Fig. 2. Experimental setup for PNCA.

a Schematic of the experimental setup. Pulses of light produced by a modelocked laser pass through an electro-optic modulator (EOM) and are split into optical fiber delay lines (blue lines) with relative delays T₁ and T₂. Linear dot product weights are programmed by tuning the variable optical attenuator (VOA) in each delay line. Nonlinear activation using a periodically-poled lithium niobate (PPLN) waveguide is performed following the coherent interference of light pulses, with the resultant amplitudes stored on a field-programmable gate array (FPGA) and reinjected (black lines) to drive the input EOM for the next iteration. b Local 3-cell neighborhood enforced by relative delays T₁ and T₂. c The local update rule is encoded by a single perceptron with 3 programmable parameters. d PPLN nonlinear activation function. e Cells representing pixels of an image are encoded by the amplitude of light pulses with repetition period T_R in a synthetic temporal dimension. For example, pulses can be coupled using optical delay lines with T₁ = +1T_R and T₂ = +28T_R to implement the local 3-cell neighborhood shown in (b) for fashion-MNIST images