Characterization and Suppression of Parasitic Back-Reflection Noise in Transponder-Type Heterodyne Interferometry

Abstract

Transponder-type heterodyne interferometry is a versatile metrological technique for high-precision measurements, with applications in Earth's gravity-field recovery, space-based gravitational-wave detection, deep-space ranging, and Doppler tracking. However, parasitic back-reflections can contaminate phase readout and degrade measurement sensitivity. To characterize and suppress this noise, we constructed a transponder-type interferometer with coaxially aligned counter-propagating beams, achieving stable operation at a received optical power of 720 pW. An adjustable reflecting system was introduced into the master-side transmit path to simulate back-reflection under realistic conditions. Optical path scans and model fitting showed that phase errors vary periodically with the relative phase between the main and parasitic interference signals, which defines the working point. Assisted by π measurement, adjustment to low-sensitivity working points was combined with balanced detection to suppress back-reflection phase noise, achieving maximum suppression factors of 77 for single-frequency phase errors and 23 for band-limited phase-noise amplitude spectral density. π measurement also enabled working point diagnosis at 3.8 nW back-reflection power, confirming its applicability under weak back-reflection conditions. These results provide an effective approach for in situ back-reflection characterization and phase-noise suppression in transponder-type heterodyne interferometry.

arXiv comment10 pages, 6 figures