Photonic floating point multiplication using cascaded SSB-SC modulation

In this paper, we present what we believe to be a novel approach to floating-point multiplication, demonstrated experimentally for the first time. This method involves encoding floating-point numbers onto RF sub-carriers, utilizing amplitude to represent the significand and sub-carrier frequency for the exponent. We employ single-sideband suppressed-carrier (SSB-SC) modulation via IQ modulators to effectively translate the floating-point numbers into the optical domain. The process involves cascaded SSB-SC modulation coupled with balanced detection, enabling the execution of scalar floating-point multiplication. In our proof-of-concept experiment, we analyzed 10 samples with subcarrier frequencies ranging between 8 GHz and 18 GHz. The results exhibit a remarkably low error in scalar multiplication-ranging from 1% to less than 10% in the significand while maintaining error-free performance in the exponent calculation. We further conducted an energy efficiency analysis comparing fixed-point and floating-point operations for matrix-vector multiplication, demonstrating that floating-point is notably more energy-efficient, particularly for large-sized matrices or vectors. These results highlight the technique's viability for high dynamic range floating-point multiplication within photonic accelerators.