定义：基于超辐射的光源。
 
超辐射光源（也称为ASE光源）是一种基于超辐射的宽带光源（白光光源）。（它通常误称为超发光光源，后者基于另一种不同的现象即超荧光。）一般来讲，超辐射光源包含激光增益介质，其受激后辐射光然后经过放大发光。 
超辐射光源具有很低的时间相干性，由于其辐射带宽很大（与激光相比）。因此极大的降低了光斑产生的可能性，这在激光光束中经常能看到。然而其空间相干性很高，超辐射光源的输出光能够很好的聚焦（类似于激光光束），因此比白炽灯得到的光强高很多。因此这种光源非常适用于光学相干断层扫描（Optical Coherence Tomography, OCT），器件特性分析（在光纤通信中），陀螺仪和光纤传感器中。可参阅词条超辐射二极管得到更多详细的应用情况。 
最主要的一种超辐射光源为超辐射二极管（Superluminescent Diodes, SLDs）和光纤放大器。基于光纤的光源输出功率更高，然而SLDs则体积更小，成本更低。二者的辐射带宽都至少有几个纳米和几十纳米，有时甚至大于100纳米。 
对于所有高增益的ASE光源来说，都需要仔细的抑制光学反馈（例如，来自于光纤端口的反射），因此它会产生寄生激光效应。对于采用光纤的器件，光纤内部的瑞利散射会对最终的性能指标有影响。 

图1：光纤放大器产生的ASE光谱，在不同泵浦功率的情况下计算得出的曲线。随着功率的提高，光谱往短波长方向移动（增益快速增大）并且谱线变窄。波长移动对于准三能级增益介质是正常的，而谱线变窄则发生在几乎所有的超辐射光源中。

Acronym: SFS

Definition: optical sources based on superluminescence

Superluminescent sources (also called ASE sources) are broadband light sources (white light sources) based on superluminescence. (They are sometimes erroneously called superfluorescent sources, which would be based on the substantially different phenomenon of superfluorescence.) Essentially, a superluminescent source contains a laser gain medium which is excited in order to emit and then amplify luminescent light.

A superluminescent source has a very low temporal coherence, resulting from the large emission bandwidth (compared with that of, e.g., a laser). That greatly reduces the tendency for laser speckle, as are often observed with laser beams, e.g. from laser diodes. On the other hand, the spatial coherence is usually very high: the output of a superluminescent source can be very well focused (similar to a laser beam) and is thus suitable for obtaining by far higher optical intensities than with an incandescent lamp, for example. This combination of low temporal and high spatial coherence makes such devices interesting for applications such as optical coherence tomography (OCT) (e.g. in the medical sector), device characterization (e.g. in optical fiber communications), gyroscopes, and fiber-optic sensors. See the article on superluminescent diodes for more details on applications.

The main kinds of superluminescent sources are superluminescent diodes (SLDs) and fiber amplifiers. Fiber-based sources can provide much higher output powers, whereas SLDs are much more compact and also cheaper. In both cases, the emission bandwidth is at least several nanometers and often tens of nanometers, sometimes even well above 100 nm.

For all high-gain ASE sources, it is very important carefully to suppress any optical feedback, e.g. via reflections from fiber ends, because this can lead to parasitic lasing. (Using a Faraday isolator may not be sufficient.) For fiber-based devices, Rayleigh scattering from within the fiber may introduce the final performance limitations.

Figure 1: Spectra of ASE from a fiber amplifier, calculated for different pump power levels. With increasing power, the optical spectrum shifts toward shorter wavelengths (where the gain grows more quickly) and becomes narrower. The former effect is typical for sources with quasi-three-level laser gain media, whereas the latter occurs in essentially all types of superluminescent sources. The simulation was done with the RP Fiber Power software.

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