The chip integrated optical isolator is very important in the optical signal transmission system. Its functions include adjusting the optical signal transmission path, protecting the optical elements from the back stray laser interference and so on. The traditional optical isolator is based on Faraday magneto-optical effect, which is not easy to integrate on chip and has high insertion loss. The external magnetic field will also affect the surrounding photoelectric devices. In recent years, scientists have been devoted to the development of on-chip integrated optical isolators with nonmagneto-optical effects, and some progress has been made in the use of photon band transitions, optical force effects and nonlinear effects. However, there are still many problems to be solved, such as narrow working band, large insertion loss and so on. To solve these problems, Professor Wen Jianming of keneso State University and Professor Jiang liang of the University of Chicago, who are the team and collaborators of Jiang Xiaomin, Department of quantum electronics and optical engineering, Nanjing University, have realized a non magneto optic effect tunable optical isolator with high isolation and low insertion loss by using the characteristics of stimulated Brillouin scattering unidirectional transmission in silicon oxide micro ring core cavity. In the coupled microcavity system, the bulk stimulated Brillouin scattering is used to realize the non - reciprocal parity - time symmetry. The results were published in Laser & Photonics reviews (DOI: 10.1002/lpor.201900278).
Bulk stimulated Brillouin scattering is an interaction process of photoacoustic coupling. When the pump light interacts with the medium, some photons will annihilate and produce new phonons and signal photons. Due to the limitation of phase matching, signal light only exists in the opposite direction of pump light transmission. The bulk stimulated Brillouin scattering is a unidirectional excitation process. Based on this unique physical process coupled with high quality factor optical microcavity, an excellent platform for light matter interaction, the research team has realized a non-magnetic effect on-chip optical isolator. The isolator has low insertion loss and 17.7 DB isolation. It can work in the range of signal optical power from 1? W to 100? W and the isolation is adjustable. Because of the large Stokes frequency shift (about 11 GHz at 1550 nm), the pump light can be easily filtered from the signal light, so that the signal light is not affected. More importantly, the isolator can work when the signal light is input from both directions at the same time. Furthermore, the team applied the bulk stimulated Brillouin scattering to the coupled microcavity system, and realized that the non reciprocal parity time symmetry, that is, the parity time symmetry phenomenon only exists in the reverse signal light with gain effect, and the forward signal light cannot form the parity time symmetry condition due to the lack of gain. This non - reciprocal process relieves the degeneracy of the forward and reverse singularities of the coupled microcavity. Because the detection sensitivity near the singular point is much higher than that outside the singular point, the system can be used in the future to realize bidirectional and multi-functional nano particle sensor, which can detect different sizes or types of nano particles in two directions. MaterialsViewsChina
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