基于MgO:QPLN的多光参量振荡器电场调谐特性理论与实验研究

报道了基于掺氧化镁准周期极化铌酸锂(MgO:QPLN)的多光参量振荡器电场调谐特性理论与实验研究. 通过对电场调谐能力与极化结构参数间关联性的理论分析, 确定了高正负晶畴比MgO:QPLN电场调谐的可行性, 并模拟得到跨周期参量光输出波长与加载电压的关系曲线. 实验中通过对MgO:QPLN有效的电场加载, 实现了3.84 μm波段参量光的电场调谐, 频谱调谐带宽约6 nm, 调谐速率接近1 nm/kV, 进一步结合温度调谐, 实现了参量光宽谱段高精度的连续调谐. 所获得实验结果与理论模拟结果基本符合, 电场调谐在精度控制、快速响应方面相比于传统温度调谐更具技术优势.

Electric field tuning characteristic of multiple optical parametric oscillator based on MgO:QPLN

The quasi-phase matching optical parametric oscillator tuning methods, i.e. grating period tuning, temperature tuning, pumping wavelength tuning, and angle tuning are more simple and convenient than the traditional mechanical tuning which requires inserting the frequency selective element into the cavity. However, itneed to be improved for wavelength tuning in quick response and high-accuracy control. In this paper, the tunability of multiple optical parametric oscillator (MOPO) based on MgO:QPLN has been studied under an applied electric field. Based on the linear electro-optic effect of LiNbO₃, we theoretically analyze the feasibility of achieving parametric light wavelengths tuning by applying electric field of particular direction on the z-direction of LiNbO₃. We study the relationships between the ability of electric field tuning and the polarization structure parameters, and analyze the feasibility of MgO:QPLN with high positive and negative superlattice domain ratio for electric field tuning. The relationship of output wavelength and loading voltage is achieved by simulation. Simulation results show that the tuning rates of 1.57 μm signal light and 3.84 μm idler light are about 0.27 and 0.93 nm/kV, respectively. By reasonably controlling the temperature of MgO:QPLN crystal, tuning sections of the parametric light electric field could be linked orderly, and the output wavelength of parametric lights could be turned continuously in a wide range, which greatly expands the spectral bandwidth of the electric field tuning. In the experiment, a high-repetition-rate acousto-optic Q-switched Nd:YVO₄ laser at 1064 nm is applied as the pumping source. The laser works at 200 kHz with a pulse width of 9.756 ns and its maximumouput power is 22.8 W on average. When the temperature of MgO:QPLN is stable at 20℃, the average output power of 1.57 μm signal light and 3.84 μm idler light are 1.7 and 0.72 W, respectively, and the corresponding pulse width of the two parametric lights is 9.132 and 8.463 ns. By loading proper electric field on MgO:QPLN (on-load voltage：-3000 V-+3000 V), we achieve the electric tuning of the parametric light at 3.84 μm range, and the bandwidth of spectral tuning is about 6 nm with the tuning rate approaching 1 nm/kV. Combining the temperature tuning with the electric field tuning, we further achieved high-precision continuous tuning of the parametric light in a wide spectrum range. All the final experimental results agree basically with the theoretical analysis one. In addition, results show that the electric field tuning performs better than the temperature tuning in accuracy control and quick response. For MgO:QPLN-MOPO, its irregular domain configuration could work adequately by introducing the electric tuning.