Microlenses

Microlenses characterization can be performed in reflection (DHM R1000) or transmission mode (DHM T1000).

The DHM R1000 is a versatile instrument, measuring, with a nanometric vertical resolution, the topography of any microlens shape such as spherical, parabolic, cylindrical, square without a calibration process. Because no autofocusing or/and scanning procedures are necessary to perform the shape measurement, the DHM R1000 is an ideal tool for entire microlens wafer investigation and quality control. Moreover, digital processing tools, included in the Koala Software, allow fast, efficient and quantitative evaluation of shape information such as slope, radius, step height, sphericity,… A surface fitting with different models (polynomial, Zernike, spherical, cylindrical, parabolic) allows suppression of the micro-lens form factor to increase the visibility of defects, quantify the deviation of the surface in comparison to a perfect shape, and to measure the roughness parameters of the microlens surface.

The DHM T1000 has the same advantages than the DHM R1000 in terms of precision and versatility, but it measures the microlenses in transmission, The measured phase data is now related to the optical path length of the light passing through the microlens (integration of the refractive index along the thickness). A patented decoupling procedure allows  the separation of  the thickness and the unknown refractive index. In the case of a known refractive index, only a single measurement is needed to obtain the shape of the lens. For quality control of the microlens, quantitative aberration coefficients in term of Zernike polynomials can be measured with digital fitting procedures applied to the phase map. The difference between this fitting surface and the phase map increases the visibility of defects.

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