Evaluation of Raman gain coefficient distribution independent of imperfection contributions

We have previously reported a technique for measuring the distribution of the Raman gain characteristics in optical fibers. It is well known that Raman gain characteristics are affected by dopants and the effective areas in optical fibers. The Raman gain coefficient independent of the influence of effective areas will be used to investigate the longitudinal uniformity in fibers. This letter describes a method for evaluating the Raman gain coefficient distribution in a way that distinguishes it from the effects of waveguide imperfections by employing our previously reported technique. Using this method, we performed experiments on various types of fiber, and confirmed that the Raman gain coefficient can be accurately measured.     

Coated optical fibers for high-strength fusion splices

Suitable fiber-coated structures and a practical splice technique which are superior in both long-term reliability and splice operation efficiency in the field are required. A splice technique without using any dangerous chemical acids to remove the primary coat and coated fiber structures are proposed in this paper. With these techniques, an average strength of 0.88 GPa for bare fusion spliced fibers is obtained in the field, which is more than double the value compared with the average strength of 0.4 GPa obtained by the conventional splicing technique, which is used practically in the field. In addition, the splice time decreases to about one-third of the conventional splice time. The splice operation efficiency improvement is recognized for not only coated mono-fibers but for fiber ribbons.     

Design and performance of ultra-high-density optical fiber cable with rollable optical fiber ribbons

This paper proposes a novel ultra-high-density optical fiber cable that employs rollable optical fiber ribbons. The cable has great advantages in terms of cable weight and diameter, and fiber splicing workability. Moreover, it will be easy to install in a small space in underground ducts and on residential and business premises. The structural design of the rollable optical fiber ribbon is evaluated theoretically and experimentally, and an optimum adhesion pitch P in the longitudinal direction is obtained. In addition, we examined the performance of ultra-high-density cables with a small diameter that employ rollable optical fiber ribbons and bending-loss insensitive optical fibers. The transmission, mechanical and mid-span access performance of these cables was confirmed to be excellent.     

Effect of cabling on polarization mode dispersion in optical fiber ribbon cables

This paper theoretically and experimentally investigates an effect of cabling on polarization mode dispersion (PMD) in ribbon fibers helically stranded in optical fiber ribbon cables aimed at designing low PMD ribbon cables. Based on the birefringence model focused on the change in the birefringence when ribbon fibers are cabled, the helical pitch of optical fiber ribbon cables is designed to minimize the maximum PMD in the cables. A low PMD characteristic is confirmed in optical fiber ribbon cable with approximately the optimal helical pitch.     

Low-rigidity optical fiber ribbon and its application to ultra-high-density cable with bending-loss insensitive fibers

We propose a novel optical fiber ribbon using bending-loss insensitive fibers aimed at tightly and randomly assembling in small core of the cable. Proposed ribbon is designed to be capable of mass-splicing and to suppress local bending and strain increase caused by cabling and cable bending by reducing flexural rigidity against bending under high fiber density assembling. We manufactured the cable with proposed ribbons and achieve the maximum fiber density of a 4.1 fiber/mm² for 400-fiber cable in conjunction with good optical loss and strain characteristics.     

Resin selection and high-speed coating of optical fibers withUV-curable materials

As a result of the curing properties of UV-curable resins, a selection criterion for UV-curable resins for high-speed fiber coating is proposed. The method is based on specifying two parameters of a UV-curable resin, which designate the Yong's modulus of cured resin. The method was used to coat graded-index fibers with the selected resins and it was demonstrated that the optical loss changes due to the coating process are small. The change of the fiber ribbon was within 0.1 dB/km under temperature changes between -40 °C and +60 °C     

Tensile strength of reinforced fusion-spliced optical fibers

Tensile strength characteristics of reinforced fusion-spliced optical fiber are important to establish a stable optical line in the field. This paper describes theoretical and experimental results on the strength of reinforced fiber. The stripped fiber strengths of fused splice parts and nonheated parts were measured and were found to be different. When a tension is applied to the reinforced fiber, the induced fiber stress is evaluated along its axis. The strength characteristics of reinforced fiber were investigated, based on the stress distribution and the different strengths of fusion-spliced fiber. It is reported that the strength after reinforcement can be predicted and that the strength depends on the adhesive modulus of rigidity. The adhesive design is also presented to obtain necessary strength of reinforced fiber under an allowable failure probability.     

Design and characteristics of multi-hundred-core optical-fiber cable for use in subscriber feeder lines

This paper describes a design method for optical-fiber cable consisting of optical-fiber ribbons encased in loose tubes. The influence of excess fiber length on optical loss in a loose tube is evaluated and the required clearance is obtained. The optimum combination of the clearance and the tube stranding pitch is obtained in order to suppress fiber strain. The tube dimensions are also discussed and are determined to protect fiber ribbons from lateral load. A 600-fiber-structure cable is manufactured according to the obtained design results; the transmission and mechanical performances are confirmed to be excellent.     

Hole-assisted fiber design for small bending and splice losses

This letter describes the bending and splice loss characteristics of hole-assisted fibers and reveals that the distance between the hole and the fiber core is a key parameter regarding these losses. We found that the normalized hole distance against the core radius must be two or greater for practical deployment.     

Fiber-Optic Distributed Strain and Temperature Sensing With Very High Measurand Resolution Over Long Range Using Coherent OTDR

We describe a novel fiber-optic technique for measuring distributed strain and temperature that uses a coherent optical time-domain reflectometer (OTDR) with a precisely frequency-controlled light source. Using this technique, we achieved temperature measurements in an 8-km-long fiber with a resolution of 0.01degC and a spatial resolution of one meter. This temperature resolution is two orders of magnitude better than that provided by the Brillouin based sensing technique.