Ultralong multimode optical fibre fault location using Raman optical time domain reflectometry

The OTDR technique using the stimulated Raman scattering effect (ROTDR) is applied to ultralong multimode optical fibre fault location. In experiment, Stokes light pulses at 1.6 ?m wavelength, which are the most advantageous for fault location, are used. It is shown that the multimode fibre break, more than 80 km long, is locatable, and fibre loss at 1.6 ?m is measurable by the ROTDR technique.     

Molecular hydrogen behaviour for loss increase of silica fibre in cable filled with water

Evaluation of molecular hydrogen diffusion into silica fibre, which causes a loss increase at 1.24 ?m wavelength, and the accumulation mechanism for hydrogen in cable are reported. It has been found that loss increase around 1.24 ?m wavelength due to hydrogen greatly depends on the ambient hydrogen pressure. The hydrogen pressure in LAP sheath cable easily increases due to metal corrosion and the sealing effect of the sheath.     

Transverse strain sensing based on optical fibre Solc filter

We present an optical sensor based on Solc filter to measure the transverse strain. The Solc filter is made of highly birefringent fibre by twisting its optical axes back and forth in equal sections. When a polarised light goes through the sensor, a periodic transmission response is obtained with a certain free spectra range (FSR) determined by the modal birefringence and the section length. The transverse strain can be measured by the shift of FSR from the transmitted response as the transverse stress changes the birefringence. More importantly we find that the measurement of transverse strain is free from the influence of temperature. We theoretically analyse the sensor model and simulate it by Jones Formalism. It is found that the sensitivity can achieve 7.14 pm/με. The influence of section length, wavelength of light source, modal birefringence and number of sections on the sensitivity is also investigated.     

Efficient generation of near-i.r. stimulated light scattering in optical fibres pumped in low-dispersion region at 1.3 ?m

By pumping a low-loss single-mode fibre in the low-dispersion wavelength region with a 1.3 ?m Q-switched Nd:y.a.g. laser, efficient near-i.r. (1.15?1.6 ?m) stimulated light scattering has been obtained. The peak wavelength for the stimulated Raman emission is found to be fibre-length dependent, and the threshold pump power is as low as 10 W, when coupled into a 150 m fibre.     

S-band Brillouin erbium fibre laser

A multi-wavelength Brillouin erbium fibre laser, which operates in short wavelength band (S-band), is proposed and demonstrated. The system employs both linear gain and nonlinear gain from a 20 m S-band erbium-doped fibre and a 500 m singlemode fibre, respectively, to generate an optical wavelength comb with spacing of approximately 0.084 nm. Two 80/20 couplers were used in the system as an internal feedback of generated Stokes signal to produce cascaded Brillouin Stokes for multiwavelength operation. A stable output laser comb of up to seven lines was obtained with a Brillouin pump of 3.5 mW and a 980 nm pump of 200 mW.     

Chromatic dispersion measurement by white-light interferometry on metre-length single-mode optical fibres

Chromatic dispersion near 0.8 ?m in a short (~1 m) single-mode optical fibre is determined by a white-light interferometric technique. In particular, the wavelength-dependent group delay of the fibre is obtained directly from the spectra of the output light from a Mach-Zehnder interferometer illuminated by a GaAlAs LED. Its application in single-mode fibre studies in the 1.3 ?m wavelength region is discussed.     

Chromatic dispersion measurement over a 120 km dispersion-shifted single-mode fibre in the 1.5 ?m wavelength region

Chromatic dispersion in the 1.47?1.60 ?m wavelength region is measured successfully for a dispersion-shifted fibre over 120 km by the LD phase-shift method. The measured value of a 123 km spliced fibre agrees well with the sum of chromatic dispersion values of its constituent fibres. This confirms the additive rule of chromatic dispersion for long dispersion shifted fibre in the 1.5 ?m wavelength region.     

Design and fabrication of dispersion-shifted depressed-clad triangular-profile (DDT) single-mode fibre

A new depressed-clad triangular-index-profile single-mode fibre with dispersion minimum shifted to the 1.55 ?m region is investigated. Fibres with high cutoff wavelength (?1.1 ?m) and low dispersion slope (?0.052 ps/km nm2) at their minimum dispersion wavelength (?1.55 ?m) were fabricated. Results from 226.7 km of fibre show an average loss of 0.241 dB/km at 1.55 ?m and 0.232 dB/km at the loss minimum.     

Spontaneous Brillouin noise in long-distance high-bandwidth optical-fibre transmission

The light propagating in a single-mode optical fibre is found to be converted gradually into forward-scattered spontaneous Rayleigh-Brillouin power. The Brillouin component has a linewidth of -500 MHz and constitutes ~1/200 of the propagating power at 1.3 ?m wavelength after 600 km. The measured backscatter-Brillouin shift coefficient is ?0.15 GHz/wt% GeO2.     

34 Mbit/s optical fibre transmission system experiment at a wavelength of 2.4 ?m

Data transmission at 34 Mbit/s has been performed over a fluoride glass fibre at a wavelength close to the 2.55 ?m minimum-loss wavelength of the fibre, using an externally modulated He-Ne laser and a graded-composition GaInAs photodiode with spectral response optimised for 2.55 ?m operation.     

CW single-pass Raman generation in optical fibres

Continuous wave single-pass Raman generation has been observed in optical fibres. Experiments showed that the first and the second Stokes have been observed with 0.6 W and 4.8 W of 1.064 ?m pump power input, respectively, in a 35 km single-span VAD (vapour phase axial deposition) fibre with the loss of 1.13 dB/km at 1.064 ?m. The threshold for the CW first Stokes was 1.25 W and complete conversion of the pump to the first Stokes was obtained with the pump power of 4 W.     

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.     

Polarising fibre coupler with high extinction ratio

Fused polarising fibre couplers have been fabricated using single-polarisation single-mode fibres. When circularly polarised light is fed into the coupler, one of the two orthogonal polarisation modes suffers strong attenuation, and only one polarisation mode couples in the fused biconical taper region. The extinction ratio of the coupler is 41 dB at a wavelength ? = 1.3 ?m with a coupling ratio of 48:52.     

Single-mode fibres with extremely high-Δ and small-dimensionpure GeO2 core for efficient nonlinear optical applications

Single-mode fibres with 8.2% Δ and a 1.4 μm diameter-GeO ₂ core have been prepared for efficient stimulated Raman effect. When pumping a 2.7 m-long fibre by a Q-switched and mode-locked Nd:YAG laser (λ=1.064 μm), the first Stokes light (λ=1.114 μm) and second Stokes light (λ=1.169 μm) have been observed at the input peak power levels of 24 W and 40 W, respectively. These results indicate that the above critical power levels are approximately 10^-2~10^-3 smaller than those for the high-silica single-mode fibre     

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.     

Interferometric measurements of minimum dispersion spectra in short lengths of single-mode fibre

A Mach-Zehnder fibre interferometer and a fibre Raman laser are used to measure modal group delays with subpicosecond resolution. Chromatic dispersion spectra, in several metres of fibre, are obtained within the 1.06?1.62 ?m wavelength region.     

Detailed evaluation of an attainable repeater spacing for fibre transmission at 1.3 ?m and 1.55 ?m wavelengths

An attainable repeater spacing at 1.3 ?m and 1.55 ?m wavelengths using a step-index monomode fibre cable is given, after detailed consideration of total loss as well as total dispersion of an optical fibre. The longest attainable repeater spacing at 1 Gb/s is about 100 km at 1.55 ?m wavelength using a single-mode laser diode and a monomode fibre with a relatively small core-cladding refractive index difference, e.g. about 0.2%.     

In-line single-mode wavelength division multiplexer/demultiplexer

A single-mode fibre optic wavelength division multiplexer/demultiplexer at 1.32 ?m and 1.55 ?m, constructed from a fused evanescent wave coupler, is described. This device has an insertion loss of less than 0.05 dB and a wavelength isolation of 16 dB at 1.32 ?m and 18 dB at 1.55 ?m.     

Chromatic dispersion measurement of a single-mode fibre by improved optical heterodyne interferometry

The chromatic dispersion of a single-mode fibre is successfully measured by means of an optical heterodyne detection method with temporal resolution of 0.01 ps. The heterodyne signal is detected at the near end of the fibre of length approximately 1 m using laser diodes operating in the 1.19?1.51 ?m wavelength region.     

Single-pass Raman generation pumped by a mode-locked laser

Single-pass Raman generation pumped by a mode-locked Nd:YAG laser is investigated for long-span and low-loss fibres. The peak wavelength of the first Stokes jumps dramatically from 1.114 ?m to 1.12 ?m at 1.65 W average input power. The first Stokes increases rapidly between the inputs of 1.65 W and 2.1 W. These characteristics of single-pass stimulated Raman scattering are discussed in terms of group velocity matching.