Formation and characterization of stochastic subwavelength structures on polymer surfaces

When PMMA is exposed to plasma, a stochastic surface morphology forms under certain conditions. The surface shows a notable transmittance increase in the visible spectral region. Moreover, the technology is an inexpensive alternative to the deposition of interference coatings to increase the light transmission of polymeric optical elements. The principle of antireflective subwavelength structures is also known from the "moth's eye". This work is driven by the need to fabricate such broadband antireflective morphologies on arbitrary shaped surfaces of different kinds of polymers. Beside PMMA, three transparent thermoplasts were chosen to analyze the physical processes in order to understand the structure formation. The plasma-polymer interaction was supported by Monte Carlo method to investigate the energy transfer of the ions on the substrate. The optical effect of the structured surfaces has been optimized by the use of spectrophotometry. The structure formation has been analyzed by AFM and SEM. The revealed effective pin shape was correlated with the results from spectral reverse engineering. The structure formation has been established on the surface of the polymers and shows a self-organized nature, since the topography was not prescribed from outside before or during the process. The differences in size, shape, and antireflective effect are specific for the particular polymer. The structure formation results from a combination of physical sputter-erosion and chemical etching. Aspect ratios of the pin structure above 1 can only be explained by anisotropic etching due to impact of high energetic plasma-ions. The structure has been modeled as effective medium, which allows for the subsequent description by means of graded-index layers. The occurrence of scatter losses can be kept low and might be negligible for many applications. Particular PET surfaces show an industrially appropriate transmittance increase in the visible spectral region after plasma treatment

Formation and characterization of stochastic subwavelength structures on polymer surfaces

When PMMA is exposed to plasma, a stochastic surface morphology forms under certain conditions. The surface shows a notable transmittance increase in the visible spectral region. Moreover, the technology is an inexpensive alternative to the deposition of interference coatings to increase the light transmission of polymeric optical elements. The principle of antireflective subwavelength structures is also known from the "moth's eye". This work is driven by the need to fabricate such broadband antireflective morphologies on arbitrary shaped surfaces of different kinds of polymers. Beside PMMA, three transparent thermoplasts were chosen to analyze the physical processes in order to understand the structure formation. The plasma-polymer interaction was supported by Monte Carlo method to investigate the energy transfer of the ions on the substrate. The optical effect of the structured surfaces has been optimized by the use of spectrophotometry. The structure formation has been analyzed by AFM and SEM. The revealed effective pin shape was correlated with the results from spectral reverse engineering. The structure formation has been established on the surface of the polymers and shows a self-organized nature, since the topography was not prescribed from outside before or during the process. The differences in size, shape, and antireflective effect are specific for the particular polymer. The structure formation results from a combination of physical sputter-erosion and chemical etching. Aspect ratios of the pin structure above 1 can only be explained by anisotropic etching due to impact of high energetic plasma-ions. The structure has been modeled as effective medium, which allows for the subsequent description by means of graded-index layers. The occurrence of scatter losses can be kept low and might be negligible for many applications. Particular PET surfaces show an industrially appropriate transmittance increase in the visible spectral region after plasma treatment

Deposition and spectral performance of an inhomogeneous broadband wide-angular antireflective coating

The gradient index coatings and optical filters based on them are a challenge for fabrication. In a round-robin experiment basically the same hybrid antireflection coating for the visible spectral region has been deposited with three different techniques: electron beam evaporation, ion beam sputtering and radio frequency magnetron-sputtering. Spectral performances of such one-side and both-side coated samples have been compared with corresponding theoretical spectra of the designed profile. Also, reproducibility of each process is checked

Miniature curved artificial compound eyes.

International audienceIn most animal species, vision is mediated by compound eyes, which offer lower resolution than vertebrate single-lens eyes, but significantly larger fields of view with negligible distortion and spherical aberration, as well as high temporal resolution in a tiny package. Compound eyes are ideally suited for fast panoramic motion perception. Engineering a miniature artificial compound eye is challenging because it requires accurate alignment of photoreceptive and optical components on a curved surface. Here, we describe a unique design method for biomimetic compound eyes featuring a panoramic, undistorted field of view in a very thin package. The design consists of three planar layers of separately produced arrays, namely, a microlens array, a neuromorphic photodetector array, and a flexible printed circuit board that are stacked, cut, and curved to produce a mechanically flexible imager. Following this method, we have prototyped and characterized an artificial compound eye bearing a hemispherical field of view with embedded and programmable low-power signal processing, high temporal resolution, and local adaptation to illumination. The prototyped artificial compound eye possesses several characteristics similar to the eye of the fruit fly Drosophila and other arthropod species. This design method opens up additional vistas for a broad range of applications in which wide field motion detection is at a premium, such as collision-free navigation of terrestrial and aerospace vehicles, and for the experimental testing of insect vision theories

CURVACE - CURVed Artificial Compound Eyes

International audienceCURVACE aims at designing, developing, and assessing CURVed Artificial Compound Eyes, a radically novel family of vision systems. This innovative approach will provide more efficient visual abilities for embedded applications that require motion analysis in low-power and small packages. Compared to conventional cameras, artificial compound eyes will offer a much larger field of view with negligible distortion and exceptionally high temporal resolution in smaller size and weight that will fit the requirements of a wide range of applications

A lightweight, inexpensive robotic system for insect vision

Designing hardware for miniaturized robotics which mimics the capabilities of flying insects is of interest, because they share similar constraints (i.e. small size, low weight, and low energy consumption). Research in this area aims to enable robots with similarly efficient flight and cognitive abilities. Visual processing is important to flying insects' impressive flight capabilities, but currently, embodiment of insect-like visual systems is limited by the hardware systems available. Suitable hardware is either prohibitively expensive, difficult to reproduce, cannot accurately simulate insect vision characteristics, and/or is too heavy for small robotic platforms. These limitations hamper the development of platforms for embodiment which in turn hampers the progress on understanding of how biological systems fundamentally works. To address this gap, this paper proposes an inexpensive, lightweight robotic system for modelling insect vision. The system is mounted and tested on a robotic platform for mobile applications, and then the camera and insect vision models are evaluated. We analyse the potential of the system for use in embodiment of higher-level visual processes (i.e. motion detection) and also for development of navigation based on vision for robotics in general. Optic flow from sample camera data is calculated and compared to a perfect, simulated bee world showing an excellent resemblance