Rayleigh-based OTDR with dynamic modal crosstalk suppression.

We propose and demonstrate a novel approach for measuring the modal attenuation of the splice loss of a purely LP11 mode group by using a Rayleigh-based OTDR with a dynamic modal crosstalk (XT) suppression technique for few-mode fibers (FMFs). With the proposed approach, the Brillouin loss interaction with a Brillouin Stokes beam co-propagating with the OTDR probe removes the modal XT caused at the modal conversion point and suppresses the accumulated modal XT that is detected. A preliminary experiment is demonstrated using spliced FMFs with a core-offset. Experiments revealed that the proposed technique can accurately measure the splice loss variations of a purely LP11 mode group.

Distributed spatial mode dispersion measurement along strongly coupled multicore fibers based on the correlation analysis of Rayleigh backscattering amplitudes.

We describe a method for measuring spatial mode dispersion (SMD) distribution along a strongly coupled multicore fiber (SC-MCF). The SMD has been defined for characterizing an SC-MCF, and it changes with respect to local fiber bending and twisting. However, conventional measurement methods characterize only the overall SMD, and cannot identify fiber portions where the environmental conditions affect the SMD. This paper demonstrates distributed SMD measurement along an SC-MCF by auto-correlating Rayleigh backscattering amplitudes obtained with coherent optical reflectometry. We confirm our method experimentally, and distinguish the difference between the SMD growth along twisted and non-twisted fiber sections in concatenated SC-MCFs.

Long-range measurement of Rayleigh scatter signature beyond laser coherence length based on coherent optical frequency domain reflectometry.

Long-range C-OFDR measurement of fiber Rayleigh scatter signature is described. The Rayleigh scatter signature, which is an interference pattern of backscatters from the random refractive indices in fibers, is known to be applicable to fiber identification and temperature or strain sensing by measuring its repeatability and its spectral shift. However, these applications have not been realized at ranges beyond the laser coherence length since laser phase noise degrades its repeatability. This paper proposes and demonstrates a method for analyzing the optical power spectrum of local Rayleigh backscatter to overcome the limitation imposed by laser phase noise. The measurable range and spatial performance are also investigated experimentally with respect to the remaining phase noise and noise reduction by signal averaging with the proposed method. The feasibility of Rayleigh scatter signature measurement for long-range applications is confirmed.

Individual loss distribution measurement in 32-branched PON using pulsed pump-probe Brillouin analysis.

We describe loss distribution measurement in a passive optical network (PON) using pulsed pump-probe Brillouin analysis. A preliminary experiment is demonstrated using a 32-branched PON constructed in the laboratory. We analyze the signal to noise ratio of this measurement and show that the method can realize a 25 dB dynamic range in 90 seconds (10000 times averaging), with an event location resolution of 10 m, and a fiber length identification resolution of 2 m.

Distribution measurement of Raman-gain and optical-loss characteristics in optical fibers.

We propose a test method with which to measure the longitudinal distribution of Raman-gain characteristics in connected optical fibers. We describe a technique for obtaining the pump-loss distribution, knowledge of which is necessary for deriving the Raman-gain efficiency distribution, by the bidirectional measurement of Raman amplification. Based on this technique, we performed experiments and demonstrated that the Raman-gain efficiency distribution can be evaluated with the same equipment.