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

摘要

We present for the first time second harmonic generation in amorphous stoichiometric Si_3N_4 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 EH_(00) mode at 1064 nm with the higher-order hybrid transverse EH_(02) 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.