Daisuke Iida

In-Service Line Monitoring System in PONs Using 1650-nm Brillouin OTDR and Fibers With Individually Assigned BFSs

This paper introduces an in-service line monitoring technique that can locate a fault in branched optical fibers in passive optical networks (PONs) from a central office. This technique can upgrade the conventional optical fiber line testing and monitoring system. To distinguish a backscattered signal from each branched PON fiber, we employ the fibers with individually assigned Brillouin frequency shifts (BFSs) fibers as drop cables and a 1650-nm Brillouin optical time-domain reflectometer (B-OTDR) instead of the OTDR used in the conventional testing system. This paper describes the design of the BFS taking the outside plant environment into consideration, and discusses the performance of the proposed testing system. We also demonstrate an experimental measurement that locates a fault in a branching fiber after a 1 × 8 optical splitter, and in-service line monitoring for gigabit Ethernet PON (GE-PON) transmission systems.

Design of Identification Fibers With Individually Assigned Brillouin Frequency Shifts for Monitoring Passive Optical Networks

We propose a method for monitoring branched sections in passive optical networks (PONs), where identification fibers are used to distinguish each branched section. We clarify the required characteristics for the separation of the Brillouin frequency shifts of each identification fiber. We design and fabricate identification fibers with well-controlled nuB values for PON monitoring based on the required characteristics. The realized Brillouin frequency shift difference is less than 40 MHz from the target, and we achieve a 1-GHz Brillouin frequency shift separation and a 0.06-dB splice loss for standard single-mode fiber. We also demonstrate fault location in a PON using identification fibers connected to a 4-branched splitter. The bending loss in the branched section is successfully located by using the designed identification fibers and a Brillouin optical time domain reflectometer

Detection Sensitivity of Brillouin Scattering Near Fresnel Reflection in BOTDR Measurement

We discuss the effect of Fresnel reflection on BOTDR measurement. We show that the theoretical detection sensitivity with respect to Brillouin scattering is limited by the pulse modulation effect and phase noise of the light source that is incorporated into the Brillouin spectrum by way of the Fresnel reflection, when the Brillouin sensor is located near the Fresnel reflection point. We describe the detection sensitivity in the presence of Fresnel reflection in terms of the minimum detectable sensor length. In regard to the pulse modulation effect, we find that when the pulsewidth is short, the noise in the Brillouin spectrum is large and the detection sensitivity deteriorates. We derive quantitative equations and confirm the equations experimentally. When the pulsewidth is 10 ns with a 1-MHz linewidth laser, the boundary Fresnel reflection determining whether or not we can measure a 1-m sensor fiber near the Fresnel reflection is about 30 dB lower than that for a 100 ns pulsewidth. A 1-m sensor fiber near the Fresnel reflection could be measured with a 10-ns pulse only when the Fresnel reflection was very low at about . Moreover, the effect of the laser linewidth is also discussed analytically. The analysis suggests that a laser with a narrower linewidth will provide better sensitivity.

Bending and connection loss measurement of PON branching fibers with individually assigned Brillouin frequency shifts

This paper describes the bending and connection loss measurement of PON branching fibers with individual Brillouin frequency shifts and the measurement of the peak spectrum of the Brillouin frequency shifts distributed in test fibers

Optical Correlation Domain Reflectometry Based on Coherence Synchronization: Theoretical Analysis and Proof-of-Concept

We describe a novel optical correlation domain reflectometry technique based on coherence synchronization between probe and local lights. Coherence synchronization is realized by using artificially generated low coherence lights, which are controlled by arbitrary waveform generators. Thanks to the flexibility of the electronics, we can easily design the coherence characteristics of the artificially generated low coherence lights to yield a correlation gating that filters an autocorrelation of an original laser at an arbitrary delay. The correlation gating realized by coherence synchronization is effective as long as the measurement length is less than the coherence length of the original laser. We demonstrate the measurement of the Fresnel reflection at the end of an optical fiber by using coherence-synchronized optical frequency combs that have only one correlation peak in the fiber under test (FUT). The FUT is 100 m long, and the repetition rate of the optical frequency comb generated by cascaded electro-optic modulators is 9.5 GHz, which corresponds to a 10.5 mm spacing between the periodic correlation peaks. The proposed technique removes the restriction imposed by the periodic correlation peaks present in correlation-based measurement using an optical frequency comb.

Cost-effective bandwidth-reduced Brillouin optical time domain reflectometry using a reference Brillouin scattering beam

We propose a simple and cost-effective technique that can reduce the electrical bandwidth for Brillouin frequency-shift sensors with heterodyne detection without the need for expensive instruments or a complicated system. With this technique we use only a reference fiber. The reference Brillouin scattering light in the reference fiber is used as a local light for heterodyne detection. We confirm that this method can be used for measuring the Brillouin scattering spectrum distribution with a much lower frequency bandwidth (0.2 GHz) than that employed for conventional heterodyne detection (11 GHz). The method operates in a way similar to conventional Brillouin optical time domain reflectometry with comparable accuracy. Moreover, we successfully demonstrate temperature distribution sensing and show that we can compensate for temperature variation in the reference fiber.

High-frequency distributed acoustic sensing faster than repetition limit with frequency-multiplexed phase-OTDR

We achieve fully distributed vibration sensing with a high-frequency response using frequency-encoded pulse sequences in phase-OTDR. Both frequency and position are visualized simultaneously on 5-km fiber with an 80-kHz frequency response and 20-m spatial resolution.

Low-Bandwidth Cost-Effective Brillouin Frequency Sensing Using Reference Brillouin-Scattered Beam

We propose a method that down-converts the electrical bandwidth for Brillouin frequency shift sensors with heterodyne detection without the need for any expensive instruments or a complicated system. We discuss the power and coherency of the stimulated Brillouin scattering light required for the reference fiber. We confirm that the frequency bandwidth measured with the proposed method is much lower (0.2 GHz) than that measurable with conventional heterodyne detection (11 GHz). Moreover, the proposed method can measure the dependence of the Brillouin frequency shift on temperature.

Low bandwidth and cost-effective Brillouin frequency sensing using reference Brillouin-scattered beam

We present a novel simple and cost-effective technique that can greatly reduce the electrical bandwidth for Brillouin frequency shift sensors from 11 to 0.2 GHz with only a reference fiber. Temperature change was also accurately observed. ©2008 Optical Society of America

Long-range C-OFDR measurement of Rayleigh scatter signature of fiber beyond laser coherence length

We demonstrate a method to utilize the fiber Rayleigh scatter signature measured with C-OFDR exceeding the laser coherence length. The method overcomes the laser phase noise limitation by analyzing the local scatter power spectrum.