We have developed a cryogenic characterization platform for ultrafast photodiodes, whose time domain responses are extracted by electro-optic sampling using femtosecond laser pulses in a pump-probe configuration. The excitation of the photodiodes with the pump beam and the electro-optic sampling crystals with the probe beam are realized in a fully fiber-coupled manner. This allows us to use the characterization platform at different temperatures, ranging from cryogenic to room temperature. As an application example, we characterize the time-domain response of commercial p-i-n photodiodes with a nominal bandwidth of 20 GHz and 60 GHz at temperatures of 4 K and 300 K and in a large parameter range of photocurrent and reverse bias. For these photodiodes, we detect frequency components up to approximately 250 GHz, while the theoretical bandwidth of our sampling method exceeds 1 THz. Our measurements demonstrate a significant excitation power and temperature dependence of the photodiodes’ ultrafast time responses, reflecting, most likely, changes in carrier mobilities and electric field screening. Since our system is an ideal tool to characterize and optimize the response of fast photodiodes at cryogenic temperatures, it has a direct impact on applications in superconducting quantum technology such as the enhancement of optical links to superconducting qubits and quantum-accurate waveform generators.

我们开发了超快光电二极管的低温表征平台，其时域响应是通过在泵浦探针配置中使用飞秒激光脉冲进行电光采样来提取的。泵浦光束对光电二极管的激发以及探测光束对电光采样晶体的激发以完全光纤耦合的方式实现。这使我们能够在从低温到室温的不同温度下使用表征平台。作为一个应用示例，我们表征了标称带宽为 20 GHz 和 60 GHz 的商用 pin 光电二极管在 4 K 和 300 K 温度以及大光电流和反向偏压参数范围内的时域响应。对于这些光电二极管，我们检测的频率分量高达约 250 GHz，而我们的采样方法的理论带宽超过 1 THz。我们的测量结果表明，光电二极管的超快时间响应具有显着的激发功率和温度依赖性，很可能反映了载流子迁移率和电场屏蔽的变化。由于我们的系统是表征和优化低温下快速光电二极管响应的理想工具，因此它对超导量子技术的应用具有直接影响，例如增强超导量子位和量子精确波形发生器的光学链路。