The paper presents an original and simple optical excitation technique of 3D micro-resonators. The method is based on the laser beam-waist use without any additional excitation framework such as integrated waveguides or tapered fiber. This is particularly powerful for 3D resonators like spheres or microtoroids. Tests have been performed at visible (470 nm) and infrared light (broad band source 800-880 nm) on polymeric 3D micro-resonators elaborated by microfluidic techniques. By using adequate protocol for such flexible beam-waist technique, spectral analysis on resonant cavities of different sizes confirm the excitation of the expected whispering gallery modes, revealing free spectral range values close (around 5%) to the analytical ones.