Integrated Optical Add-drop Multiplexer With Parent-sub Microring Structure

With the development in multi-core technology, higher on-chip data transmissionrate is required for advanced high performance computer processor. However, it isincreasingly difficult to meet such requirements with traditional electricalinterconnection. On-chip optical interconnection, especially with wavelength divisionmultiplexing (WDM) technology, is a promising solution to achieve broader bandwidth,lower power consumption and less crosstalk. In the on-chip optical networks withWDM system, integrated optical add-optical multiplexer (OADM) is a key componentthat serves as an optical router.In this thesis, we are dedicated to the three key problems in the current integratedOADM based on microring resonators: to extend free spectral range (FSR), to obtainuniform channel spacing and to increase shape factor. For this purpose, a novel structureof parent-sub microring is proposed and demonstrated. The FSR could be extended bytaking advantage of coupled microrings with different radii. Uniform channel spacing isobtained by using resonances of a single ring (the parent ring) to process multiplechannels. The channel crosstalk is compressed by the high-order filter response fromseries-coupled microrings. The main achievements in this thesis are as follows:With numerical simulation, the transmission spectra of all output ports arecalculated by transfer matrix method and the performance of the device is verified. Inparticular, an optimum relation between coupling coefficients that guarantees flat-topfilter response is derived. The impact of fabrication error on device performance isanalyzed and the design principle for a practical device is summarized.Secondly, a four-channel OADM based on parent-sub microring structure isfabricated. We not only explore the fabrication process and technological conditions byourselves, but also entrust a foundry to fabricate chips to verify its compatibility withstandard CMOS process. In our own fabrication process, a new method is introduced toreduce the ripples on the SiO2cladding above the waveguides and thus improve thequality of the micro-heater. Our method is to deposit a layer of SiO2by PECVD firstand then add a layer of spin-on-glass. Thus the surface flatness of the cladding layer isimproved without deteriorating the propagation loss in the waveguide. At last, for device testing, a modified method is adopted for thermal tuning oncurrent fiber-waveguide coupling test platform. By tuning the resonance wavelengths ofsub-rings according to those of the parent ring through thermo-optic effect, afour-channel optical add-drop multiplexer is achieved. The bandwidth of passband is0.15-0.25nm with a drop loss of2dB. The through port extinction is18dB and thechannel crosstalk can be less than-20dB. The channels can also be independentlyswitched between the states of dropping and passing through by thermal tuning of thesub-microrings. In our experiment, the thermal tuning efficiency is as high as0.27nm/mW.