定义：
主要包含五氧化二磷（P2O5）的玻璃材料。

磷酸盐玻璃是主要包含五氧化二磷（P2O5）的玻璃材料，通常还包含其它化学组分。它可以作为激光增益介质，同时可以用于体激光器和光纤中。它最主要的优点在于对稀土离子的高兼容性（参阅稀土掺杂增益介质），例如铒（Er3+），镱（Yb3+）和钕（Nd3+）离子。
即在磷酸盐玻璃种可以掺杂高浓度激光活性稀土离子，而不会引起团簇等不利效应，该效应会产生淬灭效应而影响激光器性能。磷酸盐掺铒光纤中的掺杂浓度远高于石英光纤，高几个百分点是可能的。这可以实现短的光纤激光器和放大器，这不是该玻璃的唯一优势，还包括： 

• 短的光纤激光器谐振腔可以得到大的自由光谱范围，更容易实现单频工作。 
• 分布反馈激光器本身很短，而高掺杂磷酸盐光纤可以实现更有效的泵浦吸收。 
• 超短脉冲光纤激光器如果采用较短的光纤更不容易受非线性效应的影响。 

磷酸盐玻璃的一些其它性质包括： 

1. 高光学透射率的光谱范围从0.4μm到2μm，比石英玻璃稍窄。 
2. 磷酸盐玻璃中稀土离子的跃迁截面和上能态寿命很合适。例如，适合用于得到大增益带宽的光纤放大器，由于跃迁截面的光谱形状很宽和平滑。 
3. 磷酸盐玻璃的转变温度较低，约为365 °C。因此，磷酸盐玻璃端口在高功率工作时受热更易熔化。因此采用磷酸盐玻璃实现高功率光纤激光器和放大器时需要注意泵浦注入时不要使玻璃熔化。 
4. 磷酸盐玻璃比石英玻璃的光纤损伤阈值低很多，并且热导率也低很多。 
5. 与很多增益介质不同的是其光热系数dn / dT 是小于0的。这表明直接的热对热透镜效应的影响是负的（散焦），而附加的应力和膨胀效应的贡献是大于0的（聚焦）；总体的结果是热透镜效应很弱。 
6. 磷酸盐玻璃的非线性系数很低，比石英玻璃小3倍。 

磷酸盐和氟化物玻璃的混合物称为氟磷酸盐玻璃。类似的，还有磷硅酸盐玻璃和铝磷酸盐玻璃。这些玻璃也通常用作激光器增益介质。 

磷酸盐光纤和石英光纤结合一起得到的装置可能存在问题，因为两个不同材料由于具有不同的转变温度，因此熔接非常困难（当然也是有可能的）。

Definition: certain glasses from which certain optical fibers and laser gain media can be made, for example

More general terms: optical glasses

Phosphate glasses are glass materials based on phosphorus pentoxide (P2O5) with some added chemical components. They are used as laser gain media – both in bulk lasers and in the form of optical fibers. One of their primary advantages is their very high solubility for rare earth ions (→ rare-earth-doped laser gain media) such as erbium (Er3+), ytterbium (Yb3+) and neodymium (Nd3+). This means that high concentrations of laser-active rare earth ions can be incorporated into phosphate glasses without detrimental effects such as clustering, which could degrade the performance via quenching effects. For example, erbium-doped fibers can be made with much higher doping concentrations than silica fibers: several weight percent are possible. This allows the construction of rather short fiber lasers and amplifiers, which can be beneficial not only for reasons of compactness:

• A short fiber laser resonator implies a large free spectral range, making it easier to achieve single-frequency operation.
• A distributed feedback laser is inherently rather short, and a highly doped phosphate fiber then allows for more efficient pump absorption.
• A fiber amplifier for ultrashort pulses is less prone to nonlinear effects if it is made from a short fiber.

Some other characteristics of phosphate glasses:

• The spectral range with high optical transmission is about 0.4 μm to 2 μm – narrower than for silica glasses.
• The transition cross sections and upper-state lifetimes of rare earth ions in phosphate glasses are often favorable. For example, they are often well suited for making fiber amplifiers with large gain bandwidth, as the spectral shape of the transition cross sections is wide and quite smooth.
• Phosphate glasses have a very low glass transition temperature, typically below 400 °C. Therefore, phosphate fiber ends melt relatively easily when being heated in high-power operation. Special care is therefore required for pump injection when realizing high-power fiber lasers and amplifiers with phosphate glasses.
• Phosphate glasses exhibit a much lower optical damage threshold and a lower thermal conductivity than silica glasses.
• The opto-thermal coefficient dn / dT is negative, in contrast to many other gain media. This means that the direct thermal contribution on thermal lensing is negative (defocusing), whereas additional stress and bulging effects are positive (focusing); overall, thermal lensing can be rather weak.
• The nonlinear index of phosphate glasses is very low – nearly 3 times lower than for silica glasses.

Mixtures of phosphate and fluoride glasses are called fluorophosphate glasses. Similarly, there are phosphosilicate and aluminophosphate glasses. Such glasses are also often used as laser gain media.

The combination of phosphate and silica fibers in a device can be problematic, since fusion splicing of these different materials is difficult (although not impossible) due to the very different glass transition temperatures.

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