Recall that one of the last elements POET needed to perfect to create the Optical Interposer platform was the vertical mirror. 

Vertical Mirrors: In addition to in plane coupling of light, POET’s optical interposers utilize vertical mirrors to enable out of plane coupling. The vertical mirrors are used with topentry photodetectors and for wafer level test. Fig. 5 shows the construction and performance (0.5dB coupling loss) achieved by the vertical mirrors when coupled to a PD.

Item 701 in the Celestial patent provides for a vertical mirror for in-plane coupling of of the laser chiplet which also utilized a  lens. Hello Vanguard who is working with POET specifically for this purpose.

"Our optical interposer together with Vanguard Automation's facet-attached-microlenses creates a powerful platform for electro-optical engines for transceivers, co-packaged optics, light engines and sensing devices. Incorporating microlenses improves the coupling efficiency of light as it passes from one photonic device to another, which in turn reduces power consumption of the combined solution. The precise alignment and printing of the microlenses at wafer-level offers significant scalability and enhances our ability to address new markets with a uniquely powerful solution."

POET is integration technology. The optical interposer was developed and perfected by POET and I think a logical conclusion is that Celestial AI is utilizing  this optical interposer as shown in the Celestial diagram. Including the gratings that POET was working on to allow top insertion at any point within the fabric.

Lets  finish by pointing to following statement made by POET,

Poet Technologies and Vanguard Automation will initially collaborate to integrate the microlenses on Poet's LightBar products, aimed at AI (artificial intelligence)-ML (machine learning) accelerators and bio-sensing applications to validate power efficiency improvements and the viability of chip-scale, wafer-level manufacturing using microlenses. Poet expects to start sampling LightBar products incorporating Vanguard Automation's microlenses to customers in the second half of 2023.