定义：
通过切割光纤端口得到干净的表面。

光纤切割在光纤光学中是一种很重要的技术。当需要将光纤连接在一起，或者需要熔接在一起，或者将光射入光纤中，光纤端口需要处理得到干净的表面。通常，该表面需要非常平，至少在光纤纤芯区域非常平（有时需要在整个截面），并且表面有时需要垂直于光纤轴或者与光纤轴有一确定的角度。 
切割是获得这种表面的基本方法，有时是实现该目标进行的第一步。它是对裸光纤进行有控制的破坏过程。首先对光纤施加张力或者弯曲之前先将光纤的一端折断，例如，采用锋利的钻石，碳化物或者陶瓷叶片。这会使光纤在之前提到的点处折断：折断过程发生在整个光纤截面。通常，切割过程能得到两个干净的光纤表面。 
在光纤切割之前，需要采用包层剥离工具将光纤包层剥离，或者将其用合适的溶液溶解掉。后一技术即化学剥离在有问题的情况下需要用到，但是需要的时间更长。也可以采用热学剥离。 
当光纤端口比较脏时需要重新切割，因为很难直接清洁光纤端口。

目录

• 1 光纤切割工具
• 2 有问题的情况
• 3 判断切割结果
• 4 附加处理：抛光
• 5 光纤碎片的安全隐患

光纤切割工具
用于光纤切割的工具称为光纤切割刀。在词条光纤切割刀中描述了几种不同类型的切割机。一些简单便宜的切割刀经过一定的调节就足够应用于简单的情况。如果需要得到更高质量的切割面，并且不依赖于操作者的情况，需要采用机械精准的接合器，通常会更加昂贵。

有问题的情况
机械光纤切割刀的最优设置，尤其是施加的应力，与玻璃材料和光纤直径密切相关。通常光纤切割刀预先设置好的为标准直径为125微米的二氧化硅光纤。例如，要切割氟化物光纤或者硫化物光纤，需要根据多次重复的切割结果得出合适的参数值。
当光纤直径很大时，例如大于200微米，会很难切割，这时需要更大的张力。
光子晶体光纤问题更多，尤其当其具有很大的空气孔时，切割过程中最好减小光纤张力。采用空气包层的双包层光纤则面临更多的困难。
切割非标准光纤需要经过多次试验才能得到好的结果。有些情况甚至不能工作，这时需要更加繁琐的技术，例如研磨。若先采用合适的切割，再进行研磨会更快。

判断切割结果
可以从不同的角度判断切割的质量，主要根据应用的需要：

• 如果光纤需要熔接，切割的光纤表面需要与光纤轴严格垂直，并且在整个光纤截面上都需要很平滑。如果某一光纤有一个小的突起，即使在边缘附近距离光纤纤芯很远，也不能将两个光纤表面熔接在一起。并且只有在表面平滑的情况下，软化光纤的表面张力在熔接过程中才会最大限度的使光纤自对准。另外，由于非垂直切割得到的扭结形状会产生很大的耦合损耗，尤其是对于大模式面积光纤。
• 如果仅仅是将光从光纤端口入射进去，或者从端口提取光，而不需要将光纤端口与其它固体部分发生接触，只需要在光纤纤芯区域保证表面平滑即可。如果能够控制光纤的指向（或者一个聚焦的或者准直的透镜）来校正倾斜角，那么即使不是垂直切割也不太相干。
•  如果在应用时对背向反射非常敏感，则需要比较大的切割角度。由于回波损耗与切割角度指数相关，例如当切割角为6°时则不满足需要，而需要8°。（光纤的有效模式面积越大，需要的切割角度越小。）
• 相反的，如果需要利用光纤端口的菲涅尔反射（例如，制作光纤激光器），需要切割角度很小，远小于光纤模式对应的光束发散角。在这一角度考虑，大模式面积光纤更加需要。

有时需要显微镜来仔细观察得到的光纤表面。存在手提式的显微镜用于这一目的，并且熔接装置通常都包含一个显微镜。
在使用光纤之前检查其切割端面非常必要，否则可能会引入很大的错误。即使采用机械精准的切割刀也不一定得到可信的结果，因为它还需要准确的设定，并且可能由于切片的缺陷而影响结果，这不容易被发现。

附加处理：抛光
若需得到非常高质量的光纤表面，通常在切割之后进行抛光处理。可以将光纤端口放入一个空心玻璃管内，用胶水固定。胶水使光纤强度变大，然后将其放入抛光装置中。光纤与玻璃管同时被抛光。这一过程可以得到任意取向的非常高质量的光纤表面。但是这比简单的切割过程耗时长很多。

光纤碎片的安全隐患
切割光纤后会得到很小的光纤碎片，其端口非常锋利。如果沾在手指上就有可能进到眼睛里。它们还会插入皮肤并且很难拔出来。另外也不能吞掉光纤碎片。
因此，光纤碎片在丢弃之前需要被妥善放置在一个带标记的容器里面。并且，需要做一些预处理使其能在工作区域看到，例如可以在工作区域底下放置黑色的垫子。 
 

Definition: preparing fiber ends with clean optical surfaces by controlled breaking

Fiber cleaving is an important technique in the area of fiber optics. When optical fibers are connectorized, when they should be fusion-spliced or when light should be launched into fibers, the fiber ends need to be prepared such they have clean surfaces. Usually, such surfaces should be as flat as possible, at least over the area of the fiber core (sometimes over the full cross-section), and often it is important that the surface is either perpendicular to the fiber axis or has a well-defined angle against the fiber axis.

Cleaving is the standard method to obtain such surfaces, or sometimes the first step towards that goal. It is a process of controlled breaking of the glass of a bare fiber. It begins with making a tiny fracture (scratch) on the side of the fiber, e.g. with a sharp diamond, carbide or ceramic blade, before or while some defined tension or bending is applied to the fiber. This causes the fiber to break, starting at the mentioned fracture point: the fracture rapidly propagates over the full fiber cross-section. Often, the cleaving leads to a very clean surface of the obtained two fiber parts.

Note that cleaving is not cutting, as the bulk of the process is just breaking. Only the initial tiny break is prepared with a blade.

Before cleaving, a fiber coating needs to be stripped off with a coating stripper tool, or dissolved with a suitable solvent. The latter technique – chemical stripping – may be required in problematic cases, but takes more time. Thermal stripping may be another option.

Sometimes, a new cleave is required when a fiber end has become dirty, as it is hard to reliably clean fiber ends.

Fiber Cleaving Tools

Tools for fiber cleaving are called fiber cleavers. Different kinds of such instruments are explained in the article on fiber cleavers. Simple and inexpensive cleavers, based e.g. on some pen-shaped scribes, are sufficient for simple purposes, when used with proper training. For a higher and more consistent cleave quality, which is less dependent on the operator, mechanical precision splicers are used, which are substantially more expensive.

Problematic Cases

The optimum settings of a mechanical fiber cleaver – in particular, the applied tension – substantially depend on details like the glass materials and the fiber diameter. Often, fiber cleavers are pre-adjusted for silica fibers with the standard diameter of 125 μm. For fluoride fibers or other mid-infrared fibers, for example, one may have difficulties finding suitable parameters for repeatable cleaving results.

Fibers with particularly large diameters, e.g. beyond 200 μm, can also be difficult to cleave. They need a higher tension force.

Photonic crystal fibers are also more problematic, particularly if they have large air holes. A somewhat reduced fiber tension during the cleaving process may help. Double-clad fibers with an air cladding are particularly challenging.

Cleaving of non-standard fibers may take many experiments and substantial practicing time until it works well. In some cases, it will not work at all, and more cumbersome techniques such as polishing (see below) are then required. Of course, a reasonable cleave is desirable as a starting point for quicker polishing.

Judging the Cleaving Results

The quality of the obtained cleaves has different aspects, the relevance of which depends on the application:

• If fibers should be fusion-spliced, the cleaved surfaces should be quite precisely perpendicular to the axis and must be smooth over the whole fiber cross-section. For example, one could not properly but together the fiber surfaces if a fiber had a small protrusion (a part standing out), even if that is only near the edge, far away from the fiber core. Also, only for smooth regular surfaces, the surface tension of the softened fibers will optimally self-align the fibers during the fusion process. In addition, a kink shape due to non-perpendicular cleaves can cause substantial coupling losses, particularly for large mode area fibers.
• If one only wants to launch light into a fiber end, or extract light from a fiber end, without having to bring the fiber end into contact with some other solid part, it may be fully sufficient to have a smooth surface only over the area of the fiber core. Some deviation from a normal (perpendicular) cleave may be irrelevant if the orientation of the fiber (or possibly that of a focusing or collimation lens) can be controlled for correcting the tilt angle.
• If the application is very sensitive to back-reflections, a large enough cleave angle is required. As the return loss depends exponentially on the cleave angle, it may not be acceptable e.g. to obtain only 6° instead of 8°. (Note that the larger is the effective mode area of the fiber, the smaller is the required cleave angle.)
• Conversely, if the Fresnel reflection of a fiber end needs to be exploited (e.g. for building a fiber laser), it is important to keep the cleave angle small – well below the beam divergence angle corresponding to the fiber mode. Large mode area fibers are more critical in this respect.

A microscope may be required to properly inspect the obtained fiber surfaces. There are hand-held microscopes for such purposes, and fusion splicing apparatuses also often contain a microscope.

Note that it is often very worthwhile to carefully inspect fiber cleaves before using them, as later on it may be much more tedious to locate a fault. Even with a mechanical precision cleaver, the results may not be fully reliable, because they require correct settings and can be spoiled by a defect blade, which is not easy to recognize.

Additional Treatment: Polishing

For very high-quality fiber surfaces, it is often necessary to apply some polishing procedure after cleaving. One may, for example, insert the fiber end into a hollow glass tube and fix it there with a glue. The tube gives the fiber a higher strength and is inserted into a polishing apparatus. The fiber is polished down together with the glass tube. This procedure allows one to produce a high-quality surface with an arbitrary well-defined orientation of the fiber surface. However, it takes substantially more time than simple cleaving.

Laser Cleaving of Fibers

There are laser-based devices (containing a CO₂ laser) which allow the preparation of fiber ends as an alternative to cleaving. Strictly speaking, the used process is not cleaving (which is a mechanical breaking process) but rather something like laser cutting. Nevertheless, it has become common to name it laser cleaving, because it produces similar results.

The reliability and resulting quality is substantially better than with real mechanical cleaving, and this of course leads to substantial advantages in terms of yield and working time. That is particularly the case when polishing steps have to follow; the time spent on those (and the amount of used consumables) can be reduced due to the improved starting quality. On the other hand, a laser lever is of course substantially more expensive than a mechanical cleaver.

Particularly substantial advantages of laser leaving are obtained when working with fiber arrays, since multiple fibers can be very quickly and consistently processed together.

Safety Risks from Fiber Scraps

When fibers are cleaved, one obtains small fiber scraps, which have extremely sharp ends. They may stick to a finger and can then be transported into an eye. They can also easily penetrate the skin and are hard to pull out. Fiber scraps should also not be ingested.

For such reasons, it is important to carefully dispose fiber scraps into a properly marked container (collection bin) before they get lost. Also, one should take precautions to make them well visible in the working area, for example by using a black pad below the working area. In addition, one should avoid any eating or drinking near the work area.