Norbert Arndt-Staufenbiel

New technology for electrical/optical systems on module and board level: the EOCB approach

Besides the optical wide and local area networks (WAN and LAN) there is a growing request for short-distance solutions like in backplanes, boards, and modules. Optical interconnections within systems and packages transmit data rates up to some Gbit/s with low loss, crosstalk, EMV sensitivity or reflections. But here the fibers provide no satisfying assembling strategies. To find a more efficient solution, the Fraunhofer IZM has developed a packaging concept, which is based on a hybrid carrier containing both, electrical and optical interconnects: the EOCB (Electrical Optical Circuit Board). The key element is an additional optical layer with waveguide structures. This layer is handled by standard PCB technology. The result is, that waveguides are incorporated into the circuit board. For first tests we used the hot embossing process for foil structuring. After core filling and sealing it with an overcladding, the optical layer is given into the PCB process. But other solutions for the waveguide structuring are possible too. They are currently under development. The EOCB uses multimode waveguides to relax assembly tolerances. It has an interface to common SMD technology. Therefore the EOCB concept merges-with current methods of manufacturing equipment. Special optoelectronic components have been designed and fabricated to demonstrate the concept. First results will be presented on the integration of the future information medium light into the board.

Glass panel processing for electrical and optical packaging

Glass is a perfect substrate material for electrical and optical packaging. The integration concept to bridge board and chip level using thin glass substrates by lamination in between of PCB base material will be presented. Different thin glasses are commercial available and will be reviewed. Furthermore the paper reviews glass panel processing in the area of display and electro/optical packaging focusing on integration advantages for photonic packaging. Ion exchange technology for large panel processing to integrate high-performing optical waveguides will be demonstrated for multi-mode beam propagation. Based on glass based photonic system-in-package (SiP) which is done on wafer level the up scaling on panel size of those processes is discussed in detail and experimental results are presented.

Advanced thin glass based photonic PCB integration

The central aim of the overall is the realization of electro-optical circuit boards (EOCB) by using thin glass as known from display technology. Such technologies give the possibility to develop products with improved performance, higher reliability, lower costs and higher energy efficiency. A crucial building block is the integration of optical signal transmission within the EOCB. A presentation of size-enlarged EOCB with holohedrally integrated glass foils is subject of the paper. These EOCB are capable to provide future bandwidth standards through integrated optical waveguides for high speed intra system optical data transmission as well as sensor technology. Therefore structuring technologies have been developed that are compatible to the industrially introduced PCB manufacturing. Already established processes as well as new approaches were analyzed for their eligibility and have been applied for the EOCB process.

Out-Of-Plane Coupling Using Thin Glass Based Arrayed Waveguide Components

Nano-photonics and electrical-optical integration are rapidly growing fields with a strong potential for applications in a wide spectrum covering optical sensing, data & telecommunication. Its merit of ultra compactness and planarity becoming a challenge since the periphery remained micro-level and out-of-plane coupling becomes necessary. We introduce new planar optical coupling elements for electrical-optical circuit boards, sensors and nano-devices. The novel photonic packaging technology using thin glass foils bridge the growing field of nano-photonics to the micro-photonic periphery. Innovative features are added to this technique to leverage its generic usage and first experimental results are presented.

Specific glass fiber technologies: lensing and laser fusion

Besides the common fiber technologies like splicing, polishing and coating there is a demand for specific methods for advanced packaging solutions in the field of telecom and medical applications. We present here three of such methods for lensing glass fibers that can be used to increase optical performance and reliability as well as to reduce the packaging efforts. These technologies are very useful for micro optical assembly, i.e. fiber connectors for high power applications, collimators and telecom transceivers and endoscope imaging or sensor systems. At the Fraunhofer Institute for Reliability and Microintegration Berlin special photonic packaging solutions are developed. Optical interconnects have been obtained a great importance for optical data transfer. Optical fibers are necessary for disturbance free communication of high data rates via long distances. Optical system components perform generation, distribution, transformation, amplifying and processing of optical signals. Thats why optical systems are a assembly of different kinds of functional basic elements such as optical fibers, splitters, switches, modulators, transmitters and detectors. Furthermore, industrial applications need a reliable and cost effective coupling of optical fibers to those systems.

New options for chip-to-chip photonic packaging by using thin glass-based waveguide substrates on board and module level

Electrical-optical integration is a rapidly growing field with a strong potential for applications in a wide spectrum covering optical sensors, data & telecom, respectively. The driving forces are bandwidth demand, power efficiency and increased channel density. For higher degrees of integration thin glass substrates provide very suitable properties. The technology of the glassPack concept relies on the realization of the passive single mode and multi mode optical waveguides within the thin glass substrates and benefits of the excellent optical, electrical, and thermal properties of glass itself. Suitable technologies are ion-exchange and direct optical butt coupling by laser fusion. The planar integrated single- or multi-mode waveguide is characterized by a graded refractive index profile. The laser fused fiber interconnect shows a determinate coupling loss. Also, planar waveguide array coupling elements of very flexible design can be applied for optical coupling and 90 degree light deflection. Novel innovative features are added to this packaging technique to leverage its generic usage. For electrical wiring thin film technologies and through glass vias have been demonstrated to address high integrate photonic System-in-packaging solutions. All together makes glass to the perfect platform for optical as well as electrical interconnects on board and module level. Multi-mode interconnects in thin glass layers of an EOCB as well as a glass based transceiver module show the integration potential of that approach. The demonstrated development goes hand in hand with ongoing trends in the area of silicon photonics to provide a suitable packaging and interconnection platform. Also the gap between single mode fiber interconnects and single mode SoI (silicon-on-insulator) waveguides in ICs (integrated circuit) can be bridged by the glass based interconnects on board and module level. The paper presents the glass packaging state-of-the art and discusses solutions to overcome demands in future.

Array fiber welding on micro optical glass substrates for chip-to-fiber coupling

High bandwidth parallel optical transceivers are highly demanded for optical interconnects in data centers and in high performance computing. Such transceivers are composed of VCSEL- and photodiode components which have to be fiber coupled, and the appropriate driving and amplifying circuitry. For high density fiber optical connectors lens arrays for improved coupling efficiency have to be used. We propose an advantageous adhesive free method to interconnect optical fibers with such kind of lens arrays. Common approaches using adhesive bonding have high challenges in terms of yield, reliability and optical performance. We introduce our novel fiber welding approach for joining directly fused silica fibers on borosilicate glass substrates with integrated micro optics, e.g. lenses and lens arrays. It is a thermal process with a precise heat input by CO2-laser processing, which is combinable with sequential passive or active alignment of each single fiber to the substrate causing flexibility and highest coupling efficiencies. Since the fiber is accessed only from one side, a two dimensional high-density fiber array can be realized. The manufacturing time of such an interconnection is very short. Due to the adhesive free interface high power transmission is enabled and the occurrence of polymer caused misalignment and degradation are prevented. The paper presents current results in thin glass-based opto-electronic packaging. In particular our laboratory setup for array fiber welding and experimental results of such connections will be discussed and compared to UV-adhesive joining. Also further investigation, for example optical characterization and reliability tests are included. Finally a machine concept, which is under development, will be discussed.

Analysis of multi-mode to single-mode conversion at 635 nm and 1550 nm

We propose two low-cost and robust optical fiber systems based on the photonic lantern (PL) technology for operating at 635 nm and 1550 nm. The PL is an emerging technology that couples light from a multi-mode (MM) fiber to several single-mode (SM) fibers via a low-loss adiabatic transition. This bundle of SM fibers is observed as a MM fiber system whose spatial modes are the degenerate supermodes of the bundle. The adiabatic transition allows that those supermodes evolve into the modes of the MM fiber. Simulations of the MM fiber end structure and its taper transition have been performed via functional mode solver tools in order to understand the modal evolution in PLs. The modelled design consists of 7 SM fibers inserted into a low-index capillary. The material and geometry of the PLs are chosen such that the supermodes match to the spatial modes of the desired step-index MM fiber in a moderate loss transmission. The dispersion of materials is also considered. These parameters are studied in two PL systems in order to reach a spectral transmission from 450 nm to 1600 nm. Additionally, an analysis of the geometry and losses due to the mismatching of modes is presented. PLs are typically used in the fields of astrophotonics and space photonics. Recently, they are demonstrated as mode converters in telecommunications, especially focusing on spatial division multiplexing. In this study, we show the use of PLs as a promising interconnecting tool for the development of miniaturized spectrometers operating in a broad wavelength range.

Building blocks for actively-aligned micro-optical systems in rapid prototyping and small series production

In recent years there has been considerable progress in utilizing fully automated machines for the assembly of microoptical systems. Such systems integrate laser sources, optical elements and detectors into tight packages, and efficiently couple light to free space beams, waveguides in optical backplanes, or optical fibers for longer reach transmission. The required electrical-optical and optical components are placed and aligned actively in more than one respect. For one, all active components are actually operated in the alignment process, and, more importantly, the placing of all components is controlled actively by camera systems and power detectors with live feedback for an optimal coupling efficiency. The total number of optical components typically is in the range of 5 to 50, whereas the number of actors with gripping tools for the actual handling and aligning is limited, with little flexibility in the gripping width. The assembly process therefore is strictly sequential and, given that an automated tool changing has not been established in this class of machines yet, there are either limitations in the geometries of components that may be used, or time-consuming interaction by human operators is needed. As a solution we propose and present lasered glass building blocks with standardized gripping geometries that enclose optical elements of various shapes and functionalities. These are cut as free form geometries with green short pulse and CO2 lasers. What seems to add cost at first rather increases freedom of design and adds an economical flexibility to create very hybrid assemblies of various micro-optical assemblies also in small numbers.

Optical System Components for Navigation Grade Fiber Optic Gyroscopes

Interferometric fiber optic gyroscopes belong to the class of inertial sensors. Due to their high accuracy they are used for absolute position and rotation measurement in manned/unmanned vehicles, e.g. submarines, ground vehicles, aircraft or satellites. The important system components are the light source, the electro optical phase modulator, the optical fiber coil and the photodetector. This paper is focused on approaches to realize a stable light source and fiber coil. Superluminescent diode and erbium doped fiber laser were studied to realize an accurate and stable light source. Therefor the influence of the polarization grade of the source and the effects due to back reflections to the source were studied. During operation thermal working conditions severely affect accuracy and stability of the optical fiber coil, which is the sensor element. Thermal gradients that are applied to the fiber coil have large negative effects on the achievable system accuracy of the optic gyroscope. Therefore a way of calculating and compensating the rotation rate error of a fiber coil due to thermal change is introduced. A simplified 3 dimensional FEM of a quadrupole wound fiber coil is used to determine the build-up of thermal fields in the polarization maintaining fiber due to outside heating sources. The rotation rate error due to these sources is then calculated and compared to measurement data. A simple regression model is used to compensate the rotation rate error with temperature measurement at the outside of the fiber coil. To realize a compact and robust optical package for some of the relevant optical system components an approach based on ion exchanged waveguides in thin glass was developed. This waveguides are used to realize 1x2 and 1x4 splitter with fiber coupling interface or direct photodiode coupling.