Optimization of Al 2 O 3 :Er3⁺waveguide technology for active integrated optical devices

Abstract

Amorphous Al 2 O 3 is a promising host material for active integrated optical applications such as tunable rare-earth-iondoped laser and amplifier devices. The fabrication of slab and channel waveguides has been investigated and optimized by exploiting reactive co-sputtering and ICP reactive ion etching, respectively. The Al 2 O 3 layers are grown reliably and reproducibly on thermally oxidized Si-wafers at deposition rates of 2-4 nm/min. Optical loss of as-deposited planar waveguides as low as 0.11±0.05 dB/cm at 1.5-µm wavelength has been demonstrated. The channel waveguide fabrication is based on BCl 3 /HBr chemistry in combination with standard photoresist and lithography processes. Upon process optimization channel waveguides with up to 600-nm etch depth, smooth side walls and optical losses as low as 0.21±0.05 dB/cm have been realized. Rare-earth-ion doping has been investigated by co-sputtering from a metallic Er target during Al 2 O 3 layer growth. At the relevant dopant levels (~10 20 cm -3 ) lifetimes of the 4 I 13/2 level as high as 7 ms have been measured. Gain measurements have been carried out over 6.4-cm propagation length in a 700-nm-thick Erdoped Al 2 O 3 waveguide. Net optical gain has been obtained over a 35-nm-wide wavelength range (1525-1560 nm) with a maximum of 4.9 dB.