arXiv subjects

Luo Qi

Publications and source records attributed to Luo Qi.

6 recordsLinked to original sources

arXiv2026

Metasurface-integrated VCSEL designed for polarization control in optical Ising machines

The orthogonal polarization states of vertical-cavity surface-emitting lasers (VCSELs) can be used to describe candidate solutions to the Ising Hamiltonian, which is useful for solving quadratic unconstrained binary optimization problems. However, the natural anisotropy of VCSELs tends to overly favor one polarization state, which impedes the system from working as desired. In this work, we have designed and fabricated a metasurface, which may lead to a VCSEL with reduced undesired anisotropy. By changing the geometric size of nano-structures in the metasurface, the polarization state of the output light can be altered. Based on the injection-locking theory and spin-flip model, we numerically show that VCSELs with lowered anisotropy are more easily affected by the injection locking needed in Ising systems. Additionally, we numerically study the evolution of a 3-bit VCSEL-based Ising system and verify that the computational accuracy of the photonic Ising machine can be improved to more than twice that of its counterpart with higher anisotropy.

physics.optics↗

arXiv2026

Integrated Photonic Devices in Thin-Film Barium Titanate: Opportunities and Challenges

Thin-film barium titanate (BaTiO3, or BTO) has emerged as a promising electro-optic (EO) material for integrated photonics due to its exceptionally large Pockels coefficients, low optical loss, and compatibility with heterogeneous integration. Recent advances in epitaxial thin-film growth, crystal orientation control, ferroelectric domain engineering, and scalable integration have enabled EO performance in thin-film BTO approaching bulk-like properties on photonic platforms. This review provides a comprehensive overview of integrated photonic devices based on thin-film BTO, including fundamental material properties, thin-film growth and integration strategies, passive waveguide configurations, EO response at both the film and device levels, and relevant optical applications. We review the role of film orientation, domain structure, and device geometry in determining accessible EO coefficients and modulation mechanisms, as well as the distinctions between intrinsic and effective EO responses demonstrated at the film and device levels. Representative studies are compared in terms of film-quality-related metrics and device performance figures of merit, alongside emerging applications realized in BTO-based platforms. Finally, we discuss the remaining challenges and outline future development directions toward high-performance BTO-based integrated photonic systems.

physics.optics↗

arXiv2026

Passive All-Optical Nonlinear Neuron Activation via PPLN Nanophotonic Waveguides

Artificial intelligence (AI) is transforming modern life, yet the growing scale of AI applications places mounting demands on computational resources, raising sustainability concerns. Photonic integrated circuits (PICs) offer a promising alternative, enabling massive parallelism, low latency, and reduced electrical overhead, particularly excelling in high-throughput linear operations. However, passive and fully optical nonlinear activation functions with equally superb performance remain rare, posing a critical bottleneck in realizing all-optical neural networks in PICs. Here, we demonstrate a compact and integrated all-optical nonlinear activation method, experimentally realized through strong second-order optical nonlinearities in periodically poled lithium niobate (PPLN) nanophotonic waveguides, achieving 80% absolute conversion efficiency. This activation exhibits a sigmoid-like, wavelength-selective response with femtosecond-scale dynamics and light-speed processing, operating passively without external control and auxiliary signals. We validate its feasibility for neural inference by cascading the PPLN-driven activations with a linear silicon PIC, demonstrating all-optical nonlinear neuron expressivity. Moreover, combining the measured nonlinearity with linear operations calculated by the PIC, we show that PPLN-activated multi-layer optical neural networks can achieve performance on par with digital implementations in real-world tasks, including airfoil regression and medical image classification. These results pave the way toward scalable, high-speed, and fully integrated all-optical neural networks for next-generation photonic AI hardware.

physics.optics↗

arXiv2020

Detection-device-independent verification of nonclassical light

The efficient certification of nonclassical effects of light forms the basis for applications in optical quantum technologies. We derive general correlation conditions for the verification of nonclassical light based on multiplexed detection. The obtained nonclassicality criteria are valid for imperfectly-balanced multiplexing scenarios with on-off detectors and do not require any knowledge about the detector system. In this sense they are fully independent of the detector system. In our experiment, we study light emitted by clusters of single-photon emitters, whose photon number may exceed the number of detection channels. Even under such conditions, our criteria certify nonclassicality with high statistical significance.

quant-ph↗

arXiv2018

Multiphoton nonclassical light from clusters of single-photon emitters

We study nonclassical features of multiphoton light emitted by clusters of single-photon emitters. As signatures of nonclassicality, we use violation of inequalities for normalized correlation functions of different orders or the probabilities of multiphoton detection. In experiment, for clusters of 2 to 14 colloidal CdSe/CdS dot-in-rods we observe nonclassical behavior, which gets even more pronounced for larger clusters.

quant-ph↗

arXiv2016

Autonomous absolute calibration of an ICCD camera in single-photon detection regime

Intensified charge coupled device (ICCD) cameras are widely used in various applications such as microscopy, astronomy, spectroscopy. Often they are used as single-photon detectors, with thresholding being an essential part of the readout. In this paper, we measure the quantum efficiency of an ICCD camera in the single-photon detection mode using the Klyshko absolute calibration technique. The quantum efficiency is obtained as a function of the threshold value and of the wavelength of the detected light. In addition, we study the homogeneity of the photon sensitivity over the camera chip area. The experiment is performed in the autonomous regime, without using any additional detectors. We therefore demonstrate the self-calibration of an ICCD camera.

quant-ph↗