1560nm激光经PPLN和PPKTP晶体准相位匹配倍频研究

Investigation of Quasi-Phase-Matching Frequency Doubling of 1560nm Laser by Use of PPLN and PPKTP Crystals

将1560nm光栅反馈复合腔半导体激光器产生的连续激光注入掺铒光纤放大器,放大至约5 W,分别采用周期极化铌酸锂(PPLN)和周期极化磷酸氧钛钾(PPKTP)晶体单次穿过进行准相位匹配倍频,对应获得约336mW和210mW的780nm激光输出,倍频效率约为7%和4.4%。通过监视倍频光纵模,显示其具有良好的单频输出特性。此外,还扫描测得了Rb原子D2线的吸收光谱,表明780nm激光的频率调谐范围大于10GHz。采用无调制偏振光谱技术将1560nm半导体激光器频率锁定至87 Rb 5S1/2(Fg=2)-5P3/2(Fe=3)超精细跃迁线上。相对于自由运转450s内1560nm激光频率起伏约4MHz,锁定后可将残余频率起伏压低至1.5MHz左右。

The continuous-wave （CW） light obtained by the 1560 nm external-cavity diode laser （ECDL） is amplified to about 5 W by a erbium-doped fiber amplifier （EDFA）. The periodically poled lithium niobate crystal and the periodically poled potassium titanium orde phosphate crystal are used to perform single-pass qusi-phase-mached frequency. The 780 nm laser power of about 336 mW and 210 mW, the frequency doubling efficiency about 7 % and 4.4 % are abtained. It shows that the good characteristic of single frequency output by monitoring the longitudinal mode of 780 nm laser. Additionally, the absorption spectra for Rb atom line D2 are scanned, and the tunable range of the 780 nm laser is more than 10 GHz. The ECDL is locked to 87 Rb 5S,/2 （Fg= 2）- 5P3/2 （Fe=3） hyperfine transition via modulation-free polarization spectroscopy. Compared with frequency fluctuation of about 4 MHz for ECDL free running within 450 s, the residual frequency fluctuation can be squeezed below about 1.5 MHz after being locked.