On-chip optical image memory based on inverse-designed multi-channel power splitters

In optical computing systems for image tasks, optical signals of image data are usually generated by signal modulators, whose speed limits computational performance.To address this, a framework of image memory that can permanently store the image and instantaneously generate its corresponding optical signals has been proposed.In this framework, an original image is sliced into non-overlapping sub-images, each of which contains 3 pixel 3 pixel or 5 pixel 5 pixel, and these subimages are respectively stored in storage units, which are nine-channel or 25-channel power splitters (PSs).The gray values of pixels in each sub-image are sequentially mapped to the light intensity of channels in each PS.These PSs are inversely designed by combining the adjoint method (AM) and the finite-difference frequency-domain method.Using this method, high-performance memory has been realized based on PSs, with a maximum 33.37 dB signal-to-noise ratio.Using multiobjective AM, the storage capacity has been doubled according to the working wavelengths.For example, two sub-images with pixels arranged as 'T' and 'L' shapes can be retrieved at 1310 and 1550 nm, respectively.This framework provides highly stable, non-volatile image storage, and instantaneous generation of optical signals for future all-optical computing systems.