Design And Fabrication Of Guided-mode Resonant Tunable Optical Filters
Uddin, Mohammad Jalal
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Tunable optical filters have many applications in optical communication, multispectral and hyper-spectral imaging, bio-sensing, and display application. In optical communication, tunable optical filters (TOF) are used extensively in different wavelength division multiplexed (WDM) related applications. In display applications TOFs have been being used as color filters (CF) to separate primary colors from incident white light. In this study, two types of TOFs have been designed and fabricated: 1) thermo-optic tunable optical filters (TOTOF) working in optical communication bands and 2) tunable color filters (TCF) working in visible wavelength range.TOTOFs with deep (120 nm grating depth) and shallow (20 nm grating depth) grating structures are designed and fabricated in this study. A deep TOTOF using strongly modulated gratings has been designed, which exhibits 0.07 nm bandwidth with less than 1% sideband in C band optical communication window. The existence and parametric dependence of such narrow band filter are investigated. Designed filter can be tuned 13 nm with 100°C change in temperature. Deep and shallow grating TOTOFs with reasonably narrow bandwidth are fabricated. Fabricated deep grating TOTOF exhibits 12 nm FWHM (theoretical FWHM = 7 nm) and a tuning range of 15 nm with tuning efficiency of 0.15 nm per degree Celsius in C communication band. Fabricated shallow grating TOTOF has a 7 nm FWHM (theoretical FWHM = 3.1 nm) and a tuning range of 12 nm with tuning efficiency of 0.12 nm per degree Celsius in L communication band. Design and fabrication of tunable color filters (TCF) is done in the second part of this dissertation. Three types of tunable color filters: angle-tuned color filters, polarization controlled TCFs, and color filter arrays (CFA) have been investigated. The filters consist of a silicon nitride (Si3N4) grating along with a homogeneous Si3N4 layer on glass substrate.Two types of angle-tuned filters: red and blue-shift color filters are designed and fabricated in this study. In red-shift filter, the pixel response moves from blue to red color with increasing incident angle; the pixel response moves other way in blue-shift filters. An experimental maximum efficiency of 95% is observed in the red-shift color filter whereas an experimental efficiency of 75% is reported in blue-shift color filter. Polarization controlled tunable color filter tunes displayed color by the change of input light polarization. Red-yellow and green-blue tunable color filters have been designed and fabricated. The fabricated red-yellow filter shows red color with 99% efficiency for transverse electric (TE) polarized light and yellow color with 80% efficiency for transverse magnetic (TM) polarized light; fabricated green-blue filter exhibits green color with 90% efficiency for TE polarized light and blue color with 80 % efficiency for TM polarized light. A color filter array (CFA) is designed and fabricated with three physical pixels spaced side by side to exhibit three primary colors. More than 90% experimental efficiency with reasonable bandwidth is achieved for three primary colors.