Research On Silica Based Visible Etched Diffraction Gratings

Various substances in nature have specific emission and reflection spectral characteristics,according to which the target can be detected and classified.And a spectrometer is an apparatus that separates the polychromatic light into the corresponding frequency spectrum by refraction,diffraction or interference,typically used in spectroscopic analysis to identify materials.Nowadays,non-destructive and reliable spectroscopic analysis has become a powerful tool for the detection of constituents,contents and structures of matter,which is extensively applied for biomedicine,atmospheric measurement,water quality inspection,food safety detection,space exploration,material research,quality assessment,ecosystem monitoring among several other fields.Rather than the expensive and bulky instrument in biological and chemical laboratories,spectrometer-on-chip realizes on-site real-time rapid sample detection and analysis on a small,low cost and effective chip,thus has broad market and application prospects.Aimed at visible spectroscopic analysis,in this thesis we are devoted to the study of silica based visible etched diffraction gratings(EDG).The thesis starts from the basic principle and important design parameters of EDG,and the one-stigmatic method,two-stigmatic method and three-stigmatic method are introduced in detail and compared with each other.Also the numerical simulation method of EDG is presented.Then,a silica based visible EDG is designed for visible spectroscopic analysis.The existing problems including very small grating tooth cohesive surface and poor unifonnity of insertion loss in the case of small diffraction order(m = 1)and large spectral range(400 nm?700 nm)are analyzed in detail.In this regard,the corresponding optimization process and improving scheme are proposed respectively.By changing the central output waveguide position and rotating the angles of grating facets,the insertion loss uniformity in a wide wavelength range is achieved.Besides,considering the difficulty of obtaining large spectral analysis range and high spectral resolution at the same time,a cross-order EDG design is introduced.After that,the fabrication process and the test scheme of silica based visible EDG are studied in detail.The key technology steps of the device fabrication are introduced,including silica deep etching,aluminum plating of grating facets.Finally,the measurement results are analyzed and with the supplementary experiment,the future research work is prospected.