本文采用远场光斑法和光强法测量了石英单模光纤的数值孔径. 实验结果表明，由光纤耦合条件不同导致的光斑形状变化，对数值孔径的测量影响不大，单模光纤的纤芯直径小，导致出射光存在较强的衍射现象，对数值孔径的测量造成较大的影响，无论采用光斑法还是光强法，需以衍射第 1 次极大为计算标准，尽量选择光斑中心为亮斑时测量其数值孔径. 此外，用远场光斑法进行测量时，观察屏到光纤的距离要合适，太短或太长都会增加实验误差.

Numerical aperture ( NA) of single-model quartz fiber is measured by the method of

far-field spot and light intensity. The experimental results reveal that the influence of the shape

of light spot changed with the op- tical coupling condition on the value of NA is not distinct

a lot. The strong diffraction due to the very small fiber core can affect the

measurement of NA remarkably. The first sub-maximum of the diffraction peak needs to be con-

sidered in the calculation in both methods. NA is measured when the center diffraction spot is

bright. The distance between the fiber and the observation plane is suitable in order to

decrease the experiment errors. Too long or too short distance can make the error increase

when using the far-field spot method.