Splicing_Efficiency

Optical Communication EPM755 Course Work Submitted By Submitted To Muhammad Rafiqul Islam Prof. Tong Sun Msc Telecommunication and Network SEMS Student Number: 080036286 City University ………………………………………………………………………………………….. Contents 1. Introduction …………………………………………….…………….3 1. Fibre Splicing Technique ……………………………………………4 3.1 Fibre Splicing Loss …………………………………………………..5 3.1.1 Intrinsic parameter …………………………………………..5 3.1.2 Extrinsic parameter ………………………………………….5 1. Fibre splicing efficiency …………………………………….……….6 1. Reflection Loss at the End surface of fibres……………..….6 2. Offset Fibre …………………………………………………..6 3. Loss due to angular misalignment of a splice …………...…7 4. End separation of fibre ………………………………………7 5. Deformation of end surface fibre …………………………....8 6. Differences in fibre parameter ……………………………....8 Conclusion …………………………………………………………………………....8 Reference …………………………………………………………………………..…9 Optical Fibre Splicing Efficiency 1.1 Introduction: Communication may be broadly defined as the transfer of information from one point to another. When the information is to be conveyed over any distance a communication system is usually required. Different communication technology has been evolved for data transmission. In recent years amongst all other communication medium optical fibre has been regarded most efficient. [pic] Fig-1: Typical fibre optics Fibre optics has got rich history of its evolution. Optical communication is started at 1609 by Italian scientist Galileo, Galileian telescope [7]. Moreover as early as 1880 Alexander Graham Bell reported the transmission of speech using the light beam [2]. Optical communication is occupied with hitherto refinement. Optical fibre has been widely accepted because of its low loss, low dispersion and less susceptible to noise due to propagating through glass having special geometric properties which result high data rate. Different signal processing has been employed for efficient communication at both transmitter and receiver. But long distance wiring is remained a remarkable problem for all kind of guided medium. There are many occasions when the fibre optic splices are needed. One of the most common occurs when a fibre optic cable that is available is not sufficiently long for the required transmission run. In this case it is possible to splice two cables to make a permanent connection. As fibre optic cable are generally only manufactured in lengths up to five kilometres [8], when lengths of tens or hundreds kilometres are required, for example, then it is necessary to splice two lengths together. Fibre splicing is in simplest form a permanent joint formed between two individual optical fibres in the field or factory. Fibres when spliced suffer a splicing loss because they differ from each other in refractive index, physical properties and dimension and also because they offset, tilt and undergo end separation during splicing [3]. This phenomenon of splicing loss is not seen in copper conductor cables, but as for our fibre optics concern must not be forgotten. In this report we will concisely summarize different splicing techniques and respective loss as it is of secondary scope. But we will broadly evaluate fibre splicing loss and efficiency. Splicing is better efficient than demountable connection and coupling method of joining fibres is called termination. Fibre splicing typically results in lower light loss and back reflection than termination making it the preferred method when the cable runs are too long for a single length of fibre or when joining two different types of cable together, such as a 48-fiber cable to four 12-fiber cables. Splicing is also used to restore fibre optic cables when a buried cable is accidentally severed [1]. 2.1 Fibre Splicing Techniques There is extensive development of fibre splicing techniques in many countries, and various practical methods, apparatus and accessories for field splicing have been reported are in use. Optical fibre splicing requires the following condition [3]: 1. Field splicing can be done easily in short time. 2. Splicing loss is small 3. The splice is reproducible 4. The splice is sufficiently strong 5. Splicing is economical 6. The properties of splice are reliable and stable for long time 7. The length to be spliced is small and diameter of each fibre to be spliced is small. Splices may be divided into two broad categories depending upon the splicing technique utilized. These are fusion or welding and mechanical splicing. Fusion splicing is accomplished by applying localized heating e.g. flame or arc electric at the interface between two butted, prealigned fibre ends causing them to soften and fuse. Typical loss in fusion splicing is 0.1 dB. However prefusion technique gives 0.09 dB loss in multimode fibre. Fusion splicing of single mode fibre with typical core diameter between 5 and 10 micron gives 0.3dB loss due to self alignment phenomenon. [2] [pic] Fig-2: Fusion splice A possible drawback with fusion splicing is that the heat necessary to fuse the fibre may weaken the fibre in the vicinity of the splice. Mechanical splicing, in which the fibres are held in alignment by some mechanical means, may achieved by various methods including the use of tubes around the fibre ends i.e. tube splice or V-grooves into which the butted fibre are placed . Typical loss in mechanical splicing is 3dB. Amongst other mechanical splicing elastomeric splice and Springroove can be mentioned which is of 0.12dB and 0.25dB respectively. Latter one is more secured of being used a drop of epoxy resin. Mechanical splices has more cost per splices than fusion splice. As for the performance concern of each splicing method, the decision is often based on what industry you are working in. Fusion splicing produces lower loss and less back reflection than mechanical splicing, because the resulting fusion splice points are almost seamless. Fusion splices are used primarily with single mode fibre where as Mechanical splices work with both single and multi mode fibre. [1] Multiple simultaneous fusion splicing of an array of fibres in a ribbon cable has been demonstrated for both multimode and single mode fibres which has got remarkable performance. Splice losses using this technique with multimode graded index fibre range from 0.04dB to maximum 0.12dB where as for single mode fibre the loss range is 0.13dB to 0.4dB [2]. [pic] Fig-3: Mechanical splice All these techniques seek to optimize the splice performance though both fibre end preparation and alignment of the two joint fibres. The more precise you need the alignment (better alignment results in lower loss) the more you pay for the machine. 3.1 Fibre Splicing Loss Fibres when spliced are observed optical power loss at the splicing point of two ends of optical fibre because of its geometric properties. An Optical Time Domain Reflectometer (OTDR) can be used for splice loss measurement. A cable section-containing splices are normally shown as knees on the optical power loss OTDR graph [4]. As per the procedure (ANSI/TIA/EIA-455-8-2000), splice loss measurements with an OTDR must be conducted from both directions and averaged (by adding with signs) for accurate splice loss. Actual splice-loss is the measured splice-loss in both directions divided with two. [pic] The parameters, which control loss in any fibre joining method, can be classified as Intrinsic and Extrinsic parameters. 1. Intrinsic Parameters Intrinsic or fibre related parameters are determined when the fibre is manufactured and cannot be controlled by the individual doing splicing. Mode Field Diameter (MFD) is the most important intrinsic parameter. More splice loss can be observed for higher difference in MFD values. The MFD is a characteristic, which describes the mode field (cross-sectional area of light) travelling down a fibre at a given wavelength. When fibres with different MFD values are spliced together, a MFD mismatch occurs at splice point. With the help of the following formula splice loss due to MFD mismatch can be calculated from MFDs (in micron) of two fibres [4]. [pic] 3.1.2 Extrinsic Parameters Extrinsic, or splice process related parameters are those induced by splicing methods and procedures. Splice process parameters include lateral and angular alignment, contamination at the fibre end and core deformation due to un-optimized heating & pressing. These external parameters can be controlled/minimized by improving skill of the individual doing splicing and by automated fibre alignment and fusion cycles. It has been observed that splice loss between two identical fibres with same MFD and geometry parameters is as high as 0.04 dB. This excess loss is due to miss alignment and other splicing process parameters [4]. Other important extrinsic parameter is fibre end angle. Proper fibre end preparation is the most fundamental step to get acceptable splice loss. Generally end angle less than two degrees gives acceptable field splice loss. Further sections will be involved to explain efficiency with respect to equation. 4.1 Fibre Splicing Efficiency Fibre splicing efficiency is inspired by a number of sources. 1. Reflection Loss at the End surface of fibres 2. Offset of Fibre 3. Loss due to misalignment of a splice 4. End Separation of Fibre 5. Deformation of End Surface of Fibres 6. Differences in fibre parameters 4.1.1 Reflection Loss at the End surface of fibres When light travels through media having different refractive indexes it reflects and is refracted at the boundary of such media. If, between two fibres, there is a different type of medium, for example air, a loss is caused by the reflection between the boundaries of such media. Splicing efficiency of such media is expressed by [pic] Fig-4: End surface separation [pic] Where K=n1/n0 Eta= splicing efficiency n1= refractive index of medium 1 n0= refractive index of medium 0 If two fibres are not closely in contact with each other, and in absence of air layer between them then reflection loss of 0.32dB occurs. In order to get rid of it matching oil of nearly refractive index of fibres could be fused together directly. 4.1.2 Offset of Fibre Loss caused by the offsetting of fibres in the splice is called offset loss. Splicing efficiency of single mode fibre is defined by [pic] w=0.65+1.619/v^3/2 + 2.879/v^6 K=n1/n0; del=(n1-n2)/n1; V=2*pi*a*n1(sqrt(2del/lamda)) X=offset [pic] Fig-5: offset of fibre 4.1.3 Loss due to angular misalignment of a splice If the fibres are not perfectly parallel there will be increased losses due to difficulty in relaunching into the fibre. Even a slight angle results in a mismatch in NA. [pic] Fig-6: angle misalignment For single mode fibre: [pic] Where n=fibre index of refraction w(omega)=mode filed radius theta= angle of misalignment (0 is perfect, 90 is orthogonal) lamda=wavelength of light For multimode [pic] Where NA= numerical aperture 4.1.4 End Separation of Fibre When the gap of end separation fibre is s then splicing efficiency is [pic] [pic] Fig-7: End separation 4.1.5 Deformation of End Surface of Fibres Splice efficiency when end face is curving convexly for step index fibre [pic] [pic] Fig-8: end face convex 4.1.6 Differences in fibre parameters Splicing loss due to difference in fibre parameter is possible chiefly in following ways 1. Difference in core diameter 2. Difference in Numerical Aperture Conclusion Single mode fibres have small optical cores and hence small mode field diameter (MFD); they are less tolerant of misalignment at a joint. Mechanical splices capable of achieving acceptable performance, typical loss 0.05 to 0.2 dB, but somewhat expensive to purchase and time consuming to install. Splicing is of paramount importance for efficient data transmission. Apart from deploying efficient splicing technique some other useful mechanism has been fabricated which spontaneously exhibits efficient splicing performance. Gradient-index fibre lenses are used to fabricate high-strength (>100 kpsi) fusion splices between micro structured optical fibres. High coupling efficiencies are attainable (