本篇論文裡，相較於傳統光學濾波器是以多層薄膜堆疊的方式濾波，我們想利用導波模態共振濾波器這種簡單結構的濾波器。希望未來能應用於雷射共振腔裡的高反射鏡，使得出光的雷射為一個很純和指向性高的波長。所以我們理論設計的濾波器，其頻譜特性的目標為：高品質因素，故共振線寬能小於0.1nm；提高雜訊比，側帶高穿透率區域能大於700nm；最大穿透率能超過90％。而共振波長則以紅外波段為主。 我們提出的結構分別為：波導和光柵材料選擇SiNx，低被覆層為二氧化矽。先利用波導理論設計出波導厚度與特徵模態，爾後利用相位匹配得到光柵的週期，接著引入等效介質理論觀察側帶的穿透率。最後經過製程的容忍度分析，並實際製作出設計的導波模態共振濾波器，對模擬進行比對和驗證。 設計出的導波模態共振濾波器，在TE和TM模態下會有不同的結構參數。在光柵厚度為30nm下：針對TE模態，共振波長在1550.4nm，共振線寬為0.1nm，側帶高穿透率區域為680.8nm，品質因素為15504，最大穿透率為0.93。而TM模態，共振波長在1549.9nm，共振線寬為0.011nm，側帶高穿透率區域為733.76nm，品質因素為140902，最大穿透率為0.926。成功設計出符合我們目標的導波模態共振濾波器。 製程則以TE模態為例，實地量測後共振波長在1.58μm，共振線寬為0.92nm，側帶高穿透率區域為415nnm，品質因素為1718，最大穿透率約為0.94，這與將結構參數代入模擬計算得到的頻譜特性大致吻合。至此，我們成功的實際製作出滿足我們設定目標的導波模態共振波器。In this letter, the two-layer ultranarrow bandstop guided-mode resonance filter with a flattened sideband within a wide spectral range is implemented by using the combination of a subwavelength grating, a waveguide layer with multiple guided modes, and a lower cladding layer with a quarter-wave thickness. The proposed filter based on a free-standing silicon nitride membrane suspended on a silicon substrate is realized by using the anisotropic wet etching to remove the substrate beneath the silicon nitride layer. Both of grating and waveguide structures are fabricated simultaneously on a silicon nitride membrane. Moreover, the silicon dioxide membrane playing a role on modifying the spectral response of proposed GMR filter is deposited beneath the free-standing silicon nitride layer. The incident light is TE mode and the thickness of grating is 30nm. The resonance wavelength of proposed band-stop filter is controlled at 1550.4nm with a linewidth (FWHM) less than 0.1 nm. The improved spectral performance including the sideband can be extended to be nm with the maximum transmittance greater than 93%. The quality factor is 15504. However, the incident light is TM mode and the thickness of grating is 30nm. The resonance wavelength of proposed band-stop filter is controlled at 1549.9nm with a linewidth (FWHM) less than 0.011 nm. The improved spectral performance including the sideband can be extended to be nm with the maximum transmittance greater than 93%. The quality factor is 140902.
