Micro/nano Waveguide-type Optical Filters And Photodetectors On Si Substrate

The progress of information and communication technology has significantly changed people's life style, and promoted the rapid development of economy and human society. While optical communication has dominated today's long-haul communication, it is expected to extent its application to access network and interconnects. Accordingly, photonic integrated devices, which have been widely used in optical commnication, are attracting more and more research attention. To achieve lower cost and better performance, higher integration density is desirable for photonic integrated devices. While using waveguides with high refractive index contrast is a main method to reduce the size of photonic integrated circuits (PIC), integrating all kinds of optical functions on silicon substrate is the most promising way in terms of functional integration because of its unsurpassable low cost. This thesis is focused on on the above two aspects of increasing PIC's integration density.Firstly we briefly review the fundamentals of optical waveguides. The slab waveguide mode is solved analytically, while the basic concepts of waveguides are introduced. Numerical simulation is necessary to solve waveguide problems with more complex situations. Various numerical simulation methods are introduced, including finite difference method (FDM), beam propagation method (BPM), and the finite-difference time-domain (FDTD) method.Three kinds of silicon-based waveguides with high index contrast are investigated. By exploring and optimizing the deep etching process, the deeply-etched SiO2 ridge waveguides are fabricated for the first time. According to the measurement results, this kind of waveguide can afford a bending radius as small as several tens of microns. With different core widths, the propagation loss ranges from 0.33 to 0.81dB/mm and the sidewall scattering is the main source of loss. Multimode interference couplers based on the deeply-etched SiO2 ridge waveguide are also fabricated and show fairly good performances. For lower cost, SU-8 polymer ridge waveguide and devices are fabricated, including Y-branches, arrayed waveguide gratings (AWG) and microring resonators (MRR). Ultrasharp SOI (silicon-on-insulator) nanowire bends (with a bending radius of R<2μm) are analyzed numerically. We have found 3D-FDTD method is necessary and feasible for this simulation after comparing different numerical methods. Subsequently, the bending losses of different waveguide sizes and structures are determined. The relationship between the intrinsic Q-factor of an MRR and the bending radius is also obtained.We investigate two typical kinds of optical filters, namely, AWG and MRR, based on silicon nanowire waveguides. Firstly, dual-tapered auxiliary waveguides at the exit of the waveguide array are introduced to improve the channel uniformity of a Si-nanowire-based AWG demultiplexer. By using a hybrid simulation method, the dual-tapered auxiliary waveguides of the AWG demultiplexer are optimized reliably and efficiently. As a result, the total number of channels allowed in the designed AWG demultiplexer is 50% more than that of the conventional one. Then we demonstrate the design, fabrication and measurement of the SOI MRR suitable for ultra dense WDM applications with a channel spacing of 0.1 nm. The demultiplexer is realized by cascading MRR with different resonant wavelengths. The fabricated MRR has a Q-factor of 4×104. In order to ensure that the resonant wavelength difference between neighbouring MRR is 0.1nm, we introduce micro-heaters and separately tune the resonant wavelength of each MRR by using a thermal-optic effect.Integrating III-V materials on Si is a promising candidate to realize both passive and active optical functionalities on a single silicon chip. Various heterogeneous integration technologies are reviewed with an emphasis on the adhesive die-to-wafer bonding process that we adopt. By using this technology, we investigate an InGaAs PIN photodetector integrated on SOI waveguides. The light is evanescently coupled from the SOI waveguide to the photodetector. The serious light absorption by p-contact layers is greatly reduced by introducing a central opening on these layers. The thickness of the i-InGaAs layer is also optimized towards phase matching between the SOI waveguide mode and the detector mode. The fabricated photodetector performs well in terms of very low dark current (～10pA), high responsivity (1.1A/W), and a wide wavelength range covering the whole S, C and L communication bands.