Kimmo Solehmainen

Adiabatic and Multimode Interference Couplers on Silicon-on-Insulator

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

Erbium-doped waveguides fabricated with atomic layer deposition method

Atomic layer deposition was used in preparing erbium (Er)-doped waveguides. Ridge-type Er-doped Al/sub 2/O/sub 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.

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

Two types of low-loss converters between different optical waveguides on silicon-on-insulator are demonstrated. A vertical taper between 9.4- and 3.8-/spl mu/m-thick single-moded rib waveguides gives an excess loss of 0.7/spl plusmn/0.2 dB with negligible polarization dependency. The second structure converts a 9.7-/spl mu/m-thick rib waveguide into an equally thick and highly multimoded strip waveguide with a negligible loss (<0.07 dB) for the fundamental mode. The fabrication of both structures is based on a simple two-step etch process with a relaxed mask alignment tolerance and no need for epitaxy.

Dry-etched silicon-on-insulator waveguides with low propagation and fiber-coupling losses

Optical rib waveguides with various widths and heights were fabricated on silicon-on-insulator (SOI) substrates. Silicon etching was based on dry etching with inductively coupled plasma (ICP)-type reactive ion etcher. The etching process was developed to ensure low optical losses. Propagation loss of 0.13/spl plusmn/0.02 dB/cm was measured for the fundamental mode at the wavelength of 1550 nm in a curved 114-cm-long waveguide. The reflection losses were suppressed by applying atomic layer deposition (ALD) in the growth of antireflection coatings (ARCs).

Design and fabrication of arrayed waveguide grating multiplexers on silicon-on-insulator platforms

We report on the design, fabrication, and optical characteristics of arrayed waveguide grating (AWG) devices on silicon-on-insulator (SOI) platforms to act as multiplexers in a hybridly integrated wavelength division multiplexing (WDM) transmitter for telecommunications and datacom applications. In order to achieve efficient coupling to laser diodes, SOI layers with 4-µm-thick Si were used to form rib waveguides. The AWG devices comprised eight channels with a channel spacing of 200 GHz around a center wavelength at 1550 nm. AWG integration with variable optical attenuators is demonstrated to add channel equalization ability.

Oxidation of Aluminum in Ozonated Water

The oxidation of silicon and copper alloyed aluminum thin films in ozonated water was studied. Experiments were performed in a wet bench at different temperatures. The oxidation was studied mainly by optical methods and sheet resistance measurements. The films oxidized only slightly at 5 and 15°C. At 25 and 35°C an oxide film formed faster. The thickness of the oxide as well as the sheet resistance of metal films increased in the course of time. Since ozonated water processing cause only slight oxidation of aluminum thin films it is suggested that this resist removal process can be utilized in integrated circuit processing.

AWG Based DWDM Multiplexers Combined with Attenuators on SOI

We report on the design, fabrication and optical characteristics of SOI based AWG multiplexers combined with attenuators. The AWG devices and attenuators comprised 8 channels with 200 GHz channel spacing around 1550 nm wavelength.

Erbium-doped planar waveguides with atomic layer deposition method

In this work the feasibility of the atomic layer deposition (ALD) in producing erbium-doped waveguides is studied. Two microns thick erbium-doped aluminum oxide layers were grown with ALD on silica-coated silicon wafers. The waveguides were patterned using photolithography and wet etching. Resulted single-mode ridge-type waveguides were measured to obtain absorption, emission, fluorescence lifetime, and gain characteristics. Optical pumping was done using the 980 nm wavelength. The material showed broad emission spectrum with FWHM of 52 nm and maximum absorption of 6.2 dB/cm at 1530 nm. Maximum signal enhancement of 2.6 dB/cm was measured at 1530 nm for the 20 dBm signal power.