We propose an image monitoring system operable with -15 dBm power-over-fiber (PoF). By analyzing the power characteristics, we optimized the power charging and achieved image transmission every 6.3 h using -15 dBm PoF.

We propose a still image monitoring system powered by a weak optical power supply sourced from an unused port of a PON splitter. An experimental setup was constructed to evaluate fundamental characteristics, including charging time and power consumption. Results show that the proposed system can transmit a still image every 13.4 h using a power-over-fiber of -10.8dBm.

We demonstrate a vibration position estimation system based on bi-directionally placed polarizer-based fiber optic sensors using two different wavelengths for improving estimation accuracy. The feasibility of the proposed method is verified through experiments.

In this study, we reveal the distinct frequency response of optical cables and internal fibers, and provide insight into parallel data transmission using modulated vibrating signals and Mach-Zehnder interferometers configured within optical cables. The results highlight the importance of selecting the appropriate vibration frequency for internal fibers. In addition, the results of evaluating the bit error rate characteristics of parallel data transmission using two carrier frequencies indicate that for reliable parallel data transmission, it is important to select carrier frequencies that are not affected by crosstalk.

We propose a PON protection system that can be operated with a weak power over fiber, such as video signal light from an unused port of a passive optical network splitter.

Interest is growing in the use of telecom fiber networks for sensing purposes. Notably, vibration sensing has the potential not only for network health monitoring but also for generating new revenue sources. Interferometry is an appealing option for vibration sensing because of its simple structure and low cost. This method can be implemented using two inactive single-mode fibers (SMFs). However, two inactive SMFs may not always be available. In addition, interferometry using two SMFs typically requires access to both ends of the SMFs, which can sometimes be impractical. Therefore, a method for achieving single-end vibration sensing using a single SMF while maintaining simplicity and low-cost is necessary. In this paper, we propose a novel vibration sensing method that is based on inter-modal interference using the two-mode region of conventional SMFs. The proposed method forms an interferometer with one SMF using the fundamental and second-order modes as two separate paths. By analyzing the interference between the two modes, one can detect the vibration applied to the SMF. We also extend the method to enable single-end vibration sensing by adding a reflector at the far-end of the SMF. Proof-of-concept experiments demonstrated the capability of single-end vibration sensing.

In this paper, we propose a method of estimating vibration positions using a bidirectionally applied polarizer-based fiber optic vibration sensors (B-PFOSs) system. The feasibility of this method is verified experimentally.

We propose a vibration sensing method using the two-mode region of conventional single-mode fibers. Our method detects vibrations by observing and analyzing transmitted power variations due to interference between the fundamental and second-order modes.

A novel data transmission method, where a vibration signal is applied to the outside of an optical fiber cable, is proposed. In this method, a vibration signal is received using an optical fiber vibration sensor.

Nondestructive methods for measuring the mode dispersion distribution of SDM fiber that utilize Rayleigh backscattering observed with coherent optical frequency-domain reflectometry are reviewed. Experiments on few-mode and coupled multicore fibers are presented.

We review a novel technique that we recently proposed for detecting a temporal increase in macro/micro-bending loss before it causes outages in optical fiber networks. We briefly describe the measurement principle and some recent achievements.

We propose a scheme to compensate for inter-channel crosstalk (XT) caused by laser phase noise in frequency division multiplexing coherent optical time domain reflectometry (FDM-OTDR). To clarify the influence of laser phase noise in FDM-OTDR, we adopt a simple model assuming that the laser field spectrum including phase noise is approximated by a Lorentzian shape. With this simple model, the increase in inter-channel XT caused by spectral broadening can be described by using linear response theory. According to the linear response theory, we can compensate for the OTDR dead-zone degradation with a Wiener filter. We compare theoretical calculations of the OTDR trace with experimental results.

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.

Linear optical sampling is presented as a useful method to characterize mode-by-mode impulse responses or the spectral transfer matrix of multimode optical systems. In a two non-degenerate linear-polarization (LP) mode transmission line, which actually supported six independent spatial modes, 6 × 6 spectral transfer functions were simultaneously measured using multiplexed mode-by-mode impulse responses in series. According to the singular value analysis of the matrix, the mode-dependent loss spectrum was analyzed over a frequency bandwidth of several hundred GHz, which was determined by the spectra of the probe and reference pulses. The technique would be useful for characterizing various multi-spatial-mode fiber systems that are intensively being developed to overcome the limit in capacity of single-mode optical fibers.

Mode-by-mode impulse responses, or spectral transfer matrix (STM) of birefringent fibers are measured by using linear optical sampling, with assist of polarization multiplexed probe pulse. By analyzing the STM, differential mode delays are estimated.

We report the impulse response measurement of weakly-coupled homogeneous multicore fiber accomplished by coherence-recovered linear optical sampling, which simultaneously realizes a picosecond-level time resolution and a dynamic range of over 70 dB. The observed core-by-core impulse responses include a directly transmitted pulse and plateaus that are yielded by inter-core couplings. A consideration of the observed results suggests that the group velocities are perturbed, and the core with the slowest group velocity alters along the fiber. We also found that the polarization states of the plateaus alter in the time axis of the impulse response chart, with a correlation width as short as the pulse width: we presume that this phenomenon is observed because the polarization change that occurs during propagation is transferred to the coupled signals with the shrinkage of the time axis. Next, we selected a 100 m-long piece of fiber, and measured the group delay of each core. We found that the variation of the core-by-core group delays was not similar to that of the long fiber, and it may change considerably with bending induced in the fiber. These results also suggest a variation in the local group delays over the length of the fiber.

This paper clarifies the requirements for applying 1-mu m-band mode-detection optical time domain reflectometry (OTDR) to the loss monitoring of trunk cables with the goal of detecting slight changes in macro/micro-bending that are missed by conventional OTDR. In light of the requirements, the measurement system is enhanced through the use of coherent detection to fulfill the required range performance. Moreover, the enhanced system modulates the optical frequency and the state of polarization of the probe light during the measurement to suppress amplitude fluctuations in the backscattered waveforms. A field test is carried out to confirm the performance of the enhanced measurement system. The results demonstrate that the measurement range of over 40 km is achieved while amplitude fluctuations are reduced to as low as 0.02 dB.