Fig. 2: Integrated thin-film lithium niobate photonic circuit implementation of computing core.

a Optical microscope and scanning electron microscope images of the building blocks used in the integrated TFLN circuit: waveguide array (top left) for signal routing; grating coupler (top center) for efficient in- and out-coupling of light; ring resonator (top right) for evaluating the propagation loss and etch quality; fan-out splitter tree (bottom center) to distribute light into distinct spatial channels; microwave transmission line (bottom left) for delivering efficient EO modulation; and on-chip terminator (bottom right) for high-quality microwave impedance matching. b Optical microscope image of seven weight modulators in the TFLN accelerator. c Full image of one computing core (our circuit contains two such computing cores on the same chip). d Scanning electron microscope image of a high-quality waveguide featuring low propagation loss, enabling low optical energy consumption for the entire circuit. e Cross-section illustration of the TFLN circuit, including gold, nickel-chromium (NiCr), lithium niobate, silicon dioxide, and silicon. \(d=100\,{{\rm{nm}}}\), \(w=1.5\,{{\rm{\mu }}}{{\rm{m}}}\), \({h}_{0}=300\,{{\rm{nm}}}\), \({h}_{1}=1.0\,{{\rm{\mu }}}{{\rm{m}}}\), \({h}_{2}=800\,{{\rm{nm}}}\), \(t=300\,{{\rm{nm}}}\), \({t}_{1}=4.7\,{{\rm{\mu }}}{{\rm{m}}}\), \({t}_{2}=525\,{{\rm{\mu }}}{{\rm{m}}}\). f Measured terminator resistance vs. length. g EO forward transmission (\({S}_{21}\) EO) and electric-electric input reflection (\({S}_{11}\,\)EE) response of the modulators in our circuit. Our circuit features a combined total of 31 spatial channels (32 designed, but one failed during the fabrication process). All modulators have a bandwidth beyond 40 GHz (measurement limited by our detector bandwidth). h Representative \({V}_{\pi }\cdot L\) of the modulators (length 1 cm) in our circuit.