On April 17, Jin Xianmin's team of Shanghai Jiaotong University, in cooperation with Professor Xia Keyu and Professor Lu Yanqing of Nanjing University, published the latest research results in the international authoritative journal of physics review express titled "vector vortex beam emitter embedded in a photonic chip", showing the vector vortex optical radiator chip. The embedded generation of vectorial vortices makes it possible to realize the integration of generation, transmission and control in a single chip. Combined with the ability of array integration, the work lays a foundation for the large-scale integrated utilization of photon orbital angular momentum freedom resources, as well as the development of high-capacity communication and high-dimensional quantum information processing. The technology of the embedded vector vortex optical radiator photon integrated chip has obtained the international PCT patent.
Besides frequency, space mode, time energy and other degrees of freedom, photons can also carry spin angular momentum and orbital angular momentum. Spin angular momentum is related to the polarization of light and is widely used to encode information in two-dimensional Hilbert space of quantum optics. Unlike spin angular momentum, orbital angular momentum has infinite topological charge and inherent orthogonality, which can provide huge resources for mode multiplexing and is expected to be used to solve the problem of channel capacity reduction in communication systems. The vector vortex beam carries the spin and orbital angular momentum of light at the same time, which provides additional degrees of freedom and new resources for modern optics, classical and quantum information technology. Its inherent infinite dimension is expected to be used to improve data capacity to maintain the unprecedented growth of big data and Internet traffic, as well as the quantum computer used to build high-dimensional Hilbert space.
Beyond the demonstration of principle, the large-scale application of the vector vortex beam urgently needs to develop the photon integration technology, which can generate, transmit and even process the vector vortex beam on the photon chip. At present, it has been widely studied from the radiation vector vortex beam on the chip surface to the free space. However, it is still a long-standing challenge to generate and transmit the vector vortex beam in the chip.
Figure 1. Vector vortex optical radiator and array embedded in photon chip
After years of research, Professor Jin Xianmin and his team from the integrated quantum information technology center (iqit) of Shanghai Jiaotong University have prepared the world's first orbital angular momentum waveguide photon chip in 2018. Through femtosecond laser direct writing technology, an optical waveguide with doughnut cross section can be directly constructed to support and transmit the photon orbital angular momentum beam [Phys. Rev. Lett. 121, 233602 (2018)]. The next big challenge is controllable production. After repeated experiments, Jin Xianmin's team has successfully broken through the problem of controllable generation of vector vortices in the photonic integrated chip by regulating the evanescent wave coupling between the on-chip single-mode waveguide and the doughnut waveguide. By adjusting the phase matching conditions in engineering, the first and second order vector vortex beams can be generated in a controllable way, and the conversion efficiency is as high as 74%.
In cooperation with Xia Keyu and Lu Yanqing of Nanjing University, the research team theoretically deduced the relationship between the direct writing laser energy and the structure parameters of the photon chip, which provided the basis for the laser direct writing high-performance customized photon chip, and successfully constructed the generalized coupled mode theory including the vector vortex optical mode and the material dielectric tensor. The establishment of the theory not only helps to understand the mutual transformation of multiple modes, the evolution of waveguide field and the influence of imperfect processing, but also fills in the lack of the coupling mode theory of orbital angular momentum mode, which can provide an important support for the effective control of orbital angular dynamics in the photon integrated chip.
Professor Jin Xianmin, Professor Xia Keyu and Professor Lu Yanqing are the co authors of the article, and Chen Yuan is the first author. The research team thanks the major projects of Shanghai Science and Technology Commission and the key projects of NSFC for their timely help, as well as the national key R & D plan and the strong support of Shanghai Education Commission.
Paper link:
https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.124.153601
https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.121.233602
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