Optical probe employing an impedance matched sub-lambda transmission line

Abstract

The present invention is an optical probe for emission of light from a region smaller than a wavelength. The optical probe includes a transmission line fed by an optic fiber and an impedance matched coupling. In a first embodiment the optical probe ends with a surface-wave transmission line including a central conductor and a coaxial dielectric. The diameter of the central conductor at the optic fiber is selected to substantially match the transmission impedance of the surface-wave transmission line to that of the optic fiber. The diameter of the central conductor decreases to a diameter smaller than the use wavelength at the tip end. The far end of the dielectric preferably includes a concavity to shape the resulting electric fields. In an alternative embodiment, the optical probe includes a coaxial transmisson line. The optic fiber includes a section having a decreasing diameter outer cladding and a section having no outer cladding. The coaxial transmission line includes a central conductor and a dielectric having a diameter substantially equal to the diameter of the core. An outer conductive layer is concentric with the two sections of the optic fiber and the dielectric. In a further alternative embodiment the impedance matched coupling includes a resonant cavity tunable to minimize the voltage standing wave ratio in the optic fiber.