publications

2026

1. arXiv

   CRoPE: Efficient Parametrization of Rotary Positional Embedding

   Beicheng Lou and Zifei Xu

   arXiv preprint arXiv:2601.02728, 2026

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   Rotary positional embedding has become the state-of-the-art approach to encode position information in transformer-based models. While it is often succinctly expressed in complex linear algebra, we note that the actual implementation of Q/K/V-projections is not equivalent to a complex linear transformation. We argue that complex linear transformation is a more natural parametrization and saves near 50% parameters within the attention block. We show empirically that removing such redundancy has negligible impact on the model performance both in sample and out of sample. Our modification achieves more efficient parameter usage, as well as a cleaner interpretation of the representation space.

2025

1. Comp. Phys. Comm.

   RCWA4D: Electromagnetic solver for layered structures with incommensurate periodicities

   Beicheng Lou and Shanhui Fan

   Computer Physics Communications, 2025

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   We describe RCWA4D, an electromagnetic solver for layered structures with incommensurate periodicities. Our method is based on an extension of the rigorous coupled wave analysis. We illustrate our method on the example of twisted bilayer photonic crystal and show that various properties of such structures can be reliably simulated. The method can be generalized to multi-layer structures in general in which each layer is periodic or quasi-periodic.

2. Nat. Photon.

   An adaptive moiré sensor for spectro-polarimetric hyperimaging

   Haoning Tang^*, Beicheng Lou^*, Fan Du, and 8 more authors

   Nature Photonics, May 2025

2024

1. ACS Photon.

   Free-Space Beam Steering with Twisted Bilayer Photonic Crystal Slabs

   Beicheng Lou, Haoning Tang, Fan Du, and 3 more authors

   ACS Photonics, May 2024
2. PRL

   Three-Dimensional Reconfigurable Optical Singularities in Bilayer Photonic Crystals

   Xueqi Ni, Yuan Liu, Beicheng Lou, and 5 more authors

   Phys. Rev. Lett., Feb 2024

2023

1. Sci. Adv.

   Experimental probe of twist angle–dependent band structure of on-chip optical bilayer photonic crystal

   Haoning Tang^*, Beicheng Lou^*, Fan Du, and 6 more authors

   Science Advances, Feb 2023

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   Recently, twisted bilayer photonic materials have been extensively used for creating and studying photonic tunability through interlayer couplings...

2. ACS Photon.

   Inverse Design of Optical Switch Based on Bilevel Optimization Inspired by Meta-Learning

   Beicheng Lou, Jesse Alexander Rodriguez, Benjamin Wang, and 2 more authors

   ACS Photonics, Feb 2023
3. arXiv

   On-Chip Multidimensional Dynamic Control of Twisted Moiré Photonic Crystal for Smart Sensing and Imaging

   Haoning Tang^*, Beicheng Lou^*, Fan Du, and 8 more authors

   arXiv:2312.09089, Feb 2023

2022

1. ACS Photon.

   Tunable Frequency Filter Based on Twisted Bilayer Photonic Crystal Slabs

   Beicheng Lou and Shanhui Fan

   ACS Photonics, Feb 2022
2. Sci. Adv.

   Tunable guided resonance in twisted bilayer photonic crystal

   Beicheng Lou, Benjamin Wang, Jesse A Rodríguez, and 2 more authors

   Science Advances, Feb 2022

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   We experimentally demonstrate tunable guided resonance in twisted bilayer photonic crystals. Both the transmission spectra feature resonances with frequencies strongly dependent on the twist angle...

3. arXiv

   Saved you a click: Automatically answering clickbait titles

   Oliver Johnson, Beicheng Lou, Janet Zhong, and 1 more author

   arXiv preprint arXiv:2212.08196, Feb 2022
4. arXiv

   Wormhole MAML: Meta-Learning in Glued Parameter Space

   Chih-Jung Tracy Chang, Yuan Gao, and Beicheng Lou

   arXiv preprint arXiv:2212.14094, Feb 2022

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   In this paper, we introduce a novel variation of model-agnostic meta-learning, where an extra multiplicative parameter is introduced in the inner-loop adaptation. Our variation creates a shortcut in the parameter space for the inner-loop adaptation and increases model expressivity in a highly controllable manner. We show both theoretically and numerically that our variation alleviates the problem of conflicting gradients and improves training dynamics. We conduct experiments on 3 distinctive problems, including a toy classification problem for threshold comparison, a regression problem for wavelet transform, and a classification problem on MNIST. We also discuss ways to generalize our method to a broader class of problems.

2021

1. PRL

   Theory for Twisted Bilayer Photonic Crystal Slabs

   Beicheng Lou, Nathan Zhao, Momchil Minkov, and 3 more authors

   Phys. Rev. Lett., Feb 2021

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   We analyze scattering properties of twisted bilayer photonic crystal slabs through a high-dimensional plane wave expansion method. The method is applicable for arbitrary twist angles and does not suffer from the limitations of the commonly used supercell approximation. We show strongly tunable resonance properties of this system which can be accounted for semianalytically from a correspondence relation to a simpler structure. We also observe strongly tunable resonant chiral behavior in this system. Our work provides the theoretical foundation for predicting and understanding the rich optical physics of twisted multilayer photonic crystal systems.

2. Appl. Phys. Lett.

   Wide wavelength-tunable narrow-band thermal radiation from moiré patterns

   Cheng Guo, Yu Guo, Beicheng Lou, and 1 more author

   Applied Physics Letters, Feb 2021
3. NeurIPS

   Meta-learning from sparse recovery

   Beicheng Lou, Nathan Zhao, and Jiahui Wang

   In Fifth Workshop on Meta-Learning at the Conference on Neural Information Processing Systems, Feb 2021

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   Meta-learning aims to train a model on various tasks...

4. IMRN

   Hyperbolic Jigsaws and Families of Pseudomodular Groups II

   Beicheng Lou, Ser Peow Tan, and Anh Duc Vo

   International Mathematics Research Notices, Feb 2021

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   In our previous paper, we introduced a hyperbolic jigsaw construction...

5. PRApplied

   Inverse design of plasma metamaterial devices for optical computing

   Jesse A Rodríguez, Ahmed I Abdalla, Benjamin Wang, and 3 more authors

   Physical Review Applied, Feb 2021

2020

1. ACS Photon.

   Inverse Design of Photonic Crystals through Automatic Differentiation

   Momchil Minkov, Ian A. D. Williamson, Lucio C. Andreani, and 5 more authors

   ACS Photonics, Feb 2020

2019

1. arXiv

   Tunagan: interpretable gan for smart editing

   Weiquan Mao, Beicheng Lou, and Jiyao Yuan

   arXiv preprint arXiv:1908.06163, Feb 2019

2018

1. Geom. Topol.

   Hyperbolic jigsaws and families of pseudomodular groups, I

   Beicheng Lou, Ser Tan, and Anh Duc Vo

   Geometry & Topology, Feb 2018

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   We show that there are infinitely many commensurability classes of pseudomodular groups...