By Jiaqi Gu, Hanqing Zhu, Chenghao Feng, Zixuan Jiang, Ray T. Chen and David Z. Pan.

This repo is the official implementation of "L2ight: Enabling On-Chip Learning for Optical Neural Networks via Efficient in-situ Subspace Optimization".

L2ight is a closed-loop ONN on-chip learning framework to enable scalable ONN mapping and efficient in-situ learning. L2ight adopts a three-stage learning flow that first calibrates the complicated photonic circuit states under challenging physical constraints, then performs photonic core mapping via combined analytical solving and zeroth-order optimization. A subspace learning procedure with multi-level sparsity is integrated into L2ight to enable in-situ gradient evaluation and fast adaptation, unleashing the power of optics for real on-chip intelligence. L2ight outperforms prior ONN training protocols with 3-order-of-magnitude higher scalability and over 30X better efficiency, when benchmarked on various models and learning tasks. This synergistic framework is the first scalable on-chip learning solution that pushes this emerging field from intractable to scalable and further to efficient for next-generation self-learnable photonic neural chips.

• Python >= 3.6
• pyutils >= 0.0.1. See pyutils for installation.
• pytorch-onn >= 0.0.1. See pytorch-onn for installation.
• Python libraries listed in requirements.txt
• NVIDIA GPUs and CUDA >= 10.2

• core/
  • models/
    • layers/
      • custom_conv2d and custom_linear layers
      • utils.py: sampler and profiler
    • sparse_bp_*.py: model definition
    • sparse_bp_base.py: base model definition; identity calibration and mapping codes.
  • optimizer/: mixedtrain and flops optimizers
  • builder.py: build training utilities
• script/: contains experiment scripts
• train_pretrain.py, train_map.py, train_learn.py, train_zo_learn.py: training logic
• compare_gradient.py: compare approximated gradients with true gradients for ablation

• Pretrain model.
  > python3 train_pretrain.py config/cifar10/vgg8/pretrain.yml

• Identity calibration and parallel mapping. Please set your hyperparameters in CONFIG=config/cifar10/vgg8/pm/pm.yml and run
  > python3 train_map.py CONFIG --checkpoint.restore_checkpoint=path/to/your/pretrained/checkpoint

• Subspace learning with multi-level sampling. Please set your hyperparameters in CONFIG=config/cifar10/vgg8/ds/learn.yml and run
  > python3 train_learn.py CONFIG --checkpoint.restore_chekcpoint=path/to/your/mapped/checkpoint --checkpoint.resume=1

• All scripts for experiments are in ./script. For example, to run subspace learning with feedback sampling, column sampling, and data sampling, you can write proper task setting in SCRIPT=script/vgg8/train_ds_script.py and run
  > python3 SCRIPT

• Comparison experiments with RAD [ICLR 2021] and SWAT-U [NeurIPS 2020]. Run with the SCRIPT=script/vgg8/train_rad_script.py and script/vgg8/train_swat_script.py,
  > python3 SCRIPT

• Comparison with FLOPS [DAC 2020] and MixedTrn [AAAI 2021]. Run with the METHOD=mixedtrain or flops,
  > python3 train_zo_learn.py config/mnist/cnn3/METHOD/learn.yml

@inproceedings{gu2021L2ight,
  title={L2ight: Enabling On-Chip Learning for Optical Neural Networks via Efficient in-situ Subspace Optimization},
  author={Jiaqi Gu and Hanqing Zhu and Chenghao Feng and Zixuan Jiang and Ray T. Chen and David Z. Pan},
  booktitle={Conference on Neural Information Processing Systems (NeurIPS)},
  year={2021}
}