Optical substrates with parallel surfaces are widely used in todays photonics devices. Whether they have flat (screens, filters, beamsplitters, crystals) or spherical (such as optical domes) surfaces, the metrology of such objects is complicated as they can cause unwanted interference which compromise the precision of the optical metrology performed.
We have developed a new instrument whose optical path is similar to that of Fizeau-type interferometers, but which uses a light source with low temporal coherence. This implementation brings to main advantages: it avoids the generation of interference generated by the back surface of the thin-plane parallel optics to be tested; it provides a significant degree of freedom when it comes to choosing a wavelength of test. This makes it possible to characterize optical components independently of their thickness, spectral transmission and coatings.
In this communication, we will detail the method developed and compare it with other wavefront sensing solutions. We will present results obtained on different samples and discuss the promise of this solution for manufacturing testing, whether for in situ process control or end-of-line testing.
Despite (thin) Plane-Parallel Optics are present in most of our optronics consumer goods, research optical setups or industrial systems, the metrology of such optical components remains challenging. This is principally because having parallel front and back surfaces makes it difficult to filter optical signal coming from each diopter. In the specific case of Fizeau interferometers arrangements for example, fringe pattern generated by the three-beam interference is not suitable for precise surface shape reconstruction of the sample of interest.
Imagine Optic has developed and patented a new approach that brings easy access to the optical testing of such samples, based on the combination of incoherent light and Shack Hartmann wavefront sensing. We will present the technique principle and how it works as implemented in a metrology system we called MESO. We will report the validation process of the approach and showcase results on real samples highlighting the advantages of the technique.
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