We fabricated buried circular cladding waveguides with different cross-sectional diameters in neodymium-doped yttrium aluminate crystals via femtosecond laser direct writing at a repetition rate of 500 kHz. Continuous-wave waveguide lasers operating at 1079 nm were successfully achieved at room temperature using an optical pump with 803-nm light. In addition, the guiding properties of the cladding waveguides fabricated using various laser-writing conditions were investigated. The fabricated waveguides exhibited excellent performance, with an insertion loss of 1.2 dB at a wavelength of 1.06 μm. Confocal micro-Raman and micro-photoluminescence analyses were performed to investigate the crystalline lattice modifications induced by the FsLDW. The lasing slope efficiency of the cladding waveguide with a diameter of 40 μm reached 29.2% with a maximum output power of 183 mW, and the cladding waveguide with a diameter of 60 μm exhibited a lasing slope efficiency of 29.9% and a maximum output power of 155 mW.
We report on the fabrication of active optical waveguide splitters with circular cladding geometry in Nd:KGW crystals using direct femtosecond laser writing. Y-branch waveguides capable of one to two beam splits were fabricated with a single 60-μm-diameter straight waveguide as the input end and two 30-μm-diameter output ends. The full branching angle between the two output arms changed from 1.0 deg to 2.4 deg. Confocal micro-Raman and microphotoluminescence spectra were used to investigate the Y-branch waveguides. Under the action of an optical pump at 806 nm, simultaneous continuous-wave laser oscillation at a wavelength of 1067 nm in both arms of the Y-branch waveguides was achieved. The laser output was spatially multimodal with a power-splitting ratio of 49.7:50.3 between the arms. A maximum laser output power of 106 mW and slope efficiency of 27.3% were achieved in the active Y-branch waveguide splitter with a splitting angle of 1.0 deg.
Depressed cladding, buried waveguides, and beam splitters in z cut LiNbO3 crystals were fabricated by femtosecond laser inscription. Straightforward cladding waveguides were optimized by varying the laser writing conditions. Minimum propagation losses of 0.74 dB / cm at 1.05-μm wavelength were obtained. Two-dimensional 1 × 2 and three-dimensional 1 × 4 beam splitters were realized. 1 × 2 Y-splitters with circular cladding geometry are fabricated with 60-μm diameter input ends, corresponding to two 30-μm diameter output ends, respectively. The full branching angle between the two output arms are changing from 0.5 deg to 2.4 deg. The splitters were characterized both experimentally and numerically, showing excellent properties including symmetrical output ends and equalized splitting ratio. 1 × 4 splitters with square cladding geometry reached splitting ratios of 26 ∶ 26 ∶ 22 ∶ 26. The micro-Raman spectra indicate the slight microstructural lattice changes in the track and core region.
Channel waveguides in Nd:GdVO4 crystals were fabricated by using low-repetition-rate (1 kHz) femtosecond laser inscription. The influences of pulse energy and scanning velocity were investigated. Guiding occurs in the surroundings of the focal spot. Single-line, double-line, and double-layer waveguides were realized. The near-field mode images, refractive-index profile reconstruction, and mode analysis of waveguides are presented. The double-line waveguides show strong guidance at 632.8 nm with a loss of about 0.5 dB/mm and an index increase of 3×10−4. The mode profile asymmetry of single-line waveguide has been improved by using multipass scanning.
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