Abstract-Atomic layer deposition was used in preparing erbium (Er)-doped waveguides. Ridge-type Er-doped Al 2 O 3 waveguides were patterned on silica-coated silicon wafers using photolithography and wet etching. Optical absorption, emission, fluorescence lifetime, and signal enhancement measurements were performed. Polarization dependence of the absorption spectrum and birefringence of the waveguide were measured. The material showed strong absorption and wide emission spectrum around 1530 nm with full-width at half-maximum of 52 nm. Signal enhancement of 6 dB was measured for a 3.9-cm-long waveguide.Index Terms-Aluminum oxide, atomic layer deposition (ALD), erbium (Er), optical amplification, optical waveguides.

Abstract-Adiabatic and multimode interference (MMI) 3-dB couplers based on silicon-on-insulator rib waveguides were fabricated and measured. For testing purposes, pairs of identical couplers were cascaded to form Mach-Zehnder interferometers.The adiabatic couplers showed excess on-chip loss of 0.5 dB, extinction ratio (ER) of 15-20 dB, and a wide spectral range. The MMI couplers processed on the same wafer showed similar loss per coupler, higher ER, and limited spectral characteristics.

Low-loss converters between optical silicon waveguides of different sizes and types

Multi-step processing for a silicon-on-insulator (SOI) platform was developed. It allows the incorporation of additional grooves and steps into the basic optical waveguide structures, so that light can be adiabatically coupled between waveguides with different cross-sections. The processes were based on simple fabrication methods easily scalable for mass production. Two options for the fabrication sequence were tested, both having one silicon etch step with an oxide mask and another etch step with a resist mask. The applicability of the developed processes was tested with different waveguide structures. An additional groove etched beside a bent 10 µm thick rib waveguide suppressed the bend losses to below 1 dB/90 • with a 5 mm bending radius. A waveguide mirror exhibited optical losses below 1 dB/90 •. The excess losses of a vertical taper between 10 and 4 µm thick rib waveguides were 0.7 dB. A converter between a rib and a strip waveguide showed negligible losses, below 0.07 dB.

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