Manufacturing of Er-doped planar waveguides on silica-on-silicon using femtosecond laser-induced plasma

We report fabrication and characterisation of the erbium-doped planar waveguide on a silica-on-silicon (SOS) wafer-offering low loss and strong light confinement suitable for engineering optical waveguide amplifier for the C-band (1530–1565 nm) of the optical fibre communication. Here we describe an ultrafast laser plasma doping (ULPD) technique that is carried out using the plasma induced by a femtosecond laser (wavelength 800 nm) with a repetition rate of 10 kHz and a pulse duration of 45 fs. The ULPD method presented here had been applied successfully for rare earth materials doping on SOS substrates previously using a fs-laser with a pulse duration of 100 fs and at a repetition rate of 1 kHz. The fabricated planar optical waveguide layer onto the SOS substrate has been analysed for thickness, refractive index, optical propagation loss, photoluminescence intensity, and photoluminescence lifetime. We report a low propagation loss of <0.4 dB/cm in the C-Band, a long lifetime of 13.21 ms at 1532 nm, and the largest lifetime-density product 6.344 ×10 19 s cm −3. The low loss planar slab waveguide and a high lifetime-density product promise the further possibility of fabricating strip-loaded waveguides on the SOS platform. The proposed active waveguide fabrication methodology is potentially useful for manufacturing planar integrated optical waveguide amplifiers and lasers compatible with silicon-based photonic integrated circuits.