NxN光纖光柵輔助耦合器的分析與在分波多工的應用

Abstract

光纖光柵輔助耦合器原先的模擬方法主要以耦合方程式法為主，而耦合方程式法只能模擬正弦式光柵簡單結構，而難以模擬更為複雜之結構。且耦合方程式法所使用之近似較多，對於光柵折射率波動振幅過大的情況下或光柵長度較短時，所得到的結果較不準確。 故我們提出一套新的方法來模擬NxN光纖光柵輔助耦合器的結構，本方法使用的近似比耦合方程式法更少，可以更準確的模擬出元件的性質，其可以模擬的結構之複雜度不但大為增加且更有彈性。 我們將此方法應用在模擬分波多工濾波器。將原舊有模擬方式模擬之正弦式2x2光纖光柵輔助耦合器之結構改為以本方法模擬之2x2 Sinc-Apodized光纖光柵輔助耦合器結構。我們發覺到以我們的方法模擬之結構其對波頻之選擇敏感度遠優於舊有之結構。接著我們將此結構推衍到3x3光纖光柵輔助耦合器，模擬後並得到相當好的結果，故顯然我們此方法其日後將具十分廣泛之應用性及實用性。

Nowadays the main simulation method modeling Grating-Assisted Couplers is Couple Mode Equations Method. However, this method can only be applied to sinusoidal simple grating structure but not more complicated systems. Besides, when the variation of grating refractive index is too large or the length of the grating is too short, the result will be much more inaccurate due to the huge amount of approximation in this method. As a result, we proposed a new method combing Couple Mode Equations Method and Transfer Matrix Method for modeling NxN Grating-Assisted Couplers. Though there is less approximation in it, we can have a better result simulating the property of the device. The range and the complexity of the modeling structure increase a lot. We applied our method to WDM Add/Drop devices, replacing the original 2x2 Grating-Assisted Couplers' sinusoidal structure by Sinc-apodized structure, which is simulated by our new method. The dropped-wavelength's spectrum of our structure is much sharper than the old one. Additionally, we extended the structure to 3x3 Grating-Assisted Couplers and gathered a spectrum as good as 2x2 Sinc-apodized Couplers.So it is obvious that there is a wide and attractive application field of our method.