Micro-Fabrication as Enabler for Sub-µm Photonic Alignment Marcel Tichem, Johan F. C. van Gurp, Tjitte-Jelte Peters, Vincent A. Henneken Delft University of Technology, Micro and Nano Engineering Laboratory, Delft, The Netherlands m.tichem@tudelft.nl Abstract In the manufacturing of photonic packages, the alignment of the components must often meet strict precision demands. For several applications, sub-micrometre alignment must be achieved, and this precision needs to be maintained once the components are aligned. In our research we explore the use of micro-fabrication technology as the enabler for reaching sub- µm alignment precision. Two main concepts are presented: the use of micro-actuators for active alignment and the use of mating structures for passive alignment. Results from MEMS- based active fibre alignment and multi-port passive chip-to- chip alignment are described. Finally, the paper discusses the limits and applicability of the two concepts. Introduction Within the domain of microsystem integration, the assembly and packaging of photonic components poses a technical challenge. The components in the package or device need to be precisely aligned, in order to maximize the efficiency of light coupling. The typical critical components of a photonic package include optical fibres, diodes (laser diodes or photodiodes) and more recently Photonic Integrated Circuits (PICs), e.g. fabricated in III-V materials, and which have multiple optical waveguides. Required alignment precision may be at sub-µm level (≈ 0.1−0.2µm), depending on the mode size and wavelength of the light. Positioning and fixing the position of photonic components at these levels of precision is technically challenging, In addition, applications in consumer devices and instruments require cost-competitive solutions. As an example, the cost of InP-based PIC fabrication has reduced over the past years, which makes the packaging the bottle- neck process, both technically and cost-wise speaking. Current technology for precise photonic integration includes the use of micromanipulators [1] and laser adjustment procedures [2]. In passive alignment, mating geometric features [3] and vision system-based approaches have been explored [4]. Solder self-alignment, in combination with end-position defining geometric features is also proposed [5]. Currently known alignment precision between two components in passive alignment is around ±1 µm for optical fibres [6] and ±0.5-1.0 µm for chip-to-chip waveguide alignment [7, 8]. In our research we explore concepts for photonic alignment which use micro-fabrication as core enabling technology to create high-precision alignment and fixing approaches. In this context, micro-fabrication refers to all lithography-based fabrication processes to realise geometric features and more complex functions in a wafer-based production scenario. Lithography allows creating features with high precision in relative position, and allows creating functions at small size scale. The cost can be competing provided that devices are produced in sufficient volumes. This paper introduces two main distinct concepts for sub- µm photonic alignment we have explored in our research. The two concepts are the use of integrated active alignment functions (MEMS-based actuators; MEMS stands for MicroElectroMechanical System) and passive alignment functions using geometric features respectively. In the passive alignment concept we attempt to work towards ± 0.1 µm precision. For specific situations, active and passive alignment are very close then in achievable precision, and this asks for a further comparison of the two approaches. The paper first elaborates on main alignment concepts. Then, typical designs and results from our research for the two main alignment concept (MEMS-based active alignment and geometrically constrained passive alignment) are described. Finally, the concepts are compared and conditions for successful application are identified. Alignment concepts Fig. 1 shows the main approaches to photonic alignment. Generally speaking, component alignment can either be done in an open-loop assembly process or in a closed-loop assembly process. Fig. 1. Alignment strategies. In an open-loop assembly process, the final position of the components is determined by fabricated features in the components. A reliable assembly process is needed which brings the components in the final location. A reliable assembly process is a process which is free from alignment failure mechanisms, e.g. errors due to curing of the bonding material, stick slip phenomena, or dirt. In a closed-loop assembly process, during the assembly of the components feedback is used to control the position. This can either be position information for instance provided by camera systems, or performance information, like the amount of coupled light. The last mentioned scenario requires that the active optical component is switched on during alignment. This approach is referred to as active alignment, while the other approaches are referred to as passive alignment. Active alignment generally