The work in LIQUORICE brings together know-how from different fields, much of which was developed during the ERC consolidator grant PhotonicSWARM. Within this proof-of-concept project we made important progress towards realizing the desired proof of concept, but we did not yet achieve a successful conclusion at the end.
One key component we worked on was the photonic chip with the programmable waveguide mesh. For this, we realized multiple suitable circuit designs, fabricated in IMEC’s iSiPP50G silicon photonic process, as well as variations in more experimental process flows. We also developed the necessary postprocessing steps for these chips, to implement a ‘tank’ that can contain the liquid crystal after the photonic chip has been combined with the LCOS chip
The second key element in the system is the LCOS chip itself. This is a component which we sourced commercially. We identified possible suppliers that were willing to provide bare LCOS chips in sufficient quantity, and support us with the associated drivers and test boards. However, here we encountered a setback, as the supplier with who we started the collaboration discontinued their work on LCOS displays (as the market for microdisplays is rapidly shifting from LCOS to micro-LEDs). We did manage to secure sufficient chips and supporting material to continue working on the proof-of-concept, but for future developments we will have to explore alternative partners.
The main work in LIQUORICE relates to the assembly process, essentially making a liquid crystal cell with the LCOS chip on one side, and the silicon photonics on the other. This imposes multiple challenges. The silicon chip is not flat, and needs additional metallization to provide a good reference ground. The assembly itself also introduced challenges to get good adhesion between the two layers, and make sure the cell is hermetically sealed. We tested multiple materials and bonding schemes, and reached a process that we deem satisfactory. This was not without obstacles, and we encountered significant delays in this development.
Once the cell is assembled, it will need filling with liquid crystal. This is performed in vacuum. Because the cell geometry of our device is substantially different from standard liquid crystal cells, we decided to rethink the filling process to make it more reliable. This is currently still work in progress.
In parallel, we tested how we could electrically control the LCOS display, looking into different driving schemes that control the resolution, refresh rate and precision of the display. These will affect how well we can control our programmable photonic chip.
The work on this proof-of-concept is therefore not finished yet, and we hope to demonstrate its functionality, even after the end of the project.
