Mr. Rohan Kundu Profile

Rohan Kundu

at Fraunhofer-Institut für Angewandte Optik und Feinmechanik IOF

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Publications (2)

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Proceedings Article | 2 October 2023 Presentation + Paper

Multi-aperture pattern projection using arbitrary shaped microlenslets

R. Kundu, D. Michaelis, P. Schreiber, P. Schleicher, A. Schöneberg, R. Leitel, A. Tünnermann, U. Breyer

Proceedings Volume 12666, 1266608 (2023) https://doi.org/10.1117/12.2675559

KEYWORDS: Stray light, Lens arrays, Projection systems, Light emitting diodes, Light sources and illumination, Design and modelling, Collimation, Crosstalk, Micro optics

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Micro-optical projectors consist of a double-sided, aligned microlens array (MLA) with an absorptive slide mask array buried under the entrance condenser lenslets. While the exit lenslets project the slides, the condenser lenslets realize Kohler illumination of the multiple projector channels. To achieve high system transmission, the condenser lenslets have to be positioned in a space-filling arrangement. For arbitrary projected shapes, the slide further reduces the effective fill-factor of a channel. We propose to increase fill-factor and simplify architecture of the MLA by replacing the buried slides by condenser lenslets with certain elementary shapes, building an irregular entrance array with space-filling parqueting. The condenser lenslets´ apertures are imaged by the projector lenslets towards certain positions in the far-field, controlled by the decentration between condenser contour and projector vertex. This enables for optional ‘jigsawing’ of the intended pattern from elementary images. Any residual MLA regions, that cannot be covered by condenser lenslet apertures, can be excluded from projection by patterning with diffusor structures, which scatter away incident light under large angles. Now, that we have excluded the buried mask array, such double-sided MLA can be replicated not only as precise polymer-on-glass elements (POG), but also by cheaper high-volume techniques like injection molding (IM), making the latter attractive for the automotive industry. An automotive projecting chase light blinker based on this concept, employing controlled channel crosstalk, replicated as POG is presented. IM replication of MLA is currently underway. We evaluate the performance and present a brief outlook of mask-less, multi-aperture microoptics.

Proceedings Article | 21 June 2019 Presentation + Paper

Enhanced field-of-view structured illumination projector using stacked microlens arrays

Rohan Kundu, Peter Schreiber, Peter Dannberg, Stephanie Fischer, Chen Li, Uwe Zeitner, Andreas Tünnermann

Proceedings Volume 11062, 110620Y (2019) https://doi.org/10.1117/12.2525813

KEYWORDS: Projection systems, Light emitting diodes, Micro optics, Lenses, Computer aided design, Microlens array, Optical design, Manufacturing, Monochromatic aberrations, Optical lithography

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Current LED based structured illumination projectors use commercial objective lenses to project the pattern, leading to an increased size of the projector. We present a compact, pseudo-random pattern generator with an enhanced field of view (FOV) of 60° × 60° to project structured light for machine vision applications. The miniaturization of optics is achieved by utilizing the multi-aperture approach. Currently such multi-aperture projection optics have an FOV of about 20°. Enlarging the FOV of microlenses results in higher geometric aberrations. Aberration correction for wide FOV is done by distributing the optical power over several microoptical surfaces, as in traditional optical systems, leading to a design of stacked microoptics. The correction of dominant aberrations like astigmatism is done by employing anamorphic microlenses. Further enhancement of the FOV is achieved by continuously varying the FOV of the individual lenslets over the microlens array (MLA). Thus, every channel of the array projects light to a different region of the image plane, resulting in a symmetric and continuous filling of the FOV across the image field. Consequently, anamorphic irregular or 'chirped' MLAs with lenslets of varying focal length and orientation depending upon its location in the MLA are designed. This also requires the projection optics to be illuminated with a field dependent incidence for which a two lens condenser optic is designed. A regular condenser lens array couples the light into the channels similar to the scheme for Köhler illumination, while the stacked microoptics along with a bulk field lens image the slide object on to the projection plane. A corresponding prototype with stacked and chirped microoptics with buried apertures and slide structures is realized using advanced reflow technology and characterization of such an arrayed pattern projector is presented.

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