Bert Jan Offrein

Polymer-Waveguide-Based Board-Level Optical Interconnect Technology for Datacom Applications

On the basis of a realized 12times10 Gb/s card-to-card optical link demonstrator, the capabilities of a polymer-waveguide-based board-level optical interconnect technology are presented. The conception and realization of the modular building blocks required for this board-level optical interconnect technology are described in detail. In particular, we report on the fabrication and characterization of board-integrated optical low-loss polymer waveguides that are compatible with printed circuit board (PCB) manufacturing processes. We also explain our fully passive alignment technique, superseding time-consuming active positioning of components and connectors. To realize optical transceiver modules comprising vertical cavity surface emitting laser (VCSEL) arrays with laser drivers and photodetector arrays with transimpedance amplifiers (TIAs), a mass-production concept based on wafer-level processing has been elaborated and successfully implemented.

A 90nm CMOS integrated Nano-Photonics technology for 25Gbps WDM optical communications applications

The first sub-100nm technology that allows the monolithic integration of optical modulators and germanium photodetectors as features into a current 90nm base high-performance logic technology node is demonstrated. The resulting 90nm CMOS-integrated Nano-Photonics technology node is optimized for analog functionality to yield power-efficient single-die multichannel wavelength-mulitplexed 25Gbps transceivers.

160 Gb/s Bidirectional Polymer-Waveguide Board-Level Optical Interconnects Using CMOS-Based Transceivers

We have developed parallel optical interconnect technologies designed to support terabit/s-class chip-to-chip data transfer through polymer waveguides integrated in printed circuit boards (PCBs). The board-level links represent a highly integrated packaging approach based on a novel parallel optical module, or Optomodule, with 16 transmitter and 16 receiver channels. Optomodules with 16 Tx+16 Rx channels have been assembled and fully characterized, with transmitters operating at data rates up to 20 Gb/s for a 27-1 PRBS pattern. Receivers characterized as fiber-coupled 16-channel transmitter-to-receiver links operated error-free up to 15 Gb/s, providing a 240 Gb/s aggregate bidirectional data rate. The low-profile Optomodule is directly surface mounted to a circuit board using convention ball grid array (BGA) solder process. Optical coupling to a dense array of polymer waveguides fabricated on the PCB is facilitated by turning mirrors and lens arrays integrated into the optical PCB. A complete optical link between two Optomodules interconnected through 32 polymer waveguides has been demonstrated with each unidirectional link operating at 10 Gb/s achieving a 160 Gb/s bidirectional data rate. The full module-to-module link provides the fastest, widest, and most integrated multimode optical bus demonstrated to date.

A very short planar silica spot-size converter using a nonperiodic segmented waveguide

To reduce the coupling loss of a fiber-to-ridge waveguide connection, a planar silica spot-size converter for a wavelength of 1.55 /spl mu/m is implemented in the form of a nonperiodic segmented waveguide structure with irregular tapering. A simple single-step lithography process is sufficient for the fabrication of the planar structures. An evolutionary algorithm has been successfully applied for the optimization. The simulated results obtained with a three-dimensional (3-D) finite difference beam propagation method (FD-BPM) program are compared with measurements of implemented couplers, showing very good agreement. A waveguide-to-fiber coupling efficiency improvement exceeding 2 dB per converter is shown. Structures obtained with this approach are very short (/spl sim/140 /spl mu/m) and simple to integrate on the same wafer with other planar structures such as phased arrays or ring resonator structures.

Chip-to-chip optical interconnects

Terabus is based on a silicon-carrier interposer on an organic card containing 48 polymer waveguides. We have demonstrated 4times12 arrays of low power optical transmitters and receivers, operating up to 20 Gb/s and 14 Gb/s per channel respectively

A strong electro-optically active lead-free ferroelectric integrated on silicon

The development of silicon photonics could greatly benefit from the linear electro-optical properties, absent in bulk silicon, of ferroelectric oxides, as a novel way to seamlessly connect the electrical and optical domain. Of all oxides, barium titanate exhibits one of the largest linear electro-optical coefficients, which has however not yet been explored for thin films on silicon. Here we report on the electro-optical properties of thin barium titanate films epitaxially grown on silicon substrates. We extract a large effective Pockels coefficient of r(eff) = 148 pm V(-1), which is five times larger than in the current standard material for electro-optical devices, lithium niobate. We also reveal the tensor nature of the electro-optical properties, as necessary for properly designing future devices, and furthermore unambiguously demonstrate the presence of ferroelectricity. The integration of electro-optical active films on silicon could pave the way towards power-efficient, ultra-compact integrated devices, such as modulators, tuning elements and bistable switches.

Cascaded Mach-Zehnder wavelength filters in silicon photonics for low loss and flat pass-band WDM (de-)multiplexing.

We present 1-to-8 wavelength (de-)multiplexer devices based on a binary tree of cascaded Mach-Zehnder-like lattice filters, and manufactured using a 90 nm CMOS-integrated silicon photonics technology. We demonstrate that these devices combine a flat pass-band over more than 50% of the channel spacing with low insertion loss of less than 1.6 dB, and have a small device size of approximately 500 × 400 µm. This makes this type of filters well suited for application as WDM (de-)multiplexer in silicon photonics transceivers for optical data communication in large scale computer systems.

SiON high-refractive-index waveguide and planar lightwave circuits

The rapidly growing optical communication market requires photonic components with ever-increasing functionality and complexity that can be fabricated reliably at low cost. Of the various approaches used to fabricate photonic components, those based on planar waveguides have achieved high performance and represent a promising path toward compact integration of optical functions. We present an overview of an approach used to produce an optical single-mode waveguide. Through its strong mode confinement, the approach makes it possible to integrate optical filter functions with higher functionality, as required for high-data-rate communication networks. The waveguide is based on the use of a silicon oxynitride (SiON) core and silicon oxide cladding layers, and can be fabricated using conventional chip fabrication techniques. Using the new approach, conventional passive optical components such as arrayed waveguide gratings for wavelength-division-multiplexed transmission systems can be fabricated in a more compact way than using standard silica-on-silicon waveguide methods. Moreover, the realization of more enhanced, adaptive optical functions such as finite- impulse-response as well as infinite-impulse-response filters is possible. Reconfiguration is achieved through the thermo-optic effect. A reconfigurable gain-flattening filter and an adaptive dispersion compensator are presented as examples.

Adaptive gain equalizer in high-index-contrast SiON technology

An adaptive gain equalization filter is presented. The filter is based on the resonant coupler principle, a cascade of power couplers and delay lines. Reconfigurability and tuning is achieved by varying coupling strength and delay line length via the thermo optic effect. A device consisting of seven delay line stages was realized in high-index-contrast silicon-oxynitride technology. This device flattens the ASE spectrum of an EDFA to a ripple of less than 0.5 dB over 35 nm. The on-chip losses are 2 dB.

Resonant coupler-based tunable add after-drop filter in silicon-oxynitride technology for WDM networks

We present a tunable add-drop filter for wavelength division multiplexing (WDM) networks based on the resonant coupler (RC) principle. The device operates in the 1550-nm window with a wavelength spacing of 1.6 nm (200 GHz) and a periodicity of 6.4 nm (800 GHz). The splitting of the add and drop functions in an add-after-drop configuration results in extremely low homowavelength crosstalk and allows the individual design of the add and drop subfunctions to be optimized. The design of the flat-passband drop function is presented in detail. The compact filter is realized in high-index-contrast silicon-oxynitride technology, which permits small bending radii of 1.5 mm. Phase errors in the delay lines of the RC devices are compensated using the thermooptic effect, which is also used to tune the device. Measurement results on packaged devices show fiber-to-fiber losses of between 5 and 7 dB. The isolation of the transit WDM channels to the drop port is greater than 27 dB, and the rejection of the drop channel is 33 dB. The components are polarization insensitive and have been integrated in an add-drop WDM subsystem.