Tolerance Design of Optical Micro-Bench by Statistical Design of Experiment

초록

Design rule of optical micro-bench and tolerance of positional error of components assembled onto the bench are investigated in case of simple linear connections of incoming and outgoing optical fibers with and without ball lenses. Since there are many error variables with wide range of values that affects the optical coupling, the efficient array with reduced number of combinations is generated using statistical design of experiment and coupling efficiencies are calculated. From 3 dB point, the tolerance of each position error is determined. For the fiber-to-fiber connection with ball lenses, the longitudinal and lateral positional errors have the strong interaction each other to the coupling efficiency and thus should be limited simultaneously. Figure 1 shows the schematics which defines positional variables with possible errors. Figure 2 shows the coupling efficiency as a function of ΔL1 and ΔL2 with L1 = L2 = 60 um. From Figure 2, the tolerance limit of the input port can be set as -25 um≤ΔL1≤35um and that of the output port -40um≤ΔL2≤40um. The effect of off axis alignment error, ΔX1 and ΔX2, on the coupling efficiency is shown in Figure 3. The 3dB condition shows the tolerance of -2um ≤ ΔX1≤1.8um and -3um≤ΔX2≤3um. It is found the efficiency depends more on the errors in the input stage as following relationship.