Photonic dot product engine for optical signal and information processing

Abstract In this paper, a novel 2 x 2 Mach-Zehnder-interferometer (MZI)-based dot product calculator is proposed and analyzed in the silicon-on-insulator (SOI) platform. To calculate the dot product, a phase-shifted Bragg grating (PSBG) modulator is placed in each arm of the MZI for the phase modulation at the resonant wavelength, followed by a 3-dB 2 x 2 directional coupler (DC) as the output to convert the phase difference into the intensity distribution across bar and cross ports. Moreover, an electro-absorption modulator (EAM) is implemented between the PSBG and the DC to change the intensity of the passing light in both arms. Theoretical modelling shows that by adjusting the phase difference and the absorption strength, individually, multiplication of two input values can be achieved using the proposed design. Numerical analysis over 10,000 dot product operations with 7-bit precision for input values reveals a mean squared error (MSE) of 2.67 x 10^-5. Superior to the current prior art of MZI-based processors with coherent light sources, by cascading multiple proposed designs operated at different wavelengths, vector-by-vector multiplication can be realized in parallel, leveraging the wavelength-division multiplexing (WDM) scheme and the Bragg reflection mechanism. It, therefore, paves the way for large-scale optical information processing systems with high throughput.