A dual-pass differential Fabry–Perot interferometer (DPDFPI) is one candidate of the interferometer configurations utilized in future Fabry–Perot type space gravitational wave antennas, such as Deci-hertz Interferometer Gravitational wave Observatory. In this paper, the working principle of the DPDFPI has been investigated and necessity to adjust the absolute length of the cavity for the operation of the DPDFPI has been found. In addition, using the 55 cm-long prototype, the operation of the DPDFPI has been demonstrated for the first time and it has been confirmed that the adjustment of the absolute arm length reduces the cavity detuning as expected. This work provides the proof of concept of the DPDFPI for application to the future Fabry–Perot type space gravitational wave antennas.

双通差分法布里-珀罗干涉仪 (DPDFPI) 是未来法布里-珀罗型空间引力波天线（例如分赫干涉仪引力波天文台）中使用的干涉仪配置的候选之一。在本文中，研究了DPDFPI的工作原理，并发现了为DPDFPI的运行调整腔体绝对长度的必要性。此外，使用 55 厘米长的原型，首次演示了 DPDFPI 的操作，并已确认绝对臂长的调整可减少腔失谐。这项工作为未来法布里-珀罗型空间引力波天线的应用提供了 DPDFPI 的概念证明。