矽基片偏極性積體分光元件之研究

Abstract

偏極性分光元件為ㄧ基本的光學元件，可應用在光纖通訊及感測器上。在 我們的研究中，採用以矽基片為基底而做出的絕熱Ｙ分差式偏極性分光器 ，其所用到的材質，如二氧化矽、摻入磷的二氧化矽玻璃、氮化矽、都可 以現行成熟的矽半導體技術做出。而此元件的輸出入端波導皆為摻磷的二 氧化矽由於它的折射率和光纖相近，較無耦合上的問題。所謂絕熱式元件 即當電磁波的模數不會因傳導過此元件時發生改變，此種元件的好處在於 沒有嚴格的尺寸容忍度，在我們所模擬的元件中ＴＥ模的電場選擇較大折 射率的氮化矽波導，而ＴＭ模則選擇摻磷的玻璃波導。而分析上所考慮到 因素為絕熱條件及同步干涉，為了達成絕熱的過程，Ｙ分差的分離角度一 定要很小，在我們所模擬的元件中為數厘弳度。由於在製作過程要以光罩 來做出元件的形狀，所以Ｙ分差會以格子的型式出現，此會造成階梯的形 狀，而產生同步干涉的現象。為了避免此種現象，所選擇的階級長度必須 滿足一定的條件，否則在輸出端會產生許多不希望的散射模場． An optical TE--TM mode beam splitter is a fundamental device and will be useful in integrated devices for fiber communications and sensors. Many approaches have been taken to implement the device. In our work an adiabatic Si--based Y-- branch TE--TM mode beam splitter has been investigated. The materials used to simulate the device are silicon dioxide, p-- glass, silicon nitride which are all compatible with the mature silicon technology. Besides, the input and output waveguides are the p--glass core which are convinient to couple with the fiber for their close refractive indices. An adiabatic device in which power is not transferred from one mode to another as the modes propagate across the device has the adavantage that it needs no critical lengths to be adjusted or tuned. In our device the TE field will choose the nitride core and the TM field the p--glass core for their close refractive indices, respectively. The design considerations are adiabatic conditions and coherent interferences. For achievement of the adiabatic passage through the device the branching angle must be small, around several milliradians in our device. For the branch is realized in the available photography, there must have steps along the branching waveguide. To avoid the coherent interference effect which increases the crosstalk at the output, the step lengths must be small. The analytical tool is the MPFE (Mode Propagation by the Fourier Expansion) method.