| 摘要: | 次奈米窄帶濾光片是一種非常精密且困難的薄膜技術，而其一項很重要的應用是光通訊用的高密度波長多工分工器(DWDM)。在實際的製作上，濾光片的均勻性是一項非常重要的課題。 窄帶濾光片的設計概念是基於Fabry-Perot干涉儀的原理，我們推導了全介質窄帶濾光片的理論並分析了設計參數與均勻性之關聯。基本上，多腔式窄帶濾光片的均勻性主要與空間層的設計有關。如果在設計時，每一個單腔都用相同的空間層設計，則濾光片的光譜將不隨著薄膜厚度均勻性而變化，可以得到好的光譜曲線。另外，如果採用較厚且折射率較低的材料或是厚度均勻性較好的材料來設計空間層，則可以得到比較好的中心波長均勻性。 除了採用好的設計可以得到較好的均勻性，薄膜材料在厚度均勻性也扮演很重要的關鍵。在這方面，我們採用離子蝕刻法來調整薄膜材料的厚度分佈。薄膜材料的厚度均勻性和電子槍蒸鍍薄膜厚度的分佈與離子源蝕刻薄膜厚度的分佈有關。藉由調整離子源特性參數，如離子束電壓、離子束電流及加速電壓可以將薄膜厚度的均勻性調整到最佳狀態。 離子蝕刻法可以調整薄膜厚度的均勻性，但問題是DWDM要求的精密度非常高，誤差須小於萬分之ㄧ，因此我們提出STF法來解決這個問題。不同於以往利用單層薄膜來量測厚度的均勻性，我們採用單腔窄帶濾光片以量測其中心波長來分析薄膜厚度的均勻性，其精密度可達10-5。 最後，我們利用以上幾項技術來製作DWDM。在沒有任何改良前，只有監控點光譜是好的，可用面積幾乎是零。採用空間層的設計後，整個基板的光譜都是好的，但考慮中心波長後，可用面積只有10公分基板的4.4%，單一通道可用面積為185 mm2佔2.3%。再加上離子蝕刻法及STF法，則50 mm直徑的均勻性可達+/-0.003%，而20 mm直徑的均勻性可達+/-0.0006%。單一通道可用面積為2300 mm2佔29%。 One of the important applications of sub-nanometer narrow band-pass filters is for dense wavelength division multiplexing, DWDM, in fiber optic communication systems. To fabricate a sub-nanometer narrow bandpass filter is a very tough coating technology. Particularly, uniformity is one of the most important issues in the fabrication of narrowband pass filters for DWDM. The basic design of narrow bandpass filter is constructed on the Fabry-Perot interferometer. We have derived the theory of all-dielectric narrow bandpass filter for DWDM by multiple-beam interferometry. The dependence of the uniformity on the design of filters has been derived and analyzed theoretically. Essentially, the uniformity of multicavity DWDM filters is dependent on the spacer design of each cavity. First of all, using a same spacer layer in each cavity can insure the spectra are the same and independent on the tooling factors of materials. Besides, by using high order and good tooling factor of material or low index material to be a spacer will achieve the improvement of the uniformity. Excepting the improvement of designing a DWDM filter with large tolerance of layer thickness to obtain the good uniformity, the tooling factors of the materials also play the important role. We provide a technology of ion etching effect to improve the uniformity of the tooling factors. Based on the analyses, the uniformity of filters has indeed been improved not only by the tooling factor of each material deposited by E-gun, but also by the etching profile of the ion source. The etching profile could be controlled by adjusting of the working parameters of the ion source, such as the ion-beam voltage, ion-beam current, and acceleration voltage. The parameters have to be controlled to an optimum condition to accommodate the deposition rates of the two coating materials. The ion etching effect provides a method to modify and improve the tooling factors. However, it is a problem to measure the film thickness with very high precision. To verify the tooling factor to be less than 1/10,000, the accuracy of the thickness has to be at the order of sub-atom. We provide an analyzed method of shaping tooling factor (STF) to improve and enlarge the useful coating area. Instead of deposited a single layer, a single cavity of narrow bandpass filter was deposited and measured the central wavelengths to analyze the distribution of thickness. Using the method of STF the precision of tooling factors can be as good as less than 10-5. Finally, we applied the technologies shown above including the spacer design rules, ion-etching technique, and shaping tooling factor to achieve the best result. Before any improvement, the useful coating area is limited at the monitoring point. By applying the spacer design rules, the useful coating areas cover 4.4% of the 10-cm substrate. Besides, the useful coating area for a single channel is about 185 mm2, 2.3% of the whole substrate. In addition, under the improvements of ion-etching technique and the shaping tooling factor, the uniformity of the DWDM filter was better than +/-0.003% over an area of 50 mm in diameter and +/-0.0006% over that of a 20 mm diameter. The useful coating area for a single channel exceeds 2300mm2, 29% of the whole substrate, which is twelve times of the area if only the design was improved. |
