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22 September 2010 Performance and limitations of quasi-phase matching semiconductor waveguides with picosecond pulses
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Proceedings Volume 7750, Photonics North 2010; 77501K (2010)
Event: Photonics North 2010, 2010, Niagara Falls, Canada
Quasi-phase matched (QPM) second-order nonlinear optical processes in compound semiconductors are attractive for frequency conversion because of their large nonlinear susceptibilities and their mature fabrication processes that permit monolithic integration with pump lasers and other optical elements. Using quantum well intermixing (QWI), we have fabricated domain-disordered QPM (DD-QPM) waveguides in GaAs/AlGaAs superlattices and have previously demonstrated continuous-wave (CW) Type-I second-harmonic generation (SHG) and pulsed Type-II SHG. CW experiments were complicated by Fabry-Perot resonances and thermal bistability. Experiments using a 2-ps pulsed system were affected by third-order nonlinear effects, group-velocity mismatch (GVM), and poor spectral overlap with the conversion bandwidth. A better evaluation of the conversion efficiency may, however, be determined by using longer pulses in order to avoid these complications. By this, the effective CW conversion efficiency and χ(2) modulation can be ascertained. In this paper, we demonstrate SHG in DD-QPM waveguides with reduced parasitic effects by using 20 ps pulses. The waveguide structure consisted of a core layer of GaAs/Al0.85Ga0.15As superlattice into which QPM gratings with a period of 3.8 μm were formed using QWI by As2+ ion implantation. For a Type-I phase matching wavelength of 1583.4 nm, average second-harmonic (SH) powers produced were as high as 2.5 μW for 2 ps pulses and 3.5 μW for 20-ps pulses. At low input powers, the SHG average power conversion efficiency of the 2-ps system was more than 10 times larger than the 20 ps system. As power was increased, the SH power saturated and conversion efficiency decreased to nearly equal to the 20-ps system which remained consistent over the same power range. This is attributed to a reduction in third-order nonlinear effects, a smaller pulse spectral width that overlaps better with the conversion bandwidth, and less pulse walkoff for the 20-ps pulses. Thus, by using 20-ps pulses over 2-ps pulses, we achieved similar output SH powers and potentially higher SH powers are possible since there was no observed saturation at high input power.
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Sean J. Wagner, S. Chaitanya Kumar, Omid Kokabee, Barry M. Holmes, Usman Younis, Majid Ebrahim Zadeh, David C. Hutchings, Amr S. Helmy, and J. Stewart Aitchison "Performance and limitations of quasi-phase matching semiconductor waveguides with picosecond pulses", Proc. SPIE 7750, Photonics North 2010, 77501K (22 September 2010);

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