Radiation Hardened Architecture of a Single-Ended Raman-Based Distributed Temperature Sensor

Abstract

Raman-based Distributed Temperature Sensors (RDTS) allow performing spatially resolved (1 m) reliable temperature measurements over several km long Optical Fibers (OFs). These systems are based on the temperature dependence of the intensities of both the Stokes and anti-Stokes components of the Raman back-scattered signal. One of the specific issues associated with RDTS technology in radiation environments is the differential Radiation Induced Attenuation (RIA) between the two components that induces huge errors in the temperature evaluation. Such problem is particularly evident for commercially available single-ended DTS using one laser source. Doubleended configuration could be used to correct for the differential attenuation but are limited by RIA in terms of sensing range. In the present work, we show how a Radiation-Hardened-by-Design DTS (RHD-DTS) overcomes the observed radiation issues keeping the single-ended interrogation scheme. In the tested RHD-DTS two infrared excitation laser sources (∼1550 nm and ∼1650 nm) are employed: the wavelength of the Stokes component due to the first excitation source coincides with the wavelength of the second excitation; vice versa, the wavelength of the anti-Stokes component due to the second excitation source coincides with the wavelength of the first excitation. The overall result is that the two signal intensities are automatically corrected for the differential RIA all along the OF sensor length and the temperature measurements becomes robust against radiation effects. This study demonstrates the potential of such a sensor by reporting preliminary experimental results obtained with a prototype developed by Viavi Solutions exploiting radiationsensitive or radiation-hardened optical fibers.

Remote monitoring of Molten Core-Concrete Interaction experiment with Optical Fibre Sensors & perspectives to improve nuclear safety – DISCOMS project

“…However, with the hypothesis of the sole effect of temperature on the Brillouin frequency shift, measurements wavelengths Raman DTS instrument is mandatory for temperatures greater than 500°C [13]. appear to be compatible with thermocouple data (Fig.…”

“…DISCOMS consortium therefore recommends: 1) Radiation hardened Raman DTS technique to provide reliable temperature measurements up to 700°C [13], 2) Spontaneous Brillouin technique to provide strain and temperature shifts profiles up to 1000°C, even in case of optical fibre break, but also for its resilience to ionizing radiations [14]. Instrumentations capable to dissociate strains from temperature could also be preferred if this is of crucial importance [15].…”

The Relevance of Point Defects in Studying Silica-Based Materials from Bulk to Nanosystems

“…The presence of such point defects makes the response of any type of fiber a specific field of investigation. So while pure silica, F-doped, and N-doped fibers are relevant in temperature and strain sensors in harsh environments, Al and P-doped fibers are promising candidates as dosimeters [9,[109][110][111][112][113][114][115][116][117][118]. In the first case, the radiation hardness is fundamental, since low RIA gives the opportunity for long-range transmission and to produce point or distributed sensors, eventually with large sensing ranges.…”

“…Raman-based temperature sensors represent an example of devices where the RIA can generate problems [109,112].…”

“…In Raman scattering, the ratio between the Stokes and anti-Stokes lines intensity, which was observed respectively at higher and shorter wavelengths with respect to the excitation light (typically a laser line), is related to the temperature. This can be used as a temperature-distributed sensor using an OTDR (optical time domain reflectometry) with opportune calibration procedures [109,112]. Figure 5a and its caption briefly describe the operation configuration of OTDR.…”