The Study Of Silicon Based Tapered Directional Coupler For Multi-dimensional Multiplexed System

The rapid development of optical communications brings significant convenience to our life.It also requires more technologies to enlarge the transmission capacity of communication network.The multi-dimensional multiplexing system,which employs two or more multiplexing technologies simultaneously to obtain an ultrahigh bandwidth,has emerged as required.Hence,it is important to improve the performance of the devices and make it suitable for multi-dimensional multiplexing system.On the other hand,great breakthroughs have been made in silicon integrated optical circuits,which means the lower power consumption and larger integration are gradually becoming the trend of future optical communications.Therefore,it is of great significance to study the silicon based devices for multi-dimensional multiplexing system.The directional coupler,which is one of the key components in optical communication system,has been widely applied and studied.However,the conventional directional coupler is wavelength and polarization sensitive.Moreover,it can only support the fundamental mode in most applications.The research contents of this dissertation focus on the applications in the multi-dimensional power splitter and the polarization splitter/rotator?PSR?.The devices are designed on silicon-on-insulator?SOI?platform and the performances are improved by introducing tapered waveguides to directional couplers.Main contents are summarized as follows:?1?The principle of the directional coupler based on coupled-mode theory is introduced.According to the coupled-mode theory,the performance of the tapered directional coupler is analyzed with the numerical computation method.The design and optimized algorithm employed in this dissertation are briefly discussed,as well as the fabrication technics and the test methods,which all provide the theoretical supports for the next research.?2?Three kinds of schemes based on tapered directional couplers have been proposed to improve the performance of 3 dB couplers.Firstly,we propose an on-chip broadband 3dB coupler by using series-tapered waveguide structure.Particle Swarm Optimization?PSO?is utilized to handle multiple parameters simultaneously.The optimized results show that the coupling ration varies 0.5%over the wavelength region of 100 nm.Then,we propose and experimentally demonstrate a polarization-insensitive 3 dB coupler by using tapered three-guide structure.The measured wavelength-dependent power imbalance is less than1.1 dB and the maximum polarization-dependent imbalance is about 1.0 dB in the wavelength region from 1520 nm to 1600 nm.Finally,a dual-mode 3 dB power coupler based on SOI platform for mode division multiplexing system is proposed and demonstrated.The device has a 50:50 coupling ratio around the wavelength of 1550 nm for both fundamental and first order transverse magnetic?TM₀ and TM₁?modes.The measured insertion losses for both modes are less than 0.7 dB.The crosstalks are about-14.3 dB for TM₀ mode and-18.1 dB for TM₁ mode.?3?A broadband and fabrication-tolerant PSR is proposed and fabricated on SOI platform.Benefiting from the counter-tapered structure,the PSR exhibits a large bandwidth and fabrication tolerance.Air cladding is employed to break the vertical symmetry,thus the device is fabricated with a single step of exposure and etching.The measured results show that the TM₀-TE₀ polarization conversion loss is less than 0.8 dB,while the TE₀-TE₀ insertion loss is less than 0.5 dB,over the wavelength region from 1520 nm to 1580 nm.The crosstalks for the two polarizations are lower than-18 dB.