The Design Fabrication And Application Of Silicon-based Slot Waveguide

Silicon photonics has been an important branch of modern optics research.Due to its high refractive index,transparency in telecommunication wavelength,rich nonlinear properties and compatibility with the CMOS technology,silicon-on-insulator devices are likely to become the mainstay of integrate optics application.In the past twenty years,all kinds of silicon based devices have been demonstrated,such as modulators,dectectors and light emitting devices.Optical transmission between two silicon-based telecommunication modules has been realized,which marks a milestone of silicon photonics.In recent years,hybrid integration becomes more and more attractive.That means integrate various devices made of different materials into silicon-on-insulator platform.One of the strategies is using hybrid silicon slot waveguide.A slot waveguide can enhance the optical intensity in the low refractive index region.This feature makes it beneficial to enhance the light-matter interaction in the slot region.Slot waveguides can be used in all-optical high-speed signal processing.The response time of a hybrid slot waveguide can be as short as a few picoseconds,while the response time of a silicon strip waveguide is on a nanosecond-scale.A hybrid slot waveguide can increase the optical signal processing speed and the nonlinear efficiency.However,its large transmission loss limits its further applications.This dissertation is about the design,fabrication and application of silicon slot waveguides,especially focuses on the third-order nonlinear application of hybrid silicon slot waveguides.The main works include:(1)To confirm that light can be transmited in the slot waveguide,we fabricate a slot microring resonator,by means of electron-beam lithograpgy and inductively coupled plasma etching.We measure the transmission spectra of the slot microring.The extinction ratio of the spectrum is 24dB in 1556nm and quality factor is up to 7000.The result shows that the slot microring has small scattering loss due to the sidewall roughness.(2)In the etching process,the etch rate for the slot waveguide with narrow slot(e.g.less than 100nm)is lower than the other part,result in a ridge slot waveguide.To discover the properties of the ridge slot waveguide,we simulate the optical mode of the waveguide.We find it can be used to increase the sensitivity of the slot waveguide in gas sensing.For a slot waveguide sensor on 220nm SOI,when the unetched silicon layer is 20nm,the sensitity of the obtained ridge slot waveguide is 0.445,higher than the value of a fully-etched slot waveguide(0.267).(3)In order to discover the ability for integration of the slot waveguide,we investigate the coupling strength between two identical slot waveguides.By calculating the coupling length of two slot waveguides,we find that the coupling length of a slot waveguide with a 50nm-wide slot is comparable to a 300nm-wide strip waveguide.In the other word,a sub-50 nm slot waveguide has good optical isolation.(4)In order to increase the third order nonlinear coefficient of the hybrid slot waveguide and supresss the two-photon absorption in silicon,we propose a rectangular nonlinear cladding hybrid slot waveguide.The two-photon absorption figure of merit of the optimized waveguide is up to 4.4,indicating excellent third-order nonlinear properties.Meanwhile,anomalous waveguide dispersion is required to realize efficient four-wave mixing process.However,it is difficult to achieve anomalous dispersion in silicon vertical slot waveguide.In order to decrease the normal dispersion in silicon vertical slot waveguide,we propose a multilayered silicon hybrid vertical waveguide structure.After geometry optimization,the dispersion of a Si/As2S3 hybrid vertical waveguide is between ±300 ps/nm/km is a 500nm span from 1450 to 1950 nm.