本論文利用基因演算法設計一非週期晶籌極化反轉鈮酸鋰結構，結構中包含多個光參量產生器機制與非對稱正負晶籌長度比設計，用來產生多個通訊波段的雷射訊號，且藉由電光調制的方式對光參量振盪器之輸出訊號光進行電光波長調制。有別於以往使用模擬退火法的方式來優化AOS結構，基因演算法優化之NOS結構因無同長度區塊的限定，所以自由度較大，所優化的結構在轉換效率、光譜保真度與製程容忍度都有較好的表現。
實際製程晶片並量測後，本設計在光參量振盪器訊號光的電光波長調制率於晶片溫度120℃時有最佳值0.7325nm/KV/mm，且在設計之相位匹配溫度40℃上升到100℃後都有良好的輸出訊號光相對功率比，也成功改善了光譜保真度低的問題。
未來可進一步修改晶體設計，改善電光調制範圍不廣的缺點，並改以環型共振腔的方式共振輸出訊號光，進一步窄化訊號光頻寬，達成快、精確與穩定的可調式窄頻寬雷射源，於在光通訊系統、訊號處理與積體光學等領域中有不容小看的競爭力。;In this study, we have developed a genetic algorithm to calculate a nonperiodic optical superlattice (NOS) structure in LiNbO3 crystal for achieving EO spectrum tuning in multiline intracavity optical parametric oscillators (IOPOs) in telecom C band region. The NOS structure is quasi-phase-matched to perform 1064-nm pumped multiple optical parametric down conversion processes with an engineered certain asymmetric domain length ratio for achieving a desired EO spectrum tuning. The major advantage of an NOS structure calculated by genetic algorithm over the aperiodic optical superlattice (AOS) structure calculated by simulated annealing method that has been adopted in our previous studies is its larger degree of design freedom without suffering from the limitation of setting a unit domain block for building an AOS structure. Besides, the NOS structure has better performance in conversion efficiency, spectral shape fidelity, and fabrication tolerance.
When the fabricated NOS LiNbO3 chip (with an asymmetric domain length ratio of ~0.434) is operated in a 1064-nm pumped dual signal-line (1540 and 1550 nm at 40oC) IOPO, we successfully achieve a highest spectral tuning rate of 0.7325 nm/(kV/mm) in the system at a temperature of 120℃ with much improved spectral-shape fidelity during tuning.
In the experiment, we encountered a measurement problem of power decay with time during the application of a high tuning electric field (>500 V/mm) along the z-axis of the NOS LiNbO3 crystal, the origin is not yet known. The use of a cw OPO is desirable for reducing the problem as well as for having highly narrowed OPO lines.
This novel EO spectrum tunable dual-line IOPO system can be of great potential in many applications such as optical communications, signal processing, THz generation, and integrated optics.
