The alignment of optical components is a key factor when designing and manufacturing multifiber optical systems. This problem can be treated as a standard multiobjective optimization problem and solved by numerical optimization methodologies. The core diameter of a single-mode fiber is ~9 µm, and any slight misalignment during manufacturing will cause signification optical losses in connections. Previous studies have shown that the currently used alignment methods for multifiber devices can increase the optical power summation of all fibers, but the results are not very accurate. This study first compares different numerical optimization methodologies that can be used to find the ideal connection position. Two indices are used to judge the performances of different methods: the required time and the optical power. Next, a two-stage optimization strategy is proposed to obtain a fast and accurate result. In the first stage, the Nelder-Mead simplex method is used to move toward the optimum position quickly. In the second stage, the steepest descent method with polynomial interpolation is applied to improve the accuracy because of the stability of the method.
The performance of the alignment governs the quality of the optical communications. The active alignment methods
search the position with highest optical power and connect fiber on this position. Thus, active method can adjust the
connection for different properties on the fiber end-face. In the literatures, the methods for the multi-fiber alignment can
increase the optical power summation of all fibers, but the results are not very accurate. This study used the numerical
optimization methods, the gradient based and non-gradient based methods, for the optical component alignment, and
discusses the performance on different optimization methods applied on multi-fiber alignment. There are two indexes
used to judge the performances of different methods: the required time and the optical power. It is obvious that the
gradient based methods can have the results with better optical power, and the non-gradient based methods are very fast
to converge, but the optical powers are still very small comparing to the gradient based methods.
Optomechanics is defined as the science or engineering of maintaining the proper shapes and positions of the functional
elements in an optical system. At the optomechanical interface, manufacturing tolerances affect the shape and position of
the surface in a lens system. Even very small variations will cause extra aberrations which degrade the optical
performance of a lens system. The traditional approach to the optomechanical tolerance design is a top-down process.
The optical designers typically designate the critical to quality parameters, such as tolerances of tilts, decenters, and
locations of optical elements. A significant drawback of this top-down process is that the tolerances determined by
optical designers do not take the real manufacturing and assembly process into consideration. As a result, some
tolerances are too tight for the manufacturing, and the yield rate of the production is difficult to improve. The objective
of this study is to develop a surface based optomechanical tolerance model that calculates the variation of the critical to
quality parameters for a lens system. The distribution of these parameters can be treated as inputs to the optical design.
Therefore, the optical performance will be predictable than the top-down approach, and the manufacturability of the
optical system can be improved.
Alignment of optomechanical components is important when designing and manufacturing optical systems. This study used an optical fiber as a case study to develop an alignment method. The core diameter of a single-mode fiber is about 9 µm, and any slight misalignment or deformation of the optical mechanism will cause significant optical losses in connections. Previous studies have shown that the currently used alignment methods are not efficient, and the precise position for the connection is not easy to locate. This study proposes a two-stage method to overcome these problems. In the first stage, the Nelder-Mead simplex method is used to move quickly to the optimum solution. In the second stage, a numerical optimization method is used to improve the accuracy. This study compares different numerical optimization method that can be used to find the ideal connection position. It can be concluded that the most stable method for the search direction is the steepest-descent method, because the light intensity distribution is similar to a Gaussian one, and the most efficient method for the step-size determination is polynomial interpolation. Therefore, the second stage uses the steepest-descent method with polynomial interpolation.
The core diameter of a single-mode fiber is about 8 to 10µm. Any slight misalignment or deformation of the optical mechanism will cause significant optical losses at connections. Previous studies have concentrated on improving the manufacturing process to obtain high-precision components. Although the precision can be controlled, misalignment may still occur owing to the contact stress on the connecting interface. This study used the finite-element method to simulate the contact status, and used MT-series connectors as examples. The connectors use a guide-pin structure to align the two contact surfaces, and use a spring or clip to maintain tight contact. Because the MT ferrules are made of plastic materials, they are softer than ceramic ones and the deformation strains are more significant. For the finite-element analysis, a solid model of the MT ferrule with a convex end, oblique angle, and fiber protrusion can be constructed according to the JIS C5981 standard. Results of a simulation, integrating the optimization technique and ANSYS software, showed that the fiber center displacement for the commonly used oblique PC connectors would be 0.9 µm. This will significantly affect the eccentricity tolerances for single-mode applications, because a maximum of 1.5 µm is acceptable. Using the resulting new standard (eccentricity <0.6 µm) to select ferrules, and making them into connectors, it is found that the insertion losses in 98% of connectors are less than 0.3 dB. This result satisfies the requirement for single-mode applications.
The alignment for optomechanical components is important in designing and manufacturing optical systems. This study
uses optical fibers for example to find suitable optimization strategies for optomechanical alignment. The core diameter
of the single-mode fiber is about 6μm to 9μm. Any slight misalignment or deformation of the optical mechanism will
cause signification optical losses during connections. The alignment methods can be divided into passive and active
ones. In the passive alignment, optical connectors, ferrules, and sleeves are used to align two optical fibers. In the active
alignment, the best connection position with minimum connection losses must be found, and users usually take a lot of
effort to do this. This study uses different optimum methodologies: non-gradient-based, gradient-based, and Hessian-based
methods, to find the optimum position. The non-gradient-based method has low accuracy and the efficiency cannot
be increased. The gradient-based methods seem to have better efficiency to find the optimum position because it uses
gradient information to calculate the search direction in every iteration. Finally for the Hessian-based methods, it is
found that the advantage of using Hessian matrix is not obvious because the light intensity distribution is similar to the
Gaussian distribution.
KEYWORDS: Connectors, Finite element methods, Optics manufacturing, 3D modeling, Signal attenuation, Single mode fibers, Ceramics, Solids, Surface finishing, Polishing
The core diameter of the single-mode fiber is about 0.006mm to 0.009mm. Any slight misalignment or deformation of the optical mechanism will cause signification optical losses during connections. Previous studies often concentrated on improving the manufacturing process to obtain high precision components. Although the precision can be controlled, misalignment may still occur due to the contact stress on the connecting interface. This study uses the finite element method to simulate the contact status, and takes the MT series connectors for examples. The MT series connectors use the guide-pin structure to align the both contact surface, and use the spring or clip to keep tight contact. Because the MT ferrules are made of plastic materials, they are softer than ceramic ones and the deformation strains are more significant. For the finite element analysis, the solid model of the MT ferrule can be constructed according to the fiber protrusion, oblique angle, physical contact (PC) radius, and JIS C5981 standard. Using the ANSYS software, simulation result showed that, the fiber center displacement would be 0.9μm for the usually used oblique PC connectors. It will significantly affect the eccentricity values for the single-mode applications because only 1.5μm can be accepted. Using this new standard (eccentricity < 0.6μm) to select ferrules, and making them into connectors, it is found that the insertion losses of 98% connectors are less than 0.3 dB. This result satisfies the requirement for single-mode applications.
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