It often becomes necessary to align an optical fiber with another optical fiber or an optical device such as a light-emitting diode, a laser diode, or an optoelectronic device such as a modulator. This can involve either carefully aligning the fiber and placing it in contact with the device to which it is to couple, or can use a lens to allow coupling over an air gap. In some cases the end of the fiber is polished into a curved form that is designed to allow it to act as a lens.
In a laboratory environment, the fiber end is usually aligned to the device or other fiber with a fiber launch system that uses a microscope objective lens to focus the light down to a fine point. A precision translation stage (micro-positioning table) is used to move the lens, fiber, or device to allow the coupling efficiency to be optimized.
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