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2025

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03

Light | Cloud and Light: High-Density & Multi-Task Optical In-Memory Computing

Author:


Introduction

On-chip Optical Neural Network(on-chip ONN) has been extensively studied due to its high-bandwidth, low-loss, and low-latency computational characteristics and CMOS-compatible manufacturing process. However, challenges remain in simultaneously achieving high-density integration and multi-tasking capabilities.

 
Recently, a research team led by Professor Chen Hongwei of the Department of Electronic Engineering, Tsinghua Universitydeveloped an ultra-compact multi-tasking chip for in-memory optical computing based on silicon-based photonic diffraction structures. This embeds most network computing parameters into fixed passive optical structures, while using a small number of electronic parameters to accomplish multi-tasking. This work has advanced research on the general optical computing framework and applications in next-generation artificial intelligence platforms.

 

The results are published inUltra-compact multi-task processor based on in-memory optical computinginLight: Science & ApplicationsTsinghua Universitydoctoral student Liu Wencanis the first author of the paper, and Tsinghua UniversityProfessor Chen Hongweiis the corresponding author.

Ultra-compact on-chip optical in-memory computing architecture

The research team, through innovative design of the diffractive optical computing chip, ensured that a single optical chip is no longer for a specific task, but aims to be a general processing unit for various task inputs. The optical chip serves as an in-memory computing unit with fixed weights, paired with a lightweight backend network to handle multi-tasking scenarios, achieving an "optical fixed weight + electrical lightweight network" computing paradigm. The team integrated most of the trained neural network weights as subwavelength diffractive elements into the chip. Therefore, during computation, only the input data needs to be modulated; accessing network weights from memory is unnecessary, and computation is completed during light propagation.

 

To achieve higher integration and computing density in the diffractive chip, while reducing energy consumption and improving model accuracy, the research team used a deep regression neural network in model simulation to replace traditional modeling of light propagation using Maxwell's equations. The team utilized a deep regression neural network with complex-valued parameters to simulate and predict the propagation of the light field in the chip. This significantly increased prediction speed while achieving accuracy comparable to simulation, and enabled a computing integration density as high as 60,000 parameters/mm².

Figure 1: Overall system processing flow chart and application schematic in edge computing architecture

 

For Multi-task Processing Applications

The research team demonstrated the system's performance on multi-classification and multi-regression tasks. For multi-classification tasks, classifying three independent datasets, the system achieved performance comparable to electronic networks while reducing electronic power consumption parameters by 90%. For multi-regression tasks, the system could highly fit multiple groups of convolutional kernels, and achieved higher computational accuracy with fewer electronic parameters in convolutional neural networks. Moreover, the proposed system can be used for edge applications, processing multi-task inputs through a series of internal optical chips for high-speed and low-power data processing. The processed data is then transmitted to a cloud database, and further lightweight computations are performed on various terminals based on specific task requirements.

Figure 2: System processing flowchart and experimental results comparison for multi-classification tasks

 

Summary and Outlook

This research proposes a novel on-chip optical multi-tasking processor architecture, improving the integration and reconfigurability of in-memory optical diffractive chips. By fixing most parameters within an ultra-compact, in-memory optical diffractive chip structure, it achieves multi-tasking capabilities while increasing the parameter integration density and computational capacity of current photonic chips by an order of magnitude. This work not only advances optical computing architectures but also holds great potential for future large-scale, high-performance computing systems.

 

 

Paper Information

Liu, W., Huang, Y., Sun, R., et al. Ultra-compact multi-task processor based on in-memory optical computing. Light Science & Applications 14, 134 (2025).

https://doi.org/10.1038/s41377-025-01814-0