The Study Of Silicon Based MMI And Its Application In All-Optical Signal Processing

Considerable influence has been brought to people’s life because of the optical fiber communication. With the fast development of it, higher transmission speed, lower power consumption and larger integration become more and more important. Integrated optical circuit has been proposed in1970s and with the fast development in recent years, silicon based integrated optical circuit, which has got so many breakthrough, should be the most valuable technology in the future. The research of active and passive devices based on silicon is very important, and most of all, silicon based device using in all-optical signal processing has got more and more interest.Thanks to its compact capacity, easy fabrication and large fabrication tolerance, multi-mode interferometer (MMI) has been used in many field such as power splitter, MZM switch, modulator, demodulator, laser and AWG et al. The research content of this dissertation is the silicon based MMI using in all-optical signal processing. Firstly, we will introduce the basic theoretical knowledge, design method, as well as the fabrication technics of the MMI. Then, based on MMI, many other devices will be designed and fabricated, which will be used in all-optical signal processing such as multi-channel optical format conversion, dual-polarization signal processing and the key device in integrated coherent receiver. The major research achievements and contributions are summarized as followings:(1) The basic principle of MMI is introduced and the two types of MMI, one type based on conventional silicon waveguide and the other type based on photonic crystal waveguide, are investigated. The fabrication technics of coupling grating and MMI based on different silicon-on-insulator (SOI) structures are deeply discussed.(2) MMI used in WDM all-optical signal processing is proposed and further demonstrated on SOI. The design and fabrication methods of DI based on MMI are discussed. Single DI and DI cascaded with AWG are fabricated. With the DI cascaded with AWG, all-optical signal processing such as4×40Gb/s RZ to NRZ format conversion,4×20Gb/s DPSK demodulation and4×40Gb/s NRZ to RZ format conversion with the help of optical nonlinear device semiconductor optical amplifiers (SOA) are achieved successfully. (3) MMI used in dual-polarization signal processing is proposed and further demonstrated on SOI. First, the meaning and conventional methods of dual-polarization signal processing are discussed. The2D photonic crystal grating coupler used in dual-polarization signal processing is proposed, with this method, a2D photonic crystal grating coupler cascaded with a DI to form a loop circuit is proposed and fabricated. With this compact device, the demodulation of dual-polarization DPSK is achieve successfully.(4) MMI used in integrated coherent receiver is proposed and further demonstrated on SOI. An ultra-compact dual-polarization QPSK receiver is proposed based on MMI and photonic crystal.4×4MMI as90°hybrid and4×4MMI cascaded with AWG are discussed and fabricated.(5) MMIs based on photonic crystal waveguides are studied theoretically and experimentally. The influence to the imaging phenomenon of MMI based on different photonic crystal structures is deeply discussed. MMIs based on photonic crystal waveguides as180°hybrid and90°hybrid are proposed. An efficient way to decrease the coupling loss of the single mode silicon waveguide and the photonic crystal waveguide is proposed and demonstrated. DI based on photonic crystal MMI is designed and fabricated, with this device, the demodulation of DPSK is achieved successfully.