Fraunhofer HHI’s hybrid photonic integration technology based on SiN and polymer waveguiding platforms enables photonic integrated circuits operating at wavelengths from the infrared down to the visible. Hybrid photonic integration processes allow integrating active photonic building blocks such as lasers and active sections, as well as non-reciprocal and non-linear functionalities. Those features prove the large potential of Fraunhofer HHI’s hybrid photonic integration technology in application domains such as sensing and quantum technologies.
A photonic engine for the integration of multi-lane optical transceivers is presented. The building blocks are InP-based electro-absorption modulated lasers and photodiodes capable of operating at 50 GBaud with PAM-4 modulation, and a low-cost polymer waveguiding chip providing routing of the multiple lanes and connectivity towards standard single-mode fibers. An automatic process for the hybrid assembly of the different building blocks has been developed, and photonic integrated circuits with up to 16 lanes have been demonstrated. Furthermore, high-frequency flexible interconnects with bandwidths beyond 100 GHz provide a connectivity solution between photonics and high-speed electronics.
Fraunhofer HHI's hybrid integration platform PolyBoard combines polymer passive waveguides with InP and other materials. We present new functionalities integrated in PolyBoard:
Isolation: With a microoptical bench integrated into polymer isolators can be built.
Quantum and sensing: By integrating nonlinear materials into the microoptical bench, 2nd (775 nm), 3rd (515 nm), and 4th (387 nm) harmonic generation could be observed
3D: First results for a 2x4 phased array have been achieved
Flip-chip laser active alignment: We have developed an active alignment process, which also works for flip-chip lasers which are impossible to electrically contact during the alignment process.
First automation results show the potential for cost effective volume scaling.
Nonreciprocal optical functionalities like optical isolators and circulators are key components for the suppression of unwanted optical feedback in lasers and are also widely used for light routing in fiber-based measurement systems such as optical coherence tomography. Therefore, they are important building blocks in integrated optics, which promises further miniaturization and cost reduction of optical elements for telecom, datacom, and sensing applications. In this work, we experimentally demonstrate a four-port polarization independent optical circulator on a polymer-based hybrid integration platform. The circulator consists of polymer waveguides and two thin-film polarization beam splitters (PBSs) inserted into waveguides via etched slots. Crystalline, pre-magnetized bulk Faraday rotators (FRs) and half-wave plates (HWPs) are inserted into free-space sections, formed by pairs of waveguide butt-coupled GRIN lenses. For a first demonstrator, on-chip losses down to 5 dB and optical isolations up to 24 dB were measured, depending on the different input and output constellations, as well as the polarization. By applying an external magnetic field opposite to the magnetization of the faraday rotators, it is possible to repole the magneto-optic material, leading to reversely circulating light inside the device. This enables optical switching between ports in form of a latching switch, which maintains its state after removing the external magnetic field.
3D photonic integration introduces a new degree of freedom in the design of photonic integrated circuits (PICs) compared to standard 2D-like structures. Novel applications such as large-scale optical switching matrices, e.g. for top-of- rack cross connect switches in data centers, benefit from the additional design flexibility due to their waveguide crossing-free architecture and compact footprint. In this work, a novel 3D 4×4 multi-mode interference coupler (MMI) based on HHI’s polymer-based photonic integration platform PolyBoard is presented. The fabrication process of the PolyBoard platform allows for the realization of vertically stacked polymer waveguide layers. Cascading two of the presented 3D 4×4 MMIs will form the building block of future large-scale 3D switching matrices. The 3D 4×4 MMI structure comprises two waveguide layers separated by a distance of 7.2 μm, with two input and two output waveguides in each layer, and a multimode interference (MMI) section in between. The vertical MMI section serves as the interconnection between the different waveguide layers and distributes the incoming light from each input waveguide across the four output ports of the 4×4 MMI. Design rules and fabrication methodology of these novel structures are presented in detail. Preliminary measurements demonstrate the proof-of-concept indicating an insertion loss below 9.3 dB, including fiber-chip coupling loss and the 6 dB intrinsic loss.
Recent developments in versatile polymer-based technologies and hybrid integration processes offer a flexible and cost-efficient alternative for creating very complex photonic components and integrated circuits. The fast and efficient test, optimization and verification of new ideas requires an automated and reproducible simulation and design process supporting flexible layout-driven and layout-aware schematic-driven methodologies. Targeting very complex designs, even small fabrication tolerances of one building block could make a huge difference on the performance and manufacturability of the whole structure. To reduce risk of failure and to make performance predictions by virtual prototyping reliable, the simulation model of each single building block needs to be working correctly based not only on the appropriate mathematical and physical equations, but also on adequate information provided by the foundry where the final structure will be manufactured.
The PolyPhotonics Berlin consortium targets to address these design challenges and establish a new versatile integration platform combining polymer with Indium-Phosphide and thin-film filter based technologies for numerous photonics applications in the global communications and sensing market. In this paper we will present our methodologies for modelling and prototyping optical elements including hybrid coupling techniques, and compare them with exemplary characterization data obtained from measurements of fabricated devices and test structures. We will demonstrate how the seamless integration between photonic circuit and foundry knowledge enable the rapid virtual prototyping of complex photonic components and integrated circuits.
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