We demonstrate the first electro-optic switch operating at cryogenic temperatures of 4 K with a high electro-optic bandwidth of >18 GHz. Our novel technology exploits the Pockels effect in barium titanate thin films co-integrated with silicon photonics and offers low losses, pure phase modulation, and sub-pW electro-optic tuning.

Interconnects have become a severe bottleneck in today's computing hardware. For large-scale data centers in particular, the interconnect situation is even more severe. The interconnect bandwidth and bandwidth density have to be increased on all system-levels. The ideal technology to increase the density is Si photonics (SiPh). While the integration of most of the SiPh components has been mastered already on a 90 nm CMOS platform, the integration of III-V materials to yield directly-modulated lasers still poses a major challenge. This integration is considered as the cornerstone for reaching a complete, yet cost-competitive, SiPh-CMOS marriage. Most concepts shown so far either lack CMOS-compatibility or have device dimensions that hinder the integration of the laser into a standard BEOL. To allow for a common BEOL between SiPh and CMOS, we integrate the III-V material between the FEOL and BEOL, within the first interlayer dielectric ILD0'. Such integration imposes tight requirements on device dimensions as well as several technological challenges that have to be mastered. We report here on decisive aspects of such integration. This represents a major step towards a full integration of III-V, SiPh and CMOS.

We report on a novel III-V-on-silicon-photonics device architecture with an excellent modal overlap with the III-V material. Using this concept, we demonstrate hybrid photo-detectors with very low dark currents, a responsivity of up to 0.8 A/W and a low capacitance of 0.2 pF.

Big Data and cloud-based applications drive the increasing amount of data traffic between and within data centers. Optical interconnect technology offers a larger bandwidth-distance product, interconnect density and power efficiency as copper based links. Integrated silicon photonics provides a tight integration between the optical functions with electronics on a single silicon die at the competitive cost-level of CMOS technology. All necessary silicon photonic building blocks operating at 1.3 μm and 1.55 μm have already been demonstrated. However, one of the remaining challenges is the system-level assembly, including a scalable connectorization scheme for very high optical I/O counts. To overcome this limitation, we demonstrate in this paper a silicon photonic packaging solution using polymer waveguides, which can be routed tightly to the silicon chip edge. As a first step towards this implementation, the optical coupling between a silicon photonics chip and the polymer waveguides is here discussed. The experimental results of the coupling loss and tolerance to misalignments between a silicon waveguide and a single-mode polymer waveguide processed on the chip are reported.

We report on recent developments of our board-level optical interconnect technology towards polymer waveguide flexes and on the adaption of connectorization and electro-optical assembly methods to be used in optical backplanes and high-density optical subassemblies.

report on the co-packaging of electrical CMOS transceiver and VCSEL chip arrays on a flexible electrical substrate with optical polymer waveguides. The electro-optical components are attached to the substrate edge and butt-coupled to the waveguides. Electrically conductive silver-ink connects them to the substrate at an angle of 90 degrees. The final assembly contacts the surface of a package laminate with an integrated compressible connector. The module can be folded to save space, requires only a small footprint on the package laminate and provides short electrical high-speed signal paths.With our approach, the electro-optical package becomes a compact electro-optical module with integrated polymer waveguides terminated with either optical connectors (e.g., at the card edge) or with an identical assembly for a second processor on the board. Consequently, no costly subassemblies and connectors are needed, and a very high integration density and scalability to virtually arbitrary channel counts and towards very high data rates (20+ Gbps) become possible. Future cost targets of much less than US$1 per Gbps will be reached by employing standard PCB materials and technologies that are well established in the industry. Moreover, our technology platform has both electrical and optical connectivity and functionality.

For the realization of a polymer waveguide based optical backplane link for computing applications, we developed a method to passively align multiple layers of polymer waveguide flex sheets in a single MT compatible ferrule. The minimal feature forming the backplane is a 192 channel link. This link is equipped with four MT connector at each end, and is performing a shuffling of the channels. We describe the passive alignment used to realize the connectors. The achieved accuracy demonstrated in a 48 channels connector consisting of 4 polymer sheets carrying 12 waveguides each, is shown to be better than ±5μm. The connection losses between a 48 channel MT fiber connector and the realized polymer waveguide connector were found to be about 2dB. Compared to fiber connectors, the presented concept using polymer waveguides has several advantages. The most relevant are that only few assembly steps are needed, it is based on a totally passive alignment scheme and it can easily be executed by standard pick and place tools.

Optical link technology will play an increasingly important role for board-level interconnects in servers and supercomputers as a means to keep pace with the increasing intra-system bandwidth requirements. Low-cost and high density optical packaging concepts are required. We describe the development of board-level interconnects based on polymer waveguide technology. In this paper, we focus on flexible optical waveguide sheets and the passive alignment of optical connectors.

We have jointly developed the material and processes to integrate silsesquioxane optical waveguides on printed circuit boards for high-speed datacom applications, using a low-loss, reliable and commercially available polymer designed for 850 nm.

In the long-distance telecom, local-area, and rack-to-rack link classes, optical interconnects have gradually replaced electrical interconnects. We believe that this trend will be continued in the short-distance card-backplane-card datacom link class. Convincing arguments for the predicted transition from electrical to optical interconnects are bandwidth-length advantages, density benefits, crosstalk reduction, and finally cost considerations. Based on this forecast, we currently develop a board-level optical interconnect technology facing several challenges, such as I) the manufacturing of reliable polymer waveguides, II) the elaboration of simple light-coupling concepts, III) the development of high-speed electro-optical modules, and IV) the application of cost-efficient packaging approaches. The successful mastering of all these tasks is a prerequisite for convincing high-speed system designers and porting optical interconnect technology into future product development plans. In this paper, we will present different achievements of our optical interconnect technology, e.g.: - 10 Gb/s per channel over 1 m link length, - optical link propagation loss below 0.05 dB/cm at 850 nm, - linear link densities up to 16 channels/mm, - feasibility of 2D channel arrays (e.g. 4 times 12), - a fully passive, low-cost alignment concept with a position accuracy of les 5 mum, enabling coupling losses < 0.5 dB, and - electro-optical transmitter and receiver modules operating at 10 Gb/s per channel. Finally, we will report on the successful realization of a 12 times 10 Gb/s card-to-card optical link demonstrator.

We report on a card-to-card optical interconnect demonstrator with passively aligned butt-coupled optoelectronic modules onto waveguides embedded into the printed circuit board (PCB). After describing selected building blocks, we will present experimental results obtained with the demonstrator hardware consisting of a parallel 12-channel at 10 Gb/s (120 Gb/s) optical card-to-card link.

A successful implementation of optics into PCBs (printed circuit boards) requires a precise passive alignment of optical elements relative to the optical waveguides in the board. We tackled this challenge with a novel concept that allows the passive alignment onto a PCB of any optical or optoelectronic building block with a precision of a few micrometers. Markers, structured into a copper layer during manufacturing, are used as a position reference for the polymer waveguide fabrication and for the formation of mechanical alignment features. To form the latter, laser drilling, a standard process for via formation in PCBs, is used. We were able to demonstrate repeated insertions of adapter elements into these alignment slots with a standard deviation of 3 mum for in-plane displacements. Afterwards, optical modules were mounted onto the adapters, using a standard MT interface provided by the adapter. We measured a standard deviation of the order of 5 mum for the in-plane and out-of-plane misalignments of the module with respect to the optical waveguides. The passive alignment concept demonstrated enables accurate and simple plug-in of any kind of element, in particular of optical and opto-electronic elements, into a PCB. The concept is based on established PCB manufacturing processes, which is crucial for the development towards a low-cost optical interconnect technology

Polymer waveguides embedded in a printed circuit board offer a substantial increase in the achievable bandwidth density compared with today's electrical interconnects. We present our results on the polymer waveguide technology and the building blocks that perform the optoelectronic conversion. Specific challenges in integrating optics in a printed circuit board are addressed. Data transfer measurements are presented.

Compared with electrical interconnects, optical interconnects offer several advantages, such as higher channel bandwidth and density, longer reach, and insensitivity to electro-magnetic interference. We developed an optical printed circuit board (PCB) technology platform and demonstrate a 12 ◊ 10 Gbps optical link between boards. Embedded polymer waveguides guide the optical signals, which are generated and detected by 12-channel optoelectronic modules. A polymer waveguide flex is used as optical link between boards. All connections between elements are based on passively aligned, standard MT interfaces, keeping costs low and providing compatibility with parallel fiber optics. The technology is also compatible with standard PCB processes. Optical Interconnects The increasing performance of microprocessors leads to higher bandwidth requirements for the data flow to and from the processor. Today, all signaling on a PCB is performed electrically, using copper lines that are integrated in the board. However, issues such as propagation loss and interchannel crosstalk, limit the scalability of electrical interconnects to ever higher bandwidth densities. A possible solution for these issues is the implementation of optical interconnects. Optical interconnects feature a higher bandwidth ◊ length product, are more power-efficient and enable a higher channel density than electrical interconnects above a certain data rate. It is especially this higher channel density of optics that drives the research on optical PCB technology for inter- system interconnects (1). However, we expect that before optical interconnects can find widespread use in PCBs, first the following two requirements have to be met: First, passive alignment, whereby the optical elements are simply plugged into the board without the need for optical monitoring and/or further fine adjustment, and, secondly, compatibility of optical PCB production with standard PCB manufacturing processes.