The use of an optical waveguide to attain a numerical aperture of unity in computational coherent optical imaging applications is described. It is shown that for the case of a one-dimensional (slitlike) object radiating into an optical waveguide consisting of two plane-parallel mirrors the complex field amplitude across any cross section of the waveguide contains sufficient information to reconstruct the object's transmittance function with a numerical aperture of unity. We include the derivation of an inversion algorithm for performing the object reconstruction as well as computer simulations of the procedure.