针对熔融拉锥系统制得的熔锥型微纳光纤耦合器, 选择适当的连续函数描述其光场分布, 采用归一化的三角分布和矩形分布的加权叠加, 以及高斯分布和三角分布的加权叠加实现了模场沿 耦合器区域的连续变化; 利用局部模式耦合理论推导出腰区及腰区附近锥形区的耦合系数计算公式, 并得到微纳光纤耦合器输出光功率随拉伸长度的变化曲线.计算结果表明, 随着拉伸长度的增加, 光能量在两臂中来回交替耦合的程度变小并且呈现包络样, 直至腰区耦合功能消失.通过实时监测拉制微纳光纤耦合器的输出光功率, 得到火焰扫描宽度以及氢气流量对双纤失去耦合效应拉伸长度 的影响: 火焰扫描宽度(均匀腰区)越宽, 拉伸长度临界值越大; 氢气流量(熔融度)越大, 拉伸长度临界值越小.实验结果显示, 当光纤耦合器腰区直径达到1.6 μm时, 耦合功能消失, 两输出端口 光功率相同且恒定, 微纳光纤耦合器具备稳定的光学传输特性.

Choose the appropriate continuous function to describe the light field distribution of fusion biconical optical microfiber coupler which is made by a fusion tapering system. The weighted superposition of normalized triangular and rectangular distributions combine the weighted superposition of Gaussian and triangular distributions are used to achieve continuous changes in the mode field along the coupler region. The local mode coupling theory is used to derive the calculation formulas for the coupling coefficients of the optical microfiber coupler waist region and the tapered region near the waist region, and get the change curve of optical microfiber coupler output optical power with stretched length. Calculation results show that as the stretch length increases, the degree of light energy coupling back and forth alternately in both arms becomes smaller and appears envelope-like, until the coupling function of the waist region disappears. Among monitoring real-time data of the optical microfiber couplers′ output optical power, the effects of flame scan width and hydrogen flow on the length of two arms loss coupling effect are obtained. The flame scan width is wider, the uniform waist region is wider, the critical value of the stretch length is larger. The greater the hydrogen flow, the greater the melting degree, the smaller the critical value of the stretch length. The experimental results show that when the diameter of the fiber coupler reaches 1.6 μm, the coupling function disappears, the optical power of the two output ports is the same and constant, and the optical microfiber coupler has stable optical transmission characteristics.