怎么定义特种光纤？

衣食住行，处处离不开纤维，光导纤维就是其中一类可以传输光信号的纤维。如今光纤也不仅仅用于通讯技术，利用纤维状的特征以及材料选择的灵活度，光纤在传感、能量、医疗等等领域都崭露头角。

怎么定义特种光纤？根据“RP Photonics Encyclopedia”介绍，就是“具有特殊设计或材料的光纤”。

Definition: optical fibers with special designs or materials

定义：具有特殊设计或材料的光纤

More specific terms: fluoride fibers, phosphate fibers, active fibers, polarization maintaining fibers, tapered fibers, photonic crystal fibers

更具体的术语：氟化物纤维，磷酸盐纤维，主动纤维，保偏纤维，锥形纤维，光子晶体纤维

Author（作者）: Dr. Rüdiger Paschotta

Specialty optical fibers are usually understood as optical fibers that have at least one special property, distinguishing them from standard fibers. However, there is no universally accepted definition of the term standard fiber. One may regard a standard fiber as a simple step-index fiber, made with standard material (in case of glass fibers: silica) and with common values of parameters like the core size and numerical aperture. 

特种光纤通常被理解为具有至少一种特殊特性的光纤，将其与标准光纤区分开。但是，现在也并没有标准纤维的普遍接受定义。我们一般可以将标准纤维视为简单的阶跃折射率纤维，它是由标准材料（在玻璃纤维的情况下为二氧化硅）制成，并具有诸如纤芯尺寸和数值孔径之类的参数的通用值。

 

Specialty fibers can then belong to various groups:

特种纤维可以属于下列分类：

Some fibers use non-standard materials. For example, there are fluoride fibers that can transmit in longer(infrared) wavelength regions (mid - infrared fibers). Also, there are phosphate glass fibers, which can be morehighly doped with laser-active rare earth ions. Radiation-resistant fibers are made from materials that are less affected by radiation and used for example in space applications. Some fibers are made from monocrystalline material; they are called single - crystal fibers. Single - crystal fibers are suitable for far higher power levels, particularly in the domain of ultrashort pulse amplification. But it istentatively more difficult to obtain a high output beam quality due to the inherent multimodenature. There are even liquid core fibers, offering wideband infrared transmission. Special materials may also be used for fiber coatings and jackets.

有些纤维使用非标准材料。例如，有氟化物纤维、硫系玻璃纤维，重金属氧化物纤维等可以在更长（红外）波长范围内传输（近、中红外纤维）。

 

此外，还有磷酸盐玻璃纤维，可以易于进行更高程度的活性稀土离子掺杂。耐辐射纤维由受辐射影响较小的材料制成，例如用于太空应用。一些纤维是由单晶材料制成的。它们被称为单晶纤维。单晶纤维适用于高功率激光器，特别是在超短脉冲放大器应用领域有突出性能。但是由于固有的多模特质，难以获得较好输出光束质量。另外，还有液芯光纤，可提供宽带红外传输。更重要的是，特殊材料也可用于纤维的涂层。

 

Active fibers, being doped with laser-active ions(generally with rare-earth ions), are often generally regarded as specialty fibers. Double-clad fibers, having an additional larger waveguide structure for pump light, are even more special.

掺有激光活性离子（通常掺有稀土离子）的主动纤维通常被视为特种材料纤维。双包层光纤具有更大波导结构用于泵浦光。

 

Some fibers exhibit extreme or specially tailored parameters, such as an unusually large fiber core diameter or a very high numerical aperture. Also, there are large mode area fibers, exhibiting particularly large-fiber modes. Dispersion-shifted fibers have tailored chromatic dispersion properties. In dispersion - decreasing fibers, the chromatic dispersion even varies over the length.

有些光纤表现出极端的定制参数，例如异常大的纤芯直径、方形纤芯、或很高的数值孔径。大模面积的光纤表现出特别大的模式。色散位移光纤具有定制的色散特性。在色散缓变光纤中，色散甚至会随着长度而变化。

 

There are fibers where the waveguide function is not obtained simply with a somewhat increased refractive index in the core ( step-index fibers), but in some other way. For example, there are photonic crystal fibers, containing air holes and therefore also being called holey fibers.

有些光纤不能简单地通过纤芯中的折射率略有增加而获得波导功能（阶跃折射率光纤），而是通过其他方式获得。例如，包含空气孔的光子晶体纤维，也称为孔状光纤或微结构光纤。

 

Polarization - maintaining fibers of different designs can be used to maintain a linear polarization state over arbitrarily long propagation distances. Single - polarization fibers guide only light with a certain polarization direction.

保偏光纤的结构类型灵活，可用于在任意长度传播距离上保持线性偏振的状态。单偏振光纤仅传导具有特定偏振方向的光。

 

Tapered fibers have been stretched to obtain reduced fiber diameter, which usually changes along the length. They can be used, for example, for mode field adapters.

锥形纤维被拉伸以获得较小的纤维直径，该直径通常沿长度变化。它们可以用于类似模式适配器等器件。

 

As there can be so different special properties, it is preferable to use a more specific term than specialty fibers, particularly in scientific publications.

这些特种工光纤由于具备种类繁多的特殊性能，因此在专门的应用领域一般会使用比“特种纤维”更具体的术语，尤其是在科学出版物中。

个人觉得 “RP Photonics Encyclopedia”中对特种光纤的定义还是非常准确的。最后一句话很重要，特种光纤在很多应用领域都起到了关键作用，领域之间的跨界很大，甚至没有交集（比如石油、和医疗），所以涉及到某一个行业，还是利用该行业内公允的术语来命名某一种光纤更为方便。

审核编辑：刘清