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.
Integrated spot size converters (SSCs) are key components for efficient coupling between Photonic Integrated Circuits (PICs) and fibre-arrays. We report a compact SSC which is suitable for integration into dense arrays with a pitch down to 25 μm and compatible with our generic InP-based platform technology, which supports integration of SOAs and Electro Optical Modulators with a range of passive components. The small pitch supports coupling tens of on-chip optical waveguide ports to fiber arrays via a low-loss dielectric interposer chip. The density allows the design of a customized optical bus between the InP PIC and the interposer chip. The dielectric chip may simply expand to the pitch of a fiber array but also contain low-loss passive circuitry like delay-lines, high Q-filters and multiplexers. The latter enables the formation of a hybrid integration platform with our InP-based technology. Efficient coupling is obtained by adiabatically transforming the sub-micron modes of the InP waveguides to the 3 μm diameter mode of the interposer. We tested our SSCs by coupling to a lensed fibre with a mode field diameter of 2.5 μm. Coupling losses were found to be as low as 0.6 dB per fiber chip coupling for device lengths of a few 100 μm. We also measured the crosstalk from one input port to output ports adjacent to the targeted output port. We present simple design rules for reducing the crosstalk to neighbouring output ports below -50 dB. The quality and uniformity of the SSCs is demonstrated by fabrication of an 8 x 8 AWG demultiplexer between two SSC arrays placed at input and output ports. We measured an insertion loss between fibres of 4 dB for the central channel of the AWG, which is record low for an InP-based device.