量子光频梳用于高灵敏时延测量的研究

High-precision time synchronization plays an important role in the area of fundamental scientific research and real applications. Accompanying with the remarkable improvements in the ability of generating and measuring high-accuracy time-frequency signal, seeking for new time-transfer techniques between distant clocks with much further improved accuracy attracts intensions world-widely. The achievable accuracy of time synchronization is mainly determined by the accuracy of measuring the time of arrival of the pulses. The quantum-optimized time-transfer scheme based on optical femtosecond frequency comb was proposed. By using the balanced homodyne detection technology combined with proper pulse shaping on the local oscillator, the arrival time can be measured in real time with a precision reaching a new shot noise limit on the measured timing information, and the precision can be immune from the effects of atmospheric parameters, such as pressure, temperature, humidity and so on. Applying a multimode squeezed mode-locked femtosecond laser as the signal pulse, the measurement accuracy can further breakthrough the shot noise limit. Therefore, based on this scheme, it is possible to achieve a time synchronization accuracy reaching the order of yoctosecond . This project intends to carry out improvement of key technologies involved in the quantum-optimized time transfer scheme. The main contents are focused on: the carrier-envelope offset (CEO) frequency stabilization of the investigated 100 fs-scale Ti:sapphire mode-locked laser, analyzing and filtering the residual phase noise of the CEO-stabilized femtosecond laser based on a broadband passive cavity, highly-efficient generation of the multimode squeezed femtosecond laser and measurement based on the phase-locked balanced homodyne detection. Finally, through combining these technical achievements, a timing measurement with a precision reaching yoctosecond will be achieved. The achievements will form a technical basis for the future realization of ultra-precise time synchronization systems.

随着时间频率的精度不断提高，实现比现有精度大幅提高的新一代时间传递技术的研究受到广泛关注。时间同步可能达到的精度由测量脉冲到达时间的准确度决定。基于飞秒光频梳的量子优化时间传递方案被提出，利用平衡零拍探测技术结合脉冲整形的本地参考源，可实现实时且精度达到散粒噪声极限的到达时间测量，测量准确度还可免受传输路径各参数变化的影响；应用具有压缩特性的量子光频梳替代传统光频梳，将使测量精度突破散粒噪声极限。因此，基于该方案，实现10^(-24)秒量级的时间同步精度成为可能。本项目在现有研究基础上，拟开展基于飞秒光频梳的量子优化时间同步所涉及的关键技术优化研究，实现：百飞秒级飞秒脉冲激光的高精度载波包络偏频锁定及剩余相位噪声抑制，高压缩度量子光频梳的产生和高效的平衡零拍探测技术。通过有机整合各项技术成果，实现10^(-24)秒级的时间延迟测量，为超高精度的时间同步系统进行技术储备。

时间同步可能达到的精度由测量脉冲到达时间的准确度决定。较经典光频梳而言，量子光频梳可用于实现突破量子噪声极限的时延精密计量，有望应用实现比现有精度大幅提高的新一代时间传递技术。本项目开展量子光频梳的产生及测量所涉及的关键技术优化研究，实现超高灵敏度的时延测量，进而为超高精度的时间同步技术提供储备。项目取得的主要进展包括：1）研制了高性能平衡零拍探测器，探测器的共模抑制比高达79dB@1MHz，且极大抑制了平衡零拍探测器低频处电子学噪声。2）实现了飞秒脉冲激光高精度载波包络偏频的锁定，频率波动标准差为4mHz，相对于光载波中心频率稳定度为1.18×10^(-17)@1s，锁定时长超过半小时。3）制备了高压缩度量子光频梳，研究了不同谐振腔精细度、输出耦合镜透过率以及晶体长度对量子光频梳压缩特性的影响。获得了3.6±0.2 dB的最大真空压缩，考虑损耗后为7.0±0.2 dB，实验结果与理论分析相符。4）使用2.2 dB位相压缩的量子光频梳实现了最小测量极限为(28±2)×10^(-24) s/√Hz的高灵敏时延测量演示。5）针对阈值以上泵浦的简并光学参量振荡器（DOPO）产生的非临界压缩光场存在横向幅角随机旋转而导致无法利用本底探针光对其压缩特性进行稳定探测的问题，理论上提出一种非临界压缩光场的探测方案，可以很好抵消压缩光场的空间模式随机旋转引入的探测输出动态波动，得到3dB的稳定探测结果，且对本底探针光的相位波动具有鲁棒性。6）利用谐振腔的时域模式滤波及共振增强特性，实验产生了基于外腔倍频的300MHz双色高重频飞秒激光。进一步对实验产生的双色高重频飞秒激光场的倍频效率、共振光谱、光束质量等特性进行了分析，为后续开展高重频量子光频梳实验研究奠定了基础。