Patent ID: 9631923
Date: 2017-04-25
CPC Classifications: G01B,G01L

Claim:
1. A system for measuring strain between two fixed points, comprising: an optical fiber having a first end, a second end, and a central portion secured between the two fixed points; a first light source outputting a light signal having predetermined characteristics and a first frequency and coupled to the first end of the optical fiber; a second light source outputting a light signal having the same predetermined characteristics and a second frequency different from the first frequency and coupled to the first end of the optical fiber; a back scatter detector coupled to the first end of the optical fiber for receiving a return light signal from the optical fiber and for outputting a signal based thereon, the back scatter detector including an associated frequency control element having a frequency corresponding to a predetermined calculated response frequency based on the first frequency and the second frequency, the predetermined calculated response frequency different from the first frequency and the second frequency; a forward scatter detector coupled to the second end of the optical fiber for receiving a forward light signal from the optical fiber and for outputting a signal based thereon, the forward scatter detector including an associated frequency control element having a frequency corresponding to the predetermined calculated response frequency; a processor coupled to receive the signals from the back scatter detector and the forward scatter detector, the processor generating an output signal proportional to the strain between the two fixed points based on a magnitude of the signals from the back scatter detector and the forward scatter detector at the predetermined calculated response frequency; and wherein the output signal at the predetermined calculated response frequency is produced based on second order effects applied to the light signal at the first frequency and to the light signal at the second frequency.