Un objectif est un système optique constitué d'un ensemble de lentilles optiques simples ou composées (doublets ou triplets) en verre minéral ou organique qui forment une succession de dioptres sphériques, asphériques ou plans qui caractérise le premier élément de l'instrument d'optique qui reçoit les rayons lumineux émanant de l'« objet » (d'où l'origine étymologique du mot). Les rayons lumineux, issus de cet objet observé distant traversent l'objectif et en forment une . Quand l'objet est situé à grande distance, voire à l'infini, l'image se forme au foyer image de l'objectif. Dans le cas d'un objectif simple et peu épais, la focale est sensiblement égale à la distance qui sépare le foyer du centre de l'objectif (distance frontale image). Pour un même objet observé, plus la focale est longue et plus l'image obtenue est grande. Types Par définition, dans un instrument d'optique, les rayons lumineux entrent toujours par l'objectif et :

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Dielectric-sphere-based microsystem for optical super-resolution imaging

Gergely Huszka

Well-established imaging techniques proved that features below the diffraction limit can be observed optically using so-called super-resolution microscopies, which overcome Abbe's resolution limit. In traditional far-field microscopy, the introduction of fluorescent samples and engineered light paths was key for this breakthrough. In parallel, near-field techniques with similar performance were developed, but they suffered from a limited field-of-view. The merge of the two approaches was already demonstrated ~15 years ago, when micrometer-sized dielectric objects positioned on a sample were found to be able to image the sample with super-resolution. By observing the sample through the micro-object with a classical optical microscope, the latter could capture a virtual image showing sub-diffraction details. Although this way the near-field information transfer into the far-field by the micro-object was proven and found to be key for enabling super-resolution imaging, the limited field-of-view, as determined by the size of the micro-object, remained an issue. In this dissertation, a novel method is presented that provides a microscopy technique capable of achieving super-resolution without field-of-view restrictions. Based on previous studies, dielectric microspheres were chosen for this imaging technique. First, the working principle of these microspheres was explored by investigating both the illumination and the reflected light path. These findings provided a better understanding on the phenomena working behind microsphere-assisted imaging and allowed to create an engineering toolbox that can be used to design microsphere-based optical systems. This was followed by an investigation on microfabrication techniques, in order to create a microchip that can serve as a bridge between a single microsphere and the macro-sized-components of a classical optical microscope. The resulting chip was later embedded in a custom fixation system that allowed scanning of this microsphere over the sample, while keeping its position fixed compared to the microscope objective. The microscope mounted camera recorded pictures during the scan, which were used to generate a large field-of-view super-resolution image by stitching. After initial successes, the setup was improved in terms of robustness and application range. The new version allowed field-of-view in the millimeter range, while it could be operated in both oil- and water-immersion. Parallel imaging with an array of microspheres was also implemented, which further enhanced the imaging speed. The algorithmic background (including an automated scanning and image reconstruction protocol) of this microscopy method was developed in-house. Its validation showed superior performance compared to existing software. Future developments (e.g. employment of 3D-printing for mass-production, imaging in vivo biological samples, metrology applications) are envisioned. The findings presented here may pave the road for an easy-to-use, generalized super-resolution imaging system.

EPFL2018

Multiple-Field Approach for Aberration Correction in Miniature Imaging Systems Based on Wafer-Level Production

Nicolas Bongard, Hans Peter Herzig, Toralf Scharf

IIn mobile imaging systems, the most difficult element to integrate is the objective lens. Here we present an intermediate approach between the costly traditional objectives and the low-resolution objectives inspired by the compound eyes of insects. Our multi-field approach uses a small number of optical channels each imaging a portion of the desired field of view. The full-field image is reconstructed digitally. The optics of each channel is kept simple for wafer-level fabrication and its size is sufficient to obtain a reasonable resolution. We present the design and fabrication of a prototype using 9 plano-convex lenses for 9 channels. Glass lenses glued on a wafer are used to image a full-field of ±40° with an f-number of 3. The images obtained shows field curvature correction. A simple image reconstruction scheme is presented. In conclusion, multi-field objectives fabricated with micro-optics technology are thin, simple to mount, robust, and easily replicated

SPIE Digital Library2013

Point spread function models for digital holographic microscopy

Christian Depeursinge, Mihaela Marian

Few models, based on the diffraction theory, are proposed in order to evaluate the point spread function of different microscope objectives used in a digital holographic microscope. Because in holography the phase information is essential, a 3D amplitude point spread function (APSF), modulus and phase, is necessary, in order to properly deconvolute the 3D images obtained. Scalar Debye theory, paraxial approximation and vectorial Debye theory are used to solve the diffraction problem and the theoretical predicted 3D APSFs obtained. with these models are compared.

SPIE2004

Dielectric-sphere-based microsystem for optical super-resolution imaging

Gergely Huszka

EPFL2018

Objectif optique

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Dielectric-sphere-based microsystem for optical super-resolution imaging

Multiple-Field Approach for Aberration Correction in Miniature Imaging Systems Based on Wafer-Level Production

Point spread function models for digital holographic microscopy

Multiple-Field Approach for Aberration Correction in Miniature Imaging Systems Based on Wafer-Level Production

Point spread function models for digital holographic microscopy

Dielectric-sphere-based microsystem for optical super-resolution imaging