B-OTDR Brillouin reflectometer BOTDR (Brillouin optical time domain reflectometer). Another kind of reflectometers is based on the Brillouin scattering. In the typical reflectometers the Rayleigh scattering is employed for analysis. The BOTDR reflectometer utilizes the phenomenon of the inelastic Brillouin scattering, related to generation of acoustic wave at frequency fB. The signal resulting from the Brillouin scattering, with a frequency redshifted by fB , propagates backward along the examined optical fiber. The frequency value depends on the optical fiber properties, stresses in the core, temperature. Typical values are of the order of 13 GHz for 1310 nm and 11 GHz for 1550 nm.
The scattered light gets back to receiver via the coupler like in the OTDR based on the Raleyigh scattering. The receiver set in BOTDR is of the coherent type, with the heterodyne detection. The continuous laser acts as the heterodyne. The heterodyne light is mixed with the scattered light. Its frequency is lower than the transmitted frequency by a value smaller than the frequency fB. The received modulation of the signal is at about 100 MHz.
The advantages of BOTDR in comparison with OTDR are the following:
- larger measurement dynamics
- larger sensitivity of attenuation changes measurement, which enables the detection of mechanical stresses existing in the optical fiber that can results in fiber breaking.
Brillouin Optical Time Domain Reflectometry (BOTDR) is a distributed fiber optic strain sensing system, which can detect temporal and spatial changes of external physical parameters at large-scales and on a continuous basis. Nevertheless, there are still many problems in the application . According to the deformation characteristics obtained from sinkhole collapse modeling and calibration testing, we analyzed the mechanic relation between the soil and sensing fiber, and studied the application of distributed optical fiber sensing technology as a predictor of potential sinkhole collapse.
Application of the DTS System.
- Oil and Gas Pipeline Monitoring
- Oil and Gas Well Monitoring
- Refinery Efficiency Sensing
- Structural Health Monitoring (SHM)
- Dam Monitoring
- Geohazard Monitoring
- Highway Safety Monitoring
- Quality Inspection of Fiber Optic Cable
- Border Security Monitoring
- Cryostat Temperature Sensing
- Building Fire Detection