Precisely moulded plastic splices for optical fibres

Optical fibre splices having highly precise V-grooves were moulded by electroformed cavities on etched silicon chips. Splices were produced by transfer moulding, using improved phenolic resin. They showed a quite low average splicing loss of 0.05 dB and sufficient stability to withstand the ambient temperature variation.     

Low-loss splices for single mode fibres

A technique for producing low-loss splices in single-mode fibres has been developed and evaluated. The splices are made by sandwiching the fibre butt-joint ends between a glass V-groove block and a flat glass plate, both of which are made by fibre-drawing techniques. A new splice-loss measuring technique is described. The majority of splices made on identical fibres have losses of less than 0.01 dB.     

Ceramic capillary connector for 1.3 ?m single-mode fibres

A low-loss demountable connector with a precision-made ceramic capillary is presented for 1.3 ?m single-mode fibres. The field-assembly connector can be assembled without adjusting fibre core alignment to the centre of a plug. By using a plastic thin film, an average connection loss of below 0.3 dB is obtained.     

Fusion splices for single-mode optical fibers

A practical low loss splicing method based on the discharge fusion for single-mode fibers was developed. Average splice losses of 0.4, 0.2, and 0.1 dB for fibers with 5.2, 7, and 10 μm core diameters, respectively, are obtained by a simple apparatus utilizing the self-alignment effect due to the surface tension of melted fiber ends. The surface tension effect is analyzed both experimentally and theoretically. Experimental splice losses, both after and during heating, coincide with the theoretical estimated values. It was found that the optimum heating temperature for low loss splices is near 2000°C at 8.5 W electric discharge power. Splicing loss causes are examined. The main cause of the practical splice loss is the residual core axis misalignment caused by an insufficient surface tension effect and core eccentricity with respect to cladding.     

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.     

Mechanical optical fiber splices

Carefully designed mechanical optical fiber splices have achieved record field performance with respect to loss, productivity, and reliability. Design principles, mechanical splicing hardware, and field results are presented for multimode and single-mode, array, and individual-fiber mechanical splices.     

Low-loss fusion splices of optical fibers

A low-loss splicing method, based on discharge fusion of optical fibers by a simple apparatus and by applying pressure between fibers before fusion, was developed. Average splice losses of about 0.07 and 0.15 dB for single-mode (SM) fibers having core diameters of 10 and 7μm, respectively, and 0.02 dB for 50-μm core diameter graded-index (GI) fibers are obtained. Fusion loss and fusion time are obtained minimum for better end preparation having low initial alignment losses at critical pressure and temperature. Mathematical expressions for the variation of fusion time and splice loss with effect of applied pressure between the fibers, for different practical axis alignment, showing the optimum condition to have minimum splice loss are made. Experimental fusion losses are analyzed in terms of residual misalignment of off axis, angular tilt of the fibers during aligning, and air gaps in the splicing zone. Optimum fusion time is obtained by considering the forces due to applied pressure, thermal expansion, and surface tension in the viscous melted glass of the fiber. Theoretical curves of fusion times and splicing losses versus applied pressure agree with the experimental results. The decrease of fusion time to about 1.3 times and splice loss to about two times were found when applied pressure is varried from low to its critical value of 20-25 g. The splice losses are found at a minimum for the operating temperature range of 1980°C to 2140°C for silica fibers. Experimental results of the histogram of bar chart of splice losses agree with the derived mathematical expressions assuming a statistical distribution function of splice losses.     

Low-loss joints between dissimilar fibres by tapering fusion splices

A technique is reported for reducing the splice loss between dissimilar or similar fibres. The technique involves tapering a fusion splice to produce a mode transformer which converts the fundamental mode of one fibre to that of the other with negligible loss. Results of theoretical calculations are presented which show the fundamental mode field shape at the splice junction and the estimated joint loss between two dissimilar fibres as a function of the splice diameter. Initial experiments are reported which have achieved splice loss reductions from 1.5 dB to 0.56 dB and 0.7 dB to 0.15 dB between dissimilar and similar fibres, respectively, at 1.3 ?m.     

Substrate-tube lithography for optical fibres

We describe the first use of substrate-tube lithography to build complex structures into MCVD fibre preforms. While the basic process is illustrated with high-birefringence fibres of 1.9 and 3 mm beat lengths and a two-core fibre, the technique is more general and may lead to a new class of integrated optical devices.     

Triple-ball connector for optical fibres

A demountable fibre connector which uses two interlocking sets of three balls to locate the fibres accurately and simultaneously to align the two parts of the connector has been constructed. The samples tested so far, using Corning stepindex fibre, have shown average losses of less than 0.2 dB with index matching and less than 0.5 dB without. The connector is cheap, easy to make and could be assembled in the field.     

New method for centring optical connectors and splices by single mode excitation

The LP/sub 1,n/ mode family exhibits an azimuthal dependence of mode conversion at a misaligned splice or connectors. This property leads to an accurate method for centring monomode and multimode connectors based on LP/sub 11/ mode rotation.<>     

Hybridised sol-gel process for optical fibres

A new method of making fibres by sol-gel processing consists of overcladding a consolidated core derived from vapour deposition techniques with a cast colloidal gel. The gel, comprising 95% of the fibre mass, is dehydrated in chlorine and consolidated about the core to produce fibres having losses as low as 0.43 dB/km.     

Technique for jointing small-core optical fibres

A simple technique for making permanent joints between optical fibres is described. The technique is suitable for small-core fibres, as well as those in which the core is not well centred in the cladding. Because the precision components required to make the alignment are reused, the cost per joint is low.     

Fusion splicing machine for optical fibres

A fusion splicing machine has been developed with an integrated fibre cutter and support for the splice case inset with splice magazine. The optical fibres and the electrodes can be manipulated, with the result that the splice losses are minimal and optical fibres with different melting points can be fused. Since the splices are not mechanically strong, tension relief facilities for the splice play an important part.     

Fluoride glasses for infra-red optical fibres

Fluoride glasses in the ZrF4-BaF2-RF3 system (R=Gd, Yb) have been investigated as potential low loss materials for achievement of fibres transmitting wavelengths at about 3?5 ?m. Optical measurements confirm the interest in such components and PbF2 doping allows substantial refractive index increases, making for feasible doped core glass preforms.     

Bandwidth results for liquid-core optical fibres

Bandwidths derived from pulse-dispersion measurements have been obtained as a function of length for tetrachloroethylene-filled samples. The results show that collimated launching and/or detection gives considerable improvements over wide-angle beam excitation and detection for lengths below about 300 m, but little above about 800 m. A degree of agreement is obtained with results for some theoretical models.     

Novel proof-tester for optical glass fibres

A compact novel proof-tester has been developed which strains the fibre by bending it over known diameter rollers. The proof-tester truncates the Weibull strength distribution at the expected level, indicating that it induces little damage in fibre with a thin primary coating.     

New primary coating method for optical fibres

A new primary coating method for optical fibres has been developed. A locally heated and softened thermoplastic tube, in which the fibre is passing through, is drawn to form a coating layer on the fibre. This method has large advantages in forming a precisely concentric coating layer and fabricating a strong fibre.     

High-precision moulded connector for single-mode optical fibres

High-precision moulded connectors for single-mode optical fibres have been developed using accurate electroformed cavities. The accuracy of moulded ferrules was greatly improved to less than 1 ?m by preparing a high-precision master and a strict moulding condition control. They had a low average connection loss of 0.48 dB and could be produced by a simple moulding process.