Dynamic Phase Demodulation Algorithm for Phase-Sensitive OTDR With Direct Detection

A dynamic phase demodulation algorithm for direct detection <inline-formula> <tex-math notation="LaTeX">$\Phi $ </tex-math></inline-formula>-OTDR is proposed and experimentally demonstrated. It offers a way for single channel direct detection <inline-formula> <tex-math notation="LaTeX">$\Phi $ </tex-math></inline-formula>-OTDR, which is the simplest and most cost-effective structure, to realize phase demodulation. Through making use of the redundant information between the sensing series from the vibration impacted region, the local extreme points(LEP) of the sensing series can be divided into two types. The second type LEP offers light phase quadrant information, and then the phase can be further reconstructed through anti-trigonometric function. Single frequency and amplitude-modulated waveforms have been correctly demodulated. The demodulated phase amplitude agrees well with theoretical value, which shows a potential application in strain measurement.