低阈值温度调谐PPMgLN红外光参量振荡

Low-threshold and Temperature Tunable Optical Parametrical Oscillator Based on Periodically Poled MgO∶LiNbO_3 Crystal

研究了温度调谐下周期极化镁掺杂铌酸锂晶体的红外光参量振荡特性。采用外电场短脉冲极化技术，在大小为7．0mm×50．0mm×1．0mm的Z切高镁掺杂（摩尔分数0．05）铌酸锂上制备出了准相位匹配光学微结构器件，极化周期为30．0μm。以输出波长为1064nm的声光调QNd：YAG固体激光器作为基频泵浦光开展了光参量振荡研究。实验表明：泵浦该PPMgLN晶体，实现了室温下低阈值红外光参量振荡产生，阈值功率仅为45mW（重复频率1kHz）。在泵浦输入功率为225mw时，有36mW信号光输出，转换效率达到16．0％，通过调谐晶体温度（20—180℃），获得了调谐范围为1503—1550nm波段的OPO信号光，实现了低阈值可调谐红外光的稳定输出。

Coherent sources of picosecond pulses that are tunable in the near infrared are interesting for many applications and more significantly for fundamental and applied research in nonlinear optics and telecommunications. Optical fiber and waveguide components usually require relatively low-peak-power optical sources for diagnosis or excitation, thus making high-repetition-rate synchronously pumped optical parametric oscillator （OPO） an attractive solution for this application. Quasi-phase-matched OPO based on periodically poled lithium niobate （PPLN） offer a high nonlinear coefflcient, low loss, a broad operating range, versatility and large nonlinear optical coefficient （d33 - 25.2 pm/V at 1. 064 nm） in fabrication techniques. Recently many efforts were devoted to fabricating a periodically poled structure in 5% （mol fraction） MgO-doped LiNb03（ MgO： LN） because of its higher resistance to photorefractive damage and lower coercive field of - 4.5 kV/ mm at room temperature （RT） than that of LN, as well as its large nonlinear coefficient, comparable with that of LN. Temperature tuning is a unique feature of OPO, which makes its application scope enlarged. Temperature tuning feature of OPO based upon PPLN is the result that the operating temperature fluctuation of PPLN causes output wavelength shifts due to the changes of the length of PPLN and the refractive index of material. The width of PPLN grating period will change because of the expansion coefficient of material when the operating temperature fluctuates. By using short-pulse field, the periodically poled grating（A = 30.0 μm）was successfully fabricated in 1.0 mm thick MgO： LiNbO3 （ doped 5% MgO）. A high-repetition-rate optical parametric oscillator （OPO） based on PPMgLN pumped by a 1 064 nm acousto-optically Q-switched Nd： YAG laser. The threshold is 45 mW with pulses repetition rate 1 kHz at room temperature. Under the condition of 225 mW of input pump power and at 20 ℃, 36 mW of output signal power was obtained, and the conversion efficiency is 16.0%. Furthermore a tunable infrared （IR） output from 1 503 - 1550 nm was obtained by tuning the temperature of PPMgLN from 20 ℃ to 180 ℃.