894nm高温垂直腔面发射激光器及其芯片级铯原子钟系统的应用

报道了自行研制的894 nm高温垂直腔面发射激光器(VCSEL)以及基于此类器件的芯片级铯原子钟系统的应用实验结果.根据芯片级铯原子钟对VCSEL在特定高温环境下产生894.6 nm线偏振激光的要求,对器件的量子阱增益及腔模位置等材料结构参数进行了优化,确定增益-腔模失谐量为-15 nm,使器件的基本性能在高温环境下保持稳定.研制的VCSEL器件指标为:20—90?C温度范围内阈值电流保持在0.20—0.23 m A,0.5 m A工作电流下输出功率0.1 mW;85.6?C温度环境下激光波长894.6 nm,偏振选择比59.8:1;采用所研制的VCSEL与铯原子作用,获得了芯片级铯原子钟实施激光频率稳频的吸收谱线和实施微波频率稳频的相干布居囚禁谱线.

894 nm high temperature operating vertical-cavity surface-emitting laser and its application in Cs chip-scale atomic-clock system

In this study, an 894 nm high temperature vertical-cavity surface-emitting laser (VCSEL) is reported. Furthermore, a Cs chip-scale atomic clock (CSAC) system experiment based on this VCSEL is carried out.To achieve low threshold/power consumption under high temperature condition, the VCSEL epitaxial structure is optimized. Especially, the so-called gain cavity-mode detuning technology is utilized to improve the temperature sensitivity of the device output characteristics. The relationship between the structure of quantum well and the gain is simulated by using the commercial software PICS3D. In order to achieve high gain and low threshold properties, the thickness of the quantum well is optimized. Based on the theory of transmission matrix, the VCSEL cavity mode (etalon) is calculated. Finally, a -15 nm quantum well gain-cavity mode offset is utilized to achieve relatively stable cavity mode gain, which can guarantee the temperature-insensitivity of the VCSEL output characteristics.The output performance of the VCSEL device we fabricated is investigated experimentally. The VCSEL lightcurrent (L-I) characteristic is tested under different temperatures. It is found that benefiting from the gain-cavity mode offset design, the threshold can be maintained at 0.20–0.23 mA when the temperature increases from 20 ℃ to 90 ℃. Meantime, the output power of more than 100 μW is achieved at different temperature levels. By comparing with the results at room temperature, No dramatic degradation of the VCSEL high temperature L-I characteristics is found, which means that the VCSEL output characteristic is relatively temperature-insensitive. The wavelength of the VCSEL is 890.4 nm at a temperature of 20 ℃. When the temperature increases up to 85.6 ℃, the VCSEL wavelength is red-shifted to 894.6 nm (Cs D1 line), corresponding to a red shift ratio of 0.064 nm/℃. According to the polarization requirement of CSAC applications, the polarization properties of the VCSEL are studied and the results are as follows: under an injected current of 1 mA and operation temperature of 20 ℃, P_max = 278.2 μW and P_min = 5.9 μW, corresponding to a polarization ratio of 47:1; at a temperature of 85.6 ℃, P_max = 239.2 μW and P_min = 4 μW, corresponding to a polarization ratio of 59:8:1.Using the VCSEL reported in this paper as a laser source, the CSAC experiment is carried out. At 4.596 GHz of modulated frequency, the output laser of the VCSEL is collimated and interacts with Cs atoms. Finally the closed-loop frequency locking atomic clock is demonstrated. The Cs laser absorption spectrum for laser frequency stabilization, as well as the CPT signal for Cs CSAC microwave frequency stabilization is obtained.