A rapid and robust method to fabricate transmission diffractive optical elements in the visible wavelengths is presented. By additive manufacturing of a polymeric photo-resin using 2-photon lithography followed by encasing of the structure in another resin with similar refractive index, the height of the structure can be made much larger, thus trading-off fabrication height for refractive index difference of the two materials. After adjusting for resin shrinkage, different diffractive optical element designs including an m = 1 vortex plate, and Laguerre-Gaussian beams with azimuthal and radial indices of (1,1), (1,2), and (2,1) were demonstrated. Experimental results show intensity patterns matching that of simulations, including size and features, although some aberration was observed, possibly due to fabrication tolerance errors or beam misalignment. This technique adds to the toolkit of micro-optics fabrication methods using additive manufacturing and 3D printing, and it would be beneficial for rapid prototyping and integration with miniaturised systems.