Focal length modulation based on a metallic slit surrounded with grooves in curved depths

According to the numerical calculation, the relative phase of emitting light scattered by surface plasmon in a single subwavelength metallic groove can be modulated by the groove depth. The focal length of the slit-groove-based focusing structures can be adjusted in certain value if the groove depths are arranged in traced profile. With the regulation of the groove depth profile, it is possible to modify the focus position in the precision of nanoscale without increasing the size of the nanodevice. The simulation results verify that the method is effective for the design of nano-optical devices such as optical microprobes.