A resonator sensing device having an optics coupler device for communicating light between light source(s) and sensor(s) and a hollow core fiber resonator. Light from one resonator fiber tip is coupled to a second resonator fiber tip via a graded index (GRIN) lens having the appropriate pitch such that the maximum coupling efficiency is achieved and having two angled surfaces. The angled surfaces are coated with an appropriate coating having a reflectance R in order to achieve the desired degree of coupling. Light reflected by the second angled surface is captured with another lens (such as a microlens) and coupled to a third fiber segment (coupled port). The optical parameters for the GRIN lens and the microlens are tailored to have the least loss.