Silicon-based On-Chip Multiplexing Devices For Optical Interconnects

With the rapid development of the communication technology, especially the application of various smart equipments, higher demands are required for the communication networks in the "big data era" which matters the operation of the data such as storage, transporation and processing. Regarding the advantages of the compactness, lower power consumption and larger bandwidth, more and more attentions are paid on integrated optics for the applications such as optical interconnects, optical communication. The compatibility with CMOS technology of silicon photonics makes the situation more possible where optical circuits integrate with the electrical circuits together and breaks the bottleneck of the electrical interconnects in terms of the speed, power consumption for the inter-chip interconnect and intra-chip interconnect and so on. In order to broaden the bandwidth of the on-chip optical interconnects, mode-division multiplexing revives since the spectrum of wavelength-division multiplexing is saturated. And in the paper a new kind of mode-divison multiplexer as well as two kinds of hybrid multiplexers based on the silicon nanowire waveguide are designed.Firstly, the principle of the directional couplers is analyzed based on the coupled mode theory. The design process, the wavelength response, crosstalk, and the effect of the fabrication error for the proposed asymmetrical directional coupler (ADC) type mode multiplexer are studied followly. An ultra-small four-channel silicon mode multiplexer is demonstrated for the first time with a low crosstalk-20dB as well as insertion loss 0.5dB.Secondly, an optical link realizing polarization-division multiplexing (PDM) and MDM simultaneously is proposed on the silicon-on-insulator platform to increase the bandwidth, and a further study about the key component--PDM-MDM multiplexer is gone. To begin with, two kinds of compact polarization beam splitters (PBS) including a bent ADC type PBS and a cascaded ADC type PBS are designed, analyzed, fabricated and characterizaed, respectively. With the help of the cascaded ADC type PBS and six ADCs, an 8-channel PDM-MDM hybrid (de)multiplerxer is designed to multiplex four TE modes and four TM modes simultaneously. A detailed analysises about the the performance of the device and the effect of the fabrication errors are followed. A crosstalks lower than -11dB for all the channels are demonstrated which coincide with the simulation results. And then an improved 8-channel PDM-MDM multiplexer with the grating type polarizer is experimentally demonstrated to depress the polarization crosstalk.Thirdly, combining the mature arrayed waveguide grating (AWG) for the wavelength-division multiplexing (WDM), a 64-channel WDM-MDM hybrid demultiplexer with ultra-high bandwidth is proposed to allow WDM and MDM realize simultaneously. Moreover, an improved 64-channel WDM-MDM hybrid demultiplexer constructed by two bi-direcaitonal AWGs is designed to decrease the size and alleviate the fabrication error. The measured crosstalks about~-14dB make it a practical solution to further the optical bandwidth on chip.Finally, the main work is concluded and an outlook for the following work is given.