Investigation Of Silicon-based Flat-top And Steep-edge Optical Integrated Filters Based On Guided-mode Resonance Gratings

Silicon-based photonic integrated devices have attracted widespread interest for low loss,high integration,small volume,Complementary Metal Oxide Semiconductor（CMOS）process compatibility,and high interference immunity.In silicon-based integrated photonics,guided-mode resonance grating is widely used to design optical filters due to its excellent optical properties.However,the transmission spectrum of a conventional guided-mode resonance grating shows Lorentzian-type response,limiting the further application of guided-mode resonance gratings in optical communication systems.To solve this problem,the research of this thesis focuses on proposing new guided-mode resonant grating structures based on silicon-based photonic integrated devices.The main purpose of this work is to complete the design of photonic integrated filters with a flat-top and steep-edge response.The main research work and results are listed as follows:（1）A silicon-based cascaded double-layer guided-mode resonant grating structure is proposed,based on which broad-band and narrow-band flat-top and steep-edge photonic integrated filters are designed.A new physical model is established with a physical mechanism combining the guided-mode resonance and the Fabry-Perot resonance,which is then utilized to analyze and develop a broad-band filter design.The results show that the resonant wavelength of the flat-top spectrum is 1550 nm,and the full width at half maximum can be increased to 20 nm with a flatness coefficient of0.385.Furthermore,we propose a cascaded double-layer compound grating structure to achieve a narrow-band flat-top filtering response by varying the spacing between the two grating strips.The transmission spectrum is then analyzed by combining the rigorous coupled-wave analysis and eigenmode analysis.The results show that the resonant wavelength of the filter is 1549.9 nm,and the full width at half maximum of0.5 nm with the flatness coefficient of 0.334.（2）A silicon-based photonic integrated bandwidth-tunable flat-top and steep-edge filter structure is proposed,with a spectral bandwidth tuned by controlling the incidence angle.We then combine the Fabry-Perot cavity and coupled leaky mode theory to establish a new physical model of the device,which is used to analyze the filter structure in combination with the finite element method.It is found that the eigenvalues of the structure can be varied by changing structural parameters such as the grating period and the incident angle of the grating.As a result,the bandwidth of the filter spectral response can be tuned.The results show that the output spectrum of the filter is a flat-top type with a resonant wavelength of 1555.8 nm and its full width at half the maximum range from 2.9 to 18.7 nm.（3）A new silicon-based photonic integrated bandwidth-tunable flat-top and steep-edge filter structure with Si O₂substrate is proposed,of which the spectrum is flat-top and steep-edge type.And the spectral bandwidth of the filter is controlled by the incident angle.We then establish the physical model of the device and elucidate the effect of the variation for the device structure parameters on the output spectrum.The results show that the resonant wavelength is 1550 nm,and the full width at half maximum ranged from 6.0 to 20.8 nm.