Fig. 1. Sketch of the main building blocks available on the thick-SOI platform. Typical thickness of the device layer is $3\mu \mathrm{m}$, whereas the BOX thickness can vary from 400 nm to $3\mu \mathrm{m}$. We define “active” building blocks as those requiring electrical pads for either control or readout.

Fig. 2. (a) Sketch of different mode size conversions starting from an SMF coupled to the $3\text{-}\mu \mathrm{m}$ thick waveguides of a thick-SOI PIC using an optical interposer fabricated on $12\text{-}\mu \mathrm{m}$ thick SOI. The sketch also shows how the mode size can be reduced further even to couple light to submicron waveguides on a flip-chip bonded PIC that can be evanescently coupled through suitable inverse tapers. (b) Micrograph of a $12\text{-}\mu \mathrm{m}$ thick rib waveguide of a fabricated optical interposer; (c) micrograph of a strip waveguide polished down to about $3\text{-}\mu \mathrm{m}$ thickness on the opposite facet; (d) near-field image (infrared camera) of the TE and TM modes at the output facet of the interposer [shown in (c)]; and (e) packaged $3\text{-}\mu \mathrm{m}$ thick-SOI PIC coupled to a fiber array through an optical interposer.

Fig. 3. (a) SEM image of polymer lenses 3D printed in front of the end facets of four rib waveguides; (b) near-field picture of the output mode of a rib waveguide taken with an infrared camera; (c) near-field picture of the output of a lensed rib waveguide [same scale as (b)].

Fig. 4. (a) Micrograph of a fabricated URM and (b) side view of a vertical cross section of an URM via focused ion beam microscopy.

Fig. 5. (a) SEM picture of 90-deg turning mirrors on rib waveguides and strip waveguides; (b) detail of a compact imbalanced MZI based on TIR mirrors; (c) SEM picture of Euler bends with L and U shape and detail of a spiral waveguide using larger L-bends.

Fig. 6. (a) The linear change of the curvature $1/R$ as a function of the length $s$ in an Euler bend, starting from zero, reaching up to $1/R_{\min }$ and then going back to zero symmetrically. (b) Example layout of a 90-deg Euler bend (or L-bend) with unity minimum bending radius, showing the resulting effective radius $R_{\mathrm{eff}}$. (c) Simulation of the transmission of the ${\mathrm{TE}}_{00}$ mode and of five horizontal higher-order TE modes of a $1.5\text{-}\mu \mathrm{m}$-wide strip waveguide at the output of a 90-deg Euler bend as a function of the minimum bending radius. The five HOM ${\mathrm{TE}}_{n0}$ modes ($n=1,\dots ,5$) have $n$ nodes in the horizontal direction and zero nodes in the vertical direction. The wavelength is $1.55\mu \mathrm{m}$.

Fig. 7. (a) Sketch of an MZI exploiting the form birefringence of waveguides of different widths to serve as a PBS. (b) Scheme of a possible implementation of an integrated light circulator by combining PBSs, FRs, and reciprocal polarization rotators on chip.

Fig. 8. (a) Compact AWG with 100-GHz channel spacing and 5-nm free spectral range exploiting Euler bends and nearly zero birefringence waveguides, ensuring polarization-independent operation. (b) Cyclic echelle grating with 100-GHz channel spacing.

Fig. 9. (a) 3D simulation using the eigenmode expansion method of the adiabatic power transfer from a $3\text{-}\mu \mathrm{m}$ thick c-Si waveguide to a 400-nm thick and $200\text{-}\mu \mathrm{m}$ long a-Si:H tapered waveguide fabricated on top. (b) 3D sketch of two escalators to couple light to the a-Si:H waveguide and then back to the $3\text{-}\mu \mathrm{m}$ thick waveguide, showing where a functional layer can be sandwiched between the two silicon types in the region where the light is guided in a-Si:H. (c) A different type of escalator to couple light to submicron waveguides.

Fig. 10. Top views and cross sections of the three main types of phase shifters available on the platform: (a) thermo-optic (also see Fig. 1); (b) electro-optic, based on plasma dispersion through carrier injection in a PIN junction; (c) electro-optic, based on EFIPE with a high-inverse bias voltage through a PIN junction.

Fig. 11. (a) SEM picture of a fabricated NbN SNSPD before a-Si:H deposition; (b) micrograph of a detail of a fabricated chip after etching the a-Si:H waveguides; (c) sketched cross section of an a-Si:H waveguide with the NbN nanowire embedded (in green).

Fig. 12. (a) Schematic representation of QKD implementations based on a central node for photon detection where all the users are equipped with suitable and low-cost transmitters. (b) 3D sketch of the solution we are developing with our partner Single Quantum to address arrays of SNSPDs with low-loss and high-fabrication yield.

Fig. 13. Schematic representation of our plans to use optical fiber links to interface cryogenic quantum computers with supercomputers.

Fig. 14. Long-term vision of a PIC based serializer, including an IMLL as a multiwavelength light source.