Distributed fiber-optic temperature sensor using single photon counting detection

A Review of Recent Developments in Fiber Optic Sensor Technology

“…The most recent advance in this area was the development of a 1.5-µm Raman system incorporating fiber amplifiers for pump light amplification [95]. This system demonstrated a sensing range of 30 km, an RMS temperature resolution of 2.3• C, and a spatial resolution of 6.5 m. The only significant drawback of this technique is the low Raman scattering coefficient, which is approximately 3 orders of magnitude lower than the Rayleigh, necessitating the use of high input powers from the interrogating lasers and relatively long data averaging.Work on enhancing the spatial resolution [96,97] of the Raman scheme using, for example, photon-counting techniques has also been examined by a couple of research groups. These systems typically yield spatial resolutions of ∼10 cm, but the temperature resolution is typically degraded to ∼> ±3…”

A Review of Distributed Fibre Optic Sensors for Geo-Hydrological Applications

“…It is worth mentioning that improved and alternative designs have been proposed over the years, including commercially-e.g., photon-counting Raman OTDRs [53][54][55][56][57], pulse compression/coding schemes [58][59][60][61], or incoherent Raman OFDRs, in respect of which we direct the reader to the corresponding references. Remarkably, in [62], a resolution of 0.09°C in a 1100 m-long fibre with 0.39 m spatial sampling was achieved with direct detection approach.…”

A fast high-spatial-resolution Raman distributed temperature sensor

“…Commercial DTS systems are generally based on Raman optical time-domain reflectometry (OTDR), but some use Raman optical frequency-domain reflectometry or pulse-compression coded Raman OTDR; none of these offers a spatial resolution much better than 1 m. However, resolutions down to about 100 mm [5][6][7][8] or even 10 mm 9 using photon-counting receivers have been reported in the research literature, albeit at very short range, such as 10 m 8 or even 0.9 m 7 . The reason for this restriction is that photon-counting detectors are limited in their counting rates.…”

“…In the case of time-correlated single-photon counting systems, at most one photon detection per laser pulse for the entire fiber is allowable, and this results in extremely low count rates per resolution cell: e.g. 1/3500 per laser pulse 5 . Multi-photon timing techniques are more efficient 6 , but the allowable photon arrival rate is still on the order of 0.01 photon per resolution cell and per laser pulse.…”