Krzysztof Nieweglowski

Demonstration of board-level optical link with ceramic optoelectronic multi-chip module

This paper demonstrates a complete short-distance parallel optical interconnection on PCB-level basing on ceramic transmitter/receiver modules for high-speed signal conversion, integrated polymeric waveguides and the optical coupling elements. The novel technology for the structuring of PCB-compatible high density parallel optical interconnects will be described in detail. The solution for the optical coupling into the integrated waveguides is based on a micro-optical indirect coupling element with wave guiding structures. The demonstrated optoelectronic modules are 4-channel BGA ceramic multi-chip modules with 4 × 10 Gbps transmission capacity.

Optical Analysis of Short-Distance Optical Interconnect on the PCB-Level

The paper describes an optical analysis of the complete optical link on the PCB-level in regard to the optical coupling between interconnect components: vertical cavity surface-emitting laser array (VCSEL), micro-optical coupling elements, integrated waveguides and p-i-n-photodiode array. The optical coupling efficiency was evaluated using spatial coupling characteristics of the interface between micro-optics and waveguide as well as micro-optics and optoelectronic device. Especially, the investigation on the micro-optical coupling element was emphasized. The influence of technological processing of passive optical components on the optical loss was determined - the dependence of endface quality on the coupling efficiency

Analysis of Bending Effects for Optical-Bus-Couplers

Goal of the presented work is the development of an optical bus-coupler, which enables easy connection between two waveguides without interrupting the bus. It is possible to realize optical bus systems by connecting several modules onto one waveguide with a core-core-coupler. In this paper we present the concept of a bus-coupler, which is suitable for a bidirectional coupling with a definable ratio. In order to tune the coupling efficiency bended flexible planar waveguides are used, which are pressed onto the bus with a defined force adjusting the overlap area of the two coupling waveguides. We will introduce the manufacturing of the multimode waveguides on flexible substrates by photolithographic structuring. Furthermore, we present results of our investigations on the behavior of planar waveguides under bending in terms of optical losses and power distribution within the waveguide core. Based on the experimental results we will derive the requirements and design rules for the coupling element.

Energy-Efficient Transceivers for Ultra-Highspeed Computer Board-to-Board Communication

Enabling the vast computational and throughput requirements of future high performance computer systems and data centers requires innovative approaches. In this paper, we will focus on the communication between computer boards. One alternative to the bottleneck presented by copper wire based cable-bound communication is the deployment of wireless links between nodes consisting of processors and memory on different boards in a system. In this paper, we present an interdisciplinary approach that targets an integrated wireless transceiver for short-range ultra-high speed computer board-to-board communication. Based on our achieved results and current developments, we will also estimate energy consumption of such a transceiver.

Performance of step index multimode waveguides with tuned numerical aperture for on-board optical links

This paper discusses experimental results of optical characterization of low-loss, robust, high-speed optical link basing on step index (SI) polymeric multimode waveguides. In order to enhance the bandwidth of optical waveguides tuning of numerical aperture by material adoption has been implemented. However, trade-off between tolerance requirements, bandwidth and design rules have to be found. In this paper experimental performance evaluation of SI polymeric waveguides by insertion loss measurement, near- and far-field analysis and optical transmission measurements at high data rates will be investigated. The measurement results will be finally analyzed in order to derive design rules for onboard optical interconnects with multi Gbit/s × m performance.

Design and optimization of planar multimode waveguides for high speed board-level optical interconnects

This paper describes the experimental investigation on the influence of geometrical waveguide parameters and material combination (refractive index contrast) onto relevant waveguide characteristics: optical attenuation, mode conversion, assembly tolerances and calculated bandwidth. For achieving waveguide structures with different geometries a test mask with a variation of the line width was developed. The application of a material system with tunable refractive index enables the change of numerical aperture (NA) of the waveguide. The fabricated waveguides will be characterized in their far field in order to define the NA at the waveguides output. The realization of these measurements for different waveguide lengths and core cross sections enables the characterization of the numerical aperture change caused by mode conversion and mode dependent attenuation. These phenomena have influence on intermodal dispersion, which limits the bandwidth capacity of the waveguide. The additional near-field analysis on the end face of the waveguide for the aforementioned design parameters variations will illustrate the mode filling and conversion along the waveguide. Additionally, the paper will analyze the influence of waveguide design parameters on the optical propagation loss by using attenuation measurements. On the other hand, the requirement for a robust optical coupling into the board-level optical interconnects call for relaxed assembly tolerances, which are also dependent on geometrical waveguide parameters. Finally the achieved experimental results will be analyzed in order to derive design rules for low-loss, robust optical link basing on multimode waveguides and ultimately enable multi Gbps m performance.

Assembly tolerance requirements for photonics packaging of multi-cell laser power converters

Power over fiber or photonic power is an attractive alternative for powering remote sensors in electromagnetically sensitive environments. Compared to energy harvesting, it can deliver uninterrupted energy in larger amounts (up to few hundreds of milliwatts) to enable more elaborate sensing, computation or even actuation along with continuous communication requirements. From the photonic packaging perspective, the passive fiber chip coupling becomes a challenge, since non-uniform illumination causes changes in the series resistance of individual cells and varying current-voltage characteristics. The paper at hand characterizes multi-cell laser power converters in depth and describes the integral coupling efficiency from 3D spatial mapping of its maximum power point. Besides the scans for the series connected cells, individual contributions of the segments are studied by single cell characterization to discover intra-individual deviations of cell resistance and conversion efficiency, which might affect the optimal power distribution. Moreover, the spatial responsivity distribution of individual cells, depending on different finger electrode and bus bar configurations. The measurements ultimately yield an assembly tolerance analysis for passive photonic packaging of multi-cell laser power converters. The results are well suited to optimize the packaging process as well as predict the expected device performance.

Assembly tolerant design of multi-cell laser power converters for wafer-level photonic packaging

Power over fiber is an attractive alternative for powering remote sensors in electromagnetically sensitive environments. Compared to energy harvesting, it can deliver uninterrupted energy to sufficiently supply elaborate sensing, computation or even actuation along with a continuous communication requirement in distributed sensor networks, as for example in structural health monitoring. For the photonic packaging the passive fiber-chip-coupling is one of the biggest challenges. Due to non-uniform illumination of the individual sub-cells and their technological mismatch in electrical characteristics the assembly tolerances are comparatively tight and therefore the manufacturing costs are respectively high. Hence, an assembly tolerant design of the laser-power-conversion (LPC) chip has to be developed to relax the photonic packaging demands. The paper will aggregate comprehensive real characterization results of existing multi-cell laser power converters and real-life fiber light sources into a dedicated design tool. In order to decrease the tolerance requirements and to adjust the LPC to a specific output power at an optimized efficiency, various LPC designs with different cell numbers and arrangements are numerically optimized and reviewed in comparison. The model initially calculates the overlap integral with an ideal uniform illumination. Then, the model can be enhanced by using real power distributions of typically used multimode fibers. The results presented in this paper are well suited to fabricate both efficient LPCs and validate their passive alignment for wafer-level packaging.

Simulation of bended planar waveguides for optical bus-couplers

In our work an optical bus-coupler is proposed, which enables easy bidirectional connection between two waveguides without interrupting the bus using a core-to-core coupling principle. With bended waveguides the coupling ratio can be tuned by adjusting the overlap area of the two cores. In order to ensure large overlap areas at short coupling lengths, the waveguides have rectangular cross sections. To examine the feasibility of this coupling concept a simulation was performed, which is presented in this paper. Due to multimode waveguides, used in short range data communication, a non-sequential ray tracing simulation is reasonable. Simulations revealed that the bending of the waveguide causes a redistribution of the energy within the core. Small radii push the main energy to the outer region of the core increasing the coupling efficiency. On the other hand, at excessive lowered bend radii additional losses occur (due to a coupling into the cladding), which is why an optimum has to be found. Based on the simulation results it is possible to derive requirements and design rules for the coupling element.

Laser Power Converters for optical power supply

Laser Power Converters are dedicated semiconductor devices that convert optical energy into electrical energy. Opposed to solar cells they are optimised for high energy density and conversion efficiency mostly under laser illumination. These cells are applied as power supply in electromagnetically sensitive areas or for galvanic decoupling of transmitter and receiver. Depending on the application in remote sensor or actuator networks, different power needs have to be satisfied. In this paper a couple of single cells were connected in series to increase the voltage, the power and the efficiency. The measurement set-up developed for the characterisation of the cells is presented.