During the first 12 months, the consortium focused on foundational technology development across the main technical work packages (WPs):
• WP1 (Blue VCSEL Array):
We focused on the optical design and analysis of InGaN-based blue VCSELs with a focus on transverse mode control for development of single mode and polarization stable blue VCSEL. Finite-element simulations in COMSOL Multiphysics were performed to evaluate two key approaches: (i) index-guiding apertures based on etched nano-cylindrical waveguide and buried-SiO2 design, and (ii) mode-filtering through outcoupling-mirror loss modifications using surface reliefs and subwavelength gratings. We were able to find out that correct aperture dimension required to have single mode operation. And the design parameters of the surface relief required for a 6 µm aperture with single mode and polarization stable output.
• WP2 (Photonic integrated circuits and blue OPA on LNOI Platform):
The activities on the photonic integrated circuits in WP2 include simulation of devices, preparation in the cleanroom for the first chip fabrication, layout of the first chip, and fabrication of the first chip. These activities were to determine the dimensions of the passive components on the thin film lithium niobate chip, including optical waveguide, grating coupler, Multi-Mode Interference (MMI) splitter, and grating emitter. The dimensions of these devices were found through simulations in Ansys Lumerical. Furthermore, the dimensions of the optical modulator were determined through simulation.
• WP2 (Large-Scale DACs):
The activities of the electronic integrated circuits group in WP2 focus on the simulation of the digital-to-analog converter, both as a single unit and as part of an array. A central design challenge is the physical footprint of the DAC, which directly impacts the achievable integration density on the chip. To improve the integration density further, the group has investigated an in-house flip-chip packaging flow. Compared to a wire bonding packaging solution, this allows for a grid arrangement of the analog output pads, massively increasing the effective area of the chip. Additionally, steps are taken to enable in-house fabrication of interposers, which will serve as the high-speed electrical interface between the lithium niobate photonic chip and the silicon electronic chip. Developing this capability internally allows for rapid prototyping and direct characterization of the photonic–electronic link.
• WP3 (Integrated UOWC System):
This WP focuses on achieving long-distance, high-data-rate UOWC while maintaining a compact, robust, low-cost, and energy-efficient system, which is essential for developing high-performance integrated transceivers for scalable IoUT deployment. In particular, this WP addresses pointing errors under realistic ocean conditions, particularly over long link ranges, where narrow optical beams and receivers with limited fields-of-view are required to maximize the system energy efficiency. Meeting these objectives involves, on one hand, designing efficient modulation and channel-coding schemes that ensure high link reliability while minimizing transmit power to limit potential impacts on marine life; and on the other hand, developing robust acquisition, pointing, and tracking (PAT) mechanisms capable of agile, precise beam steering to sustain beam alignment despite platform motion, waves, and ocean currents.
• WP3 (Advanced packaging):
PHIX contributed to the development of the integration and packaging engine for the optical system under WP3. The main focus was on establishing a clear understanding of mechanical integration requirements between all partners and defining the basis for scalable assembly. A preliminary Bill of Materials (BOM) was created to define all critical components, their placement, integration methods, and component/part supplier. Two 3D integration concepts were developed, targeting different technical constraints.
• WP6 (Integrated field of view correction optics):
The activities encompassed in WP6 are divided in two main tasks. Under Task 1 – “Design of efficient metasurface correction optics”, we have identified the requirements and initiated the development of the representative models of the expected OPA radiation pattern for correction. Under Task 2 - “Integrated blue light metasurface optics”, we have started the development of nanofabrication processes development of SiNx on glass metasurfaces, having identified the critical process steps for thin film growth and hard mask materials for etching of such structures.
