Fig. 1. (a) In situ fabricated fiber GO lens: GO film is prepared on the fiber facet. A femtosecond laser is capable of photoreducing GO to rGO. (b) Working principle of the fiber GO lens; light is coupled into the fiber core as a source.

Fig. 2. Black line: calculated relationship between designed focal length and FWHM of the focal spot. Red line: minimum distance between designed concentric rGO zones versus the focal length.

Fig. 3. FLDW fabrication system. The laser power is controlled by two polarizers and a half-wave plate (HWP); the sample is held on a PC-controlled 3D nanometric scanning stage where a high NA objective lens is fixed and a CCD can observe the fabrication process.

Fig. 4. (a) rGO linewidth versus laser power at 5 μm/s (laser power gradually increases from left to right in the inset) and (b) versus fabrication speed at 150 μW (fabrication speed gradually increases from left to right in the inset).

Fig. 5. Microscopic image presenting the in situ fabrication of a GO lens on the fiber facet.

Fig. 6. (a) Surface topographic profile of a flat GO lens measured by AFM. (b) Topographic profile of the flat GO lens at the red dashed line. (c) Film edge thickness scanned by a step profiler.

Fig. 7. Characterization system. The fiber GO lens is fixed on a fiber holder. The objective lens is held by a PC controlled stage.

Fig. 8. (a), (d) Calculated intensity distributions in the lateral and axial planes. (b), (e) Measured intensity distributions in the lateral and axial planes. (c) Cross-sectional intensity distribution along the white dashed line in the axial planes. (f) Cross-sectional intensity distribution along the white dashed line parallel to the x axis in the lateral planes.