Cleave engine

Abstract

The fibre optic cleaving system includes a cleave engine 30 which includes a sharp blade 40 for scratching a glass of a single or ribbon of multiple optical fibres. The cleave engine is located within

Description

Field of Invention: Optical fibers are widely used in the telecommunications industry to transmit light. Optical fibers are long strands of light-transmitting material. They may be made from silica, fluoride, chalcogenide or otherwise, their purpose being to transmit light without significant loss. They may be cylindrical or of other shape in cross-section. They may be solid in cross-section with one or more cores in which the light travels or they may incorporate holes to further enhance the transmission of light. They may be single mode or multimode. They may be single fiber or multiple fibers arranged in a ribbon. Typically, the fibers have a protective plastic overcoat. Their performance depends on the ability to inject and recover light from the ends of the long strand of glass. Light may enter or leave an optical fiber if the end face of the glass is smooth and well controlled, either perpendicular or angled to the axis of the fiber or fibers. The termination of the optical fiber must be accurately controlled so that light can pass through the end face between the glass of the fiber and the surrounding air or liquid. Glass is typically very hard and so virtually impossible to cut. To form a controlled end face to the fiber, it must be cleaved by initiating a starter scratch which is propagated across the face of the fiber by an applied or internal tension. Ribbon optical fiber is widely used, whereby 2 or more fibers are arranged together in a ribbon, held together and protected by a plastic sheath. The use of ribbons of 12-fibers or more dramatically increases the transmission capacity of the optical fiber cable and is therefore desirable. There is a need to join together two such ribbons, using a ribbon fusion splicer or ribbon fiber connector. In addition, optical fiber can be pigtailed to waveguides in photonic devices made up of many parallel channels. In all of these applications the ends of the fibers in the ribbon should be smooth at a controlled angle and this is conveniently achieved by cleaving. Object of Invention: The object of this invention is effectively and economically to terminate an opticalfiber or fibers to facilitate the passage of light through the end of the fiber or fibers or to allow the joining of two or more optical fibers, either by fusing or butt-coupling. The fibers may be made of silica glass or other material which may be amorphous or crystalline. Termination of the opticalfiber or fibers may be achieved by cleaving the glass of the optical fiber, using a sharp blade edge to scratch the surface of the fiber and applied stress to the fiber to propagate the scratch across the fiber as a cleave, with the stress applied either before or after scratching of the fiber. The cleaved fiber end or ends should be mirror-smooth over the core of the fiber to facilitate the passage of light therethrough. The end of the fiber may be substantially perpendicular or it may be angled to prevent any optical back-reflections from the cleaved face from propagating back down the fiber. The object of the invention is to cleave the fiber or fibers using a tool and method which uses an accurate arrangement of the scratching blade edge, along with the required clamping of the fiber, use of an anvil to bend the fiber, edges over which the fiber is bent by the anvil and optionally stretching and / or twisting. This is achieved by incorporating most or all of these accurate arrangements within a cleave engine which can be easily manufactured and easily placed within a cleave system without the need for extreme accuracy in the manufacture of the rest of the cleave system. Summary of Invention: The optical fiber or fibers are located and clamped in a chassis of a cleaving system which includes provision of a top plane in the cleave system. The fiber or fibers may be located and / or clamped on to the top plane of the chassis at two locations, or otherwise clamped to prevent further movement of the fiber or fibers. The cleave system contains a cleave engine. The cleave engine contains a sharp blade assembly which is accurately positioned with respect to the fibers. The blade assembly may be a single part consisting of a sharp blade or may consist of a sharp blade with supports to support, mount and / or manipulate the sharp blade. The sharp blade may be attached to a support to reinforce the blade and to make its handling easier. The cleaving system may also contain an anvil which moves to bend the clamped fiber or fibers over one or more edges to contact the sharp blade edge, so scratching the fibers. The anvil may have one or more contact points which cause the fiber(s) to bend down over the edges to contact the blade edge. The fibers cleave under the influence of the stresses present within the fiber arising from their bending and, optionally, the presence of applied tensile and / or twisting forces. One or both of the edges may be located within the cleave engine or both may be located within the chassis of the cleave system or one edge may be located in the cleave engine and the other edge may be located in the chassis of the cleave system. By accurate control of the relative positioning of the bending edges, blade edge, anvil and any optional tensile and / or twisting forces, the smoothness and angle of the cleaved end may be controlled. The relative positioning of these constituent elements may be achieved by accurate machining of the cleave engine and the cleave system. To prepare a cleave, the distal ends of the fiber or fibers are stripped of their plastic coating to expose the glass of the optical fiber, which is typically made of silica and may be round or otherwise. Generally, the plastic sheath around the fiber or fibers must be removed to expose the glass of the fibers so that they may be scratched with a sharp blade edge, leading to cleaving of the fibers, the sheath often being removed by using a thermal stripper to heat and then strip the plastic sheath. The fibers cannot simply be cut because the silica is very hard, instead they must be scratched with a sharp blade edge and pulled, bent and / or twisted in order to propagate the scratch as a cleave across the fiber or fibers. With proper control of the tension, bending and / or twisting, the resultant cleaved end may be mirror-smooth over the core of the fiber and formed at a controlled angle, facilitating the entrance or exit of light into or out of the optical fiber. Typically, cleaving is achieved by a combination of stretching, bending and / or twisting the clamped fiber or fibers and scratching the fibers with a sharp blade to cause a starter crack which is propagated across the fiber by the internal stresses which have been imposed on the fiber or fibers by stretching, bending and / or twisting to cause the fiber or fibers to cleave. The fiber may be stressed before scratching or vice-versa. In order to maintain the applied internal stress during the cleave, the fibers are typically clamped at two locations, either directly on to the top plane of the chassis or surface or the fibers are placed in a holder which is subsequently fixed to the cleave system and its top plane or surface. The fiber holder both may position and clamp the fibers. If the holder securely clamps the fibers at the proximal end of the fibers, and the holder is securely fixed to or is part of the cleave system, only one further clamp on the distal end of the fiber may be required. The cleave is achieved by propagating a starter crack across the cross-section of the fiber or fibers by the application of an applied stress to the fibers which causes an internal stress in the fibers. The external applied stress may be brought about by a combination of bending, stretching and / or twisting. The fibers may be scratched first to create a starter crack, followed by application of the applied stresses to cause the cleave. Conversely, the clamped fibers may be first stretched, bent and / or twisted to establish the internal stresses and then scratched so that the internal stress propagates the crack, causing the fiber to cleave. The latter technique is preferred. If the fibers are pre-stressed prior to scratching, the fibers cleave as soon as the starter crack reaches a critical depth, typically 2-3microns deep, and the cleave is well controlled. However, if the fibers are scratched prior to the application of stress, the starter scratch is not well controlled and may be as deep as 20microns or as shallow as 1 micron or less. Consequently, the stress required to initiate the cleave varies, leading to inconsistent cleaving. The quality of the end face will be variable, leading to the appearance of roughness / ”hackle”, uncontrolled fiber end angles and large cracks on the end face originating from the scratch location. If too much stress is present in the fiber during cleaving, some of the cleaved surface may be rough with the appearance of “hackle”; if this roughness penetrates the core of the fiber, the light transmission through the fiber end will be degraded. If too little stress is present in the fiber, the depth of the crack required for the fiber to cleave is large and unwanted cracks, “halfpenny” cracks and other distortions may occur. A stress of approximately 40MNewtons / meter2 is optimal in cleaving silica fiber. It should be noted that the action of the sharp blade scratching the fibers will be resisted by the hardness of the fiber. This can damage the blade edge and change the profile of the stress within the fibers. The fibers being so scratched have a natural tendency to retreat under the action of the cutting force, hence bending the fiber inwards which has the effect of compressing the fiber locally in the region of the cutting force, making it more difficult for the blade edge to penetrate the skin of the glass to the required depth of 2-3microns under the application of 40MNewtons / meter2 of force. To counteract this tendency, the fiber can purposely locally be bent outwards towards the blade edge. Therefore, preferentially, the anvil should introduce a bend in the fiber or fibers such that the skin of the fiber in the location where the blade is scratching the fibers is under tension (due to the bending induced by the anvil) so that the blade edge can easily penetrate the skin of the fiber without introducing a local reverse bending, i.e. so that, as it is being scratched, the glass of the fiber locally peels away from the blade edge rather than closing onto the blade edge and so impeding further progress of the blade edge into the fiber to achieve the required crack depth. In order to achieve sufficient local bending of the fiber to resist the intrusion of the blade edge, and so achieve the required starter crack depth, the anvil may act close to the point of the blade edge; typically for 125micron diameter silica glass fiber, the anvil should act within 2millimeter or less from the sharp edge of the blade. Alternatively, a blade which is quickly vibrating perpendicular to the axis of the fiber or fibers may be incorporated within the cleave engine; the mounting of the vibrating blade may be fixed hence satisfying the requirement to have a reliably positioned blade. When the starter crack has reaches a critical value, the fiber will cleave with the cleave travelling at close to the speed of sound in glass (5,600m / second), with the cleave completing its passage across the fiber in 0.02microseconds. Thus, once the crack has reached a critical depth, the cleave occurs without further influence of the anvil. The starter crack should reach a critical depth as fast as possible so that the fiber does not have time to move before the blade has achieved a scratch of the required depth and so prevent unwanted stresses building up before the scratch propagates as a cleave. In this invention, we use an anvil which falls under gravity, achieving a blade velocity of 1.41 m / second after a fall of 10cm, which will create a starter crack with the 2micron critical crack depth within 1.41 microseconds, so leading to cleaving of the fiber. Previously, an ultrasonic vibrating blade has been used to create a fastmoving blade - see for example Fellows &Channon US4790465. The vibrating blade has a sinusoidal motion which is close to its maximum amplitude for approximately 1 / 5th of its cycle, i.e. equivalent to a time of 5microseconds for a blade oscillating at 50kHz. It can be seen that this invention using a falling anvil creates a scratching motion which may be faster than an ultrasonically vibrating blade and so will give a superior cleave. In order to apply stress to the fibers, the fibers may be tensioned by applying a stretching force to the clamped fibers, for instance by moving apart the clamping points. The fibers may also be stretched by displacing the fiber perpendicular to the plane of the fiber ribbon acting between the clamping points; this displacement being in addition to the bending effected by the anvil acting close to the cleave engine. The fibers may also be twisted (to achieve an angled cleaved end) by twisting one clamping point relative to the other, or by rolling the fibers with both ends clamped. It should also be noted that tension may be induced in the fiber or fibers by control of the material and shaping of the contact points of the anvil. The shape of the end of the anvil may be intentionally or unintentionally shaped so the contact point(s) of the anvil contact the fiber(s) over an extended distance LL1 (see Fig. 11c) of up to 20mm or more parallel to the axis of the fiber(s). Because the anvil contacts the fiber over such an extended distance, as well as bending the fiber, the anvil will stretch the fiber(s), so tensioning them. Thus, the radius of curvature of the contact surface of the anvil may have a larger radius of curvature than the radius of curvature of each fiber or fibers if they were displaced at a single contact point, and where the radius of curvature of the contact surface of the anvil has a radius small enough so that the fiber(s) maintain contact with the contact surface of the anvil over a substantially length exceeding 10Omicrons. Similarly, if the end of the anvil is compliant, e.g. by the use of a rubber end with one ortwo contact points, the fiber(s) will be contacted by the compliant anvil contact surface over an extended distance, so stretching them and applying a tensile stress. Thus, the contact surface of the anvil may have a hardness such that the fiber(s) have a radius of curvature larger than the radius of curvature of each fiber or fibers if they were displaced at a single contact point by hard anvil. The Shore hardness of the compliant surface may have a value between 30Shore A and 90Shore A and preferably between 50Shore A and 80Shore A. The cleaved fiber ends may be cleaved perpendicular to the axis of the fibers - and this is useful for fusion or mechanical spicing of fibers when joining two fibers together. Perpendicular cleaving is achieved by establishing an internal stress in the fibers which is substantially parallel to the optic axis of the fiber, either by pulling or by bending symmetrically, followed by or preceded by scratching of the optical fiber or fibers. Perpendicular cleaves arising from symmetric bending may be achieved in a 4-point bending arrangement, whereby a two-armed anvil contacts the fibers at two points, with the scratching blade edge positioned between and approximately equidistant between the two contact points of the anvil. Because approximately 4% of incident light is reflected from an air-glass surface due to the difference of refractive index of air and silica, in those applications where the back-reflection of light traveling in the fiber, or of light being injected into the ribbon, is deleterious to the performance of the optical system, for instance when pigtailing fibers to photonic devices, if the core of the fiber end (in which the light is travelling) is angled at about 8 degrees away from the perpendicular, the back-reflected light is directed out of the optical fiber. Angled cleaving may be achieved when the internal stresses in the fiber are non-axial and this is achieved either by twisting the optical fiber and / or by bending the fiber asymmetrically at the point of contact with the sharp blade. Non-symmetric bending is especially effective in angle cleaving a ribbon optical fiber because each fiber in the ribbon is substantially equally bent and so experiences substantially equal asymmetric internal stresses and so each fiber in the ribbon angle cleaves in the same way when scratched by the blade. Thus, an anvil with a single contact point may push down on the fibers, whereby the contact point is offset from the point of contact of the blade, angle cleaving may be achieved; see for example Murgatroyd, US8,069,691. An alternative way of producing an angled cleave is known by applying a twisting force to the optical fiber before cleaving (see Fellowes and Channon US4790465). Symmetrically bending of a clamped fiber (and optionally applying tension) will lead to a perpendicular cleave, as above. However, if the fiber is also twisted, an angled cleave will be achieved. Approximately 3° of twist per mm of clamp separation will lead to a cleaved end angled at about 8° away from perpendicular over the fiber core. Angle cleaving a ribbon fiber by twisting each fiber using a rolling motion is also known, see for example Mansfield et al. US5,842,622, but is not well controlled because the twisted fibers tend to slip and rotate in the clamps, losing the internal stress arising from twisting, leading to an inconsistent or low end angle. It should be noted that the orientation of the angling of the end of the fiber compared to the scratch position is rotated by 90° for these two different methods of angle cleaving optical fiber. When the fiber is bent asymmetrically to obtain an angled cleave, the plane containing the originating scratch arising from the blade strike is parallel to the plane containing the maximum angling of the end face. The cleaved end face is curved but controlled, with the core of the fiber at 8° from perpendicular; in addition, the centre of the fiber is dish-shaped. The portion of the cleaved end near the scratch is close to perpendicular so that the cleaved end has a blunt nose. The blunt nose is efficacious in butt-coupling a fiber or fiber ribbons against a stop or against a photonic waveguide. In contrast, an angled cleaved end arising from twisting the fiber is saddle-shaped with the longest portion of the angle cleaved end at 90° from the scratch point. This sharp end to the fiber is potentially fragile and not optimal for butt-coupling to other photonic components. It can be seen that asymmetrically bending the fiber to produce an angled end is suitable for angle cleaving ribbon fiber because all fibers can be bent in the same way and so they will cleave with the same angle. Conversely, it is difficult to angle cleave a ribbon fiber by twisting because each fiber in the ribbon would have to be both twisted in the same way and by struck by the blade at the same instant. It is also understood that it is possible to cleave the fiber or fibers without removing the protective plastic coating. Provided the glass within the coating experiences the applied stresses, if the glass of the fiber can be scratched through the coating, the underlying glass fiber will cleave because nearly all of the stresses applied to the fiber and its coating are taken up by the glass rather than the plastic coating which is relatively far softer than the glass of the fibers. In order to scratch the glass through the coating, the sharp blade edge must be caused to penetrate through the coating which is typically 62.5microns thick for a 250micron diameter coating around a 125micron diameter single glass fiber. Other fiber types have thinner coatings, such as polyimide-coated fiber, in which the coating is only 10-20microns thick. In order for the blade to penetrate any of the above coatings, the fiber should be bent by the anvil to prevent inward bending of the fiber under the influence of the cutting force. Care must be taken not to impart any sideways force to the blade, where for example a diamond blade might be twisted and so be shattered. The glass of the optical fiber or fibers may be clamped directly on to the stripped glass at one or both of the clamp points or the fiber or fibers may be clamped through the plastic coating existing or remaining around the fiber. Optionally, the clamped fibers may be tensioned and / or twisted by a stretching and / or twisting mechanism in order to impart internal stresses to the clamped fibers in addition to the stress arising from the bending. The proximal, working side of the fiber, typically retains its protective plastic coating, so preferentially the fiber should be clamped through its coating on its proximal side. This reduces possible damage to the fiber arising from the clamping. Clamping on the coating is often effective in clamping and immobilising the underlying glass of the fiber so that applied stresses can be transferred to the glass, provided the coating is adhered to the glass fiber; in cases where the coating is loosely arranged around the glass of the fiber, it is often preferable to clamp directly on to the stripped glass on the proximal and / or distal ands of the fiber or fibers. The cleaved distal offcut end of the fiber is disposed of and so any damage incurred by clamping on the stripped glass is not important and so often the distal end of the fiber may be hard clamped; the glass of the fiber is thus immobilised at two points so that it may be stressed as desired and scratched therebetween to create a cleave. The fiber or fibers may be clamped at two or more positions to prevent movement or unintended release of applied stresses during their subsequent stretching, bending and / or twisting. The fibers may be clamped with hard clamps, preventing all movement, or with compliant or elastic or semi-elastic clamps such that any movement of the fibers is insignificant during cleaving; the fibers may be partially clamped so that there is at least some resistance to their moving along their axis or rotating during the cleaving process so that at least some of the applied stresses are maintained within the fibers. The fibers may be clamped or partially clamped onto a plane or grooved surface or they may be clamped or partially clamped in a holding apparatus, such as a holder, which is fixed to or located in the chassis of the cleaver. When cleaving ribbon fiber it is important that all of the fibers in the ribbon are clamped at 2 points so that all of the fibers in the ribbon may be stressed equally and hence all of the fibers in the ribbon cleave underthe same conditions of stress; consistent and equal clamping and consistent and equal stressing for all fibers will lead to repeatable and controlled cleaving of all fibers in the ribbon. The fibers may be clamped at two points by clamping on to the stripped glass on either side of the cleaving engine. Alternatively, the proximal end of the fibers may be clamped through their coating and the distal end of the fibers may be clamped on the stripped portion of the fiber. The distal end of the fibers may be clamped through their coating if the fiber or fibers are window stripped - i.e. the part of the fiber which is to be scratched is exposed but coating remains on either side of the fiber. Single fiber may be window stripped with conventional wire strippers, removing only a small window of coating. Ribbon fiber may also be window stripped if the ribbon coating or matrix remains on the ribbon fibers on either side of the scratch point. If a glove of coating can be maintained on the offcut side of the fiber, the offcut clamp may easily clamp the coating glove and therefore achieve clamping on all of the fibers in the ribbon and consequently all of the fibers in the ribbon are clamped and so all of the fibers in the ribbon may maintain an equal amount of applied stress, as required for cleaving. Window stripping of single r ribbon fibers may be achieved by laser ablation or by chemical means, for instance using paint stripper or similar chemicals. Window stripping of a ribbon fiber may also be achieved by heating the ribbon and its plastic matrix in a thermal stripper, using for instance the JR6+ made by Sumitomo Electric, Tokyo, Japan, to a temperature of about 90°C so that the protective plastic matrix softens and the bond between the glass of the fibers and the plastic outer coating is initially broken. Cutting through the coating (without damaging the underlying glass) allows a glove of plastic coating to be slid along the fiber in the distal direction by a distance of approximately 1-50mm. Removing the ribbon from the heater allows the bond between the plastic glove and the underlying glass to reform so that the distal side of all of the fibers are fully bonded to the plastic glove. Clamping the distal end of the fibers through the glove is therefore effective in equally clamping the distal ends of all of the fibers in the ribbon. The fibers are then clamped and the exposed section of glass between the proximal coating and the distal coating glove is then bent, stretched and / or twisted and then scratched to form a cleave. Window stripping ribbon fiber is especially beneficial because the offcut fibers are still contained within the coating glove and can easily be disposed of. In this invention, a method of tensioning all of the fibers in a ribbon is achieved by applying a stretching force to the entire fiber ribbon, simultaneously stretching each fiber within the ribbon. However, the mechanism may be arranged so that the fibers cleave substantially simultaneously so that all of the fibers experience the same tension when they cleave. If one or more fibers in the ribbon is late in cleaving, this late-cleaving fiber will suffer the entire stretching force applied to the ribbon, leading to excess tension and so poor cleave quality in this final fiber. The use of a fast-moving anvil, as described in this invention, for instance an anvil falling under gravity, is effective in cleaving all fibers in a ribbon with substantially equal individual tensions. If the anvil is moving at 1.4m / second, after a fall of 10cm, the fibers are scratched within a few microseconds and, because the mechanical tensioning system will not react fast enough to change the tension on any remaining uncleaved fibers, the early-cleaving fibers in the ribbon will experience the same stretch (and therefore the same tension) as the later-cleaving fibers in the ribbon. It is understood that there are other methods for applying tension to a fiber ribbon, for instance by displacing the clamped fibers at a point between the clamping points; each fiber may be displaced perpendicular to the plane of the ribbon so stretching each fiber and so applying the same tension to each fiber in the ribbon. This displacement-to-cause-tension may be separate and in addition to the bending caused by the anvil which pushes the fibers on to the sharp blade edge to cause them to cleave, or this displacement-to-cause-tension may be achieved as part of the motion of the anvil as it pushes the fibers on to the sharp blade edge to cause cleaving. Equally, equal stretching of the clamped fibers may be achieved by displacing one or both of the clamps in a direction perpendicular to the plane of the fiber ribbon. In all these cases, there is therefore a need to prepare the glass ends of the optical fiber to allow easy fusion splicing or pigtailing. This is easily and cheaply done by mechanical cleaving, as opposed to using laser cleaving which delivers poor end-face quality and requires expensive capital equipment, for example see patent application US20210373239. In the case of cleaving ribbon fiber, for the application of pigtailing fibers to waveguides in photonic devices, the cleaved end faces of each fiber in the ribbon must be identical, arranged at a pre-determined angle to the optical axis and cleaved so that all of the fibers have substantially the same length to within 10 microns. This invention provides a method and tool to accomplish this accurate control of end face quality, end angle and length for a single fiber and ribbon fibers. The first embodiment of this invention describes a cleave system which is made up of a cleaver chassis in which is located a cleave engine which contains a sharp blade. The cleave system includes a means to locate, guide and clamp the optical fiber or fibers in two or more locations, therebetween being two edges, which may be hard, non-hard or compliant. The cleave system may include an anvil which acts to bend the fiber(s) over the edges to contact and cause the fibers to be scratched by the blade. Furthermore, outwith the clamp locations, the cleave system optionally may include a mechanism to stretch the clamped fibers and / or optionally may include a mechanism to twist the clamped fibers. The sharp blade edge may be polished crystal such as diamond, a sharp metal edge (which may be ground and polished in a linear, circular or other shape) or a ceramic blade edge or other forms making up a hard, sharp edge. The edges may be close to the sharp blade edge, within a distance of less than or equal to 20 times the fiber diameter, or they maybe more distant from the blade edge by a distance of more than 20 times the fiber diameter. The edges may be hard or they may be compliant or of intermediate hardness, but always act to impose a change in the bending of the fiber close to the edges. The two edges may be contained within the cleave engine or they may be present in the chassis of the cleave system or one edge may be within the cleave engine and the other edge may be formed in the chassis of the cleave system. The anvil may be configured so that it may be applied to displace the clamped fibers away from their optic axes, bending them over the edges such that the fibers come into contact with the blade edge contained within the cleaving engine, causing the fibers to cleave. The cleave engine containing the blade may be fixed within the chassis of the cleave system so that the fibers are bent down on to the blade by the anvil. Alternatively, the cleave engine may be movable so that it may be moved to contact the fibers which have been previously stressed. Alternatively, both the fibers and the cleave engine may both move towards each other. The cleaving engine may consist of a sharp blade for scratching the fibers. The sharp blade may be supported by a support which acts to strengthen the blade and make it easier to position. The cleave engine optionally may contain two edges overwhich the fibers are bent by the action of the anvil such that the bent fibers come into contact with the sharp blade edge, causing them to cleave. The cleave engine optionally may contain only one edge or optionally no edges, in which case the edge or edges may be located elsewhere within the cleave system, for instance by accurate machining of the chassis or the positioning of dowels in the chassis of the cleave system. The edges are always located between the clamping points. The blade may be fixed in position and orientation so that the fibers come in to contact with it by action of the anvil such that the motion of the anvil, and any optional stretching and twisting of the fibers, establishes a stress in the fibers prior to their contact with the blade edge. Alternatively, the blade and the cleave engine may be movable so that the blade edge comes in to contact with the fibers which have been previously stressed by clamping, bending, stretching and / or twisting, so scratching and causing them to cleave. The positioning of the blade edge (in the direction parallel to the axes of the fibers) relative to the edges and relative to the position of the contact point(s) of the anvil may be precisely controlled. The height of the blade edge, i.e. in the distance between the clamped fibers and the blade edge in the direction perpendicular to the axes of the fibers, may also be accurately controlled so that the distance the fibers are deflected before contact with the blade edge may be precisely controlled. The lateral positioning of the blade edge in the direction parallel to the axes of the fibers may also be controlled and the relative lateral position of the edges, blade edge and contact point(s) of the anvil may also be controlled. This lateral and height control may be established by accurate machining, moulding or otherwise of the component parts of the cleave system and the cleave engine. As well as its position, the orientation of the blade edge, and any optional motion of the blade, is accurately controlled with respect both to the optic axes of the fibers and with respect to the direction along the length of the blade and / or the motion of the blade, if any. The relative position of the blade edge and the contact points of the anvil in a direction parallel to the fiber axes is important in controlling the characteristics of the resultant cleave. The position of the anvil may be set by mounting the anvil against a first reference position or surface in the chassis of the cleave system and similarly, mounting the blade and its blade edge against the same reference position or surface; alternatively, the blade may be mounted against a second reference position or surface which is controlled relative to the first reference surface. The relative positions of the blade edge, bending edges and contact point(s) of the anvil may be fixed. Optionally, the relative positions of the blade edge, bending edges and anvil may be settable or user adjustable to optimise the cleave for different fiber diameters and types or to set up the cleave system. The edge or edges may be movable in height (relative to the blade edge) or in lateral position (in a direction parallel to the optic axis of the fibers). The point of contact of the anvil may be movable laterally relative to the position of the blade edge and the bending edges. The positioning of the blade edge, in height and lateral position, the lateral positioning of the anvil and the lateral positioning and height of the edges may be optimised by adjusting their relative positions within the cleave mechanism. In the case of a fixed blade, the blade may be movable along its length to expose unused regions of the cutting blade edge. In the case of a moving blade, the blade may be rotated or translated to expose an unused region of the cutting edge. Assuming that the stretching and twisting of the fibers is accurately and independently controlled within the cleaver, the control of the internal stress prior to cleaving is therefore largely controlled by the pre-set positioning of the blade edge, bending edges and anvil contact point(s). The appropriate value of these dimensions is dependent on the diameter and material of the fiber and can be changed by replacing the cleave engine, edges and / or anvil for a cleave engine optimised for different fiber diameters and types. Alternatively, the positioning of the blade edge, in height and lateral position, the lateral positioning of the anvil and the lateral positioning and height of the edges may be optimised for particular fiber diameters and fiber types by adjusting their relative positions within the cleave mechanism. The blade may be fixed so that it scratches the fibers as the anvil bends the fibers downwards. A fixed blade is advantageous because it is easily and reliably positioned relative to the pre-stressed fibers so that the fibers are bent by a predetermined distance before cleaving. If the two edges over which the fibers are bent are properly positioned, defined by their height relative to each other, their height above the blade edge, the separation of the edges, the location of the blade edge and the position of the contact points of the anvil, the edges may induce a symmetric bend in the fiber or fibers; in the event of symmetric bending induced within the fibers, subsequent scratching of the bent fiber will lead to a substantially perpendicular cleave. However, due to the requirement of resisting the scratching force of the blade, localised bending of the fibers by the anvil may be used to induce a further bending stress in the fibers and this stress must also be symmetric within the fibers. Symmetrical bending of the fiber or fibers may be achieved by establishing a 4-point bending geometry, consisting of the two edges and a two-armed anvil, whereby the two bending points of the anvil are laterally offset on either side of the contact point of the blade edge, with the contact points of the anvil on the fiber closely offset from the contact point of the blade edge. If no twist is present in the fiber or fibers, in the case where symmetrical stresses are set up in the fiber, a substantially perpendicular cleave is achieved. If the fibers are intentionally (or unintentionally) twisted before or after clamping, but before cleaving, a helical angled cleave is achieved. The bending edges may be hard, as defined by machined edges, dowels, etc., or they may be semi-hard or they may be compliant. The function of the bending edges is to impose a curvature on the fiber or fibers at two or more positions. Therefore, a soft edge will also suffice to act as a bending edge. It is also understood that the bending edges may be incorporated into the structure of the clamping means or may be part of the clamping means. For instance, rubber pads may be used to clamp the fiber(s) and the edge of these rubber pads may act as the bending edge or edges. It is also understood that the edges over which the fibers are bent may be located at a substantial distance from the cleave engine of 20 fiber diameters or more. These edges may be machined, or dowels or similar or the edges may be soft-edged, such as a rubber pad. It should be understood that the function of such a hard or soft edge is to change the curvature of the fibers when the fibers pass over the edges. An angled cleave may alternatively be achieved by non-symmetric stressing of the fibers prior to cleaving. This is easily achieved by using an anvil which has only one point of contact, closely laterally offset from the point of contact of the blade edge by a small distance so that the scratching force of the blade is resisted by the localised bending of the fiber; typically for 125micron diameter, the point of contact of the anvil should be 1 millimeter or less laterally offset from the blade edge, see for example Murgatroyd US8.069,691. Because a one-armed anvil induces a non-symmetric internal stress in the fibers, the fibers cleave non-symmetrically with a curved but controlled end face which is angled with respect to the optical axis, substantially eliminating any optical back-reflection. Single mode fiber has a relatively small core in which the light travels and so reduction of back-reflection only requires angling of the core of the fiber at 8 degrees away from the perpendicular. The curved end face meets the requirement of angling the core of the fiber and so reduces back-reflection. The fiber may also be twisted in addition to bending to create both a bending and a twisting stress, in addition to an optional applied tensile stress, to create an angled cleave. The cleaving engine may incorporate edges which are machined into the structure of the cleave engine or may be dowels positioned within the cleaving engine over which the fibers bend, or the edges may be otherwise constructed. Alternatively, one or both of the edges may be located away from the cleaving engine and achieved by machining, doweling or otherwise constructing an edge or edges as part of the chassis of the cleave system. The cleaving engine consists of a sharp blade edge which is positioned or moves at a well-defined distance and height from the edges over which the fibers are bent. The blade may be replaceable and / or movable. The cleave engine may be replaceable and / or movable. In a further embodiment of this invention, the cleave engine comprises a fixed blade which is securely fastened to the chassis of the cleave system. The blade is of the form of a polished blade edge. The blade may be a diamond single crystal whose edge is crystallographically oriented. The blade edge may be 3.5mm long, or longer or shorter. The diamond crystal may be brazed to a supporting metal shank which has a cuboid shape and this blade assembly is then ground and polished to form a sharp edge on the diamond. The resultant polished diamond edge may be parallel to the long face of the cuboid shank. The long face of the shank may be fastened to a flat face in the cleave chassis, using a screw, by gluing or otherwise, such that the face of the shank, and therefore the polished edge of the blade, is exactly perpendicular to the optic axis of the fiber or fibers. Consequently, when a ribbon fiber is cleaved, the length of each fiber in the ribbon is exactly equal because the blade edge is exactly perpendicular to the axes of the fibers. The side face of the shank, i.e. the face which is perpendicular to the blade edge, is pushed against and secured to a second face in the cleaver chassis which is machined to be parallel to the optic axes of the fibers and perpendicular to the plane of the fiber ribbon. Consequently, when cleaving ribbon fiber, the polished diamond edge is parallel to the plane of the fiber ribbon because the side face of the shank is perpendicular to the blade edge and so each fiber in the ribbon is at the same height from the diamond edge and so each fiber in the ribbon undergoes substantially the same bending stress. The bottom face of the shank, i.e. that face of the shank which is parallel to the plane containing the polished edge, is arranged in the cleaver chassis so that the blade edge is at a pre-determined height below the clamped fibers. Therefore, when the anvil deflects the fibers to cause contact with the blade edge, all fibers in the ribbon are bent by the same distance and so suffer the same pre-determined stress. Provided that the blade is manufactured so that its length is accurately controlled, i.e. the distance between the bottom of the shank and the blade edge is known and measured, the position of the bottom face of the shank can be adjusted, for instance by means of a setting screw or a fixed face or fixed dowel positioned in the cleaver chassis, so that the blade edge may be adjusted to a pre-determined distance below the clamped fibers. In this embodiment, the edges over which the fiber bends may be incorporated into the chassis of the cleave system. In a further embodiment of the invention, the cleave engine may include one edge as well as the blade, with the second edge incorporated into the chassis of the cleave system. In yet a further embodiment, the cleave engine may incorporate two edges as well as the blade and its blade edge. In these embodiments, the cleave engine may be manufactured with a body which contains fixing means for the blade and accurately defined bending edge or edges. The edges may be defined by the presence of dowels located in the body of the cleave engine or they may be defined by accurate machining of the body of the cleave engine. The shank and the diamond edge are secured in the body of the cleave engine, with the long face of the shank secured against a machined face in the body so that the edge of the blade is perpendicular to the optic axis of the fibers. The shank and its diamond edge are also secured in the body of the cleave engine, with another face of the shank flush with a machined face in the body so that the diamond edge is parallel to the plane of the fiber ribbon. The height of the diamond edge in the cleave engine body is also well defined, either by using a screw or by mounting the bottom face of the shank against a machined edge or dowel or otherwise in the cleave engine body. Consequently, each fiber in a ribbon is at substantially the same height above the diamond edge. The body of the cleaving engine may be accurately mounted in the chassis of the cleave system. The body of the cleave engine is mounted in the chassis so that the edge of the blade is perpendicular to the axes of the fibers and the edge is parallel to the plane of the fibers. Optionally, when the blade edge is blunted, the cleave engine body may be movable in a direction parallel to the blade edge within the cleave system chassis so as to allow an unused portion of the blade edge to scratch the fibers, this movement not to change the height or orientation of the blade edge with respect to the fibers. Optionally, the cleave engine body may be mounted in the cleave system chassis using dowel(s), bearings or other supports to allow this movement parallel to the blade edge. In a further embodiment of the invention, the cleave system may incorporate a cleave engine with its sharp blade, and optional edge or edges, whereby the fibers are clamped, and optionally stretched and / or twisted, and are bent down by an anvil by a predetermined distance to impose internal stresses in the fibers. The cleave engine is then moved so that the sharp blade edge contacts the pre-stressed fibers, scratching each of them, causing them to cleave due to the internal stresses already present in each fiber. The cleave engine may contain a blade which is substantially made up of a straight edge, such as a polished diamond edge, and preferentially the blade edge contacts all fibers in the ribbon at substantially the same time. Preferentially the cleave engine and the blade may move perpendicular to the fiber ribbon. Alternatively, the blade may comprise of a blade made of metal, ceramic or crystal or polycrystal with a polished edge. The blade may be round or straight or of an alternative shape. The cleave engine with its blade may mounted at the correct height so that it may be moved parallel to the plane of the ribbon so that it scratches each fiber in turn, causingthem to cleave. The cleaving engine should be easily and accurately manufactured with tight tolerances so that there is no requirement for subsequent setting-up of the cleaver. The accuracy of the mechanical system of the cleave engine and hence the control over the cleave properties of the fiber is achieved by accurate manufacture of the cleave engine, implying that the other functions of the cleaver may be made with less accuracy, leading to improved control of the cleave and reduced cost of the cleaver. Furthermore, the cleave engine may be easily mountable and dismountable from the rest of the cleaver to facilitate changing or advancing the blade or replacement of the cleave engine with a different engine designed for cleaving fiber of a different diameter or material. The cleave system may incorporate a mechanism which collects the offcut potions of the fiber or fibers. We will now describe the invention with reference to drawings and a detailed description of one embodiment of the invention. DRAWINGS We will now describe the details of embodiments of this invention with the aid of the following drawings: Fig. 1a shows an isometric view of a stripped ribbon fiber 1 (shown as 4 fibers for clarity) clamped to a top plane of a chassis with an anvil which falls under gravity Fig. 1b shows a top view of stripped fiber ribbon 101. In the case of a stripped single fiber 1, the fiber may be aligned by posts 12a, 12b and 13a, 13b so that it passes over the cleaving engine 30. Fig. 2a shows a top view of an anvil, with optional compliant clamps 9a, 9b, bending the fiber on to a sharp blade edge 41 to give a cleave Fig. 2b shows a side view of a two-armed anvil 51, with optional compliant clamps 9a, 9b, bending the fiber on to a sharp blade edge 41 to give a perpendicular cleave Fig. 2c shows a side view of a one-armed anvil 52, with optional compliant clamps 9a, 9b, bending the fiber(s) on to a sharp blade edge 41 to give an angled cleave Fig. 2d shows the lug 97 of a one-armed anvil 52 being pressed against a reference surface WW. Fig. 3a shows the cleave engine 30, with a blade assembly 40 and a sharp edge 41, and 2 edges 21,22 which have been machined into the cleave engine Fig. 3b shows the cleave engine 30, with a blade assembly 40 and a sharp edge 41, and 2 edges which are formed by two dowels 23, 24 which are positioned in the cleave engine by accurate machining Fig. 4a and Fig. 4b showed a polished sharp blade edge 41 made by brazing 49 a diamond 43 on to a cuboid metal shank 42 Fig. 4c shows a L-shaped support 91 attached to the shank 42 of the blade assembly 40 Fig. 4d shows a top view of the blade 40 on top of the shank 42 where the shank has a bevelled edge 451 (shown dashed) Fig. 5a shows an isometric view of a stripped fiber ribbon 1 held in a holder 19, K1, with the fibers passing over the cleaving engine 30 which is made up of a sharp blade edge 41 and two bending edges formed by 2 dowels 23, 24 (clamps 8a, 61a, and 8b, 61b - not shown) Fig. 5b shows a side view of a fiber ribbon 1,101 in a holder 19 and clamps 8a, 61a and 8b, 61b, with the fibers passing over the cleave engine 30. The fibers are first clamped and then the fibers are stretched by applying lever 66 to turn an eccentric cam 62 in direction BB1 to allow a compression spring 63 to urge apart the two clamps and so tension the fiber(s). Fig. 5c shows clamped fiber with the proximal end of the fibers being urged away from the anvil and blade after cleaving Fig 6a shows a two-armed anvil 51 pushing clamped fibers 1 down onto a sharp blade 40 located in a cleave engine 30 which also includes two dowels 23, 24 which act as bending edges which creates a substantially perpendicular cleave. Fig. 6b shows a one-armed anvil 52 pushing clamped fibers 1 down onto a sharp blade 40 located in a cleave engine 30 whereby a machined edge 78 acts as a bending edge which creates an angled cleave. Fig. 6c shows a two-armed anvil 51 which falls under gravity to contact clamped fibers 1, with the anvil travelling on a bearing 411 in a trackway 416. Figs. 7a, 7b show a cleave engine 30 with a two-armed anvil 52, suitable for creating a substantially perpendicular cleave, pressing down the fiber(s) over one bending edge located in the cleave engine and the other bending edge located in the chassis Fig. 7c shows a cleave engine 30 with an one-armed anvil 52, suitable for creating an angled cleave, pressing down the fiber(s) over a dowel acting as one bending edge 124 located in the cleave engine and the other bending edge 123 located in the chassis Fig. 7d shows a cleave engine 30 with an one-armed anvil 52, suitable for creating an angled cleave, pressingdown thefiber(s) overtwo bending edges 125,126 located in the chassis Fig 8a shows a sharp blade assembly 40, acting as the cleave engine 30, whose face 45a may be secured against a Face 55a using a screw 801. Fig 8b shows a sharp blade assembly 40, mounted in a cleave engine 30, whose face 46b may be secured against a back-wall C of the chassis Fig 8c shows a sharp blade assembly 40, mounted in a cleave engine 30, with height adjustment Q1, Q2 Fig 8d shows a sharp blade assembly 40, mounted in a cleave engine 30, whose face 46b may be secured against a back-wall D1 of the cleave engine and face D2, 55a, with the bevelled edge 451 of the shank 42 pressed into the machined corner 452 Fig 9a shows adjustment in the height Z1 of the blade edge located in the cleave engine block 26 by rotating the mounting of the blade assembly around hinge MM, using screw 301, achieving a substantially perpendicular cleave using a two-armed anvil whereby both bending edges are located in the chassis Fig 9b shows adjustment in the height Z2 of the blade edge 41 located in the cleave engine block 26 by rotating the mounting of the blade assembly around hinge MM using screw 301, for an angled cleave using a one-armed anvil 52, whereby one bending edge 323 is located in the cleave engine and the other edge 326 is located in the chassis, enabling tuning of the end angle Fig 9c shows adjustment of the relative heights of the two bending edges 223, 226 suitable for tuning the end angle of the substantially perpendicular cleave. Fig 9d shows adjustment using screw 302 in the lateral position WW of the sharp blade edge 41 by rotating the blade block around Hinge KK. Fig. 10a shows a ribbon fiber deflected in a direction PP2 by an anvil 51, 52 to a fixed displacement of distance DX2, and a sharp blade edge 41 moving perpendicular to the fiber ribbon in a direction PP1 to scratch the bent fibers Fig. 10b shows a side view of pre-bent fiber(s) being scratched by a blade assembly 302 with a sharp blade edge 901, which passes underthe bent fibers, scratching them as it passes, moving in direction SS. Fig 10c shows a cylindrical blade assembly 302 with a sharp peripheral edge 901 passing under pre-bent fibers to scratch them, with the blade travelling on a bearing 424. Fig. 10d shows a cylindrical blade 302 with a sharp peripheral edge 901 passing underneath a pre-bent single fiber whereby the anvil contact edge with its face 303 angled at angle a to prevent any sideways motion or twisting of the fiber as it is being scratched Fig 11a shows the clamped fiber(s) being stretched by means 501 moving in a direction GG, upwards with reference to the plane of the fiber ribbon 1,101 Fig 11b shows the clamped fiber(s) being stretched by means 502 moving in a direction HH, downwards with reference to the plane of the fiber ribbon 1,101 Fig 11c shows the clamped fiber(s) being stretched by means of the anvil 519 which has a width and radius of curvature suitable for stretching the fiber(s), ensuring that it maintains contact between the fibers and the contact surface 551 over a length of LL1. Fig 11d shows the clamped fiber(s) being stretched by means of the anvil 529 which has a width and radius of curvature suitable for stretching the fiber(s), ensuring that it maintains contact between the fibers and the contact surface 552 over a length of LL2. Fig 11e shows the clamped fiber(s) being stretched by means of moving one of the clamps 88b, 808b relative to the other clamp 21 in a direction QQ perpendicular to the fiber axis or axes. Description of Preferred Embodiments: In a first example of this invention, the distal end 2 of a ribbon optical fiber 1, as shown in Fig. 1a, is stripped of its plastic coating / matrix 3. The fibers 1 are clamped on to a top plane 4 located in a cleaving system 5, made up of a chassis 6, whereby the optical fibers 1 are clamped or partially clamped on to plane 4 using two clamps 8a, 8b which are located in the chassis 6 so that the clamped fibers do not subsequently move; the clamps may be hard, preventing any movement of the fibers or they may be compliant and made of EPDM, or similar, or the clamps maybe hard or semi-hard provided that the clamps restrain the fibers enough to maintain internal stress in the fibers. The clamps may clamp the stripped fibers or they may clamp the protective coating matrix and so clamp the fibers located therein. Similarly, a single optical fiber 101 may be stripped of its coating and clamped on to the top plane 4. Optionally, the clamps may be compliant, for example, comprising elastic bands made of EPDM or other material, or they may be hard or semi-hard and the clamps may clamp the stripped fiber or the protective coating. A cleave engine 30 is positioned in a gap G in the top plane 4 of the chassis 6, as shown in Fig 1a. An anvil 51 with a strike edge or edges 82,83 and 181,182 is caused to move towards the stripped fibers, pushingthem down into a gap G in the top plane of the chassis 6, so bendingthe fibers in the region of the cleave engine 30, imparting an internal stress to the fibers. In order to bring the strike point(s) of the anvil 52 into contact with the clamped fibers, the motion of the anvil may be caused by the anvil falling under the force of gravity in direction CC, as shown in Fig 6c, or the anvil may be rotated about an axis AA (shown in Fig. 2a) located in the cleave system or the anvil may be moved by other means to contact the clamped fibers. The anvil bends the stripped fibers down, over edges 21, 22, to contact the sharp blade edge 41, which scratches the fibers, causing them to cleave under the influence of the internal stresses which have been induced in the fibers. Optionally, instead of, or in addition to, using separate clamps 8a, 8b, the fibers may be clamped as part of the action of the anvil, as shown in Fig. 2a, 2b, 2c, whereby compliant elastic bands 9a, 9b act as clamps. These are each stretched around two support posts 7a, 7b fixed into the anvil 51. As the anvil approaches the fibers, the elastic bands 9a, 9b contact and clamp the fibers on to the top plane 4 of the chassis 6 on either side of the cleave engine 30; the strike edge(s) of the anvil 51 continue to push the fibers down, bending them over edges 21,22, to contact the blade edge 41. The anvil may have two contact ridges and may contact each fiber at two points, as shown in Fig, 2b, with the blade edge 41 lying between contact points 401,402, leading to a substantially perpendicular cleave. Alternatively, the anvil may have one contact ridge 403 which contacts each fiber at a single point, as shown in Fig, 2c, with the blade edge 41 lying close to and on the distal side of the contact point 603, leading to an angled cleave. The clamps 9a, 9b may be used instead of clamps 8a, 8b to clamp the fiber, or the clamps 9a, 9b may be used in addition to clamps 8a, 8b or a mix of the two clamping means may be used. A holder 19 may also be used to clamp the proximal end of the fibers through the coating 3 or onto the stripped fibers. Preferentially, the proximal end of the fiber is clamped through the remaining protective plastic coating 3 - either by clamp 8a, 9a or by a holder 19 so that the glass of the working optical fiber is not damaged by the clamping action. Optionally, the fibers may be held and / or clamped and aligned in a holder 19 which is located in the clamping system 6, as shown in Fig 1a, Fig. 2c A stripped single optical fiber 101 may be held and located in the cleaving system 5 either by being held in a holder 19 which is located in the chassis 5, or by a series of location means such as one or more pairs of posts 12a, 12b and 13a, 13b, as shown in Fig 1b. The stripped distal end of the single optical fiber passes over the engine 30 and may pass through the one or more pairs of posts 13a, 13b or other forms of alignment, to locate the fiber over the cleave engine 30. The fiber may be clamped by clamps 8a, 8b on either side of the cleave engine or the fiber may be clamped compliantly by clamps 9a, 9b, as shown in Fig 2a, 2b, which may be attached to the anvil. In the case of cleaving an optical fiber ribbon 1, the fiber ribbon has substantial rigidity in the plane of the ribbon, and so locating the fiber ribbon in the holder 19 will substantially position the fiber ribbon within the cleaving chassis 6, as shown in Fig 2b, and direct the stripped fibers to pass over the cleave engine 30 and the cleave blade 40 so that they may be cleaved. The stripped fiber 101 or fiber ribbon 1 is clamped as above and deflected by a falling anvil 51 so that each fiber is bent down over two edges 21, 22 and contacts the sharp blade edge 41 to cause the fibers to cleave. Perpendicular cleave A cleave engine 30 is located between clamps 8a, 8b in a gap G in the top plane 4 of the chassis, as shown in Fig. 1a. The cleaving engine, shown in Fig. 3a, comprises a body 26 which contains a blade assembly 40, and its sharp blade edge 41, and two well-defined edges 21,22 over which the fibers in the fiber ribbon 1, or single fiber 101, are bent by the anvil to create a cleave. Fig. 3a shows an isometric view of the edges 21, 22 and the blade 40 and its sharp edge 41, whereby the bending edges 21, 22 are created by accurate machining of the body 26 of the cleave engine. The cleave engine 30, shown in the isometric view of Fig. 3b, is made up of two bending edges and the blade 40, which is located therebetween, in which the bending edges are created by the presence of two dowels 23, 24, located in the cleave engine 30. The dowels 23, 24 and the blade assembly 40 are accurately located by machining the body 26 of the cleave engine 30 to geometric tolerances of less than 10microns; due to this accurate machining, any further alignment or positioning of the blade and dowels within the chassis of the cleave system is largely not required. Therefore, the cleave engine can easily be replaced after excessive use or substituted when cleaving different diameter fibers without compromising the quality of the cleaving performance. However, the cleave engine must be accurately mounted in the cleaver chassis 6 such that the blade edge 41 is exactly perpendicular to the optic axes of the fiber ribbon 1. This is conveniently achieved by mounting the body of the cleave engine on two alignment dowels 111a, 111b, as shown in Fig. 5a. These alignment dowels are accurately aligned using holes 112a, 113a and 112b, 113b which are machined in the chassis 6 of the cleave system such that the dowels lie exactly perpendicular to the optic axes of the fiber ribbon 1 or fiber 101 and also lie exactly parallel to the plane of the fiber ribbon 1. It is understood that other means of orienting the cleave engine are also possible. The blade assembly 40 may be a single part or multiple attached parts to form a sharp edge 41 and a shank 42, or similar, as shown in Fig. 4a. The blade consists of a single crystal diamond 43 which is polished along crystallographically hard {111} planes to form a sharp edge 41 which is typically 3.5mm long along its length. The diamond 43 is brazed at 49 onto a cuboid steel shank42 which is shown in detail in Fig 4b. The shank is of well-defined dimensions, typically of width W of 3.5mm or greater and a thickness T of 0.5mm or thicker; the shank 42 has accurately ground faces 45a, 45b which are parallel. The shank has ground parallel faces 46a, 46b and a ground bottom 47, whereby the parallel faces 46a, 46b are perpendicular to the bottom 47, and the parallel faces 46a, 46b and bottom 47 are each perpendicular to the ground faces 45a, 45b, to a geometric tolerance of 10microns. In typical manufacture of the blade 40, the diamond 43 is ground and polished to form a sharp edge 41 whereby the edge 41 is parallel to the ground faces 45a, 45b, parallel to the bottom 47 and therefore perpendicular to the sides 46a, 46b, to a geometric tolerance of 10microns. The edge 41 lies substantially half-way between the faces 45a, 45b. The diamond 43 is ground and polished so that the length L of the combined diamond and shank is accurately controlled with a length of approximately 10mm. The length L of the completed blade assembly 40 is subsequently measured and the blade assemblies 40 are sorted into batches of equal length L with a length resolution of 10microns or better. Design of blade To demonstrate this invention and method, we use a polished, single-crystal diamond to form the blade edge, as shown in FIG 4a, 4b, 4c. The blade assembly is made up of a single-crystal diamond 43 which is brazed onto a steel shankwhich has been ground into a cuboid shape. The diamond is oriented by X-ray diffraction or otherwise so that the (001) plane of the diamond crystal is arranged to be substantially parallel to the top of the blade assembly, i.e. parallel to the plane of the fiber ribbon. The diamond is ground and polished to form a sharp edge 41 which is oriented in an

[011] direction in the diamond. The single crystal diamond is ground and polished using diamond slurry to an included angle of approximately 60 degrees, with two atomically-smooth polished {111} planes intersecting in a <110> direction to form the blade edge which is parallel to face of the shank. The blade edge is typically 3.5mm long, sufficiently long to scratch a 12-fiber ribbon. This blade edge is straight to less then 10 microns. The diamond is brazed to a suitable-coated steel shank of dimensions approximately 0.5mm thick, 3.5mm wide and 10mm long. The distance between the blade edge and the bottom of the supporting shank is closely controlled and is approximately 10mm long. After the diamond has been crystallographically oriented and brazed to the steel shank, the diamond is ground and polished to a sharp edge. Because the steel shank is supplied with a parallel face, the polished diamond edge is parallel to the face of the steel shank with a geometric tolerance of 10 microns or less. It is understood that the polished blade may be made of other material such as single crystal sapphire or single crystal Boron Nitride. Alternatively, the polished edge may be made from polished hard tool steel, carbide steel or otherwise. Use of holder for positioning or advancing blade The use of dowels 111a, 111b to locate the body 30 of the cleave engine in the chassis by means of accurately drilled holes 112a, 113a and 112b, 113b in the chassis 6, as shown in Fig 5a, is convenient in allowing the blade edge to be advanced in a direction JJ along its edge to allow undamaged portions of the blade edge to be used after one portion of the blade edge has been blunted through use. An alternative method of exposing a fresh, unused portion of the blade edge to the fiber is to clamp the fiber and / or its holder at a different location on the top plane of the chassis. Initially the fiber(s) and their holders may be clamped at position K1, as shown in the view of Fig. 5a. After the blade edge has become blunted through use or misuse, the location of the holder may be moved in a direction across the fiber ribbon, for instance to position K2, so positioning the clamped fibers over an unused portion of the sharp blade edge and consequently prolonging the life of the blade. Alternatively, the fiber may be held in different locations in the holder 19, or dismountable holders may be used in which case an alternative holder may be placed in the same position K1 on the top plane 4 of the chassis, but different holders may have different locations for holding the fiber, all with the purpose of positioning the fibers at different, unused locations over the sharp blade edge 41. Description of Stretching Means Optionally, the fiber or fibers may be stretched prior to cleaving in order to impose a tensile element to the internal stress established in the fibers prior to cleaving. Preferentially, a tensile force of approximately 2N is optimal in propagating a cleave across a 125micron diameter silica fiber for an approximately 2micron deep scratch; too large a tension leads to a rough end face on the cleaved surface with the presence of hackle; a low tension will not lead to cleaving unless an overlarge starter crack is employed, giving a non-smooth cleaved end face with large half-penny cracks. Fig. 5b shows the fibers clamped at two points 61a, 61b. The two clamping points are urged apart with a spring mechanism 63; one clamp point 61a is fixed to the chassis 6 of the cleave system 5 and the other clamp point 61b is located on a carriage 62 and is optionally movable on a sliding mechanism such as a bearing B in the direction RR1, as shown in Fig 5b, under the influence of a compression spring 63. It is understood that other means of moving the carriage 62 are also possible, such as a leaf spring or springs. The fibers 1 are first clamped in the clamps 61a, 61b with the carriage 62 and clamp 61b locked in a position using a stop 65, with the compression spring 63 compressed. After the fibers have been clamped at 61a, 61b, the stop 65 is released and a lever 66 is rotated in direction BB1 about an eccentric axis 67, so that the clamps are urged apart by the spring 63; the clamps are not able to move apart because the fibers are clamped between the clamps and so the fibers are stretched, applying internal tension to the fibers parallel to their optic axes. The presence of tension in the fiber may lead to a superior cleave. When the fibers have cleaved after the anvil has pressed the fibers down on to the sharp blade edge 41, the two clamps 61a, 61b move apart underthe continuing influence of the compressed spring 63. Fig. 5b shows the offcut, distal end of the fibers moving in direction RR1 under the force of the spring 63. It is understood that other mechanisms may be used to urge apart the two clamping means 8a, 8b. It is understood that the mechanism can also be configured so that it is the proximal, working end of the fiber or fibers which is moved in direction RR2 under the action of the spring 73, as shown in Fig. 5c. This arrangement may be advantageous because the freshly cleaved fibers are moved away from the location of the anvil and the blade and this may prevent damage to the freshly cleaved fiber. Clamp 72 is fixed to the chassis 6 and clamps the distal ends of the fiber or fibers. Clamp 71 clamps the proximal ends of the fibers; in addition, holder 19 may hold the proximal ends of the fibers either directly or through their protective coating 3. The fibers are first clamped in the clamps 71, 72 with the carriage 79 and clamp 71 locked in a position against a stop 75 with the compression spring 73 compressed. After the fibers have been clamped at 71, 72 , a lever 76 is rotated in direction BB2 about an eccentric axis 77 so that the clamps are urged apart by the spring 73; the clamps are not able to move apart due to the fibers clamped between them. When the stop 75 is released, the fibers are stretched, applying internal tension to the fibers parallel to their optic axes. When the fibers are cleaved, under the continuing influence of the compressed spring 73, the clamp 71 and carriage 79 move in direction RR2, travelling on the bearing B, moving the freshly cleaved fiber end away from the blade 40 preventing damage by the blade to the cleaved fiber end faces. Description of Twisting Means Optionally, in order to effect an angled cleave fora single fiber, the clamped fiber may be twisted prior to cleaving to impart a non-axial stress to them so that they may cleave at an angle to their optic axes. This achieved by clamping the fiber at two points, optionally stretching it as above, and then twisting the clamps 61a, 61b relative to each other before engaging the anvil to bend the fiber over two edges to bring the stressed fiber in to contact with the sharp blade edge to scratch and cleave it. In this embodiment, twist may be applied together with stretching the fiber or twist may be used without the presence of the stretching mechanism described above. Description of stripping The fiber or fiber ribbon may be stripped of its protective plastic coating. In the case of a single fiber, the coating is conveniently removed with wire strippers. In the case of a ribbon fiber, a thermal ribbon stripper, such as the JR6+ obtainable from Sumitomo Electric, Elstree, UK, may be used to remove up to 30mm of coating from the distal end of the fiber ribbon. The fiber may be held in a holder or similar so that the stripped fiber passes over the cleave engine so that it may be cleaved whereby the fiber ribbon is clamped at 2 positions with the remainder of the coating may be clamped at 8a and the striped fiber may be clamped at 8b or at 9a, 9b. Alternatively, the fiber may be clamped at two locations directly onto the stripped glass of the fiber. Alternatively, the coating may be partially removed from the single fiber or the ribbon fiber to more easily facilitate fiber clamping, so creating a window in the protective coating. A ribbon fiber may be window stripped using a thermal stripper whereby the ribbon matrix is heated to loosen the binds between the plastic and the glass so that a glove of coating can be slid towards the distal end of the fibers, without fully removing it, and the glove can be left to cool, so reforming the bond between the plastic glove and the glass of the fibers. The distal end of the fibers, with their coating glove, can then be clamped and cleaved. The presence of the glove makes the clamping of the distal ends of the fibers more secure, prevents rotation of the fibers during cleaving and eases the collection of fiber offcuts after cleaving. In the case where the fiber ribbon is not fully encapsulated with a plastic matrix, rather the ribbon fiber is of a rollable ribbon type in which the protective coatings of neighbouring fibers are joined together loosely in a spider’s web design, it may not be possible to window strip the ribbon fiber. In this case a thermal stripper may be used to completely remove all of the coatings from the distal end of all of the fibers. The fiber ribbon may be clamped on its proximal side, either through a remaining portion of coating or clamped directly on to stripped glass; the proximal end of the fibers may be held in a holder which serves to arrange the fibers in a controlled fashion and the holder may be securely fixed to the chassis of the cleaver. The stripped distal end of the fiber ribbon may be clamped using a clamp which clamps all stripped fibers equally; preferentially, this clamp may have a compliant surface and be made of EPDM or similarly compliant material. Motion of Anvil: The cleave system 5 shown in Fig. 6a shows a view of a cleave engine 30 which is made up of a sharp blade 40, with its sharp blade edge 41, and two bending edges formed by two dowels 23, 24. An anvil 51 approaches the clamped (and optionally tensioned and twisted) fiber in a direction VV by falling under gravity at 9.8m / s2. If the anvil falls through a distance of 10cm before impacting the fiber, its speed of approach will be 1.4m / second. The anvil displaces the fiber or fibers, bending them over edges formed by dowels 23, 24 in the cleave engine until the fibers touch the sharp blade edge 41 and so are scratched and cleaved by the presence of stress within the fiber. Fig. 6a shows an arrangement, shown in side view, which is used to perpendicular cleave a ribbon fiber in which the two-armed anvil bends the fibers over dowels 23, 24 and contacts each fiber in the ribbon at contact points 181,182 on either side of the sharp blade edge 41. The anvil displaces the fiber or fibers by a distance Q1, until the fibers touch the sharp blade edge 41. The anvil of Fig. 6a has two arms which are extended in the direction parallel to the plane of the fiber ribbon and perpendicular to the axes of the fibers so that these arms will contact all fibers in a ribbon substantially simultaneously. The two arms of the two-armed anvil contact each fiber at points 181,182. The blade edge 41 lies between contact points 181, 182. Fig. 6b shows an arrangement, shown in side view, which is used to angle cleave a ribbon fiber in which a one-armed anvil 52 bends the fibers over two machined edges 77, 78 in the cleave engine 30 and where the anvil contacts each fiber in the ribbon at a contact points 183 on either side of the blade edge 41. The anvil bends the fiber or fibers over the machined bending edge 78 by a distance Q2, until the fibers touch the sharp blade edge 41; a second bending edge 77, shown in Fig. 6b is formed by machining of the body 26 of the cleave engine. The anvil 52 of Fig. 6b has one arm 183 which is extended in the direction parallel to the plane of the fiber ribbon and perpendicular to the axes of the fibers so that the anvil will contact all fibers in a ribbon simultaneously. The one arm 183 of the one-armed anvil contacts each fiber at points 183. The blade edge 41 is positioned close to the contact point 183 of the anvil, offset by a distance T. The blade edge 41 is closer to the contact point 183 than to the bending edge 78 i.e. T is less than E. It is understood that bending edges may be used to generate either perpendicular or angled cleaves, wherein the bending edges are created either by the provision of accurately machined edges in the chassis or body of the cleave engine or by the provision of dowels accurately located therein. Bending edges may be provisioned in any other way. The two-armed anvil 51 and its contact arm(s) 181,182, as shown in side view in Fig 6c, is attached to a carriage 410 which falls under gravity, travelling on a bearing 411 which runs on a trackway 416 machined into a pillar 417 which is attached to the chassis 6. The anvil is optionally latched at position 413 using a latch 414 prior to its action. The anvil falls under gravity until it contacts the clamped fibers pushing them down onto the sharp blade edge 41 which cleaves the fiber(s). Once the anvil has fallen far enough so that the fibers contact the sharp edge 41 and cleave, a stop 418 stops further movement of the anvil to prevent damage to the cleaved fibers and to the blade. It is understood that the action of the anvil to bend the fibers may be configured in any other way. For instance, the anvil may be moved towards the blade edge by rotating around a pivot, with the pivot located in the chassis, at A-A in Fig. 2a, or elsewhere. It is understood that a one-armed anvil (not shown in Fig. 6) may similarly contact the clamped fibers, after falling under gravity, creating angle cleaved ends. Anvil Positioning against a reference surface: The relative position of the blade edge 41, the bending edges 21, 22 and the contact points 81, 82 and / or 83 of the anvil in a direction along the axes of the fibers should be controlled to achieve a controlled cleave. Fig. 2d shows an one-armed anvil 52, which is used to create an angled cleave, which is pressed against a reference surface WW in the chassis 6 of the cleave system using a spring 210. The anvil is free to be rotated about its axis AA so that the anvil contacts the clamped fibers; preferentially, the contact between the chassis and the anvil may have a restricted area to reduce friction, as achieved by having a small raised lug 97 on the surface of the anvil, whereby the lug is a small cylinder raised from the surface of the anvil. The position of the anvil and therefore the position of the contact points 81, 82 and / or 83 are therefore fixed with respect to surface WW in the chassis. The cleave engine 30 and its blade edge 41 are also positioned accurately in the chassis with reference to surface WW by mounting them in an accurately positioned location in the chassis of the cleave system using drilled holes 112a, 112b and 113a, 113b into which are placed dowels 111a, 111b. Because the reference surface WW and the holes 112a, 113a and 112b, 113b are CNC machined in the same CNC machine setting, the holes and the reference surface WW will be exactly parallel and so the lateral distance between contact points 83 of the anvil and the blade edge 41 and the bending edge 24 will be accurately set; hence a controlled angled cleave will be created. In the case of a perpendicular cleave, the distance between the contact points 81, 82 of the two-armed anvil 51 and the blade edge 41, may be precisely controlled. Clamping may be achieved using clamps attached to the chassis or may be achieved using claps attached to the anvil. A falling anvil may be used to generate perpendicular and angled cleaves, whilst still maintaining a fixed distance from reference surface WW, whereby the anvil is pressed against a reference surface WW accurately to set the distance between the blade edge 41, the bending edges 23, 24 and contact points 81, 82 or 83 of the anvil 51, 52. The falling anvil may travel on a carriage 410 which moves on a bearing 411 to ensure that the anvil remains at a set distance from the reference surface; this may be achieved by magnetically attracting the falling anvil to a pillar 417, or otherwise. The falling anvil may be arranged in any other way to ensure that the distances between the contact points of the anvil, the sharp blade edge and the bending edges is controlled. Creating a perpendicular cleave Fig 6a shows a cleave engine 30 with two bending edges, formed by 2 dowels 23, 24 located on either side of a sharp blade edge 41. The bending edges may alternatively be formed by accurately machined edges and the machined edges and / or dowels may be located in either the cleave engine or in the chassis. An anvil 51 with two edges bends the fibers down on to the blade edge 41, contacting each fiber at two points 181,182 which are on either side of the blade edge 41. A substantially perpendicular cleave is created. The angle and quality of the resultant cleave is dependent on the distance Q1 through which the fibers are bent by the anvil, the separation X of the edges of the cleave engine, the separation P of the two arms of the anvil, the relative positions of the blade edge 41 within the two contact points 181,182 of the anvil, the relative lateral position of the anvil and blade edge with respect to the bending edges and the relative height difference between the two bending edges of the anvil. The resultant cleave has an angle which is also dependent on the relative heights of the two bending edges 23, 24, the relative height difference between the two bending edges 181,182 of the anvil 51 and the distance Q1 through which the fibers are bent before contacting the blade edge 41. The cleave engine, as shown in Fig. 6a, is used to perpendicular cleave a single 125micron diameter silica fiber. It comprises two edges which are defined by two dowels 23, 24, each of 1.5mm diameter, with a polished diamond edge 41 arranged therebetween. The dowel centres are separated by a distance X of approximately 10mm. The dowels are at substantially the same vertical height as each other, with the value of approximately zero, as shown in Fig 6a. The anvil 51 is positioned approximately equidistant between the two dowels 23, 24 which make up the bending edges. The two arms of the anvil have points of contact 181,182 with each fiber, separated by approximately 1.25mm when cleaving 125micron diameter silica fiber. The blade edge is positioned approximately equidistant between the points of contact 181,182 of the anvil. The polished diamond blade edge 41 is positioned so that the fibers are bent down by the anvil by a distance Q1 of approximately 0.15mm when the fibers contact the blade edge. The stretching mechanism shown in Fig. 5b, Fig. 5c applies a tension of approximately 2Newtons in the 125micron diameter single fiber prior to cleaving by stretching the clamped fiber underthe influence of the compression spring 63. Effective cleaving may also be achieved by different separation of the dowels in which case the bending of the fiber before impact with the blade should be optimised. Thus, increasing the separation of the dowels 23, 24 requires that the bending Q1 of the 125micron diameter fiber priorto scratching with the blade should be increased. Similarly, decreasing the separation of dowels 23, 24 requires a smaller bend of the fiber. Optimal separation of the dowels 23, 24 for cleaving 125micron diameter fiber is between 2mm and 250mm and preferably approximately 10mm. If fiber of different diameter is to be cleaved, the dowel separation and the bend require different values for optimal cleaving. Depending on the value of the above parameters, the end angle of the resulting cleave may be substantially perpendicular to within 3 degrees of square or preferentially within 0.5degrees of perpendicular. It should be noted that the bending of the fiber serves to resist the cutting force of the blade as well as imparting a bending stress into the fiber. Because smaller diameter fiber is more flexible, the points of contact of the anvil should be closer together to resist the scratching force. Cleaving 80micron diameter fiber is effectively achieved with a smaller dowel separation, typically of about 5mm, and a larger bend Q1 of typically 0.25mm and a separation of the two contact points of the anvil 81, 82 of less than 1mm, with the blade edge positioned therebetween. The optimum tension achieved by stretching the fiber also varies, is dependent on the fiber cross-sectional area. Thus, since 2N of tension should optimally be applied for 125micron diameter fiber, a smaller tension is required for80micron diameter fiber and a larger tension for 250micron diameter fiber. Angle Cleaving The cleave engine shown in Fig 6b is used to angle cleave a single 125micron diameter silica fiber. Optionally, the angle cleaving engine comprises two edges, defined by two edges, 77, 78, and a sharp blade edge 41 therebetween. A one-armed anvil 52, with one point of contact 183 acts between the edges 77, 78 and contacts each fiber or fibers at point(s) 183 and bends the fibers down to contact the blade edge 41, where the blade edge is arranged close to the point of contact 183 of the anvil with thefiber, as shown in Fig. 6b. The blade edge is positioned between the point of contact 183 and the edge 78, i.e. with the blade edge positioned to the distal side of the point of contact 183 of the anvil. The blade edge 41 should be positioned closer to the point of contact 183 than to the edge 78. The positioning of the blade edge 41 close to point of contact 183 of the anvil has two purposes, firstly to induce significant bending forces within the fiber such that the resultant stress in the fiber is non-axial and therefore leads to an angled cleave. Secondly, the blade edge 41 is positioned close to the point of contact 183 of the anvil with the fiber so that the bending of the fiber imparts a skin tension in the fiber at the point of cutting and so resists the cutting force of the blade. Because the blade edge 41 is closer to the anvil than to the edge 78, the fiber surface is under tension - i.e. experiences a skin tension - and the glass of the fiber will therefore peel away as the blade edge cuts into the fiber, so facilitating the scratching process. Conversely, if the blade edge 41 were to be closer to the edge 78 than to the point of contact 183 of the anvil, the blade edge 41 would scratch the glass at a position where the fiber surface was under compression, making it very difficult for the blade edge to achieve a deep enough starter crack and potentially damaging the blade. In order to achieve a good angled cleave, with the core at approximately 8 degrees away from perpendicular for 125micron diameter silica fiber, the separation SS4of edges 77, 78 should of order 5mm but potentially in the range of 2-50mm, as shown in Fig. 6b. The distance T between the point of contact 183 of the one-armed anvil and the blade edge 41 should be less than 2mm and preferably of order 0.5mm, but may be as small as 0.1 mm. The distance E between the blade edge 41 and the edge 78 should be greater than the distance T between the point of contact 183 of the one-armed anvil and the blade edge 41. The distance E should be greater than 0.1 mm and less than 250mm, but is preferably approximately 2mm. The distance Q2 over which the fiber is bent down by the anvil should be of order 0.125mm but may be as small as 0.05mm or as large as 5mm. Optionally, stretching giving rise to a tension of 0.1-10N may be used to achieve a superior cleave. Angled cleaving of smaller and larger diameter fibers can be achieved with appropriate choice of the above variables. The core of the fiber may be angled away from perpendicular by an angle which is optimally 8degrees from perpendicular to prevent any back-reflected light travelling back down the fiber. However, an angle of between 3 degrees and 20 degrees may also be achieved by appropriate choice of distances Q2, X, E, T, as well as tension. Optionally, in order to create an angled cleave, the optical fiber way be twisted in addition to, or instead of, stretching the fiber. The fiber is arranged, as described above in Fig. 5b and Fig. 5c, in order to cause a perpendicular cleave, i.e. clamping the fiber, symmetrically bending the fiber over two edges with a two-armed anvil onto a sharp blade edge and optionally stretching the fiber. However, after clamping the fiber the two clamps, and before cleaving, the two clamps may be rotated relative to each other. The anvil is then applied to bend the fiber over the bending edges and then onto the sharp blade edge, causing an angled cleave. A twist of approximately 3 degrees per mm of distance between the clamps is sufficient to cause a cleave which is angled over the core by an angle of approximately 8° away from perpendicular. Bending Edge(s) as part of chassis An alternative example of the cleave engine may be used for creating both perpendicular and angled cleaves. The cleave engine may comprise a sharp blade assembly 40, and its sharp edge 41, and a single bending edge 23, which is provided by a dowel, as shown in Fig. 7a, to create a substantially perpendicular cleave. The second bending edge 121 is not incorporated in to the cleave engine; instead, the second edge 121 is provided by the machining of the chassis. Thefiber(s) 1,101 are bent between edges 23and 121, displaced by the two-armed anvil with its contact points 181,182 and are pushed onto the blade edge 41 to cause a substantially perpendicular cleave. Fig. 7b shows the cleave engine 30 comprising a sharp blade edge 41 and a single bending edge formed by a dowel 24. The second bending edge 122 is located in the chassis. Substantially perpendicular cleaves may be achieved. It is also understood that both bending edges may be provided in the chassis, with no bending edges present in the body 26 of the cleave engine, with the bending edges formed by accurate machining of the chassis or by the provision of dowels. Fig 7c shows an example of an arrangement of the cleave engine 30 to create an angled cleave, in which the anvil 52 has only one arm and one contact point 183 with each fiber. The bending edge 124 is provided by a dowel located in the body 26 of the cleave engine and edge 123 is provided in the chassis 6. The sharp edge of the blade 41 is arranged close to the point of contact 183 of the anvil. It is understood that the bending edge may be provided by a dowel in the cleave engine and a machined edge in the chassis or vice-versa. It is also understood that both bending edges 125,126 may be provided in the chassis, with no bending edges present in the body 26 of the cleave engine, with the bending edges formed by accurate machining of the chassis, as shown in Fig. 7d for an angled cleave, or by the provision of dowels. Both perpendicular cleaves and angled cleaves may be realised. Example using fixed blade. Fig. 8a shows an embodiment of the invention in which the cleave engine consists of a sharp blade assembly 40 with its sharp edge 41, mounted in the chassis 6 of the cleave system 5 to achieve an angled cleave. The blade 40 and its edge 41 is positioned between two edges 131,132, whereby the edges are provided by accurate machining of the chassis, as shown in Fig. 8a, or by the provision of dowels in the chassis, or otherwise arranged. The sharp edge 41 of the blade assembly 40 is caused to lie parallel to the face 55a of the chassis. This is achieved by pushing and fixing the face of the blade shank 45a against the face 55a in the chassis 6 of the cleave system; this pushing and fixing may be achieved using screw 801 mounted in the chassis 6, or otherwise. The face 55a may be accurately machined to be perpendicular to direction RR in Fig 8a, i.e. perpendicular to the optic axes of the fibers, and so the sharp edge 41 of the blade assembly also lies perpendicular to the optic axes of the fibers. In another example of this invention, the edges 131,132 may be formed by the presence of two dowels accurately located in the chassis 6 to lie perpendicular to the fibers and where the edges and / or dowels lie parallel to the plane of the fiber ribbon. The edges may be otherwise formed. Preferentially, these faces, dowels, edges and positioning should be accurate to within a geometric tolerance of less than 10 microns. Consequently, when a fiber ribbon is cleaved, the length of each fiber is substantially equal. The tolerance of the parallelism between the blade edge 41 and the machined face is therefore defined by the accuracy only of the manufacture of the blade edge 41 and the face 45a of the shank 42, assuming that the CNC machining of the face 55a has a vanishingly small deviation from being perpendicular to the optic axes. No extra tolerance variation arises because there are no intermediate components. This is advantageous both in reduction of complexity of set up of the tool and a reduction in cost. If the blade assembly 40 and its shank 42 can be manufactured to a tight tolerance, the blade edge 41 is therefore accurately parallel to the machined face 55a. The blade edge 41 should also be aligned so that it is parallel to the plane of the fiber ribbon so that when the fibers are bent downwards towards the blade edge then all fibers 1 in the ribbon are all bent by the same distance before they touch the blade edge 41 and therefore all fibers experience the same bending forces. This is achieved by arranging a face C in the chassis, which is perpendicular to Face 55a and therefore perpendicular to the fiber axes, wherein Face C is CNC machined in the chassis with the same machine setting as that used to machine face 55a. The face 46b of the blade assembly is pressed against Face C of the chassis, as shown in top view in Fig 8b, whereby Face 46b of the blade assembly, as shown in Fig. 4c, has been accurately created to be perpendicular to the blade edge 41 during the manufacture of the blade assembly 40. The oriented blade assembly 40 may be held in position by a screw 801 or otherwise. Consequently, the blade edge 41 will be parallel to the plane of the fiber ribbon. When the fibers are bent down by the anvil, all of the fibers in the ribbon are bent down by the same distance before they touch the sharp edge and so experience the same bending forces as each other and hence cleave is a substantially identical manner. The vertical distance between the blade edge 41 and the bottom of the fiber ribbon must also be set so that the fibers experience the correct amount of bending Q1, Q2 when they touch the sharp blade edge 41 and are cleaved. As shown in side view in Fig. 8c, the blade assembly 40 and its shank 42 is manufactured so that its total length L is controlled, the location of the bottom face 47 of the shank may be set using screw 402, or otherwise, in order to set the distance Q1, Q2 between the blade edge 41 and the bottom of the fiber ribbon. It is also understood that the cleave engine 30 may be dismountably mounted in the chassis, i.e. a cleaving engine which includes provision of zero, one or two bending edges. The cleave engine may have faces D1, D2 machined into the body 26 of the cleave engine 30 against which the blade 40 is located, as shown in Fig 8d. The shank of the blade may have a bevelled edge 451 (also shown in Fig 4d) which may be pressed into the machined corner 452 between the two faces D1, D2 to allow the shank of the blade to contact both faces D1 and D2. The cleave engine 30 is mounted in the chassis using accurately positioned dowels 111a, 111b. Optionally, the blade assembly 40 may include a supporting structure 91 which allows easy manipulation of the position and orientation of the blade edge. The supporting structure 91, as shown in Fig. 4c, is in the form of a L-shaped part which is glued or otherwise attached to the blade 40. A long screw 93 may be detachably attached to the support 91 and may be used to manipulate and set the position of the blade assembly 40, after which it may be removed. It is understood that other shaped or types of support structure 91 may be used to support, position and / or manipulate the blade 40, or alternatively, no additional support structures may be necessary. It should be noted that Faces 45a, 46b and 47 are not involved in the attachment of the support 91 and so the accurately manufactured faces of the shank 42 can be used to position and orient the blade assembly 40 against faces 55a and Face C of the chassis 6 or Faces D1 and D2 of the cleave engine. The support 91 may be made of a hard material such as a metal and may provide support to the shank 42 of the blade 40 to prevent it bending during cleaving. Blade Height Adjustment A further example of this invention is shown in Fig 9a in which the height of the blade edge 41 may be adjustable and may be optimised. This allows the quality, angle and smoothness of the cleaved end to be adjusted both for substantially perpendicular cleaves and for angled cleaves. The height of the blade edge 41 of the cleaving engine 30 may be adjusted to an optimum value. This may be achieved by arranging the cleave engine 30 as a block 26 which is hinged, with the block located in the chassis 6 of the cleave system, as show in Fig. 9a. The blade 40 may be mounted in the top half 703 of the block 26. Preferentially, the cleave engine block 26 contains a live hinge MM so that the application of a screw 301 rotates the cleave engine block in direction ZZ about the hinge MM which has the effect of changing the distance Z1 between the blade edge 41 and the clamped fibers. Changes in the height Z1 allows the bending force in the fibers to be adjusted, so optimising the angle and smoothness of the cleaved ends. The cleave engine block 26 may be located in the chassis of the cleave system, for example by dowels 111a, 111b being located in holes 112a, 113a and 112b, 113b, or may be an integral part of the chassis. Optionally, the cleave engine block may be translatable across the fibers to expose an unused portion of the blade, for instance by sliding along dowels 111a, 111b. In the case where both bending edges are located in the chassis, as shown in Fig. 9a, the height of the blade edge 41 relative to the fixed edges 123,121 may be adjusted to allow tuning of the bending stress in the fiber(s), allowing optimisation of the cleave. Fig. 9a shows an arrangement for substantially perpendicular cleaving, whereby the blade assembly 40 is approximately equidistant from the two bending edges 123,121 and the anvil has 2 contact points with each fiber. The arrangement shown in Fig. 9c allows the end angle of the cleave to be adjusted to obtain a substantially perpendicular cleave. One of the bending edges 223 may be located in the body 26 of the cleave engine, either on the distal side or proximal side of the blade, with the other bending edge 221 located in the chassis. Changing the height Z3 of the blade relative to the bending edge 221 in the chassis allows the end angle of the cleave to be tuned to be substantially perpendicular. Adjusting the height Z3 of the blade edge 41 alters the end angle, allowing the end angle to be adjusted, for instance achieving a cleaved end within 0.5degrees of perpendicular. Cleaved ends with angles up to 3 degrees may also be achieved. Preferentially, but optionally, the fiber or fibers are stretched by spring 63 or otherwise, prior to cleaving, and so the tension in the fiber is not altered by the height adjustment Z3. Fig. 9b shows an arrangement for angled cleaving, in which the sharp blade edge 41 is close to the bending edge 326, the other bending edge 323 being located in the chassis as a dowel or machined edge; a one-armed anvil 52 is used. The angle and quality of the cleaved end is dependant on the height Z2. Z2 can be changed by using screw 301 to rotate the block of the cleave engine about hinge MM. Therefore the end angle achieved may be altered to a desired value. Preferentially, but optionally, the fiber or fibers are stretched by spring 63 or otherwise, prior to cleaving, and so the tension in the fiber is not altered by the height adjustment Z2. A further example of this invention may create a substantially perpendicular cleave or may create an angled cleave, as shown in Fig 9d, in which the position of the blade edge 41 may be adjustable, in a direction WW parallel to the fiber axes, relative to the position of the contact points 81, 82 and 83 of the anvil 51, 52. The distance? between contact point 83 of the anvil 52 shown in Fig. 9d and the blade edge 41 may be adjusted by application of screw 702 with the cleave engine block bending about live hinge KK. Similarly, in order to create a perpendicular cleave using a 2-armed anvil, the blade edge may be adjusted in a direction WW parallel to the fiber axes to alter the positioning of the blade edge 41 relative to the contact points 81, 82. It is understood that both hinges MM and KK may be incorporated into a single cleave engine block 26, as shown in Fig. 9d, so that both the height of the blade Z1, Z2 and the lateral position WW of the blade edge may both be adjusted. Alternatively, either hinge MM or hinge KK or both may be incorporated into the cleave engine block 26. It is also understood that height Z1, Z2, Z3 and position WW may be adjusted by other means, including the provision of other types of hinges. Moving blade to create scratch: In a further example of this invention, the fibers may be pre-stressed by bending the clamped fibers across two bending edges 421,422 to a fixed deflection DX2 (see Fig. 10a, Fig. 10b), so applying a fixed bending stress to the fibers. Subsequently, a cleave engine 30 containing a sharp blade 41, is caused to contact and so scratch the single fiber or each fiber in the ribbon. Due to the presence of pre-established stress caused by pre-bending, the clamped fibers cleave as soon as the scratch reaches a critical depth of 1-20microns. Preferentially, the cleave engine 30 with its sharp blade edge 41 is moved in a direction PP1, opposed to the direction of bending PP2, as shown in Fig. 10a, such that the blade contacts each fiber in the ribbon at substantially the same time, causing them to all cleave substantially simultaneously. In this example the blade edge is substantially linear. Alternatively, as shown in orthogonal views Fig. 10b and Fig. 10c, the cleave engine 30 with its sharp blade 41 may be moved underneath the fibers, in direction SS, in a direction substantially parallel to the plane of the fiber ribbon and perpendicularto the fiber axes, wherebythe sharp edge is set at a height that causes glancing contact between the blade edge 41 and the bottom of the fiber(s), with an interference distance H. H may have a value of between 0.5 and 50microns and preferentially approximately 10 microns. The sharp blade may be in the form of a disc 302 whose circumference 901 is ground and polished to a sharp edge, as shown in Fig. 10c; preferentially, the sharp blade is made of a hard metal such as tool steel but may be made from a single crystal of sapphire or similar hard material or may be made of a substrate impregnated with small particles of hard material such as diamond or carbide or other material. The cleave engine may be mounted on a carriage 423 and moved on a linear bearing 424 or otherwise. As each fiber is scratched in turn, the fiber cleaves under the bending (and optional tensile and twisting) force therewithin. In the case of a sharp blade made from a disc, as shown in Fig. 10c, the blade edge 901 may be sharp and round so that it may be rotated after multiple uses to expose a new portion of the scratching edge, so prolonging blade life. This example of the invention may be used for cleaving either a substantially perpendicular cleave or may be used to create an angled cleave on a single fiber or multiple fibers. It should be noted that the blade will suffer a resistive force as it tries to scratch the displaced fibers as the blade passes underneath because of the hardness of the glass of the fibers. This may introduce a twisting force to each fiber as it is being scratched, so imposing an unwanted twist in the fiber as it is being cleaved, leading to unintentional angling of the resultant cleaved end face(s). This twisting can be minimised by the use of a rubber-coated anvil to prevent twisting of the fiber as it is being scratched. Alternatively, in the case of cleaving single fibers, the end of the anvil may be angled at an angle a to prevent twisting, where the included angle between the direction of motion of the blade SS and the contacting edge of the anvil 303 is less than 90°, as shown in FiglOd. In the case of cleaving ribbon fibers where a moving blade scratches the pre-bent fibers as it passes underneath the fibers, the fibers may cleave sequentially as the blade scratches each fiber in turn as it passes beneath them. In the case where the fiber ribbon is tensioned by stretching the entire ribbon, the tension imposed on the remaining uncleaved fibers in the ribbon will progressively increase as each preceding fiber is cleaved, leading to excess tension in the later-cleaving fibers in the ribbon. In order to overcome this problem, alternative ways of tensioning the fibers maybe used. Firstly, the contact surfaces 551, 552 between the anvil and the clamped fibers may be shaped into a curve such that the fibers are stretched as well as being bent. The radius of curvature of the anvil contact surface should be such that the end of the anvil is in contact with the clamped fiber over a lateral distance LL1, LL2 exceeding 100microns in the direction along the length of the fiber(s), as shown in Figs. 11c, 11d. The anvil 51 (shown in Fig 11c) may have two arms and so be suitable for perpendicular cleaving, or the anvil 52 may have one arm (Fig. 11d) and so be suitable for angled cleaving; accurate shaping of the end of the (hard) anvil is required. Alternatively, the end of the anvil may be compliant, in which case the end of the anvil deforms under the pressure of bending the fiber, temporarily shaping the end of the anvil, so that the end of the anvil is in contact with the fiber over a prolonged distance of more than 100microns and preferably over a distance of up to 10mm. This contact between the compliant end of the anvil and the fiber(s) causes each fiber to stretch, so tensioning each fiber. Furthermore, each fiber is tensioned independently from its neighbouring fibers, so all fiberswill experience the same tension as each other as they cleave, even if they cleave at different times. The compliant end of the anvil should have a hardness of between 30Shore A and 90Shore A and preferably between 50ShoreAand 70ShoreA. Secondly, tensioning of the ribbon may be achieved by first stretching the ribbon to tension all of the fibers in the ribbon substantially equally. The stretch may then be locked into position, for instance by applying a locking means 65 or 75, as shown in Fig. 5b and Fig. 5c, to stop further movement of the clamp after the stretch has been applied. Consequently, the tension in the remaining fibers does not increase because, as subsequent fibers are cleaved, the stretch in each remaining fiber is not affected. Thirdly, tension may be applied to each fiber in the ribbon by perpendicular displacement of the fibers in between the clamping points, instead of applying tension by stretching the entire ribbon; this tension-inducing displacement may be caused by the bend imposed by the anvil which bends the fibers onto the blade, or it may be brought about by a separate deflecting means 501, as shown in Fig. 11a, moving in direction GG, which deflects the fibers at a point between the clamping points 8a, 8b and which is applied after clamping but prior to cleaving. Alternatively, as shown in Fig 11b, a deflecting means 502 may be applied in direction HH at a point between the clamping points 8a, 8b after clamping and priorto cleaving. This technique of applying tension may be used for a two-armed anvil used for creating a perpendicular cleave (Fig. 11a) and also for a one-armed anvil used for creating an angled cleave. Tension can also be introduced in to clamped fiber or fibers by displacing either of the clamps perpendicular to the plane of the fiber ribbon in direction QQ as shown for clamp 88b, which may be hard, semi-hard or compliant, as shown in Fig 11e forthe distal clamp 808b. The moving clamp may be positioned on the proximal side of the blade. In all of the above methods of tensioning the fibers, the tension in the later-cleaving fibers does not increase as the earlier-cleaving fibers are cleaved, and so may be used to create either a substantially perpendicular cleave or an angled cleave of a fiber or fibers. While embodiments of the present invention have primarily been illustrated above using a sharp diamond blade, it will be appreciated that other means may be used to create a starter crack from which a cleave will propagate to cleave the fiber. For example, a laser beam may be used to partially melt the surface of the fiber, forming a starter crack which will propagate across the fiber as a cleave under the influence of the applied stresses, where the stresses are generated using the above-described invention. Thus, it will be appreciated that the above-described embodiments are merely exemplary in nature. Thus, pursuant to embodiments of the present invention, methods are provided that may be used to create cleaved ends on a fiber or fibers, wherein the angle and quality of the cleaved fiber end are controlled. Embodiments of the present invention have been described above with reference to the accompanying drawings, in which embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth above. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” “comprising,” “includes” and / or “including” when used herein, specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms used herein should be interpreted as havinga meaning that is consistent with their meaning in the context of this disclosure and the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. All embodiments can be combined in any way and / or combination. Many variations and modifications can be made to the preferred embodiments without substantially departing from the principles of the present invention. All such variations and modifications are intended to be included herein within the scope of the present invention, as set forth in the following claims.

Claims

1. A fiber optic cleaving system for cleaving optical fiber or fibers, comprising:a cleave engine, located within a chassis, minimally containing a sharp blade assembly which includes a sharp blade edge for scratching the glass of a single or multiple optical fibers which may be arranged in a ribbonclamping means to locate and clamp the fiber or fibers at two or more positions within or on the chassis, outwith the cleave enginean anvil to displace the clamped fiber or fibers, acting at a location within the clamping locations, so imposing internal stresses on the fiberstwo edges, lying on either side of the point or points of action of the anvil, hereinafter referred to as bending edges,2. According to Claim 1, the anvil acts to bend the fiber or fibers over the bending edges to bring the fiber(s) into contact with the sharp edge of the blade assembly of the cleave engine, so scratching the fibers and causing them to cleave, each edge being located in either the cleave engine or in the chassis3. According to Claims 1-2, wherein the anvil falls under the force of gravity to bend the fibers over the two bending edges4. According to Claims 1-3, wherein the cleave engine consists of a sharp blade assembly and two bending edges5. According to Claims 1-3, wherein the cleave engine consists of a sharp blade assembly and one bending edge, the other bending edge being located in the chassis of the cleave system6. According to Claims 1-3, wherein the cleave engine consists of a sharp blade assembly, with the two bending edges being located in the chassis of the cleave system7. According to all preceding Claims wherein the clamped fibers are optionally tensioned8. According to all preceding Claims wherein the clamped fibers are optionally tensioned by stretching them by urging apart the clamping means9. According to all preceding Claims, wherein tension in the fiber(s) prior to cleaving may be provided by shaping the contact surface of the anvil with the fiber(s) such that the radius of curvature of the contact surface of the anvil has a larger radius of curvature than the radius of curvature which each fiber or fibers would experience when displaced at a single contact point, and where the radius of curvature of the contact surface of the anvil has a radius small enough so that the fiber(s) maintains contact with the contact surface of the anvil over a length exceeding 100microns.

10. According to all preceding Claims, wherein tension in the fiber(s) prior to cleaving may be provided by using a contact surface of the anvil which is compliant, with a hardness such that the fiber(s) have radius of curvature larger than the radius of curvature of each fiber or fibers would have if it were displaced at a single contact point by hard anvil, so that the fiber(s) maintains contact with the contact surface of the anvil over a length exceeding 100microns, wherein the Shore hardness of the compliant surface has a value between 30Shore A and 90Shore A and preferably between 50Shore A and 80Shore A11. According to all preceding Claims, wherein the clamped fibers are optionally stretched, subsequent to which stretching, the stretch may be fixed at a desired value by preventing further motion of the clamp(s) prior to cleaving12. Accordingto all preceding Claims, wherein the clamped fibers maybe optionally twisted before being scratched by the sharp edge of the blade assembly13. According to all preceding Claims, wherein the sharp blade assembly may be a single part consisting of a sharp blade or may consist of a sharp blade together with a support or supports to support, reinforce, mount and / or manipulate the sharp blade14. Accordingto all preceding Claims, wherein the sharp edge of the blade assembly is made of an edge formed by polishing one or more faces of a hard single crystal which may be crystallographically oriented15. According to all preceding Claims, wherein the sharp blade assembly is dismountably located in the body of the cleave engine16. According to all preceding Claims, wherein the sharp blade assembly is dismountably located in the chassis17. According to all preceding Claims, wherein the bending edge or edges of the cleave engine and / or the chassis and the two contact points of the anvil with the fiber(s) are located to give a cleaved end face within 5degrees of perpendicular and preferably within 0.5degrees of perpendicular18. According to all preceding Claims, wherein the anvil has 2 contact points with a single fiber, wherein the single fiber may be twisted after clamping and prior to cleaving and before or after bending, and such that the fiber cleaves with an end face more than 1 degree away from perpendicular19. According to all preceding Claims, wherein the anvil has one contact point with each fiber in the ribbon, with the contact end of the anvil consisting of one ridge which contacts the fiber or all of the fibers in the ribbon, to form an angled cleave, with the core of the fiber or fibers at an angle between 3 degrees and 20 degrees from the perpendicular and preferably between 6 degrees and 10 degrees from the perpendicular20. According to all preceding Claims, whereby, in the set up of the tool, the cleave engine may be raised or lowered towards the clamped fibers to alter the amount of bend in the fiber prior to cleaving in order to optimise the tensile and bending forces in the fiber.

21. According to all preceding Claims, whereby, in the set up of the tool, the cleave engine contains one bending edge and may be raised or lowered relative to a second bending edge in the chassis in order to alter the end angle of the cleave22. According to Claim 1 and Claims 6-21, wherein the anvil bends the clamped fibers over the bending edges displacing the fibers by a set distance, whereby the bending edges are located within the chassis, with further action of the anvil restricted by the presence of a stop to its movement, the anvil imposing an internal stress on the fibers, but where the sharp blade assembly of the cleave engine is not initially present, and subsequently the cleave engine is moved to bring the sharp blade edge into contact with the pre-stressed fibers to scratch them and cause them to cleave23. According to Claim 22, the cleave engine is moved to contact all of the bent fibers such that the sharp blade edge contacts all of the fibers substantially simultaneously24. According to Claims 22-23, the cleave engine is moved parallel to the plane of the plane of the fiber ribbon, sequentially scratching the bent fibers as it passes beneath25. According to Claims 1-24, a tool and method for cleaving optical fiber or fibers

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