Photonic Matrix-vector Multiplication with Low-insertion-loss and Non-volatile Ge₂Sb₂Te₃S₂ Intensity Modulators

We propose a low-insertion-loss (IL) and non-volatile optical intensity modulator based on Ge 2 Sb 2 Te 3 S 2 (GSTS), a recently proposed Se-free wide-gap phase change material. Owing to the negligibly small optical absorption of amorphous GSTS at a wavelength of 1550 nm, a non-volatile intensity modulator with a low IL of less than 0.08 dB and a high extinction ratio (ER) of 19.6 dB is realized using GSTS with a device length of 8 μm, overcoming the trade-off relationship between IL and ER in conventional Ge 2 Sb 2 Te 5 (GST). Using visible laser light irradiation, we demonstrate multilevel modulation up to 24 levels by taking advantage of the small optical absorption of amorphous GSTS and the moderately large optical absorption of crystalline GSTS compared with GST. With the proposed GSTS intensity modulators, we demonstrate 4×4 matrix-vector multiplication using a recently proposed photonic tensor core, which shows a high tolerance to hardware error accumulation. On the basis of the experimental results, we numerically confirm that a high recognition accuracy of 97.33% can be obtained using a convolutional neural network with emulated optical convolutional operations.