定义：
利用熔融石英或者其它相关材料制造的光纤。

光纤是一种长的柔性光学波导。它们主要是由玻璃或者聚合物材料制造的。熔融石英（二氧化硅）是在光纤光学中占主导作用的一种玻璃材料（尤其是在光纤通信中），因为它具有很多有利的性质： 

• 石英在很宽的波长范围内都是光学透明的。如果光纤预制棒是采用特定方法制造的非常纯（参阅光纤制造），那么在近红外光光谱区域，尤其是在1500nm波长附近，具有很低的吸收和散射损耗，为0.2dB/km量级（如图1）。 
• 石英在很高温度下可以拉制成光纤，并且玻璃转化温度范围也比较宽（相对较浅的粘度曲线）。 
• 石英光纤很用以切割和熔接。 
• 石英光纤具有很强的机械强度可以抵抗拉伸甚至弯曲，前提是光纤不是太粗并且光纤表面实现已经被处理好。采用一个聚合物保护套可以进一步的提高光纤的机械强度。石英管线端口即使采用非常简单的切割也能得到很平滑的、质量很好的表面。 
• 石英的化学组分是非常稳定的。尤其是，它不是吸湿的。 
• 石英玻璃可以掺杂各种材料。掺杂的一个目的是为了提高折射率（例如掺杂GeO2 或Al2O3 ）或者降低折射率（例如掺氟或者B2O3 ）。也可以掺杂激光活性离子（参阅稀土掺杂光纤）得到活性光纤，应用到光纤放大器或光纤激光器中。有时掺杂光纤纤芯也有时掺杂光纤包层，这样材料变成铝硅酸盐，锗硅酸盐，磷硅酸盐或者硼硅酸盐玻璃。尤其是活性光纤，纯的石英不适宜于作为宿主玻璃，因为它对于稀土离子的溶解度很低。这回由于掺杂离子形成团簇而引起淬灭效应，即使掺杂浓度适中的情况下也会发生。从这一角度考虑，铝硅酸盐玻璃更加适合。

图1：石英的损耗。在长波长区域，与振动共振效应相关的红外光吸收占主导。而较短波长区域，由无法避免的强度涨落引起的瑞利散射更加重要。在1550nm附近损耗有一个最小值约为0.2dB/km。很多通信光纤都是该量级。如果光纤包含氢氧根离子，那么在1390nm和1240nm附近还可以看到附加的峰值。 

• 石英具有很高的损伤阈值，即不易发生诸如激光诱导击穿等现象。这在应用到放大短脉冲的光纤放大器时非常重要。 
• 石英具有很低的克尔非线性效应，当非线性效应是有害效应时石英光纤的这一特性是非常有利的。然而，石英也非常适合产生克尔效应，由于很弱的吸收，因此三阶非线性系数与吸收系数的比值很大（尤其是在1500nm波长附近），而且弱的非线性效应可以在很长距离上积累利用。 

石英光纤可以应用到很多领域，例如光纤通信（非常短距离采用塑料光纤的情况除外），大多数的光纤激光器和放大器，以及光纤传感器。在发展各种不同石英光纤方面的很多工作和努力也进一步提高了这种光纤的性能，使其相比于其他材料有优势。 

还有采用纯的石英制造的光子晶体光纤，包含小的空气孔。它实现导波可以减小包层的折射率（通过提高空气的比例），也可以利用光子带隙效应。 

有些特殊领域需要采用一些非石英光纤： 

• 磷酸盐玻璃在需要稀土离子掺杂浓度的情况下需要用到。 
• 氟化物光纤包含重金属可以用于传输中红外光，以及当光纤激光器或放大器需要低能量的激光跃迁、很长的亚稳态寿命时。 
• 塑料光纤（聚合物光纤）更加便宜并且比石英光纤更粗，可以用于照明或者短距离数据传输。

Definition: optical fibers based on fused silica or related materials

More general term: optical fibers

Optical fibers are long and flexible kinds of optical waveguides. They are essentially always based either on some glass or on polymers (plastic optical fibers). Among the glasses, fused silica (amorphous silicon dioxide, SiO₂) is the dominating base material in fiber optics (particularly for optical fiber communications, → telecom fibers), because it has a number of very favorable properties:

• Silica has a wide wavelength range with good optical transparency. In the near-infrared spectral region, particularly around 1.5 μm wavelength, silica can have extremely low absorption and scattering losses of the order of 0.2 dB/km (see Figure 1), when the fiber preform is fabricated in very pure form with certain methods (→ fiber fabrication). Whereas a high transparency in the 1.4-μm region is achieved by keeping the concentration of hydroxyl groups (OH) low, a high OH concentration is better for good transparency in the ultraviolet region. For wavelength from ≈1.8 μm on, the multiphonon absorption leads to steeply rising absorption (infrared absorption edge).
• Silica can be drawn into fibers at reasonably high temperatures, and has a conveniently broad glass transition (a relatively shallow viscosity curve).
• Cleaving and fusion splicing of silica fibers works fairly well.
• A silica fiber has an amazingly high mechanical strength against pulling and even bending, provided that the fiber is not too thick and that the surfaces are well prepared. The mechanical strength of a fiber can be further improved with a suitable polymer jacket. Even simple cleaving (breaking) of silica fiber ends can provide nicely flat surfaces with sufficient optical quality.
• Silica is chemically rather stable. In particular, it is relatively resistant to water, even though humidity can cause a gradual degradation (“corrosion”), particularly at elevated temperatures; that can significantly reduce its failure stress limit. Problems may arise from hydrogen darkening, e.g. for fiber-optic sensors in oil and gas wells. In such cases, additional protective coatings may be required.
• Silica glass can be doped with various materials in order to improve various properties. One purpose of doping can be to raise the refractive index (e.g. with GeO₂ or Al₂O₃) or to lower it (e.g. with fluorine or B₂O₃). Doping is also possible with laser-active ions (→ rare-earth-doped fibers) in order to obtain active fibers, to be used e.g. in fiber amplifiers or fiber lasers. The fiber core and sometimes the fiber cladding are doped, so that the material is effectively e.g. an aluminosilicate, germanosilicate, phosphosilicate or borosilicate glass (→ silicate glasses). Particularly for active fibers, pure silica is usually not a very suitable host glass, because it exhibits a low solubility for rare earth ions. This leads to quenching effects due to clustering of dopant ions, even for moderate doping concentrations. Aluminosilicates are much better in this respect.
• Silica has a high damage threshold, i.e., a low tendency for phenomena such as laser-induced breakdown. This is important for, e.g., fiber amplifiers when applied for the amplification of short pulses.
• Silica has a particularly low Kerr nonlinearity, which is beneficial in many cases where nonlinear effects can be detrimental. Nevertheless, silica can be quite suitable for exploiting the Kerr effect since the ratio of χ⁽³⁾ and the absorption coefficient is rather large (particularly for wavelengths around 1.5 μm) due to the very weak absorption: the weak nonlinearity can be used over a long length.

Figure 1: Intrinsic losses of silica. At long wavelengths, infrared absorption related to multiphonon absorption (vibrational resonances) is dominating. At shorter wavelengths, Rayleigh scattering at the unavoidable density fluctuations of the glass is more important. There is a loss minimum of ≈ 0.2 dB/km around 1.55 μm. Some telecom fibers nearly reach that level. If the fiber contains hydroxyl (OH) ions, additional peaks at 1.39 μm and 1.24 μm can be seen in the loss spectrum.

Silica fibers dominate many applications, such as optical fiber communications (except for very short distances with plastic optical fiber), most fiber lasers and amplifiers, and fiber-optic sensors. The large efforts which have been invested in the development of various kinds of silica fibers have further increased the performance advantages of such fibers over fibers based on other materials (see below).

There are also pure silica fibers in the form of photonic crystal fibers, containing tiny air holes. Here, the guidance (waveguide function) is achieved either by a reduced effective index of the cladding (caused by a larger fraction of air) or by a photonic bandgap effect.

For special applications, certain non-silica fibers are required:

• Phosphate glass fibers can be advantageous when a high doping concentration of rare earth ions is required. There are also phosphosilicate fibers, which are silicate fibers doped with P₂O₅.
• Fluoride fibers containing heavy metals can be used for the transmission of mid-infrared light, and for fiber lasers or amplifiers where low-energy laser transitions with long metastable level lifetimes are required.
• Plastic optical fibers (polymer fibers) can be cheaper and thicker than silica fibers and are used e.g. for illumination purposes and for short-range data transmission.

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