Diamond Ring Fiber (DRF) is proposed to allow a high percentage of evanescent field exposure while maintaining low confinement loss. It provides a long and protected medium for light-matter interaction and large cavities to ease the infiltration of sensing elements. DRFs with different waveguide parameters have been analyzed theoretically and fabricated using a stack-and-draw fiber drawing technique. Mode analysis has been performed experimentally on the fabricated fibers, while the confinement loss and the percentage of evanescent field exposure are examined by simulation. DRF allows evanescent field exposure as high as 39.56% with negligible confinement loss at a wavelength of 1550 nm.