Research

Nonlinear laser manufacturing employs a microscope objective for single-beam focusing designed for biological imaging, correcting aberrations for 200-micrometer-thick glass, allowing only shallow-depth processing. Due to the vector nature of light, an ideal photonic chip requires a three-dimensional framework, necessitating unprecedented large-depth direct-write 3D lithography. Just as electron chip lithography require specialized lenses, 3D lithography machines need also to address the issue of specialized lenses. For this purpose, Hong-Bo Sun proposed a method of 4π solid-angle super-focusing through perpendicular crossed dual-beam incidence and pulse spatiotemporal overlap (a series of patented inventions). By optically overcoming the challenge of shallow processing depth, the research team developed a deep three-dimensional photonic chip "lithography machine", resolving the requirements for large-depth direct writing, precise geometric shaping, and targeted property modulation (refractive index and loss). This approach achieved a direct write depth of up to 1 millimeter, realizing waveguide core diameters (5-30 μm), coupling coefficients (0.5-3 rad/mm), losses (0.3-300 dB/cm), birefringence (0-2.7x10^-5), and birefringence axes (0-180°), continuously adjustable within the mentioned parameter ranges. Using these techniques, the research team achieved the largest reported depth and scale (110×110=12100 lines, 110 layers in the vertical direction) for waveguide array chips. Leveraging these capabilities, the research team respectively designed and fabricated non-Abelian Thouless pump photonic chips (Nature Physics, 18, 1080, 2022) and non-Abelian braiding photonic chips (Nature Photonics, 16, 390, 2022). Both chips utilized non-Abelian holonomy, enabling robust topological control over the phase and path of photons by adiabatically evolving degenerate photon states on the chip, providing a technological basis for constructing various complex non-Hermitian/Hermitian Hamiltonians in physical space and preparing corresponding chip structures.