Mikko Harjanne

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

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}

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.

-Scale Si Platform

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.

Hybrid integration of InP lasers with SOI waveguides using thermocompression bonding

A novel guided-wave optical power coupler is presented, based on two 2x2 50/50 multimode interference splitters connected with tapered waveguides that play the role of a phase shifter. By simply changing the length of this phase shifter, these double-MMI couplers can be easily designed to get any desired splitting ratio. Results of simulations are discussed and compared with the characterizations of devices fabricated on micron-scale SOI wafers, to highlight pros and cons of the proposed solution. The fabricated splitters have been found to have average losses about 0.4 ± 0.5 dB and splitting ratios ranging from 56/44 to 96/4.

Low-error and broadband microwave frequency measurement in a silicon chip

A novel method has been developed for measuring the rota- tional angle of a fibers or a waveguides polarization axis with respect to a reference angle. The reference angle is the polarization axis of the measuring device. The method also gives the true polarization extinction ratio of the measured fiber or waveguide. The method is suitable for the characterization and rotational alignment of polarization-maintaining waveguides and fibers. In particular, the method can be used to rotation- ally align the fiber-waveguide interconnections during waveguide char- acterization. The measuring device is either a linear polarizer or a polar- ization splitter that is accurately rotated with respect to the device under test. According to the experiments with a polarization-maintaining fiber, the method is very easy and inexpensive to implement, and the angular accuracy can be better than 0.2 deg.