Fig. 1. (a) Schematic illustration of the XYZ translation stage for waveguide fabrication using fs-laser helical inscription. (b) Schematic of fabrication process of waveguides. (c) Microscopic photographs of waveguide cross sections. The fabrication parameters are shown in (c).

Fig. 2. (a) Polarization analysis of the transmitted power for the helically inscribed cladding waveguide WG2. (b) Measured propagation losses of the waveguides at 632.8 nm under both π and σ polarizations. The fragments of waveguide claddings from (c) WG2, (d) WG3, (e) WG4, and (f) WG5.

Fig. 3. Spatial propagating modes from WG2 under π-polarized 633 nm and 1064 nm pumping.

Fig. 4. (a) Confocal µ-PL spectrum of the Pr3+ ions obtained under 488 nm excitation at the waveguide cross section. (b) Comparison of the µ-PL spectra around 641 nm obtained from the bulk (red line), the guiding core (blue line), and the helical track (black line).

Fig. 5. (a) Schematic showing of a waveguide structure and the areas for 2D µ-PL mappings, insets in (a) are the top and front views of the waveguide structure, indicating clearly the position of red and blue surfaces. (b), (e) Spatial dependence of the intensity, (c), (f) energy shift, and (d), (g) the change in FWHM of the 641 nm emission line obtained from a wide area covering the waveguide cross section and several sections of the loops, as indicated with the planes in red and blue in (a), respectively.

Fig. 6. (a) Optical spectrum of waveguide laser centered at 604 nm. (b) Output laser power of the waveguides as a function of incident pump power. The inset of (a) shows the normalized spatial intensity distribution of the output laser mode.