Optical fiber numerical aperture measuring method

Abstract

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.

Description

technical field [0001] The invention belongs to the technical field of optical fibers and relates to a measuring method, in particular to a measuring method for the numerical aperture of an optical fiber. Background technique [0002] Fiber lasers have developed rapidly in recent years. Fiber lasers are widely used in military, optical communications, scientific research, industrial processing, and medical fields due to their high conversion efficiency, good beam quality, and compact structure. The core optical device in the fiber laser is the doped fiber and the supporting passive fiber and energy transmission fiber. [0003] Numerical aperture is an important optical parameter of optical fiber. The physical meaning of numerical aperture is the size of optical device's ability to transmit light. For optical fiber, it means the ability of optical fiber to receive light radiation. It determines the optical fiber's light receiving angle and the divergence angle of the output,...

AI Technical Summary

Problems solved by technology

[0004] In the general specification for optical fiber GB1427b-2013, two basic methods for measuring the numerical aperture of optical fiber are stipulated: one is the refraction near-field method. Neel's equation, which allows the measurement of the refractive index n of the cladding 1 and the refractive index n of the core 2 , by the formula The value of the numerical aperture NA is calculated, but the equipment cost required by this method is very high; the second is the far-field light intensity distribution method, and the far-field numerical aperture NA is defined as the light intensity on the far-field radiation map of the optical fiber drops to the maximum value of 5 % of the sine value of the half angle, but this test method is for single-mode fiber or multi-mode fiber, and the beam energy distribution is Gaussian distribution or near-Gaussian distribution

However, high-power fiber lasers on the market mainly use large-mode field double-clad fibers. In order to obtain higher conversion efficiency and beam quality, this kind of fiber generally has a lower core numerical aperture and a higher cladding numerical aperture.

The spot energy distribution of this type of double-clad fiber is different from that of traditional single-mode fiber and multi-mode fiber. The energy is not Gaussian, so it is difficult to measure the double-clad fiber with the far-field light intensity distribution method.

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