Band 2, Heft 3

Resolving fine details of subcellular structures is key to understanding the organization and function of cellular networks. Recent advances in far-field fluorescence microscopy provide the necessary tools to analyze these structures with resolutions well below the classical diffraction limit in all three dimensions. Technical improvements go hand-in-hand with new versions of switchable fluorophores that allow nonlinear optical effects to be more efficiently used to push the resolution limit down further. High contrast combined with the wide spectrum of available colors currently endow these fluorescence-based super-resolution techniques with the power to study the complexity of subcellular organelles and the relation of their constituting components down to the molecular level and under physiological conditions. In this way, they give us a far better understanding of the assembly of macromolecular complexes and their functions within a cell than has been possible before employing conventional imaging methods. In this review, we give an overview of the technical state-of-the art of these technologies, their fundamental and technical trade-offs, and provide typical application examples in this exciting field.

The optical coherence tomography (OCT) is a non-invasive imaging technique, which recently has found important clinical micrometer applications. It allows noncontact and non-invasive cross-section imaging of the tissues with a depth resolution of about 10 µm. Similar to high-frequency ultrasound, the OCT shows real-time cross-sectional images of the tissue structures and tissue layers in a depth of a few millimeters. The OCT has evolved to an indispensable tool in ophthalmic diagnosis. An emerging application is the intraoperative use of OCT (iOCT). We developed the first commercially available device for the OCT, a universal OCT-Camera, which can be attached to the camera port of the different surgical microscopes. The OCT-Camera is completely integrated into the surgical procedure by enabling the OCT imaging before, during, and after microsurgery without interruption. The individual steps and the outcome of the surgical procedures, such as transplantation of the thin membranes or micro implants, are visualized in real time. The easy handling and first clinical applications of the iOCT were successfully demonstrated.

Optical coherence tomography (OCT), a spectroscopy technique, has been used in biomedical applications for about 20 years. It has evolved to a standard non-invasive examination procedure yielding detail-rich cross-sectional images of living tissue. With longer wavelengths in the IR spectrum and the availability of InGaAs detectors and cameras, OCT scanners now penetrate even deeper into the human tissue. This article presents technical improvements on an IR line-scan camera, which specifically benefits OCT applications.

The development of optical systems today is strongly supported by computer simulations. Computer ray tracing tools are well established in the field of geometrical optics for designing objectives, light channels, etc. Ray tracing is conceptually quite simple, which makes the implementation as well as the interpretation of ray tracing results easy, although the design of high-quality lens systems remains a challenging task. In the field of wave optics, there are software tools as well, but they are still not as mature as the ray tracing tools. The main reason for this is that numerically solving partial differential equations is numerically more complex and not as intuitive as ray tracing. Besides simple wave propagation, the main field of use of the wave optics methods today is the development of lasers and laser resonator and nonlinear optics. The optical properties of the media, in general, depend on the temperature and mechanical stresses. The interaction of the electromagnetic fields with matter, thus, has to self-consistently include thermomechanical computations.

In this study, a high volume low cost manufacturing method for microoptical microlens arrays on steep curved substrates using a microinjection molding technique was investigated. The design of the individual lenslets was performed using ZEMAX. This 3D microlens array in this study contains 1219 microlenses that are evenly distributed on its concave surface with a high fill factor. The overall field of view of this microlens array on curved substrates is more than 104°. To complete the manufacturing process, first the mold inserts were machined using a voice coil based fast tool servo technique, then the 3D microlens arrays were injection molded. The injection molding process parameters were evaluated using both experiments and numerical simulation for best molding results. In addition, both geometrical errors and optical performance tests showed that the molded polymer microlens arrays can be used in wide angle imaging applications. This study demonstrated that this combined process is capable of fabricating high precision microlens arrays at steep curved substrates at low cost. The microlens arrays created in this study have broad applications in optical, medical and biomedical domains. The success of this study provided a feasible solution for mass production of 3D microlens arrays on arbitrary substrates.

The aspherical plastic lens is commonly used in commercial optical products. The injection molding process introduces warpage and stress residue into the aspherical plastic lens. Mold flow software is generally used in injection molding simulation and successfully predicts molding warpage results. This paper attempts to link mold flow and optical design software by opto-mechanical analysis. The lens surface warpage can apply the Zernike polynomial and transform it to the optical aberration. Meanwhile, the injection molding process and the operation parameters also affect the plastic lens warpage value. Thus, according to optical software, the injection molding process parameters will affect lens optical performance. The plastic lens aberration results can evaluate the lens warpage effect and optimize the injection molding process parameters. Further, by reversing lens warpage aberration in the plastic lens model, it can preliminarily compensate for the warpage error in the lens design process.