This PDF file contains the front matter associated with SPIE Proceedings Volume 11481, including the Title Page, Copyright information, and Table of Contents.

Transparent structures that refract light and form images are present in all living animals. Due to the evolutionary process, most of the eyes feature a gradient index lens (GRIN), which helps to reduce spherical aberration and improve overall image quality. The overview of various solutions in nature for clear vision is presented and discussed with the emphasis on the optical design. Examples of the octopus eye and the rainbow trout eye are considered and analyzed. The role of the GRIN structure in the lens will be closely examined using optical models with ray-tracing.

There are two types of color mixing, namely additive color mixing and subtractive color mixing. The color disk, essentially a top with its top painted has been known since antiquity and has been used to study color mixing. This paper will briefly review the elements of color mixing and the use of color disks to study color vision and perception from the time of Ptolemy to the present day.

Accommodation of the human eye relies on multiple factors, including – object size, monochromatic and chromatic aberrations, and vergence, and corrects defocus even in monocular conditions. Previous studies have been done to understand whether the retina can decode the sign of defocus as this may play a role for emmetropization and possibly also accommodation. Yet, findings have not been unambiguous and questions remain. Thus, in this study we tried to understand how accommodation makes use of defocus blur to detect the sign of defocus by performing experiments using a fast wavefront sensor in a vision testing system while eliminating other visual cues that may otherwise confound the analysis. A new automated method has been introduced to study monocular accommodation by using a currentdriven tunable lens (TL) to induce a random sequence of defocus step changes within the accommodative range of each observer. The response was captured in real time using a Hartmann-Shack wavefront sensor (HS-WFS) operating at 20 Hz while detecting aberrations and Zernike coefficients until 4th radial order across a 3 mm limited pupil. Foveal, parafoveal and perifoveal accommodation has been studied for young emmetropes and myopes to determine until which eccentricity accommodation is triggered. Our findings show that the accommodative range diminishes with eccentricity and at 14° (diameter) and beyond it becomes largely absent.

The human visual system has the ability to perceive differences in the relative positions of spatially localized objects that are smaller than the size or spacing of foveal cones under ideal conditions. It is referred to as “hyperacuity”. Vernier acuity, a form of hyperacuity, is sensitive to spatial alignment of lines or dots and observers can judge misalignments of about 2 arc seconds. However, thresholds depend upon the psychophysical experimentation method as well as stimuli parameters such as the size, shape, color and contrast etc. We are working to standardize the test for clinical use by developing an adaptive staircase psychophysical procedure which involves a response-oriented positioning of the stimulus in a 3-Down and 1-Up design. Responses were recorded using a 3-alternative forced choice technique for 7 different gap sizes (vertical separation) of the stimulus features ranging from 128 to 2 arc minutes with a test time of about 15-20 minutes. The standard deviations of the reported aligned responses were defined as a threshold in arc seconds. We performed this pilot study on five normal, healthy subjects for method validation. Thresholds were measured for different stimuli parametric conditions. The gap size versus thresholds functions were plotted. The mean difference between the high and reverse contrast was statistically significant only for a gap size of 32 arc minutes. This pilot study aimed at developing and validating an adaptive staircase technique using a user-friendly software for clinical use in screening diseases such as glaucoma in developing nations.

The photoreceptors are responsible for the conversion of optical images into neural signals that are conveyed to the visual cortex where vision is triggered. Rod photoreceptors provide night vision whereas cone photoreceptors provide daylight vision and color perception. The photoreceptors have commonly been represented as discrete but dense array of pixels despite of their elongated cellular structure. Earlier studies have suggested that they act as biological waveguides transmitting images from the inner to the outer segments. However, this understanding may not fully encompass their role in vision which is more related to that of optical antennas organized in such a way that optical image contrast and resolution is optimized. Here, we discuss the role of the photoreceptors analyzed as three-dimensional adaptable detectors of light (voxels) using electromagnetic principles. We show that this understanding is compatible with how light is perceived when being incident onto the retina at different angles in the effect commonly known as the StilesCrawford effect. We discuss how this can explain the reduced sensitivity to aberrations and chromatic blur of the threedimensional retina when compared to the common two-dimensional understanding of image formation in the eye. We show how the same principles may impact on emmetropization and ultimately how it may play a key role to prevent the onset or progression of myopia.

Recent advancements in visualization systems have triggered a growing demand for the objective and accurate comparison of user cognitive requirements when perceiving three-dimensional images demonstrated in different ways. In this work, we present the first comparative assessment of brain activity in subjects viewing stereoscopic images and volumetric images. Electroencephalography was employed to assess the short-term changes in event related potentials and neural oscillations which were further interpreted in terms of cognitive requirements for relative depth judgments. As a result, considerably higher activity have been registered in the beta band and gamma band in case of judging relative depth of stereoscopic images in comparison to performing a similar task on the volumetric display. In addition, the higher neural activity in the parietal area and occipital area has been observed in the case of stereoscopic images in the moments which reflect cognitive responses on the depth component of the visual stimulus. We suggest that the greater demands on cognitive load may lead to a faster onset of fatigue in a long-term perspective. Overall, EEG-based assessment of brain activity indicates that the depth extraction from volumetric images requires less cognitive effort in comparison to stereoscopic images.

We know that bright fringes on the observation-screen is the Fourier transform of light intensity that passes through diffraction slit (aperture) and we know according to Parseval and Rayleigh Theorems the power or energy of a function before and after Fourier transform is not changed that means the total intensity of light emerging slits is equal to the total intensity of bright fringes on the observation screen, but on the other hand according to destructive and constructive interference of light, some portions of the light passing through the slits destructively interfere to constitute dark fringes which means the total light intensity of fringes should be less than the total intensity passing through the slit. This is a violation of the Fourier transform. On the other hand, this paper is augmented by some very new experiments which show there are no photons in the dark fringes. A diffraction experiment by sticking narrow and small width mirrors on the dark fringes that according to the classical interpretation after destructive interference on the dark fringes should be reflected and could be found by sensors at other directions (specially reflection angle) and another experiment that by making a 1mm hole in the middle of the first dark fringe, we expect that photons can be detected by the light detector after destructive interference (passing through one another) behind the observation plan but no photon is detected. Finally, this paper provides a complete physical model associated with mathematical analysis and formulation that is based on the Schrödinger equation. This model answers to single Photon (electron) double-slit experiment with a high degree of accuracy.

The Mach-Zehnder Interferometer (MZI) is used to illustrate the long-standing wave-particle duality problem. How can the photon divide at the first beam splitter and yet terminate on either arm with its undiminished energy? Why is which-way (welcher weg) information incompatible with wave interference? How do we explain Wheeler’s delayed choice experiment? The position adopted is that the photon has two identities, one supporting particle features and the other wave features. There is photon kinetic energy that never splits (on half-silvered mirrors) or diffracts (in pinholes or slits). Then there is photon probability waves that do diffract and can reinforce or cancel. Interpretations of these two identities are suggested.

The glory is a small yet eye-catching and colorful optical phenomenon that can be viewed best from an airplane or elevated position above a sun-illuminated cloud. The glory is a back-scattering phenomenon that consists of colored rings centered on the anti-solar or shadow point. Its color purity and the size of its rings both contain information about the size distribution of cloud particles doing the scattering. Glories can be particularly fun to observe when your airplane is just entering or exiting a cloud layer, so that the geometric shadow of the airplane rapidly changes size while the constant-angle glory remains relatively unchanged. Cloudbows are essentially whitened versions of the rainbow, with colors removed because of the large degree of spectral overlap resulting from the cloud droplets being much smaller than rain drops. Tips will be given for understanding where and when to look to see and understand optical glories. Numerous photographs are shown to explain what to look for when you are flying and want to see a glory or cloudbow.

Astronomical phenomena fascinate people from the very beginning of mankind up to today. In this paper the authors will present their experience with photography of astronomical events. The main focus will be on aurora borealis, comet Neowise, total lunar eclipses and how mobile devices open up new possibilities to observe the green flash. Our efforts were motivated by the great impact and high number of viewers of these events. Visitors from over a hundred countries watched our live broadcasts.

In the fabrication processes of photonic crystals, structural disorder arises in the synthesised structures from the limitations in the resolution of the synthesis processes. Elucidating the structural-disorder influence helps reducing its optical effects and allows using it in technological applications. Natural photonic structures are interesting examples to investigate due to their resilience to structural defects. The benefit and cost of these defects are so far not understood. In this contribution, we investigated the structural disorder in one-dimensional photonic crystals occurring on the wings of beetles. We performed optical simulations allowing to assess the optical benefit and cost of such disorder.

Eggshell is essential for the reproduction of birds. The optical properties of their shells may have an impact on biological functions such as heat and UV protection, recognition by the parents or camouflage. Whereas ultraviolet reflection by bird eggshells has been superficially described in the scientific literature, the physical origin of this phenomenon remains poorly understood. In this article, reflectance peaks in the near UV range were observed by spectrophotometric measurements of hen eggshells. In addition, electron microscopy imaging revealed the presence of pores within the so-called “calcified shell” part (i.e., between ca. 20 μm and ca. 240 μm deep from the outer surface). The average radii of these pores range from 120 to 160 nm. Mercury intrusion porosimetry allowed to highlight a distribution of pore radii around 175 nm. Numerical and analytical predictions using scattering theory indicate that these pores are responsible for the optical response observed in the UV range.

Biomimetic components inspired by structures found in nature have led to enhanced performance and novel applications in numerous optical systems. Replicating biological nano- and microscale features typically requires complex and expensive fabrication methods. We make use of soft lithography to copy surface features found on two Philippine weevil species: Pachyrrhynchus congestus pavonius and Pachyrrhynchus congestus ocellatus. Microscopy reveals circular scales on the carapace of P. c. pavonius with an average diameter of 0.0651 mm. Similar scales are found on P. c. ocellatus, with a mean diameter of 0.0639 mm. Iridescence effects are observed in both species. Peak reflectance for the dorsal side of P. c. pavonius shifts from 631.31 to 601.37 nm with a 30 deg change in viewing angle. With an equivalent change in viewing angle, the dorsal side of P. c. ocellatus exhibits a reflectance peak transition from 558.37 to 510.13 nm. Customized molds are constructed that allow the forming of elastomeric casts of the ventral and dorsal surfaces of both weevil types using polydimethylsiloxane (PDMS). Micrographs of the PDMS replicas confirm that surface features are copied faithfully for both species. The elastomeric copy of P. c. ocellatus (dorsal) is scanned with a 50 mW, 514 nm Ar+ laser beam focused by a lens with focal length 5 cm. Diffraction patterns comprising a central maximum with concentric rings are generated. The biomimetic cast shows promise as an alternative diffractive element for generating circular patterns with variable intensity profiles.