Markku Kapulainen

Sub-/spl mu/s switching time in silicon-on-insulator Mach-Zehnder thermooptic switch

We have demonstrated both rise and fall times below 1 /spl mu/s with 10%-90% modulation in a silicon-on-insulator thermooptical Mach-Zehnder switch. The switch is based on 9-/spl mu/m-thick and 10-/spl mu/m-wide single-mode rib waveguides. Very fast switching was achieved by using a differential control method. The switch was driven with a digital signal processor accompanied by simple electronic circuitry.

Dramatic size reduction of waveguide bends on a micron-scale silicon photonic platform

We demonstrate theoretically and experimentally how highly multimodal high index contrast waveguides with micron-scale cores can be bent, on an ultra-broad band of operation, with bending radii below 10 µm and losses for the fundamental mode below 0.02 dB/90°. The bends have been designed based on the Euler spiral and fabricated on 4 µm thick SOI. The proposed approach enabled also the realization of 180° bends with 1.27 µm effective radii and 0.09 dB loss, which are the smallest low-loss bends ever reported for an optical waveguide. These results pave the way for unprecedented integration density in most semiconductor platforms.Even though submicron silicon waveguides have been proposed for dense integration of photonic devices, to date the lightwave circuits on the market mainly rely on waveguides with micron-scale core dimensions. These larger waveguides feature easier fabrication, higher reliability and better interfacing to optical fibres. Single-mode operation with large core dimensions is obtained with low lateral refractive index contrast. Hence, the main limitation in increasing the level of integration and in reducing the cost of micron-scale waveguide circuits is their mm- to cm-scale minimum bending radius. Fortunately, single-mode rib waveguides with a micron-scale silicon core can be locally transformed into multi-mode strip waveguides that have very high lateral index contrast. Here we show how Euler spiral bends realized with these waveguides can have bending radii below 10 {\mu}m and losses below 0.02 dB/90{\deg} for the fundamental mode, paving way for a novel densely integrated platform based on micron-scale waveguides.

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).

Dual SOA-MZI Wavelength Converters Based on III-V Hybrid Integration on a

We report on the simultaneous wavelength conversion operation of a dual-element semiconductor optical amplifier-Mach-Zehnder interferometer (SOA-MZI) array hybridly integrated on a 4-μm silicon-on-insulator (SOI) waveguide platform through thermocompression bonding. The SOAs are part of a six-element SOA array with both facets coupled on SOI through vertical and horizontal alignments. The device achieves almost two orders of magnitude reduction in footprint compared with state-of-the-art hybridly integrated SOA-MZI structures. We present for the first time experimental proof of the successful operation of a dual-element SOA-MZI device based on III-V technology on SoI that serves as a wavelength converter, with one SOA-MZI yielding error-free performance with a 0.8-dB power penalty at 12.5 Gb/s and the second SOA-MZI operating error-free at 10 Gb/s with a 2-dB power penalty.

\mu{\rm m}

Abstract. We present a method to etch vertical and smooth silicon sidewalls. The so-called modified Bosch process combines a passivation step, a breakthrough step, and an anisotropic etch step within one repeatable loop. Thanks to the sidewall protection from the passivation step and the anisotropic nature of the etch step, this method can etch smoother silicon sidewalls than either a typical Bosch process or a continuous anisotropic etch process. The silicon sidewall of a 4-μm-deep waveguide structure etched by this method has a root mean square roughness below 10 nm and a peak-to-valley (P-V) roughness below 60 nm. Comparisons between silicon waveguides etched by this process and by another deep reactive-ion etching process showed remarkable improvement in propagation loss at the wavelength of 1550 nm.

-Scale Si Platform

Thermocompression bonding of InP lasers to 4 mum thick SOI waveguides has been demonstrated. Good horizontal alignment is achieved by using active alignment. Excellent passive vertical alignment is reached by using a easily controlled fabrication process.

Smooth silicon sidewall etching for waveguide structures using a modified Bosch process

Instantaneous frequency measurement (IFM) of microwave signals is a fundamental functionality for applications ranging from electronic warfare to biomedical technology. Photonic techniques, and nonlinear optical interactions in particular, have the potential to broaden the frequency measurement range beyond the limits of electronic IFM systems. The key lies in efficiently harnessing optical mixing in an integrated nonlinear platform, with low losses. In this work, we exploit the low loss of a 35 cm long, thick silicon waveguide, to efficiently harness Kerr nonlinearity, and demonstrate the first on-chip four-wave mixing (FWM) based IFM system. We achieve a large 40 GHz measurement bandwidth and record-low measurement error. Finally, we discuss the future prospect of integrating the whole IFM system on a silicon chip to enable the first reconfigurable, broadband IFM receiver with low-latency.