HTS Sampler With Optical Signal Input

We are developing waveform measurement systems using a high- superconducting (HTS) sampler. As one of the methods for introducing high-frequency signals into the sampler chip, we are testing optical input systems. A uni-traveling-carrier photodiode (UTC-PD), which has potential bandwidth of over 300 GHz, is used in the systems for converting optical signals to electrical ones in front of the sampler circuit. Our preliminary experiments revealed high enough sensitivity even at temperatures as low as below 40 K for the UTC-PD that is to be cooled with the sampler chip. In the present study, we test two types of modules. One packages the UTC-PD separately from the sampler chip, and the other integrates both of them. In the former type, the optical and sampler modules are connected using V-connectors. The modules are cooled with a cryocooler to the operating temperature of the sampler circuit, which is around 40 K. Signals to be measured are input into the UTC-PD with a 1.55-mum carrier wave. We have succeeded in observing sinusoidal waveforms of up to 20 GHz using both types of modules.