Femtosecond laser written channel optical waveguide in Nd:YAG crystal

• Channel waveguides were realized by using 1 kHz femtosecond laser inscription.
• Optical waveguides was observed in the surrounding region of writing tracks.
• The refractive index changes and the mode profiles were measured and calculated.
• Both TE and TM modes were observed in single-track and double-track waveguides.
• The propagation loss of the channel waveguide was lower than 4.1 dB.

Low-repetition-rate (1 kHz) femtosecond laser inscription is used to fabricate channel waveguides in Nd:YAG crystal. Guiding occurs in the surroundings of the focal spot. End-to-end coupling measurements reveal the near-field intensity distribution of waveguides. The index profile reconstruction, mode analysis performed by the beam propagation method of these waveguides are presented. The waveguide written with 3.0 μJ pulse energy and 100 μm/s scan velocity shows strong guidance at 632.8 nm, and a propagation loss of about 0.5 dB/mm.