Silicon-based Arrayed Waveguide Grating For Optical Interconnects

With explosive increase of information processing capacity and speed, high performance computers and servers have developed rapidly. The number of CPUs and the data transmission bandwidth among them have increased year by year. In the near future, Tbit/s-class interconnection among CPUs will become necessary. However, from the viewpoint of size and power consumption, such broadband interconnects cannot be achieved with conventional electrical wiring and face the so-called "electrical bottleneck" problem. Silicon photonics-based optical interconnection technology uses photons as information carrier, not only having the advantages of high bandwidth, fast transmission speed, immune of electromagnetic interference and low power consumption, but also making compact, high density optical integrated circuits feasible. Photonic devices, which have the function of wavelength division multiplexing, can transmit multiple signals simultaneously in single waveguide and play an important role in silicon photonics interconnection systems. In this thesis, we are devoted to the study of silicon-based arrayed waveguide grating (AWG).Firstly, basic properties of silicon nano-waveguide and its fabrication process flow are introduced. The high index contrast between the silicon core (nsj= 3.48 at 1550 nm) and the oxide cladding (nsio2= 1.44) makes the light high confined in the core layer and allows for very tight bends with radii as small as 5μm, which significantly reduces the size of optical devices and improves the integration density. Unfortunately, this reason makes silicon waveguide very sensitive to sidewall roughness-, temperature variation and polarization.And then, the theory of AWG is discussed and design procedures of AWG acting as router and multi/demultiplexer are also shown. We give the details of the semi-analytical model for simulating AWG and analyze the main sources of loss and crosstalk in AWG.Taking into account properties of the silicon nano-waveguide in combination with layout of the echelle diffraction gratings and conventional AWG, a method for solving polarization dependent problem of silicon-based AWG is proposed. Principle and structure of this method is introduced in detail and we also show two design examples for the application of dense wavelength division multiplexing (DWM) and coarse wavelength division multiplexing (CWDM) in order to understand it deeply. A birefringence compensated silicon nanowire AWG with channel spacing 20 nm and channel number 5 for CWDM optical interconnects is experimentally demonstrated, the results show that the polarization-dependent wavelength shifts (PDλ) can be reduced from 380-420 nm in theoretical analysis to 0.5-3.5 nm, below 25% of the 3 dB bandwidth of each channel response.A silicon-based AWG triplexer employing the cross-order design with an ultra-compact size of only 0.18×0.12 mm2 is realized in silicon-on-insulator (SOI) platform and the early results show that this AWG triplexer has a large PDλ. According to the birefringence compensation method we proposed and considering the context of AWG triplexer in passive optical network, a birefringence compensated AWG triplexer suited for optical network units (ONUs) is designed and fabricated, The PDλs for wavelength channels at 1490 nm and 1550 nm are reduced to less than 2.5 nm, sufficiently small for ONU triplexer applications. Although a large PDX is observed at the wavelength channel of 1310 nm, the chip-based hybrid integration method or polarization maintaining fiber can be used for connection between the AWG triplexer and the laser transmitter at 1310 nm.At last, we investigated how to improve the performance of silicon-based AWG by employing horse-shape structure for the layout of arrayed waveguides in combination with single mode and multimode waveguide. An 8x400GHz AWG with horse-shape structure is designed and fabricated, and its crosstalk is better than-18dB, which illustrates the validity of this design method. At the same time, ultra-compact reflective AWGs based on horse-shape structure and distributed Bragg reflector (DBR) are also designed and fabricated, we demonstrated the performance of 6×400GHz and 20×200GHz reflective AWGs.