JML Optical was contracted to make in high volumes a customer-designed, precision optical assembly for an FDA-regulated medical device. The assembly met all specifications and passed all in-process quality tests, but JML’s customer was experiencing a high rate of failure during system quality testing. Troubleshooting showed that the system failure was due to optical assembly performance.


How the optical assembly caused system test failure was not obvious. JML’s engineering team researched possible reasons including testing methods, material supply chain, fabrication, and assembly processes. A thorough tolerance analysis at the component level showed a clear statistical correlation between the amount of spherical aberration produced by a certain optical surface and the system-level test results.

JML proposed several changes that would address the performance issue. They included:

  • Implement a new component level testing process, focusing on spherical aberration
  • Design a new testing fixture for the assembly and calibrate it to the client’s testing equipment


After implementation of the first two changes above, the passing rate of system-level quality tests increased from 50% to 99%. The customer was able to decrease the acceptance testing rate for JML’s product from 100% to 8%.