Design And Fabrication Of As-Se Chalcogenide Waveguide With Low Optical Losses

Today's society has entered the information age with optical communication and information networks as its main features.The requirements for obtaining,transmitting,processing and storing information are becoming higher and higher.Information-related photonic devices are developing at an unprecedented speed and scale.Chalcogenide glass has been widely studied in integrated photonics due to its advantages such as higher third-order nonlinearity,ultra-fast nonlinear response time,large linear refractive index,and wide infrared transmission range.Chalcogenide optical waveguides are an important part of integrated optical devices,and it is also the key in the study of chalcogenide photonics.At present,domestic research on chalcogenide optical waveguides is limited although it has important significance and application prospects.In this thesis,the waveguide structure was firstly designed by simulation software.Then,high-quality Ge_11.5As₂₄Se_64.5 and As₄₀Se₆₀ bulk glass were used as raw materials,and Ge_11.5As₂₄Se_64.5 film as bottom cladding followed by another layer of As₄₀Se₆₀ as core was deposited on thermally oxidized silicon wafer using thermal evaporation.The waveguide was subsequently prepared on the As₄₀Se₆₀ layer by ultraviolet exposure lithography and inductively coupled plasma reactive ion dry etching.After then,a layer Ge_11.5As₂₄Se_64.5 film was deposited on the waveguide,which was used as the upper cladding.Finally,the morphology and transmission characteristics of the waveguide were further studied.Below are the related researches in details:(1)Eight ridge waveguides with different aspect ratio structures were designed using COMSOL Multiphysics simulation software,and their mode field distributions were calculated.The dispersion,zero-dispersion point positions and effective mode field areas of the waveguides of different sizes were compared.The results show that the waveguide with a ridge width of 4?m and a ridge height of 3?m has the smallest zero dispersion point(?2.1?m),and the difference between TE and TM modes on the dispersion can be ignored.The effective mode area is 7.4?m.The results provide guidance for experimental preparation of waveguides.(2)Energy dispersive x-ray spectrometer,surface profile and X-ray diffractometer were used to analyze the film composition,surface roughness and the crystallization of the film,respectively.The results show that the thermally evaporated thin film has a uniform composition and a smooth surface with a roughness of 1 nm.No crystallization can be observed in the film annealed at 150°C for 2min.However,thermal annealing can reduce the residual stress,improve the internal uniformity,and help reduce the transmission loss of optical signals.(3)The As₄₀Se₆₀ ridge waveguide was prepared by ultraviolet exposure and inductively coupled plasma reactive ion etching that are compatible with standard semiconductor processing,and an annealing treatment was introduced after photolithography to enhance the adhesion between the film and the substrate.The CF₄ and CHF₃ were selected as the etching gas to increase the CF_x group in the etching environment,so that anisotropic etching and protection were performed simultaneously.The test results show that when the flow rates of CF₄ and CHF₃ are 10 sccm and 20 sccm,respectively,the prepared waveguide has good surface and sidewall perpendicularity.(4)The cut-back method was used to measure the transmission loss of the waveguide.A 1550nm laser was used as the source on a high-precision 3D coupling platform.The input power was 1mW,and the transmission loss of the waveguides with a ridge width of 2?m,4?m,and 8?m was measured.The experimental results show that the corresponding transmission loss of three different ridge width waveguides is 2.56 dB/cm,1.47 dB/cm,and 1.4 dB/cm,respectively.Finally,this thesis summarizes the prospects for future work.The low-loss chalcogenide-based optical waveguides prepared in this thesis are expected to have broad application prospects in the field of integrated photonics.