The project was structured into three tasks:
• Task 1: Research
• Task 2: Software development
• Task 3: IPR generation, protection and licensing.
Task 1: Hardware Development.
We have researched and proposed several configurations for the implementation of defect cells both for hexagonal and square waveguide meshes. We paid particular attention to the case of single defect cells for hexagonal meshes where the external perimeter of the defect cell is still hexagonal. Figure 1 show several of the proposed designs, all of them are original. We then proceed to carry the spectral analysis of interfacing a uniform and a non-uniform cavity in terms of Vernier effect and also proposed the embedment of non-uniform single cavities inside an otherwise uniform mesh. Some representative results are shown in figure 2. From figure 2 it is shown that the spectral period of a single hexagonal cavity can be enhanced via Vernier effect by a factor of up to 22. We also proposed the design of “linear defect” type waveguide meshes, where the defects exhibit a 1D configuration. An example is shown in figure 3. We selected a simple four cell configuration that could help us to verify the viability of the concept. The design, shown in figure 4 combines 2 uniform hexagonal cell and two defect cells, each one of the latter displays a different internal cavity structure.
2.2 Task 2: Fabrication, tests, and validation
We completed a GDS file for the selected design shown in figure 4 using a flattened waveguide mesh configuration. The layout for the uniform and defect cells and the overall mesh is shown in figure 5. The GDS design and checking was concluded in February 2024, and the chip was sent for fabrication to a Silicon Photonics foundry. The fabricated chip was received in September 2024 and was initially characterized through the measurement of its testing structures before sending it for packaging, which was completed by the end of November 2024. Figure 6 shows the detail of the bare and packaged fabricated chip. The final chip test, measurement and characterization was started in December 2024 and concluded in February 2025. The measurements where carried for three different vernier cavity configuration yielding excellent agreement between theoretical and experimental demonstrations. Figure 7 shows the detail of some of these measurements.
2.3 Task 3: IPR generation, protection and licensing.
We developed our strategy roadmap taking into consideration the need to protect the results prior to publication. To speed up the project we filed our main patent application (PCT/ES2023/070615) after the signature of the Grant Agreement Period but a few days (12) before the official starting of the grant. With the exception of several conference publications in 2024 and 2025 we decided to wait until the completion of the final measurements to submit a full manuscript accounting for the work carried under this grant. An initial version was uploaded to the ArXiV platform in February 2025 and a full complete version was submitted and it is under review in the journal Science Advances.
