本研究致力於以氮化矽波導元件產生光學真實時間延遲（Optical True Time Delay, OTTD）。光學真實時間延遲，主要讓光訊號在傳播的過程中有時間的延遲，因而造成轉變回電訊號時相位的延遲。在材料的選擇上，由於光在OTTD結構的傳遞光程長，我們需要考慮到光在結構中傳遞的損耗，氮化矽波導(Silicon nitride waveguide, Si3N4 waveguide)擁有較低的傳遞損耗並且適用於較大的波長範圍，因此我們使用氮化矽單層結構作為波導主體。
OTTD結構上包含一組Delay Interferometer (DI) 搭配Complementary Phase Shifter (CPSS)， DI利用一對不對稱的波導長度並在前後端使用1x2和2x2的多模干涉耦合器產生一對互補訊號頻譜，之後接上CPSS，並利用CPSS上的加熱器達到互補訊號頻譜相位調整的功能，即可將DI所提供的固定時間延遲，形成可連續調變的時間延遲器。
實驗結果我們成功觀測到5Gbit/s與2.4Gbit/s的訊號眼圖延遲12ps，且強度的頻譜變化皆符合我們的計算結果，若將元件加以改善為雙邊的相位調製器，並且改善加熱器，則可超越24ps的延遲甚至更有機會達到預期的48ps。

This research is devoted to generating optical true time delay (OTTD) via silicon nitride waveguide components. The optical true time delay mainly introduces a time delay on a modulated optical signal, thus causing a lag in the signal phase when it is converted back to the electrical signal. In the choice of materials, due to the long transmission path of light in the OTTD structure, we need to consider the propagation loss in the structure. The silicon nitride waveguide (Si3N4 waveguide) has a lower transmission loss within a wide spectral range, so we use single silicon nitride layer as the main body of the waveguide structure.
The OTTD structure includes a set of Delay Interferometer (DI) with Complementary Phase Shifter (CPSS). DI uses a pair of asymmetric waveguides with different lengths and uses 1x2 and 2x2 multimode interference couplers at the front and back ends to generate a pair of complementary signal spectra. The signal then is connected to the CPSS, and use the heater on the CPSS to achieve the phase adjustment on one of the complementary signal spectra. After these two complementary signal spectra recombine again, they introduce a group delay, depending on the phase shift in CPSS. Therefore, we can implement a continuously adjustable time delay.
Experimental results show we successfully observed the signal eye diagrams of 5Gbit/s and 2.4Gbit/s delayed by 12ps, and the intensity spectrum variation are in good agreement with our calculation results. By optimizing the heater design, the time delay can be over 24ps and even more than 48ps.

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