Ramadan W A, Wahba H H, Shams El-Din M A
Appl Opt. 2014 Nov 1;53(31):7462-9. doi: 10.1364/AO.53.007462.
We present a significant contribution to the theory of determining the refractive index profile of a bent homogenous optical fiber. In this theory we consider two different processes controlling the index profile variations. The first is the linear index variation due to stress along the bent radius, and the second is the release of this stress on the fiber surface. This release process is considered to have radial dependence on the fiber radius. These considerations enable us to construct the index profile in two dimensions normal to the optical axis, considering the refraction of light rays traversing the fiber. This theory is applied to optical homogenous bent fiber with two bending radii when they are located orthogonal to the light path of the object arm in the holographic setup (like the Mach-Zehnder interferometer). Digital holographic phase shifting interferometry is employed in this study. The recorded phase shifted holograms have been combined, reconstructed, and processed to extract the phase map of the bent optical fiber. A comparison between the extracted optical phase differences and the calculated one indicates that the refractive index profile variation should include the above mentioned two processes, which are considered as a response for stress distribution across the fiber's cross section. The experimentally obtained refractive index profiles provide the stress induced birefringence profile. Thus we are able to present a realistic induced stress profile due to bending.
我们对确定弯曲均匀光纤折射率分布的理论做出了重大贡献。在该理论中，我们考虑了控制折射率分布变化的两个不同过程。第一个是由于沿弯曲半径方向的应力导致的线性折射率变化，第二个是这种应力在光纤表面的释放。该释放过程被认为与光纤半径存在径向相关性。这些考虑使我们能够在垂直于光轴的二维平面内构建折射率分布，同时考虑穿过光纤的光线的折射。当具有两个弯曲半径的均匀光学弯曲光纤在全息设置（如马赫 - 曾德尔干涉仪）中与物臂的光路正交放置时，该理论可应用于此类光纤。本研究采用数字全息相移干涉测量法。对记录的相移全息图进行组合、重建和处理，以提取弯曲光纤的相位图。提取的光学相位差与计算得到的相位差之间的比较表明，折射率分布变化应包括上述两个过程，这两个过程被视为对光纤横截面上应力分布的响应。实验获得的折射率分布提供了应力诱导双折射分布。因此，我们能够呈现出由于弯曲而产生的实际诱导应力分布。
