可調脊形光極化分離器及伽瑪輻射效應之研究

Abstract

本論文探討可調脊形光極化分離器之原理和製作方法，同時又探討γ射線對於該元件之波導所造成的影響。在鈮酸鋰基板上所製作的脊形結構，可改用苯甲酸與己二酸的混合酸作為質子交換源，結果有較佳的脊形結構外觀比。 元件架構為一非對稱y形分岔，下半部輸入端為一光極化轉換器，上半部輸出端為一光極化分離器。輸入端為鎳擴散波導，其兩旁外加一對指狀電極；輸出端兩分支波導分別由質子交換波導和鎳擴散波導。利用鎳擴散光波導製程極化相依的特性，選擇在適當的條件下製作可導普極化方向和非普極化方向的輸入端鎳波導，與只導普極化方向的直分支鎳波導。至於只導非普極化方向的彎曲分支波導，則利用質子交換波導只導非普極化方向的特性來製作。而指狀電極結構的極化轉換器，TE極化方向和TM極化方向可以藉由外加電場轉換，以調變輸出的TE極化方向和TM極化方向之光功率比。製作出來的可調脊形光極化分離器，在TE和TM極化光的訊熄比分別為25dB和18dB。當外加調變電壓為70Ｖ時，TM和TE極化光分別有85%和50%的轉換效率。此轉換效率優於先前所發表的結果。 在γ射線輻射效應的影響下，本研究結果發現脊形結構的熱退火質子交換式光波導具有最優異的抗輻射性與最低的傳播損耗。每增加10KGy的輻射照射劑量約只增加0.06dB/cm的傳播損耗。

The principle and fabrication of tunable ridge-type optical polarization splitter is studied and the influence of the gamma ray irradiation on the waveguides of the splitter is discussed. The ridge structure on the lithium niobate substrate is fabricated by using a mixture of benzoic acid and adipic acid to have a larger depth-to-width ratio. The splitter is essentially an asymmetric y-branch waveguide. The lower part is a polarization converter and the upper part is a TE/TM polarization splitter. The polarization converter consists of a nickel indiffusion waveguide and a pair of finger-type electrodes deposited on both side of the waveguide. The two branch of the polarization splitter is fabricated by using nickel indiffusion and annealed proton exchange (APE). Using the process-dependent polarization property of the nickel indiffusion waveguide, the input waveguide supporting both ordinary and extraordinary waves and the straight branch waveguide supporting only ordinary wave are successfully fabricated by choosing proper process parameters. The bent branch waveguide supporting only extraordinary wave is fabricated by APE waveguide due to its property of just supporting extraordinary wave. When an incident laser is passing through the polarization converter, the power ratio of TE and TM polarization can be adjusted by an applied electric field. Then the TE- and TM-polarization powers are split by the following TE/TM polarization splitter. The extinction ratio of TE and TM polarization are 25dB and 18dB, respectively. When a voltage of 70V is applied to the electrodes, 85% and 50% of the power in TM- and TE-branch waveguide are converted to the power in TE- and TM-branch waveguide, respectively, which are greater than those reported previously. Moreover, under the irradiation of gamma ray, the ridged APE waveguide exhibits the highest anti-radioactivity. The measured power transmission loss of ridged APE waveguide is 0.06 dB/cm per 10KGy, which is the lowest loss among all the waveguides tested.