A 100-km-long single-mode optical-fiber fault location

A Raman OTDR (ROTDR) fault location for a 100-km-long single-mode optical fiber has been tested. A Ge p-i-n photodiode cooled by liquid nitrogen has been used as a backscattered light receiver. The signal-to-noise ration (SNR) improvement of the cooled Ge p-i-n photodiode from a Ge avalanche photodiode (Ge APD), which operates at room temperature, is 14 dB. Spectral Stokes light power distributions, which have been emitted from a long single-mode fiber, have been measured to estimate the maximum locatable length for a single-mode fiber. It has been shown, from the measurements and calculations, that a 100- km-long and a 30-dB total attenuation at a 1.55-μm wavelength single-mode fiber fault location can be achieved with the aid of an averaging technique. On the basis of these results, a 102-km-long single-mode fiber fault location experiment has been successfully carried out.     

Highly accurate long-span chromatic dispersion measurement system by a new phase-shift technique

A highly accurate long span chromatic dispersion measurement system, which is based on a wavelength-division-multiplexing phase-shift technique and utilizes six laser diodes in1.2 sim 1.6 mum spectral region, has been developed. It is intrinsically free from error due to the fiber length variation caused by temperature changes under the measurement. The measurement accuracies of dispersion and Zero-dispersion wavelength are extremely good and within ±0.02 ps/km . nm and ±0.1 nm in 1250 ∼ 1450 nm spectral region in the case of a 10.5-km single-mode fiber measurement. The dynamic range is over 50 dB excluding system theS/Nmargin of 5 dB. Using this system, chromatic dispersion measurements of a 101.9-km pure-silica-core single-mode fiber and a 100.7 km concatenated dispersion-shifted single-mode fiber have been successfully carried out. The measured result has coincided with the arithmetical mean of those of constituent fibers.     

Marked extension of diagnosis length in optical time domain reflectometry using 1.32 ?m YAG laser

An optical time domain reflectometer was newly constructed by using a high power Nd:YAG laser operating at a wavelength of 1.32 ?m and a TeO2 acousto-optical light deflector. As a result, the maximum detectable fault location length of 34 km for single-mode fibre and that of 60 km for multimode graded-index fibre were successfully attained.     

An acoustooptical directional coupler for an optical time-domain reflectometer

An optical directional coupler in which a TeO2acoustooptical deflector (AOD) is employed has been designed and developed for use in an optical time-domain reflectometer (OTDR). A low round-trip insertion loss of 4.6 dB and low crosstalk of below -48 dB were attained for the fabricated coupler. Signals of large amplitude, such as Fresnel reflection, could be suppressed to less than - 33 dB by switching of the optical directional coupler. Amplitude fluctuation of the back-scattered signal due to polarization fluctuation in single-mode fibers is reduced to a negligible extent.     

Performance of optical cable composed of dispersion-shifted single-mode fibers

A low-loss dispersion-shifted single-mode fiber cable has been fabricated. The index-profile of the fiber is nearly parabolic and the relative index difference is 0.8 percent. An average cable loss is 0.229 dB/km at 1.55 μm, and excellent loss stability has been achieved in the cabling process and in the temperature and mechanical test.     

Theory of signal light amplification by stimulated Raman scattering in twisted single-mode optical fibers

Characteristics of signal light amplification by stimulated Raman scattering are studied theoretically for the twisted single-mode fibers. Coupling equations for orthogonal modes in the fiber are derived and solved analytically. The optical gain dependence on fiber twist rate, fiber length, and so on are numerically investigated. The Raman gain for the twisted fiber with a rate of 1 turn/m is found to be reduced by 10 dB comparing with the nontwisted fiber for the fiber length less than 2 km, while it is almost independent of twist rate for the fiber longer than 10 km.     

3 km-long single-polarisation single-mode fibre

A single-polarisation single-mode (SPSM) fibre with crosstalk of ?40 dB in a 3.2 km length has been demonstrated. No crosstalk degradation was found for lengths of more than 0.2 km. The two polarisations of the fundamental mode were split with a high modal birefringence of 8.5×10?4, which was produced by PANDA structure. The transmission loss was 2.8 dB/km at 1.56 ?m.     

Low-Loss single-mode fibre at the material-dispersion-free wavelength of 1.27 ?m

A GeO2-doped silica single-mode optical fibre with a low attenuation loss of 0.5 dB/km at 1.27 ?m, where the material dispersion of the silica glass falls to zero, has been made by a C.V.D. technique. Attention was paid to reducing OH absorption losses in the single-mode fibre.     

Fabrication of single-mode fibres by v.a.d.

A 21 km long single-mode fibre with loss values of 0.6 dB/km at 1.2 and 1.55 ?m, and 0.7 dB/km at 1.3 ?m, has been made by the v.a.d. method. This indicates the high potential of this method in the production of long low-loss single-mode fibres.     

Characteristics of Gbit/s optical receiver sensitivity and long-span single-mode fiber transmission at 1.3 µm

Sensitivity of a 1.3 μm Ge APD receiver was measured at data rates ranging from 100 Mbits/s to 2 Gbits/s, using a high-speed GaAs FET RZ driver, low-noise Si bipolar transistor (BIT) receiver amplifier, and a highly sensitive TD comparator. The required received optical level at a 10^-9error rate was -31.9 dBm for 2 Gbits/s with a Ge APD/Si BIT front end having a 50 Ω input impedance. A Ge APD/ GaAs FET front end, with a 500 Ω input impedance, brought about 2 dB improvement at 100 Mbits/s, as compared with a Ge APD/Si BIT (50 Ω) front end. A coupling loss of 4 dB, achieved by a hemispherical microlens tipped on a single-mode fiber, and a low fiber loss of 0.57 dB/km, including splice loss, enabled 44.3 km single-mode fiber transmission at 2 Gbits/s. The 1.3 μm transmission system has a data rate repeater-spacing product of 88.6 (Gbit/s)km. Prospects of Gbit/s receiver sensitivity and the 2 Gbit/s transmission system, with more than 50 km repeater spacing, are also discussed.     

Ultralow loss and long length photonic crystal fiber

We have succeeded in fabricating a low-loss and long length photonic crystal fiber (PCF) by improvement of fabrication process. The fiber is 10 km long and has a lowest loss of 0.37 dB/km at 1550 nm ever reported. We also succeeded in reducing the OH absorption loss to 3 dB/km. This is almost the half of the value ever reported. Using the low-loss PCF, we performed the first DWDM transmission experiment. DWDM signal of 8/spl times/10 Gbit/s is successfully transmitted through the PCF.     

High-bandwidth, high-numerical aperture graded-index polymeroptical fiber

A new large core (0.5-1.0 mm) graded-index polymer optical fiber was proposed to solve the connection problem of the single-mode silica fiber indoor use for high speed multimedia network. The bending loss for 10-mm bending diameter was dramatically decreased from 20 dB to less than 1 dB by preparing the high numerical aperture graded-index polymer optical fiber. The bandwidth was 585.2 MHz km which was one hundred times larger than that of any existent step-index polymer optical fibers, and the attenuation was 150 dB/km at 650-nm wavelength     

Low-loss single-mode fibres prepared by plasma-enhanced MCVD

A series of single-mode lightguide preforms capable of yielding > 20 km of 110 ?m OD fibre have been fabricated using the RF plasma-enhanced MCVD technique. The loss of kilometre lengths drawn from both ends of the preforms has been measured. At 1.3 ?m, the loss ranged between 0.55 and 0.7 dB/km. The preforms were made at deposition rates of 3.5 g/min.     

Design and performance of ultra-low-loss single-mode fiber cable in 1.5-µm wavelength region

The structural optimization of single-mode fiber for use in the 1.5-μm wavelength region is made with the aim of minimizing the total transmission-line loss over a repeater section. For example, the optimum ranges of the mode-field radius w0and effective cutoff wavelength λceare determined as 5.5 μmleq w_{0} leq 6.5 mum and 1.35μmleq lambda_{ce} leq 1.53 mum for high bit-rate transmission systems with a repeater spacing of 80 km. Based upon the design, ultra-low-loss single-mode fiber cables are fabricated. The average loss of 108 fibers in the cables is 0.19 dB/km at 1.55 μm. The total loss of a 216-km-long fiber link containing 107 splice points was 46.3 dB. Good loss stability at high temperatures as well as during the cable manufacturing processes, are achieved by the appropriate choices of coating materials and optimized fiber parameters.     

The Design and Fabrication of Monomode Optical Fiber

The design of monomode fibers is discussed in the context of optimizing fiber loss and dispersion simultaneously, with reference to the materials choices and limitations to preform and fiber fabrication by the MCVD technique. Two classes of monomode structure-matched cladding and depressed cladding-are considered. Ultralow attenuation has been achieved reproducibly in both classes of fiber. The control of fiber geometry and dispersion is also discussed. Matched cladding fiber suitable for systems operating at both 1.3 and 1.55 µm has been studied and mean losses of 0.45 dB/km at 1.3 µm and 0.28 dB/km at 1.55 µm have been achieved for a total of 130 km. The behavior of depressed cladding fiber is compared with predictions from the theory of propagation in W fibers. Depressed cladding fiber with stable guidance has been demonstrated with attenuation of 0.37 dB/km at 1.3 µm and 0.21 dB/km at 1.55 µm.     

Optimised structure for preparing long ultra-low-loss single-mode fibres

An optimised structure has been evolved for producing long lengths of ultra-low-loss single-mode fibre. Attenuation figures of 0.6 dB/km at 1.3 ?m and 0.34 dB/km at 1.6 ?m have been achieved in fibres up to 17.1 km in length. The absorption due to OH impurity has been reduced to <3 dB/km at 1.39 ?m.     

Development and performance of fully fluorine-doped single-modefibers

Fluorine doping has been used to obtain vapor-phase-axial-deposited (VAD) single-mode fibers with a loss less than 0.20 dB/km at 1.55 μm. A nonshifted design in which fluorine dopant was added mainly to the cladding and only slightly to the pure silica core part was fabricated with high yield. A similar approach has been successfully applied to dispersion-shifted fibers with a dual-shape-core index profile with encouraging results for reducing the transmission loss down to 0.20 dB/km     

Transmission loss characteristics of fluoride glass single-mode fibre

The transmission loss spectrum of a fluoride glass single-mode fibre as obtained with a new preform fabrication technique is shown. It is clearly confirmed on the loss spectrum that the obtained fibre is a single-mode waveguide in the minimum loss wavelength range (2?4 ?m). The minimum loss of this fibre is 8.5 dB/km at 2.2 ?m and the OH excess loss is 15dB/km at 2.85 ?m. This fabrication technique is effective in eliminating OH contamination.     

Multimode and single-mode fiber connectors technology

Various optical fiber connectors using a graded-index fiber have been fabricated and good performances have been obtained during field trial tests. The average connection loss of aC-type, plug-in type, andU-link connector has been found to be 0.4, 0.34, and 0.62 dB, respectively. A new field assembly (FA) type connector using a precision made ceramic capillary has also been developed. This FA type connector is fabricated for use with single-mode fibers, and has a connection loss of 0.56 and 0.52 dB at 0.85 and 1.3 μm, respectively. By using coupling experiments between laser diodes and single-mode fibers, a laser module with a coupling loss of 1.8 dB under optimum alignment conditions has been fabricated.     

Novel full-duplex SSB WDM-RoF system with SLM technique for decreasing PAPR

A novel full-duplex single-sideband (SSB) wavelength division multiplexing radio over fiber (WDM-RoF) system with selected mapping (SLM) technique for decreasing peak-to-average power ratio (PAPR) is proposed in this paper. At the central office (CO), the generated SSB signal carrying 10 Gbit/s 16-ary quadrature amplitude modulation orthogonal frequency division multiplexing (16QAM-OFDM) downstream signal with SLM technique is sent to the base station, and 60 GHz SSB optical signal carrying 10 Gbit/s 16QAM-OFDM upstream signal is sent back to CO utilizing the wavelength-reuse technology. Simulation results show the proposed method for PAPR reduction can effectively improve the sensitivity of receiver, and the power penalty of the 16QAM-OFDM downlink (uplink) signal is about 2 dB (3 dB) at BER of 1×10-3 after 42 km standard single-mode fiber (SSMF) transmission.