Research On Photonic Functional Devices Based On Non-hermitian Coupled System

With the development of integrated technology,silicon photonics devices have become one of the most important components of modern communication system due to its advantages of low loss,low cost and large bandwidth.Various photonic devices with outstanding performance are strongly desired to satisfy the fast-growing information capacity.Recently,with the lucubrating of non-Hermitian system,some interesting phenomena were revealed and studied.Considering the unique properties,non-Hermitian system can be applied on the design and improvement of photonics devices to achieve better performance and new functions.In this dissertation,the non-Hermitian system is researched,and used to design and fabricate novel photonic devices.The content of this article mainly includes:1)A single mode lasing based on polarization coupled system is proposed.The coupling between two polarization states is introduced by the polarization controller.The gain and loss are introduced by the erbium doped optical fiber amplifier and the polarization dependent of the modulator.Based on the parity-time symmetry theory,the symmetry broken phenomenon can be observed by adjusting the gain and loss,demonstrating as the single mode lasing in this system.In the experiment,the lasing power first decays with the increasing of the loss,but increases after the loss parameter gets over the phase changing point.The linewidth of the output light is 25.2 k Hz.2)A kind of close-range metal heater thermo-optic phase shifter is proposed.Based on the decoupled phenomenon in non-Hermitian system,the metal heater can be placed close to silicon waveguide,and 17 m W power consumption and 1.25 μs response time are realized.Compared to the commercial ones,the proposed phase shifter has significant improvement on the response time.Moreover,a 1×8 phased array is demonstrated to verify its potential of large scale integration.3)A chiral polarizer based on encircling exceptional point by changing coupling coefficient is proposed.Exceptional point is a particular point at which the eigenvalue and eigenvector degenerate.When the parameters evolution of the system makes a close circuit around exceptional point,the asymmetry eigenmode evolution of the system can be observed.Makes use of this phenomenon,an anti-parity-time symmetric system based on polarization coupling is demonstrated and used as a chiral polarizer.This chiral polarizer can realize 10 d B extinct ratio between transverse electric and transverse magnetic mode over a bandwidth from 1.53 μm to 1.57 μm.The proposed device has potential in the future polarization communication systems.4)A kind of high-density multi-mode multi-core integrated photonic circuit based on suppression of coupling coefficient is proposed.Based on the decoupled phenomenon in the non-Hermitian system,metal strips can be placed between silicon waveguides to reduce the power leakage,and suppress the crosstalk.Based on this principle,a waveguide array with400 nm spacing is demonstrated.This method supports over 500 nm bandwidth and arbitrary order of working modes.Moreover,a new technology for depositing metal into narrow slot is exploited.This work provides a universal solution for high-density integration.