Abstract
Refractive microlenses are nowadays widely used in optical systems. Characterizing their surface is essential to ensure their quality and to optimize their fabrication process. This is realized by optical surface profilers thanks to their vertical resolution, short measurement time and areal information. However, when measuring non-flat surfaces, errors appear caused by aberrations of the microscope objective used in such systems, which significantly limit the achievable quality of the manufactured spherical surfaces. Approaches have been proposed to tackle these errors, but none of them demonstrated its validity for measurements of high quality microlenses. In this work, we demonstrate that the surface error depends on the surface position within the field of view of the microscope objective and on the surface slope. We then explain how to record the value of this error experimentally: this can be done by measuring a reference ball placed at different positions in the field of view. We finally use a machine learning algorithm to fit the experimental data in order to correct subsequent measurements. We apply this approach to measurements performed by a 20× numerical aperture 0.6 microscope objective of a confocal microscope. The effectiveness of the proposed method is demonstrated by showing that the surface error corresponds to a RMS wavefront error of λ/7 before correction and of λ/50 after correction for glass microlenses used in the visible range. This method thus allows the use of high numerical aperture microscope objectives for an accurate characterization of microlenses. Likewise, the fabrication capability of microlenses in terms of slope and quality is greatly extended, which is especially important for aspheres or freeforms.
Highlights
Refractive micro-optics [1] is a key technology for many applications, such as fiber coupling, beam shaping, imaging and illumination systems [2,3,4]
We demonstrate that the surface error depends on the surface position within the field of view of the microscope objective and on the surface slope
The choice of the reference ball to record the surface error is based on dimensional considerations: the field of view when using the 20× numerical aperture (NA) 0.6 microscope objective under consideration is 800 μm × 800 μm
Summary
Refractive micro-optics [1] is a key technology for many applications, such as fiber coupling, beam shaping, imaging and illumination systems [2,3,4]. Among the different surface texture measuring instruments, confocal microscopes (CMs) [6] and coherence scanning interferometers (CSIs) [7] are especially suited to perform this task Both techniques possess a vertical nanometric resolution and provide areal topography contrarily to contact stylus scanning instruments that are developed to measure line profiles. J Beguelin et al non-contact measurement render these tools suited for large volume production These optical scanning surface profilers record images of the surface at different heights. The alternative correction method we propose is based on the assumption that the surface can be locally approximated by planes Under this assumption, the surface errors can be described as a function of the position within the field of view and the slopes of these planes.
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
