A next-generation optical surface form inspection instrument for high-volume production applications (original) (raw)

Despite the introduction of phase-shifting interferometers in the 1980's, high volume catalog and camera production lenses are still inspected using qualitative visual fringe inspection methods. This error-prone inspection technique requires the human operator to quickly judge whether the lens "passes" or "fails" based on the appearance of the fringes. Although this method is sufficient for optics with > 0.25 wave of surface figure irregularity, it is not sensitive enough to properly inspect surfaces in the increasingly common 0.1 wave regime. Furthermore, as visual fringe inspection is not quantitative, it does not produce the statistical surface measurement data that is necessary to monitor and optimize production polish process yields. To overcome these disadvantages, we have developed a robust, quantitative lens surface inspection instrument. A compact, user-friendly, and economical 60 mm aperture Fizeau interferometer directly addresses production optical test applications, providing rapid vibration-robust optical surface measurements of P-V irregularity, RMS irregularity, astigmatism magnitude, and power via a simple touch-screen interface. Pass/Fail criteria are applied to these values, enabling accurate and repeatable sorting of production optics based on these quantitative values and eliminating human interpretive error. Batch statistics are also displayed and stored for customer inspection reports and rapid polish process feedback. This paper will also describe how next-generation Fizeau interferometers serve as part of a total optical production process improvement strategy.