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.