Optical neural architectures (ONAs) use coding elements with optimized physical parameters to perform intelligent measurements. However, fabricating ONAs while maintaining design performances is challenging. Limitations in fabrication techniques often limit the realizable precision of the trained parameters. Physical constraints may also limit the range of values the physical parameters can hold. Thus, ONAs should be trained within the implementable constraints. However, such physics-based constraints reduce the training objective to a constrained optimization problem, making it harder to optimize with existing gradient-based methods. To alleviate these critical issues that degrade performance from simulation to realization we propose a physics-informed quantization-aware training framework. Our approach accounts for the physical constraints during the training process, leading to robust designs. We evaluate our approach on an ONA proposed in the literature, named a diffractive deep neural network (D2NN), for all-optical phase imaging and for classification of phase objects. With extensive experiments on different quantization levels and datasets, we show that our approach leads to ONA designs that are robust to quantization noise.

The optical neural network (ONN) is a promising hardware platform for next-generation neuromorphic computing due to its high parallelism, low latency, and low energy consumption. However, previous integrated photonic tensor cores (PTCs) consume numerous single-operand optical modulators for signal and weight encoding, leading to large area costs and high propagation loss to implement large tensor operations. This work proposes a scalable and efficient optical dot-product engine based on customized multi-operand photonic devices, namely multi-operand optical neurons (MOON). We experimentally demonstrate the utility of a MOON using a multi-operand-Mach-Zehnder-interferometer (MOMZI) in image recognition tasks. Specifically, our MOMZI-based ONN achieves a measured accuracy of 85.89% in the street view house number (SVHN) recognition dataset with 4-bit voltage control precision. Furthermore, our performance analysis reveals that a 128x128 MOMZI-based PTCs outperform their counterparts based on single-operand MZIs by one to two order-of-magnitudes in propagation loss, optical delay, and total device footprint, with comparable matrix expressivity.