Reference-assisted microring weightbank for signed multiplication

We propose and demonstrate what we believe to be a new type of incoherent photonic tensor core for signed multiplication. This structure extends a microring resonator (MR) weightbank by introducing a fixed reference power for differential activation encoding, making both operands differentially defined; the activation is represented by the difference between a fixed reference power and a dynamically modulated power, while the weight is represented by the through/drop response of an MR. This scheme enables signed multiplication with reduced hardware overhead by sharing each weighting an MR between the two counter-propagating inputs. The trade-offs are signal attenuation and potential reflection sensitivity. We demonstrate this concept using a fabricated silicon photonic integrated circuit containing two thermally tuned MRs, one for each operand of x × w. Lookup tables (LUTs) spanning -1 to +1 are constructed for both operands, and randomly ordered LUT sweeps confirmed signed multiplication with residual error standard deviations of 0.022 for the x-sweep and 0.032 for the w-sweep, both below the nominal 31-level spacing of 0.067.