Few-mode fiber based Raman distributed temperature sensing

Abstract

We proposed and experimentally demonstrated a few mode fiber (FMF) based Raman distributed temperature sensor (RDTS) to extend the sensing distance with enhanced signal-to-noise ratio (SNR) of backscattered anti-Stokes spontaneous Raman scattering. Operating in the quasi-single mode (QSM) with efficient fundamental mode excitement, the FMF allows much larger input pump power before the onset of stimulated Raman scattering compared with the standard single mode fiber (SSMF) and mitigates the detrimental differential mode group delay (DMGD) existing in the conventional multimode fiber (MMF) based RDTS system. Comprehensive theoretical analysis has been conducted to reveal the benefits of RDTS brought by QSM operated FMFs with the consideration of geometric/optical parameters of different FMFs. The measurement uncertainty of FMF based scheme has also been evaluated. Among fibers being investigated and compared (SSMF, 2-mode and 4-mode FMFs, respectively), although an ideal 4-mode FMF based RDTS has the largest SNR enhancement in principle, real fabrication imperfections and larger splicing loss degrade its performance. While the 2-mode FMF based system outperforms in longer distance measurement, which agrees well with the theoretical calculations considering real experimental parameters. Using the conventional RDTS hardware, a 30-ns single pulse at 1550nm has been injected as the pump; the obtained temperature resolutions at 20km distance are estimated to be about 10°C, 7°C and 6°C for the SSMF, 4-mode and 2-mode FMFs, respectively. About 4°C improvement over SSMF on temperature resolution at the fiber end with 3m spatial resolution within 80s measuring time over 20km 2-mode FMFs have been achieved.

A Review of Using Few-Mode Fibers for Optical Sensing

“…In optical time-domain reflectometry (OTDR) based distributed FOSs, for instance, optical pulses of meter-scale resolution are typically launched into the fiber. The pump power of these optical pulses is mainly limited by the SRS threshold, P th , which can be expressed as [20], [49]:…”

“…On the other hand, FMFs can offer traditional optical fiber sensors with higher signalto-noise ratio (SNR) levels than those designed using the standard SMFs and MMFs. This is because FMFs mitigate intermodal coupling and modal dispersion that occur in the typical MMFs, and FMFs further have higher power thresholds of nonlinearity, compared with the standard SMFs [20], [21].…”

Long-range distributed optical fiber hot-wire anemometer based on chirped-pulse ΦOTDR

“…However, this technique necessarily multiplies the acquisition time, limiting the dynamic performance of the sensor. In addition, there exist in the state of the art other high performance temperature DOFS based on different sensing principles, such as Raman scattering [40,41], Brillouin scattering [42], or even combinations of multiple techniques [43]. While these techniques may be able to provide absolute temperature measurements, they generally provide low resolution temperature measurements, and are not well adapted to dynamic monitoring.…”

Hybrid distributed acoustic-temperature sensing using a few-mode fiber

“…FMFs have been deployed in many sensing applications including designing a large scale absorption-based sensing network [7], reconstructing spatial distributions of gases that diffuse into a FMF [8], monitoring multiple parameters simultaneously [9], etc. To resolve the fiber nonlinearity dilemma and simultaneously keep the DAS operation reliable, we use the FMF as a compromise between the SMF and MMF [10]. The threshold power of nonlinearity of a typical FMF is higher than that of the SMF.…”