Abstract

Optical transfer delay (OTD) measurement enables the high performance of distributed coherent radar and optically controlled phase arrays. However, achieving high-accuracy and large-range OTD measurement in photonic integrated chips, outdoor free-space optics, and optical links with significant insertion loss is challenging. This article proposes a coherent optical phase-derived ranging (PDR) system to enhance the OTD measurement sensitivity. In the experiments, the stability of the coherent system was improved 35 times compared to the incoherent system when measuring an optical device with an insertion loss of 30 dB. The sensitivity of the proposed system reaches −80 dBm, which is 46 dB better than the commercial PDR-based product. In addition, the error introduced by the Doppler effect was eliminated with the proposed demodulation method, enabling OTD measurement of a variable optical link.