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.