Space and time multiplexing for field curvature correction in miniature imaging systems

The correction of field curvature by space or time multiplexing enables the design of a very simple imaging system for mobile device. Here, the optical design is presented and methods to correct the field curvature are discussed. This imaging system can be fabricated with wafer-level processes enabling large-scale and low cost productio

Experimental demonstration of ray-rotation sheets

We have built microstructured sheets that rotate, on transmission, the direction of light rays by an arbitrary, but fixed, angle around the sheet normal. These ray-rotation sheets comprise two pairs of confocal lenticular arrays. In addition to rotating the direction of transmitted light rays, our sheets also offset ray position sideways on the scale of the diameter of the lenticules. If this ray offset is sufficiently small so that it cannot be resolved, our ray-rotation sheets appear to perform generalized refraction

2D Optics on Bloch Surface Waves (BSWs) Based Platform: Polymer Lens and Prism

In this work, we use a novel platform concept based on Bloch Surface Waves (BSWs) and manipulate the BSWs propagation with two-dimensional (2D) dielectric patterns deposited on it. The concept opens a way to realize 2D integrated all-optics systems including sensing functionalities

Field curvature correction in multichannel miniature imaging systems suited for wafer-level production

Using multiple optical channels increases the number of design possibilities for the objectives of mobile imaging devices. For easy waferlevel fabrication, we start from a single optical element—a monocentric plano-convex lens. The quality of the areal image is used to select the size of the field of each channel. Each channel optics is axially positioned to reduce the effect of the image field curvature. The resulting device has a small number of channels and it images a full field of view of ±40 deg with an f -number of 3. Details of the optical design, of the fabrication process, and of the device performance are reported

High numerical aperture silicon collimating lens for mid-infrared quantum cascade lasers manufactured using wafer-level techniques

We present an aspheric collimating lens for mid-infrared (4-14 µ) quantum cascade lasers. The lenses were etched into silicon by an inductively coupled plasma reactive ion etching system on wafer level. The high refractive index of silicon reduces the height of the lens prole resulting in a simple element working at high numerical aperture (up to 0.82). Wafer level processes enable the fabrication of about 5000 lenses in parallel. Such cost-eective collimating lens is a step towards the adoption of quantum cascade lasers for all its potential applications

Silicon based micro-optical collimating element for mid-infrared Quantum Cascade Lasers

A realization of a high numeric aperture, aspheric, silicon based collimating element for the mid-infrared (4 – 14 microns) Quantum Cascade Lasers, suited for mass production using computer driven reactive ion etching is presented

Flicker-evoked changes in human optic nerve blood flow: relationship with retinal neural activity. Invest Ophthalmol Vis Sci.

PURPOSE. Visual flicker induces a response in human optic nerve blood flow (F onh ) and inner retinal activity, as assessed by laser Doppler flowmetry and electroretinogram (ERG), respectively. In this study the relationship was examined between the flicker-evoked changes in F onh (RF onh ) and ERG when various parameters of the stimulus were varied. METHODS. In five normal observers (mean age, 41; range, 25-62 years) F onh and ERG were recorded simultaneously in response to pure red (R) or pure green (G) flicker, as well as heterochromatic R-G flicker (30°field at the posterior pole). RF onh and the changes in the first (1F) and second (2F) harmonic amplitudes of the ERG were documented as a function of the frequency of pure luminance and equiluminant R-G flicker, the mean illuminance of 10-Hz luminance flicker, and the color ratio r ϭ R/(R ϩ G) of a 15-Hz heterochromatic R-G flicker. RESULTS. Frequency-dependent changes in RF onh were similar to those in both 1F and 2F amplitudes for equiluminant R-G flicker. RF onh and 2F amplitude increased and then saturated with increasing mean illuminance of luminance flicker. They both decreased similarly as the R-G flicker approached the r value corresponding to equiluminance. RF onh was positively correlated with both 1F and 2F amplitudes (r ϭ 0.55 and 0.31, respectively, P Ͻ 0.05) when these quantities were recorded as a function of frequency of R-G equiluminant flicker. RF onh was positively correlated with 2F amplitudes when both quantities were recorded as a function of mean illuminance of luminance flicker and r of heterochromatic R-G flicker (r ϭ 0.52 and 0.48, respectively, P Յ 0.01). CONCLUSIONS. Under specific experimental conditions, changes in human RF onh are similar to and correlated with those of the flicker ERG 1F and 2F amplitudes. These findings support a relationship between vaso-and neural activity changes in the neural tissue of the human eye. (Invest Ophthalmol Vis Sci. 2002;43:2309 -2316 R ecent experimental data obtained by laser Doppler flowmetry (LDF) in both animals and humans demonstrate that optic nerve head blood flow (F onh ) responds to modulation of retinal neural activity. 1-5 When this activity is modulated by luminance or chromatic flicker stimulation, 5 the variation of the F onh response (RF onh ), plotted as a function of various parameters of the stimulation (such as temporal frequency, modulation depth and relative chromaticity), is comparable to that of the retinal ganglion cell activity evoked by the same stimulus. 6 For example, for luminance flicker, RF onh is maximal at intermediate temporal frequencies (Tf ϭ 10 -20 Hz) and decreases at both low and high Tf, whereas, for equiluminant chromatic flicker RF onh decreases at Tf Ͼ 8 Hz. Although the ERG to flickering of uniform fields originates from a less localized retinal region than the pattern ERG, its use in the investigation of the neurovascular coupling is nevertheless legitimate, because it contains, in both monkeys 10 -13 and humans, 14,15 a component that strongly reflects neural activity in the inner retina. More specifically, whereas the first harmonic component of the response (i.e., the component at the stimulus frequency, 1F) is dominated by on-and off-bipolar cell activity (with a contribution, at low frequencies, from photoreceptors), 13 the second harmonic (i.e., the component at twice the stimulation frequency, 2F) is generated mainly from the inner retina, perhaps with a contribution of ganglion cells themselves. 12,15 The presence of a correlation of RF onh with ERG components' amplitude, when the flicker stimulus characteristics are varied, would provide evidence in support to the hypothesis that, in humans, visually evoked F onh changes are coupled with retinal neural activity. A nonselective correlation of RF onh with both 1F and 2F amplitudes would suggest a neuro-vascular coupling involving both outer (1F) and inner (2F) retinal activity, whereas a selective correlation with the 2F component would support a specific role of inner retinal activity in the neurovascular coupling. In this study, F onh and the ERG were therefore simultaneously recorded in response to various flicker stimuli with the purpose of determining whether a coupling exists between RF onh and the 1F and/or 2F amplitude components, how specific this coupling is with either ERG component, and whether the strength of this coupling depends on the type of stimulus. Physiological flicker responses can be elicited by both luminance and chromatic modulation at various frequencies. 6 A detailed analysis of these responses may therefore be accomplished by varying flicker luminance, frequency, and relative chromaticity. With the use of this approach, the study design included different experimental protocols in which stimuli of pure luminance modulation, presented at different mean illuminances and frequencies, pure chromatic modulation (equiluminant flicker) presented at different frequencies, and mixed luminance-chromatic modulation, presented at different relative chromaticities, were used. These types of stimuli provided a broad range of experimental conditions under which the association between vascular and neural responses was evaluated. From th