Graphene oxide based plasmonic nano-cavity sensor for high-performance refractive index sensing

In this work, a nano-cavity based metal-insulator-metal (MIM) structure is proposed which can be used as a high-performance refractive index sensor. The analysis of its sensing capabilities is done by determining the transmission characteristics of light through the insulating air channel between the metal layer The loss in transmission in this channel is indicative of light leaking out of it and portion of it getting coupled to nano-cavities considered in the metal layers on both sides of air channel. The analyte, whose refractive index is to be sensed, is kept in these nano-cavities. The basic structure is modified by introducing graphene-oxide (GO) on the inner wall of the nano-cavity, which further improves the confinement of light in the nano-cavities. It is also shown that increasing the number of nano-cavity duos enhances the transmission loss through the waveguide and as a result the light energy confinement in the cavity increases. Calculated values of sensitivities and Figure of Merit (FOM) of the proposed sensor structure are much higher than similar works done previously. The uniqueness of the work is two-fold; namely use of graphene oxide as an inner layer of the nano-cavity improves the sensitivity of the sensor and secondly calculating the waveguide transmission to indirectly determine the confinement of light energy in nano-cavity simplifies the analysis of the performance of the proposed sensor. The structure is simple and can be easily fabricated using standard fabrication process.