Low-coherence semiconductor light sources: devices and applications

Since the invention of the laser, there have been countless applications that were made possible or improved through exploiting its multitude of unique advantages. Most of these advantages are mainly due to the high degree of coherence of the laser light, which makes it directional and spectrally pure. Nevertheless, many fields require a moderate degree of temporal or spatial coherence, making conventional lasers unsuitable for these applications. This has brought about a great interest in partially coherent light sources, especially those based on semiconductor devices, given their efficiency, compactness, and high-speed operation. Here, we review the development of low-coherence semiconductor light sources, including superluminescent diodes, highly multimode lasers, and random lasers, and the wide range of applications in which they have been deployed. We highlight how each of these applications benefsits from a lower degree of coherence in space and/or time. We then discuss future potential applications that can be enabled using new types of low-coherence light.