Ultrafast laser inscribed cladding waveguides in Nd:YAG crystal for mid-infrared wavelength

• The guiding properties of Nd:YAG cladding waveguides at 4 μm were reported.
• The refractive index profiles of Nd:YAG cladding waveguide were simulated roughly.
• The cladding waveguide possesses the relatively low propagation losses.

We report on tubular cladding optical waveguides fabricated in neodymium doped yttrium aluminum garnet (Nd:YAG) crystal by ultrafast laser inscription. The structure can support guidance at the wavelength of 4 μm for the TE and TM polarizations. The refractive index contrasts of the cladding waveguides for the two transverse polarizations were estimated to be ΔnTE≈−7.5×10−3 and ΔnTM≈−6.5×10−3. The propagation losses of the cladding waveguides at the wavelength of 4 μm were determined to be as low as ~0.7 dB/cm for the TE polarization and ~1.0 dB/cm for the TM polarization.