Polarization-locked VCSEL with PM fiber pigtail for quantum communication

Quantum communication is a new technology requiring a stable and reliable laser source for communication security. A new kind of polarization-locked vertical-cavity surface-emitting laser (VCSEL) with polarization maintaining (PM) fiber pigtail is fabricated as a decoy state laser source. The VCSEL is packaged in a standard butterfly box integrated with thermoelectric coder (TEC) and thermistor. The optical pulse width of full-width at half-maximum (FWHM) is smaller than 400 ps with a 100-MHz on/off modulation frequency. The results reveal that modulation range is better than 4. Moreover, the polarization is stable, and the power extinction ratio is larger than 25. The center wavelength is 850 nm, and the SMSR is better than 40 dB.     

Influence of intra-cavity loss on transmission characteristics of fiber Bragg grating Fabry–Perot cavity

A theoretical model of the fiber Bragg grating Fabry–Perot(FBG-FP) transmission spectrum considering loss of FBG and intra-cavity fiber is presented. Several types of FBG-FPs are inscribed experimentally, and their spectra are measured.The results confirm that weak intra-cavity loss is enhanced at the resonance transmission peak, that is, loss of transmission peaks is observably larger than other wavelengths. For FBG-FPs with multi resonance peaks, when the resonance peak wavelength is closer to the Bragg wavelength, the more significant loss effect of resonance transmission peak is exhibited.The measured spectra are fitted with the presented theoretical model. The fitted coefficient of determinations are near 1,which proves the validity of the theoretical model. This study can be applied to measure FBG loss more accurately, without a reference light. It can play an important role in FBG and FBG-FP writing process optimization and application parameter optimization.     

体布拉格光栅外腔半导体激光器光谱特性研究

用体布拉格光栅(VBG)作为反馈元件与瓦级半导体激光器(LD)以及快轴准直柱透镜构成一个可以将半导体激光器的工作波长稳定在体布拉格光栅布拉格波长处的外腔激光器。测量了体布拉格光栅外腔激光器的波长稳定性与其工作电流、热汇温度、激光束准直装置等因素的关系。分析了波长稳定效果与半导体激光器增益谱特性、外腔结构参量等因素的关系。研究表明,在相同的工作电流、热汇温度下,当准直柱透镜直径为0.4 mm时的波长稳定效果较好;在此情况下,当热汇温度控制在30℃,工作电流从0.5 A增加到1.5 A的测量范围内,以及当工作电流固定在1.5 A,热汇温度从20℃增加到35℃时,测得的光谱特性表明,半导体激光器的工作波长可以很好地稳定在体布拉格光栅的布拉格波长处。与该激光器在同样条件下自由运转的光谱比较,可以看到,自由运转激射波长与体布拉格光栅的布拉格波长差值小于2.6 nm情况下,可以获得很好的波长稳定效果。实验也表明,当该值大于4.8 nm时波长稳定效果变差。     

相位掩模板干涉场及其对光纤光栅损耗的影响

理论分析了紫外准分子激光相位掩模法刻写光纤布拉格光栅时相位掩模板干涉场的形式以及对比度特征,并结合干涉光场对比度与光纤光栅折射率调制度的关系,通过实验证明了随着光纤与相位掩模板距离的增加,相位掩模板形成的干涉光场对比度会越来越低,这种对比度的降低导致了光纤布拉格光栅损耗的增加。进一步的分析显示:非±1级衍射能量的增加、紫外光束斜入射角度增加、紫外激光时空相干性的恶化等因素也会导致干涉场对比度降低,因此实验上要尽量避免这些不利因素的影响。该研究结果对高功率FBG刻写装置的光源、相位掩模板的选择以及光路调试等具有重要的指导意义。