Design and Simulation of a New Coaxial Probe for Near Field Scanning Optical Microscopy

Design of the new photonic devices having attractive optical properties such as subwavelength confinement of light has a numerous applications in developing nanoscale sensors, photonic integrated circuits, solar cells and etc. Abbe's diffraction limit restricts the use of subwavelength scale photonic elements due to their size and therefore new approaches are required in order to achieve desirable nanometer scale properties of these devices. Delivering light energy to nanometer scale regions can be achieved by surface plasmon polariton (SPP) waves that propagate in metal-dielectric interface. The paper presents results in FDTD (finite-difference time domain) simulation of a new coaxial probe of nanometer-scale size. Based on FDTD simulations of the coaxial probe field localization and enhancement in the region around the tip of coaxial probe has been obtained. Configuration of the probe consists of the truncated Au cone as a core, truncated dielectric (SiO₂) cone in the middle and outer metallic cladding. Simulations of the probe revealed that increasing the radius of Au core structure could lead to the enhanced field around the tip. Additionally, increasing radius of outer cladding layer doesn't affect field enhancement around the tip. Different configurations of the probe have been analyzed in the range of visible spectrum of the source and as a result the most promising configuration has been selected.