Photoinduced x(2) for second harmonic generation in stoichiometric silicon nitride waveguides

We present for the first time second harmonic generation in amorphous stoichiometric Si3N4 waveguides grown via low pressure chemical vapor deposition. An effective second-order susceptibility (χ (2)) is established via the coherent photogalvanic effect. A waveguide was designed to phase match a horizontally (parallel to the waveguide width) polarized hybrid EH00 mode at 1064 nm with the higher-order hybrid transverse EH02 mode at 532 nm. A mode-locked laser delivering 6.2-ps pulses at 1064 nm with a repetition rate of 20 MHz was used as pump. When pumped with a constant average power, it was found that the photoinduced χ (2) is established over a time of the order of 1000 s in as-manufactured waveguides, during which the second harmonic signal grows from below noise to a saturation value. The life-time of the photoinduced χ (2) is at least a week. In steady state, we obtain a maximum conversion efficiency close to 0.4% for an average pump power of 13 mW inside the waveguide. The effective second-order susceptibility is found to be 8.6 pm/V.