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Photonic wire bonding (PWB) is an enabling technology that allows the combination of the complementary strengths of different optical integration platforms in advanced photonic multichip modules. By utilizing PWB technology, compact designs with great design flexibility can be achieved while still maintaining high performance. The principle of PWB technology relies on highly precise direct-write 3D laser lithography for the printing of freeform single-mode waveguides. The PWB single-mode waveguides are printed between the optical dies of separate optical components, enabling interconnectivity between different material platforms. An advantage of the technology is that it offers a path towards fully automated mass production of interconnects without the need for active alignment. The flexible freeform geometry of the PWB and the principle of its manufacturing can compensate for a range of challenges inherent in the coupling of optical components on a submount. PWB technology can hereby offer solutions for the typical challenges of photonic multi-chip assemblies such as offsetting the pitch error of arrays, correcting for mode field mismatches between different optical devices and amending the misalignment of optical components either via manual or pick and place errors. This publication studies a solution to realize optical interconnects between edge-emitting Indium Phosphide based laser diodes and single-mode optical fiber arrays (SMF-FA). Here, the interconnects were achieved by using the PWB technology in a Vanguard Automation Symphony 1000 suite (comprising of Vanguard’s Sonata 1000 and Reprise 1000 systems). The Vanguard Automation Symphony 1000 suite can compensate for lateral as well as vertical misalignments of up to 20µm. This enables the laser diodes as well as the SMF-FA to be assembled on a common sub-mount either manually or with standard pick and place tooling equipment. The precise locations of the coupling interfaces of laser diode waveguides and the SMF are determined with an accuracy of well below 100 nm by the detection mechanisms of the Vanguard Sonata 1000 system. Based on the detected positions of the laser and SMF interfaces, the Vanguard Brightwire3D software calculates on-the-fly the optimized low-loss trajectory of the PWB. At the same time the software also calculates the taper structures on both ends of the assembly which match the different mode fields of the laser diode waveguides and the SMF. Afterwards the freeform PWB is printed by a 2-photon-polymerization process with a femtosecond laser along the trajectory pre calculated by the Vanguard Brightwire3D software. 3D printing of the PWB is achieved in a relatively short time frame and can be fully automated with Vanguard Composer software. In this publication coupling losses of less than 2dB are demonstrated for the optical interconnects of laser diodes and SMF-FA. In general, PWB can achieve low insertion losses and have shown good reliability, e.g. meeting the GR-468-CORE standard requirements of more than 2000 hours at temperatures of 85°C and 85% relative humidity, and more than 500 thermal cycles between temperatures of -40°C to 85°C. This makes the PWB technology suitable for a wide range of applications from telecom and datacom, 3D sensing like lidar and quantum applications.
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