通过观察塑料光纤远场辐射图 ,分析了阶跃型塑料光纤中的模式耦合效果 实验结果表明 ,阶跃型塑料光纤的模式耦合效果很明显 ,模式耦合从光纤传输 5米左右开始发生 ,到传输 2 0～ 30m时 ,模式耦合完成 ,光纤末端能量分布达到稳态 采用剪断法测量了塑料光纤的微分模式损耗 ,发现微分模式损耗随着模阶的增加而增加 ,大多数模阶的微分模式损耗在 15 0～ 180dB/km范围内 By observing the far-field radiation pattern of the plastic optical fiber, the mode coupling effect in the step-type plastic optical fiber is analyzed. Experimental results show that the mode coupling effect of the step-type plastic optical fiber is obvious. Mode coupling occurs from about 5 meters of optical fiber transmission to transmission 20 ~ 30m, the mode coupling is completed, and the fiber end energy distribution reaches a steady state. The differential mode loss of the plastic optical fiber is measured by the shearing method. It is found that the differential mode loss increases with the increase of the mode order and the most mode differential mode loss In the range of 15 0 ~ 180dB / km