THIS thesis describes the development of a positionable waveguide array realized in a silicon nitride / silicon dioxide (Si3N4 core / SiO2 cladding) photonic platform. The positionable waveguide array is the heart of a novel alignment approach for high precision multi-channel chip-to-chip interconnects. This alignment approach enables submicron accurate alignment of an Indium Phosphide (InP) Photonic Integrated Circuit (PIC) and a TriPleX interposer chip. Mechanically flexible waveguides with integrated alignment functionality are realized within the TriPleX interposer chip. Compared to competing alignment approaches, the proposed concept targets higher accuracy and precision and allows for an increased level of automation to lower assembly time and cost. The final alignment of the waveguides is achieved in two stages. In the first stage, both chips are flip-chip bonded on a common substrate. The result of this first stage is a coarse alignment of the waveguides of both chips, as well as mechanical fixation and electrical connection of both chips. In the second stage, integrated alignment functionality of the positionable waveguide array within the TriPleX interposer chip is used to optimally align the interposer waveguides with the waveguides of the InP PIC. Once aligned, the alignment function of the positionable waveguide array has served its purpose and the positionable waveguide array is mechanically fixed, providing an optimal alignment for the lifetime of the PIC.@en

Recent decades have seen impressive developments in the field of integrated photonics. Chips with complex photonic functionality can presently be designed and fabricated. Photonic packages consist of one or more PICs, as well as other (micro-optical) components, and a fibre (array) to establish the external optical interface. A core challenge is the assembly and packaging of these complex devices, involving sub-μm alignment of components. To overcome the limitations in multi-chip photonic packaging, a concept is proposed which uses on-chip actuators for the fine-alignment of flexible waveguide structures.@en

In this paper, we present positionable photonic waveguide arrays that are developed for optical chip-to-chip alignment. Partly suspended photonic structures, based on the Si3N4/SiO2 material platform, are equipped with thermal actuators enabling the free end of the structures to be positioned with submicrometer accuracy. A finite-element model is developed to provide insight in the way the design of the system affects the performance. The modeling results show that the expected vertical deflection and rotation are highly dependent on the array design. Measurements of fabricated devices confirm the trends that follow from the model and are used to assess the positioning performance. Moreover, the finite-element analysis gives guidelines for the design parameters of an optimal positionable photonic waveguide array. By following these guidelines, all the requirements for the intended photonic alignment can be fulfilled, which is validated by measurements. The stability over time of the positioning system is experimentally determined and is also sufficient. Measured mode field profiles of partly suspended waveguide beams with 1μm×220nm (width × thickness) sized waveguide cores show correct waveguiding functionality. Finally, an alignment experiment demonstrates how three adjacent waveguide beams within a positionable waveguide array can be actively aligned with the channels of another photonic chip. [2017-0046]@en

This paper reports on the progress related to a multichannel photonic alignment concept, aiming for sub-micrometer precision in the alignment of the waveguides of two photonic integrated circuits (PICs). The concept consists of two steps: chip-to-chip positioning and chip bonding provide a coarse alignment after which waveguide-to-waveguide positioning and fixing result in a fine alignment. For the waveguide-to-waveguide alignment, an alignment functionality is developed and integrated in one of the PICs, consisting of mechanically flexible waveguides and MEMS actuators. This paper reports on the fabrication and characterization of a mechanically flexible waveguide array that can be positioned by two out-of-plane actuators. Thermal actuators are integrated with mechanically flexible waveguide beams to enable positioning them with high precision. By adding a poly-Si pattern on top of SiO2 beams, an out-of-plane bimorph actuator can be realized. An analytical model enables estimating the curvature and the deflection of a single bimorph beam. Acquiring a small initial deflection while having a large motion range of the actuator proves to have conflicting demands on the poly-Si/SiO2 thickness ratio. In this paper, we show that suspended waveguide arrays with integrated alignment functionality have an initial deflection- they curl up- due to residual stress in the materials. The actuators can be operated using a driving voltage between 0V to 45V, corresponding to ∼50mW. Using higher voltages brings the risk of permanently changing the material properties of the heaters. The actuators can accomplish an out-of-plane crossbar translation up to 6.5 μm at ∼50mW as well as a rotation around the propagation direction of the light ranging from -0:1° to 0.1°. At a constant actuation power of ∼50mW, the crossbar shows a drift in vertical deflection of 0.16 μm over a time of 30 min.@en

This paper proposes and tests a design of electro-thermal bimorph actuators for alignment of flexible photonic waveguides fabricated in 16 μm thick SiO2. The actuators are for use in a novel alignment concept for multi-port photonic integrated circuits (PICs), in which the fine alignment is taken care of by positioning of suspended, mechanically flexible waveguide beams on one or more of the PICs. The design parameters of the bimorph actuator allow to tune both the initial relative position of the waveguide end-facets, and the motion range of the actuators. Bimorph actuators have been fabricated and characterized. The maximum out-of-plane deflection of the bimorph actuator (with 720 μm-long poly-Si) can reach 18:5 μm with 126:42mW, sufficient for the proposed application.@en

This paper describes the design, fabrication and characterization of electrothermal bimorph actuators consisting of polysilicon on top of thick (>10 μm ) silicon dioxide beams. This material platform enables the integration of actuators with photonic waveguides, producing mechanically-flexible photonic waveguide structures that are positionable. These structures are explored as part of a novel concept for highly automated, sub-micrometer precision chip-to-chip alignment. In order to prevent residual stress-induced fracturing that is associated with the release of thick oxide structures from a silicon substrate, a special reinforcement method is applied to create suspended silicon dioxide beam structures. The characterization includes measurements of the post-release deformation (i.e., without actuation), as well as the deflection resulting from quasi-static and dynamic actuation. The post-release deformation reveals a curvature, resulting in the free ends of 800 μm long silicon dioxide beams with 5 μm-thick polysilicon to be situated approximately 80 μm above the chip surface. Bimorph actuators that are 800 μm in length produce an out-of-plane deflection of approximately 11 μm at 60 mW dissipated power, corresponding to an estimated 240 ^oC actuator temperature. The delivered actuation force of the 800 μm-long bimorph actuators having 5 μm-thick polysilicon is calculated to be approximately 750 μN at 120 mW.@en

Fully automated, high precision, cost-effective assembly technology for photonic packages remains one of the main challenges in photonic component manufacturing. Next to the cost aspect the most demanding assembly task for multiport photonic integrated circuits (PICs) is the high-precision (±0.1 μm) alignment and fixing required for optical I/O in InP PICs, even with waveguide spot size conversion. In a European research initiative - PHASTFlex - we develop and investigate an innovative, novel assembly concept, in which the waveguides in a matching TriPleX interposer PIC are released during fabrication to make them movable. After assembly of both chips by flip-chip bonding on a common carrier, TriPleX based actuators and clamping functions position and fix the flexible waveguides with the required accuracy.@en