Quasi-distributed refractometer using tilted Bragg gratings and time domain reflectometry

Tilted fiber Bragg gratings (TFBGs) have been demonstrated to be accurate refractometers as they couple light from the fiber core to the cladding. Because they require spectral measurements on several tens of nanometers, demodulation techniques reported so far are not suited for quasi-distributed refractive index sensing using TFBGs cascaded along a single optical fiber. We demonstrate here that a commercial Optical Time Domain Reflectometer (OTDR) can be used to multiplex identical TFBGs refractometers written in the same optical fiber. Our solution is simple, relatively fast, cost-effective and is particularly interesting for the monitoring of long structures

Distributed Temperature Sensor Interrogator Based on Polarization-Sensitive Reflectometry

In this paper, a polarization-sensitive reflectometry technique has been investigated in order to serve as an interrogating device in distributed sensing applications. As the sensing fiber has a beat length of about a few centimeters, a high-resolution reflectometer was required. A coherent optical frequency-domain reflectometer (OFDR) was used from this perspective. The principle is based on the linear dependence of fiber beat length on temperature. The reported experimental results detail the calibration method and discuss the features of the interrogating device in terms of temperature threshold and spatial resolution. The proposed system, exploiting the Rayleigh backscatter signal, offers an interesting alternative to existing systems, mainly based on nonlinear effects