Plasmonics-based refractive index sensor for detection of hemoglobin concentration

An ultra-compact plasmonics-based sensor is investigated which is excited by Fano resonance. The structure is numerically simulated by the finite-difference time-domain method. The sensor utilizes unique waveguide geometry named as metal-insulator-metal (MIM) waveguide geometry which has an intriguing feature to confine signal far beyond diffraction light. Thus, it is used to devise ultra-compact optical circuits. The MIM waveguide is coupled to a pair of elliptical ring resonators and the interaction between the resonators excites special mode which is known as Fano resonance mode. It is a unique phenomenon which exhibits asymmetrical resonance profile and supports ultra narrow line width. Because of its exciting feature, a large value of sensitivity = 1100 nm/RIU and figure of merit = 224RIU-1 is obtained for the proposed sensor. The sensing performance of the device can be further enhanced by tailoring the geometrical parameters. The applicability of the device is also tested to detect the concentration of hemoglobin in blood. Thus, the device is well suited to design on-chip optical sensors.