Photonic crystals are an emerging field developed in recent years. The preparation and study of nonlinear photonic crystals with periodic changes in nonlinear polarizability has become a hot topic in current research. The use of nonlinear photonic crystals to expand the field of optics and fabrication of optical devices is a nonlinear photonic crystal. The important direction of research.
Prof. Wu Dong, Key Laboratory of Materials Mechanics Behavior and Design, Chinese Academy of Sciences, and Zhang Yong, Xiao Min, the National Key Laboratory of Solid Microstructures of Nanjing University, and Hu Xiaopeng and Zhu Shining, working together, using femtosecond laser domain erasing technology for the first time. A three-dimensional nonlinear photonic crystal was successfully fabricated, and a laser pointer frequency multiplication of three-dimensional quasi-phase matching was realized.
In the early research, the research team of Nanjing University successfully developed one-dimensional and two-dimensional nonlinear photonic crystals by crystal growth stripe technology and room temperature polarization technology, and showed many aspects in nonlinear beam shaping and optical quantum information processing. New application.
On this basis, the researchers are also looking forward to the development of three-dimensional nonlinear photonic crystals, revealing more novel effects. However, conventional fabrication techniques, including crystal growth techniques, room temperature electric field polarization techniques, etc., are difficult to achieve alignment of three-dimensional domain structures within the crystal. The preparation of three-dimensional nonlinear photonic crystals has become one of the confusing problems in the field of nonlinear optics in the past two decades. The emergence of femtosecond lasers has solved this problem. Thanks to the extremely short pulse width, femtosecond lasers can easily generate extremely high peak power, which causes non-linear effects such as multiphoton absorption or tunneling ionization of light and matter, allowing them to penetrate deep into the transparent medium to surpass optics. The precision of the diffraction limit is three-dimensional micromachining of the material.
The University of Science and Technology of China and the research team of Nanjing University have developed a new domain control technology: using a focused femtosecond laser to achieve fixed-point erasure of ferroelectric domains (second-order nonlinear optical coefficients) inside a lithium niobate crystal. The modulation of the second-order nonlinear optical coefficient in three-dimensional space is realized. In the process of preparing the structure, Professor Wu Dong proposed different layers of energy compensation processing technology to ensure the overall uniformity of the three-dimensional structure.
After more than two years of exploration, a three-dimensional nonlinear photonic crystal with tetragonal structure was successfully prepared in lithium niobate crystal. The three-dimensional periodic structure parameter of photonic crystal is 3 μm (x) × 3 μm (y) × 11 μm ( z). The NTU research team successfully observed the expected three-dimensional quasi-phase matching frequency doubling effect in subsequent experiments. The collinear frequency conversion efficiency of the 100 μm optical path reached 10^-4, which is consistent with the theoretical estimation.
The successful development of three-dimensional nonlinear photonic crystals provides a new material for the study of nonlinear optics and quantum optics in three-dimensional space, and also provides support for the development of three-dimensional micro-nano photonic devices.