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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.

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The core diameter of a single-mode fiber is about 8 to 10m. 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 highprecision 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 AN-SYS software, showed that the fiber center displacement for the commonly used oblique PC connectors would be 0.9 m. This will significantly affect the eccentricity tolerances for single-mode applications, because a maximum of 1.5 m is acceptable. Using the resulting new standard ͑eccentricity Ͻ0.6 m͒ 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.

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