launch numerical aperture (LNA)

launch numerical aperture (LNA): The numerical aperture of an optical system used to couple (launch) power into an optical fiber. (188) Note 1: LNA may differ from the stated NA of a final focusing element if, for example, that element is underfilled or the focus is other than that for which the element is specified. Note 2: LNA is one of the parameters that determine the initial distribution of power among the modes of an optical fiber.

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