Experimental demonstration of step-like dispersion profiling inoptical fibre for soliton pulse generation and compression

Generation of 100 GHz trains of 500-700 fs pulses using dual-frequency beat conversion in a step-like dispersion profiled fibre is reported. The authors believe that this is the first time the generation and compression of soliton pulses using such a fibre has been demonstrated. The fabrication of such fibre assemblies does not require any special facilities and relies only on conventional optical fibre technology. They believe that the use of profiling the fibre dispersion by fibre segments instead of continuously dispersion-decreasing fibre is not only possible but preferable in many applications     

Novel fibre optic gyroscope with a configuration combining Sagnac interferometer with fibre ring resonator

A novel fibre optic gyroscope, with a structure making use of the combination of a Sagnac interferometer with an active fibre ring-resonator, is proposed and analysed. The proposed gyroscope can be viewed as a generalised structure of the conventional Sagnac interferometric type fibre optical gyroscope. It has the advantages of both long fibre loop length and multipath interferences. By inserting a fibre amplifier in the loop to provide an optical gain of several dB, the relative maximum sensitivity is enhanced to approximately 30 times more than that of conventional Sagnac interferometric fibre optic gyroscopes.<>     

Sinusoidal microbending loss of HE11-mode in step-index fibres

Sinusoidal microbending losses of the HE11-mode in step-index fibres are compared by using a perturbation solution of electromagnetic wave scattering theory. The HE11-mode in a multi-mode step-index fibre is found to suffer much higher bending loss than that in a single-mode step-index fibre, except that in nearly perpendicular directions and in the perpendicular direction with respect to the fibre axis the HE11-mode in the single-mode step-index fibre shows some higher bending loss than that in the multimode step-index fibre.     

Enhanced tuning mechanism in fibre laser based on multimode interference effects

A 12 nm tunable fibre laser is demonstrated. The tuning mechanism uses an SU-8 fibre gripper for automatic alignment of a multimode fibre and gold-coated fibre (facet) mirror. Wavelength tuning is achieved using the wavelength dependent re-imaging effect that occurs in multimode fibres     

Mitigating the risk of high power damage to the BT network

Optical powers used in optical telecommunications networks have increased over time with the advent of technologies such as erbium doped fibre amplifiers, dense WDM, and fibre Raman amplifiers. Erbium fibre and Raman amplifiers with output powers up to 1 W and 2 W respectively are now available for deployment giving optical power densities of ≈14 000 MW/m² per Watt launched into a single mode fibre. This compares with 74 MW/m² for the surface of the sun. It is thus essential to ensure that the risk of optical damage to the fibre is understood and steps are taken to mitigate it where necessary. Research carried out by BT over the last few years has shown that fibres carrying relatively modest optical powers, as low as 200 mW for the most sensitive fibres, can be catastrophically damaged at tight fibre bends. Damage is caused by some of the optical power lost at the bend being absorbed by the fibre coating that may over time lead to a sudden increase in temperature to over 700 °C causing either the silica to kink mimicking a fibre break, or the coating to burn off at the bend leading to fibre failure on subsequent handling. This paper describes factors that increase the risk of short-term catastrophic damage at fibre bends, presents experimental results to show the variation in sensitivity between different fibres, and discusses new important theoretical results modelling the temperature rise in the fibre.     

Mitigating the risk of high power damage to the BT network

Optical powers used in optical telecommunications networks have increased over time with the advent of technologies such as erbium-doped fibre amplifiers, dense WDM, and fibre Raman amplifiers. Erbium fibre and Raman amplifiers with output powers up to 1 W and 2 W respectively are now available for deployment giving optical power densities of ≈ 14 000 MW/m² per Watt launched into a single mode fibre. This compares with 74 MW/m² for the surface of the sun. It is thus essential to ensure that the risk of optical damage to the fibre is understood and steps are taken to mitigate it where necessary. Research carried out by BT over the last few years has shown that fibres carrying relatively modest optical powers, as low as 200 mW for the most sensitive fibres, can be catastrophically damaged at tight fibre bends. Damage is caused by some of the optical power lost at the bend being absorbed by the fibre coating that may over time lead to a sudden increase in temperature to over 700 °C causing either the silica to kink mimicking a fibre break, or the coating to burn off at the bend leading to fibre failure on subsequent handling. This paper describes factors that increase the risk of short-term catastrophic damage at fibre bends, presents experimental results to show the variation in sensitivity between different fibres, and discusses new important theoretical results modelling the temperature rise in the fibre.     

Graded-index-type crystalline fibre for IR light transmission

A new method for making a graded-index-type crystalline fibre is proposed. A fibre for IR light transmission with crystalline claddings was desired for improving the reliability of the crystallinc fibre and for avoiding any excess loss at the core surface. A fibre with the core-cladding structure was made by complex extrusion with KRS-5 as the core and KRS-6 as the cladding. Obtaining a smooth core-cladding interface was very difficult. This problem was overcome by a diffusion of composite ions by annealing after the extrusion. The fibre has a concentration distribution that can be accounted for by a GI fibre. The transmission loss of the CO2 laser is 0.2 dB/m with a launching NA of 0.05.     

Anomalous dispersion of new doubly clad optical fibre

The letter treats a doubly clad dielectric optical fibre. We assume that the core refractive index is greater than the outer-cladding refractive index, which is greater than the inner-cladding refractive index. This optical fibre, if properly designed, has an anomalous or negative normalised guide dispersion (?2/?)d2 ?/d?2 that compensates typical glass dispersion. Single-mode operation of this doubly clad fibre can be obtained with the core radius appreciably larger than that of a singly clad fibre with the same core and outer-cladding refractive indices.     

发散纤维的光学特性

本文讨论一种发散型光学纤维,它类似于凹透镜。给出了纤维中光线的轨迹、聚焦的焦距、象距、线放大率和纤维的有效长度等计算公式。     

Effect of third-order dispersion of optical fibre on soliton interaction

It is shown that the third-order dispersion of an optical fibre can be used to reduce the mutual interaction between solitons when the fibre is operated nonlinearly. This provides a means to improve the bandwidth of nonlinear fibre.     

New coupling method for GaAs-laser?fibre coupling

A new method for coupling a diode laser to an optical fibre is described. This uses a cylindrical glass fibre as a focusing element. Optical feedback from the fibre endface has been found to have an influence on the laser output power. As a result, the light power launched into a single-mode fibre was higher than that obtainable from the laser during normal operation.     

Anisotropy in spun single-mode fibres

It is shown that the dominant process for the reduction of birefringence in a spun fibre is the averaging of the local fibre anisotropy by the rapid procession of the axes of asymmetry along the fibre. No significant change in cross-sectional geometry occurs.     

Location of imperfections in optical glass-fibre waveguides

An echo-pulse technique for the location of fibre imperfections is described. The technique has been successfully applied to a plastics-coated Selfoc fibre and a plastics-coated silica-based fibre. Both showed a break. In the Selfoc fibre, an additional fibre defect was located. The same method may be used to measure rapidly the fibre length.     

Leaky optical fibre for large mode area singlemode operation

A novel optical fibre structure is introduced for large mode area singlemode operation. The fibre consists of a cladding index profile that increases monotonically in the radial direction. It is shown that the fibre can introduce exceedingly high leakage losses to the high-order modes, while maintaining a low loss to the fundamental mode. Numerical results are presented for power-law index profiles.     

Cutoff frequencies of a parabolic-core W-type fibre

The cutoff frequencies of guided modes in a weakly guiding W-type fibre with parabolic core profile have been obtained. It is found that the cutoff frequency of the TE01-mode in such a fibre is much higher than for a homogeneous-core W-type fibre. This should allow greater ease in splicing.     

New polarisation-state control device: rotatable fibre cranks

A new all-fibre device for controlling the state of polarisation (SOP) in a single-mode fibre is proposed. It consists of two fibre elements called rotatable fibre crank (RFC) elements, each of which is equivalent to a rotatable phase plate. It features a very low insertion loss when used in a fibre circuit, because it can be spliced with input and output fibres, and that the control is endless as in a rotatable phase plate. The effectiveness of the SOP control using this device is verified experimentally.     

Simple and compact, all-fibre retro-reflector for cladding-pumped fibre lasers

Proposed is an all-fibre retro-reflector realised via shaping a fibre end into a right-angled cone for a pump reflector in cladding-pumped fibre lasers. The conical-shaped fibre-optic retro-reflector allows folded, total internal reflections for pump beams that propagate in the inner cladding of a double-clad fibre. The proposed scheme was applied to a cladding-pumped ytterbium-doped fibre laser and readily achieved over 55% of reflection for the unabsorbed pump throughput, thereby generating 29% more signal output power than without the pump retro-reflector     

Optical amplifiers for video distribution

The promise of a broadband fibre communications network has attracted the interest of CATV and Telco concerns. Various networks and topologies have been discussed. Cost is a drawback in some of the proposed networks, particularly those networks which require switching. This paper discusses a low cost broadcast tree and branch network which uses optical amplifiers to extend the network penetration. Recent work in the development of optical amplifiers suggests that the Erbium fibre amplifier may be compatible with VSB-AM. The characteristics of such an amplifier will be discussed. This scenario allows an orderly transition from the present-day AM backbone system to the tree and branch fibre architecture. Once the broadband fibre plant is in place new services can be implemented that exploit the broadband nature of fibre.     

Efficient power coupling using taper-ended multimode optical fibres

Highly efficient power coupling of up to 97% between a d.h. laser and a multimode step-index fibre is demonstrated by employing a tapered fibre launcher. Also, it is shown theoretically that a tapered end increases the effective numerical aperture of a fibre. For a Lambertian emitter, the use of a taper launcher permits the maximum coupling efficiency allowed by the Liouville theorem.     

Dispersion-shifted convex-index single-mode fibres

The structural design of the single-mode fibre with a convex-index profile is described to achieve zero dispersion at 1.55 ?m. As a result of the fibre design, it is clarified that the bending loss of the convex-index fibre is the smallest among the losses of various index profile fibres such as step, triangular and Gaussian ones.