Results and Potential Impacts:
By M30, the project has delivered a coherent set of technical and scientific results that lay the foundation for the FMCW THz spectrometer and QIP demonstrators. System-level activities established and refined the use cases, system requirements, and prototype specifications, ensuring that all updated functional layouts comply with the performance targets defined for their application domains. The system design was successfully translated into component-level specifications, and the packaging and assembly process flows were refined to minimize fabrication risks while supporting reliable integration.
On the materials and integration side, FR-4 was selected as the baseline PCB substrate for the EO-PCB motherboards, following comparative analysis with Rogers 6002. The planarization process was optimized to achieve sub-micron reproducibility (<1 µm deviation), enabling optical coupling with <1 dB loss. PolyBoard waveguides fabricated on FR-4 substrates achieved propagation losses around 1 dB/cm for both TE and TM polarizations, a significant improvement over the first iteration. Progress was also made in etching recesses and grooves for flip-chipping, with first results expected in the following period. Wafer runs for both precursor and final demonstrators have been scheduled, ensuring continuity toward system-level integration.
In photonics development, high-performance external cavity lasers (ECLs) at 780 nm and 1550 nm were designed, fabricated, and partially tested, with integration of gain sections and submodules ongoing. The 1550 nm laser submodules designed in collaboration with Tera-6G broadened the impact of the work and ensure alignment with emerging applications. Calibration methodologies were developed for both Blass matrix–based beamforming networks (for FMCW systems) and Clements matrix architectures (for QIP systems). Blass and Clements matrix chiplets were fabricated, and preliminary squeezer chiplets for quantum applications were also produced.
For actuation technologies, PZT phase actuators demonstrated stable and linear operation in the 10–30 V range, with modulation speeds around 1 MHz and improved electrical stability at reduced voltages. Although thermo-optical shifters were adopted for the main demonstrators to reduce risks and shorten fabrication cycles, the PZT results pave the way for future low-power, high-speed applications.
Work on antennas and THz integration yielded the design and simulation of single and arrayed dielectric rod antennas, with a 1×4 THz array showing promising gain and beam steering capabilities. Integration concepts for antennas with the EO-PCB and InP devices were refined, and deliverable D2.5 documented the updated design of the THz antenna array. InP-based THz emitters and receivers were fabricated according to new flip-chip design rules, with initial wafer-level characterization confirming successful performance.
The flip-chip and soldering processes advanced through extensive experimental studies of materials, alignment, and bonding. Au stud bumps, conductive epoxy, and dispensing techniques were validated, contributing to the final definition of the POLYNICES cross-section. Passive alignment guidelines were shared with partners, and initial packaging concepts for both precursor and final demonstrators were defined.
System-level progress was visible in the assembly and packaging of demonstrators. Precursor-0A was fabricated, packaged, and characterized. Testing methodologies and KPIs for FMCW THz and QIP demonstrators were defined, and early experiments validated theoretical analyses, including the first noise analysis of FMCW THz systems. Driving and readout electronics, including current sources, single-channel and 10-channel PZT drivers, and mode-hop–free laser sweeping algorithms, were developed and tested.
Potential Impacts:
The project’s results demonstrate the feasibility of an integrated EO-PCB-based approach for next-generation THz spectrometry and quantum information processing. The combination of low-loss PolyBoard waveguides, validated FR-4 integration, novel antenna designs, compact drivers, and maturing PIC technologies provides a strong technological platform with potential to address pressing needs in high-resolution sensing, secure communications, and scalable quantum photonics.
In the medium term, the adoption of wafer-scale integration processes and refined packaging flows de-risks industrial scalability. The methodologies for system calibration (Blass and Clements architectures) directly support reproducibility and standardization of system-level performance, while the progress on multi-channel drivers and modular electronics ensures compatibility with diverse application environments.
