Spatially coherent laser light can be coupled into an optical waveguide with nearly 100 percent efficiency. However, coupling light from a spatially incoherent source to a waveguide can be frustrating. Here the author describes how to efficiently couple blackbody radiation to optical fiber waveguides. The same basic principles hold for other types of waveguides, such as integrated optic waveguides. Radiation emitted from other types of extended sources, such as surface emitting LEDs or ionized gases, can be efficiently coupled to waveguides using the same techniques.
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