Four wave mixing efficiency in hydrogenated amorphous silicon waveguides

Hydrogenated amorphous silicon (a-Si:H) is emerging as a promising new platform for silicon photonics. Low temperature required for its deposition provides an excellent compatibility with complementary metal-oxide-semiconductor (CMOS) processes. Besides, recent works have pointed out that a-Si:H exhibits an enhanced nonlinear efficiency that, combined with low linear losses, makes this material as an ideal candidate for the development of all-optical signal processing silicon devices.Nevertheless data concerning a-Si:H nonlinear parameters reported in the literature, show a great variance, suggesting that the actual features of the material are strongly dependent on the deposition conditions. This paper present the results of an extensive characterisation of a-Si:H waveguides fabricated by CEA-Leti. The a-Si:H film was deposited by plasma enhanced chemical vapour deposition (PECVD) at 350°C on 1.7μm oxide layer deposited on a bulk wafer. After deposition of a silica hard mask, grating couplers aligned to the waveguides were fabricated through two steps of 193nm DUV lithography and HBr silicon etching. Several straight and serpentine waveguides (500×220 nm cross-section) were obtained with lengths varying from 0.2 cm to 8 cm. Finally, a 500nm oxide upper cladding was deposited on top of the waveguides.The nonlinear efficiency have been tested by means of a four wave mixing (FWM) experiment using an intense continuous wave (CW) pump and a weaker signal, tunable in the range 1530-1560 nm.