Figure 1: Femtosecond laser writing of tilted integrated waveplates.

Conceptual scheme of the method enabling the direct writing of optical waveguides acting as integrated waveplates with tilted axis. (a) Traditional writing scheme adopting a focusing objective with moderate NA; the symmetry of the writing layout creates birefringent waveguides with the optical axis (OA) aligned as the writing beam direction; actual waveguide writing is performed by a transverse translation of the glass sample (indicated by the purple arrow). (b) Equivalent waveguides can be created by underfilling a high-NA oil-immersion objective. (c) Offsetting the writing beam before the objective results in waveguide writing with an inclined laser beam; the resulting waveguide has an optical axis tilted by an angle θ that depends on the amount of offset d of the writing beam with respect to the objective axis. (d) Reduced beam size and offset at the objective aperture is achieved by a small transverse shift of a long focal lens placed at a distance L from the focusing objective (see Methods for details).