The invention belongs to the technical field of optical fibers, and discloses an
optical fiber numerical aperture measuring method. The method comprises the steps that an
optical fiber to be measured is selected; the end faces of both ends of the
optical fiber to be measured are
cut to be flat, and are horizontally placed; the output end of the optical
fiber to be measured is adjusted, so that the
vertical projection of the output end of the optical
fiber to be measured is located at the center of a rotating disk; a
light source is injected into the input end of the optical
fiber to be measured through a
laser injection device, is output by the output end of the optical fiber to be measured, and is projected on a white screen to form a
light spot; the rotating disk is rotated, so that scribed lines on the white screen are tangent to both sides of the
light spot; point readings theta1 and theta2 on the rotating disk are recorded, and are substituted into a formula described in the description; and the
numerical aperture NA of a cladding is calculated. The method provided by the invention has the advantages of fast test and accurate and objective result, can measure a conventional single-mode optical fiber, a multimode optical fiber, a double-clad optical fiber, a
power transmission optical fiber and the like, and can solve the problem that the
numerical aperture of a large optical fiber is difficultly measured in the prior art.