超稳及超低相位噪声低温蓝宝石振荡器技术研究

Precise time reference plays a significant role in telecommunications, defense, navigation and metrology etc. Therefore, it is important to further improve frequency stabilities of the oscillators. Currently, high-precision oscillators consist of quartz-crystal oscillators, microwave masers, H-masers, and cryogenic sapphire oscillators. As a special type oscillator, cryogenic sapphire oscillator has superior performances than that of others. We plan to design and build a cryogenic sapphire oscillator based on pulse tube cryo-cooler in China. Based on our former research experience, we will use high-purity sapphire to ensure a high Q factor, and use optimized thermal insulation design and vibration isolation to obtain an extremely low short term frequency stability (10^(-16) at 1s); A very low level phase noise (-120dBc/Hz at 1Hz) can be reached through further improvement of temperature control, magnetic shielding and usage of low-noise electronic components. The successful implementation of the cryogenic sapphire oscillator will reduce the caesium fountain clock local oscillator Dick-effect, improve its performance level to reach quantum projection noise limit.

精确的时间基准在电信、国防、导航和度量等重要应用领域起着举足轻重的作用，因此进一步提高振荡器的频率稳定性意义重大。目前精度比较高的振荡器包括石英晶体振荡器、微波激射器、氢钟以及低温蓝宝石振荡器。其中，低温蓝宝石振荡器作为一种特殊的振荡器，其性能远优于其他振荡器。本项目计划在我国设计并搭建一套基于无氦脉冲管冷腔系统的蓝宝石振荡器。在本申请人前期研究工作基础之上，通过利用高纯度的蓝宝石获得高Q值，利用优化设计的热隔绝和振动隔离获得极高的短稳（10^(-16)@1s）；进一步提高温控和磁屏蔽水平以及利用低噪声元器件将可以改善相位噪声水平（-120dBc@1Hz）。低温蓝宝石振荡器的成功实现将有助于提高铯喷泉钟本振稳定度水平，消除迪克效应，使喷泉钟达到量子投影噪声极限。

低温蓝宝石振荡器（CSO）具有超高短期频率稳定性和极低相位噪声，使其可用于深空探测、基础物理研究等对频率源精度要求极高的领域。本项目主要通过调研、设计和探索新的技术来提高低温蓝宝石振荡器的性能。该项目原计划使用国际上最好的蓝宝石搭建一套频率稳定性为10-16@1s、相位噪声在载波10GHz偏置1Hz处为-120dBc/Hz的低温蓝宝石振荡器(CSO)。经过标定，我们发现国内生产的蓝宝石与国际上最好的蓝宝石性能相当，所以我们选用国内生产的蓝宝石进行系统搭建。受限于相位噪声与艾伦方差测试仪的精度，目前没办法测量所搭建的第一套CSO实际性能指标，所以我们正在搭建第二套系统进行比对。目前自由运转的低温蓝宝石振荡器性能实现了频率稳定度7x10-14@1s，相位噪声-90dBc/Hz。