the structural dimensions. In particular, they presented different dependences on a refraction index of the medium in an individual resonator. One resonance exhibited a remarkable shift with the increase of the refraction index; however, the other resonance remained unchanged. On the basis of this unique characteristic of differing sensitivities, self-reference sensing is discussed. The nanosensor yielded a high sensitivity of 917 nm/RIU and a figure of merit of 180 RIU−1. This work is helpful in terms of the design of on-chip optical sensors with high sensitivity and improved detection accuracy in complicated environments.

Magnetic-field sensor with self-reference characteristic based on a magnetic fluid and independent plasmonic dual resonances

“…Because the right resonance is not sensitive to a change of the external magnetic field, it can be used as a reference. This is the characteristic of a self-reference sensor [37,40]. Thus, a self-reference magnetic -field sensor is achieved and the detection accuracy of the sensor can be improved.…”

Plasmonic sensor with self-reference capability based on functional layer film composed of Au/Si gratings

“…[16] Resonance-based structures are generally attractive in the field of sensors, as the resonance position (angle or wavelength) is usually easy to detect, and in most cases, surface plasmon resonance (SPR) is very sensitive to changes in analyte environments. [17][18][19][20][21][22][23] In the context of refractive index (RI) sensing, external environmental factors, such as optomechani-cal drifts and temperature changes, decrease the sensing accuracy and correctness of SPR-based sensors. [24][25][26][27] Therefore, it is useful to develop RI sensors with multiple signal channels to eliminate the influence of external environmental factors.…”

Multiple Fano resonances with flexible tunablity based on symmetry-breaking resonators

“…As a result, the frequency interval of the Fano resonances is usually very large, ranging over hundreds of nanometers. Recently, multiple Fano resonances were achieved with the aid of different cavities that provided several discrete states [26,29,30]. For instance, two U-shaped resonators were designed in order to obtain independent dual resonances [30].…”