Chromatic Modulation Research Articles

Electrochromic nanopixels with optical duality for optical encryption applications

Abstract Advances in nanophotonics have created numerous pathways for light–matter interactions in nanometer scale, enriched by physical and chemical mechanisms. Over the avenue, electrically tunable photonic response is highly desired for optical encryption, optical switch, and structural color display. However, the perceived obstacle, which lies in the energy-efficient tuning mechanism and/or its weak light–matter interaction, is treated as a barrier. Here, we introduce electrochromic nanopixels made of hybrid nanowires integrated with polyaniline (PANI). The device shows optical duality between two resonators: (i) surface plasmon polariton (SPP)-induced waveguide (wavelength-selective absorber) and (ii) ultrathin resonator (broadband absorber). With switching effect of between resonant modes, we achieve enhanced chromatic variation spanning from red to green and blue while operating at a sub-1-volt level, ensuring compatibility with the CMOS voltage range. This modulation is achieved by improving the light–matter interaction, effectively harnessing the intrinsic optical property transition of PANI from lossy to dielectric in response to the redox states. In our experimental approach, we successfully scaled up device fabrication to an 8-inch wafer, tailoring the nanowire array to different dimensions for optical information encryption. Demonstrating distinct chromaticity modulation, we achieve optical encryption of multiple data bits, up to 8 bits per unit cell. By capitalizing on the remarkable sensitivity to the angular dependence of the waveguiding mode, we further enhance the information capacity to an impressive 10 bits per unit cell.

Einstein beams and the diffractive aspect of gravitationally-lensed light

The study of light lensed by cosmic matter has yielded much information about astrophysical questions. Observations are explained using geometrical optics following a ray-based description of light. After deflection the lensed light interferes, but observing this diffractive aspect of gravitational lensing has not been possible due to coherency challenges caused by the finite size of the sources or lack of near-perfect alignment. In this article, we report on the observation of these wave effects of gravitational lensing by recreating the lensing conditions in the laboratory via electro-optic deflection of coherent laser light. The lensed light produces a beam containing regularities, caustics, and chromatic modulations of intensity that depend on the symmetry and structure of the lensing object. We were also able to observe previous and new geometric-optical lensing situations that can be compared to astrophysical observations. This platform could be a useful tool for testing numerical/analytical simulations, and for performing analog simulations of lensing situations when they are difficult to obtain otherwise. We found that laboratory lensed beams constitute a new class of beams, with long-range, low expansion, and self-healing properties, opening new possibilities for non-astrophysical applications.

Parasympathetic and sympathetic control of emmetropization in chick

Emmetropization can be altered by temporal visual stimulation and the spectral properties of the visual environment. The goal of the current experiment is to test the hypothesis that there is an interaction between these properties and autonomic innervation. For that purpose, selective lesions of the autonomic nervous system were performed in chickens followed by temporal stimulation. Parasympathetic lesioning involved transection of both the ciliary ganglion and the pterygopalatine ganglion (PPG_CGX; n = 38), while sympathetic lesioning involved transection of the superior cervical ganglion (SCGX; n = 49). After one week of recovery, chicks were then exposed to temporally modulated light (3 days, 2 Hz, Mean: 680 lux) that was either achromatic (with blue [RGB], or without blue [RG]), or chromatic (with blue [B/Y] or without blue [R/G]). Control birds with lesions, or unlesioned, were exposed to white [RGB] or yellow [RG] light. Ocular biometry and refraction (Lenstar and a Hartinger refractometer) was measured before and after exposure to light stimulation. Measurements were statistically analyzed for the effects of a lack of autonomic input and the type of temporal stimulation.In PPG_CGX lesioned eyes, there was no effect of the lesions one-week post-surgery. However, after exposure to achromatic modulation, the lens thickened (with blue) and the choroid thickened (without blue) but there was no effect on axial growth. Chromatic modulation thinned the choroid with R/G.In the SGX lesioned eye, there was no effect of the lesion 1-week post-surgery. However, after exposure to achromatic modulation (without blue), the lens thickened and there was a reduction in vitreous chamber depth and axial length. Chromatic modulation caused a small increase in vitreous chamber depth with R/G.Both autonomic lesion and visual stimulation were necessary to affect the growth of ocular components. The bidirectional responses observed in axial growth and in choroidal changes suggest that autonomic innervation combined with spectral cues from longitudinal chromatic aberration may provide a mechanism for homeostatic control of emmetropization.

Optimized Multi-Primary Modulation for Visible Light Communication

Multi-primary modulation scheme has the potential to provide robust visible light communication links and mitigate any color fluctuations by providing identical chromaticity modulation alphabets. This work describes constellation optimization technique for multi-primary modulation (MPM), which shows that using different power levels for the primary lights can lead to obtain the same color and, furthermore, enhance the Euclidean distances between data symbols in the multi-dimensional color space. The bit error rate performances of the optimized MPM and the original non-optimized MPM schemes are evaluated considering indoor optical wireless channel models with additive white Gaussian noise. The results show that the optimized MPM provides better spectral efficiency and outperforms the original non-optimized MPM scheme by achieving up to 3.5 dB Signal-to-noise ratio gain for the same spectral efficiency and, therefore, opens doors for implementation of robust visible light communication links exploiting multi-color light sources.

Preparation and Chromaticity Control of CoTiO3/NiTiO3 Co-Coated TiO2 Composite Pigments.

In this study, home-made amorphous TiO2 microspheres with good mono-dispersity and large numbers of mesopores on the surface were used as substrates. The intermediate microspheres were obtained by adding Co/Ni sources with different Co/Ni molar ratios in a water bath and making them react by water bath heating. By calcining the intermediate microspheres deposited on the TiO2 ones, a core–shell structured spherical CoTiO3/NiTiO3 inorganic composite pigment was prepared. The synthesized pigments were characterized by X-ray diffraction (XRD), Raman spectroscopy, field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectrometry (EDS), laser particle size (LPS) analysis and colorimetry. The results show that when the calcination temperature is 800 °C and the Co/Ni molar ratio is 0.5:0.5, the pigments consist of a TiO2 core and outer ilmenite CoTiO3/NiTiO3 shell. Moreover, the surface of the product microspheres is smooth, and the particles are of regular sphericity with a uniform particle size of about 1.8 μm. The colorimetric analysis from the samples calcined at 800 °C shows color changes from yellow-green to dark green as the Co/Ni molar ratio increases (0.1:0.9 to 0.9:0.1). A Co/Ni molar ratio that is too high or too low results in the formation of by-products such as Co3O4 or NiO, respectively, which adhere to the product surface and affect the chromaticity of the product. This work has enabled the chromatic modulation of yellow-green inorganic pigments, providing a solution for the preparation of spherical inorganic pigments that are more suitable for industrial inkjet printing.

A quadratic model captures the human V1 response to variations in chromatic direction and contrast.

An important goal for vision science is to develop quantitative models of the representation of visual signals at post-receptoral sites. To this end, we develop the quadratic color model (QCM) and examine its ability to account for the BOLD fMRI response in human V1 to spatially uniform, temporal chromatic modulations that systematically vary in chromatic direction and contrast. We find that the QCM explains the same, cross-validated variance as a conventional general linear model, with far fewer free parameters. The QCM generalizes to allow prediction of V1 responses to a large range of modulations. We replicate the results for each subject and find good agreement across both replications and subjects. We find that within the LM cone contrast plane, V1 is most sensitive to L-M contrast modulations and least sensitive to L+M contrast modulations. Within V1, we observe little to no change in chromatic sensitivity as a function of eccentricity.

Temporal filtering of luminance and chromaticity in macaque visual cortex

SummaryContrast sensitivity peaks near 10 Hz for luminance modulations and at lower frequencies for modulations between equiluminant lights. This difference is rooted in retinal filtering, but additional filtering occurs in the cerebral cortex. To measure the cortical contributions to luminance and chromatic temporal contrast sensitivity, signals in the lateral geniculate nucleus (LGN) were compared to the behavioral contrast sensitivity of macaque monkeys. Long wavelength-sensitive (L) and medium wavelength-sensitive (M) cones were modulated in phase to produce a luminance modulation (L + M) or in counterphase to produce a chromatic modulation (L − M). The sensitivity of LGN neurons was well matched to behavioral sensitivity at low temporal frequencies but was approximately 7 times greater at high temporal frequencies. Similar results were obtained for L + M and L − M modulations. These results show that differences in the shapes of the luminance and chromatic temporal contrast sensitivity functions are due almost entirely to pre-cortical mechanisms.

Suprathreshold contrast response in normal and anomalous trichromats.

Maximum likelihood difference scaling was used to measure suprathreshold contrast response difference scales for low-frequency Gabor patterns, modulated along luminance and L-M color directions in normal, protanomalous, and deuteranomalous observers. Based on a signal-detection model, perceptual scale values, parameterized as $ d^\prime $d', were estimated by maximum likelihood. The difference scales were well fit by a Michaelis-Menten model, permitting estimates of response and contrast gain parameters for each subject. Anomalous observers showed no significant differences in response or contrast gain from normal observers for luminance contrast. For chromatic modulation, however, anomalous observers displayed higher contrast and lower response gain compared to normal observers. These effects cannot be explained by simple pigment shift models, and they support a compensation mechanism to optimize the mapping of the input contrast range to the neural response range. A linear relation between response and contrast gain suggests a neural trade-off between them.

1550 nm pumped upconversion chromaticity modulation in Er3+ doped double perovskite LiYMgWO6 for anti-counterfeiting

1550 nm near-infrared (NIR) light excited lanthanide ion (Ln3+) doped up-conversion (UC) materials with tunable emission color have great application potential in optical anti-counterfeiting and it is essential to explore new stable phosphors and expand the emission color gamut for multicolor security printing. Herein, a new type of double perovskite tungstate UC phosphors LiYMgWO6: Er3+ with green and red double color emissions under 1550 nm excitation were synthesized by high temperature solid-state method. The emission color output of LiYMgWO6: Er3+ was adjusted from yellow-green to red by introducing Ho3+ ion to enhance the red emission and suppress the green emission. Fluorescent lifetime measurements were carried out to illustrate the color modulation mechanism. As a proof of concept, the fluorescent printing inks based on as-prepared phosphors were synthesized and fluorescent labels with special patterns were designed to demonstrate the anti-counterfeiting application.

A Quadratic Model of the fMRI BOLD Response to Chromatic Modulations in V1

A Quadratic Model of the fMRI BOLD Response to Chromatic Modulations in V1

Modelling Contrast Sensitivity for Chromatic Temporal Modulations

The temporal contrast sensitivity to isoluminant chromatic flicker was measured for three observers using the method of adjustment. The isoluminant stimuli were created for each observer individually, based on a technique similar to heterochromatic flicker photometry. The chromatic flicker stimuli were sinusoidal modulations, defined in the CIE 1976 UCS (u', v') chromaticity diagram. The chromaticity varied around a base color along a certain modulation direction with a certain amplitude at a certain frequency. Nine base colors, four modulation directions and seven frequencies were used, resulting in thirty-six temporal contrast sensitivity curves per observer. An exponential model was fitted to the resulting contrast sensitivity expressed as 1/Δ(u', v'), 1/ΔLMS and 1/Δlms. The model resulted in an average R2 value higher than 0.93 for the three different measures of contrast sensitivity. The two parameters of the model (i.e. the slope β1 and intercept β0) were found to significantly depend on the base color and direction of the chromatic modulation. This means that Δ(u', v'), ΔLMS and Δlms are not suitable measures to predict the sensitivity to temporal chromatic modulations in different locations of the color space.

Spatio-chromatic sensitivity explained by post-receptoral contrast.

We measured and modeled visibility thresholds of spatial chromatic sine-wave gratings at isoluminance. In two experiments we manipulated the base color, direction of chromatic modulation, spatial frequency, the number of cycles in the grating, and grating orientation. In Experiment 1 (18 participants) we studied four chromatic modulation directions around three base colors, for spatial frequencies 0.15-5 cycles/deg. Results show that the location, size and orientation of fitted ellipses through the observer-averaged thresholds varied with spatial frequency and base color. As expected, visibility threshold decreased with decreasing spatial frequency, except for the lowest spatial frequency, for which the number of cycles was only three. In Experiment 2 (27 participants) we investigated the effect of the number of cycles at spatial frequencies down to 0.025 cycles/deg. This showed that the threshold elevation at 0.15 cycles/deg in Experiment 1 was at least partly explained by the small number of cycles. We developed two types of chromatic detection models and fitted these to the threshold data. Both models incorporate probability summation across spatially weighted chromatic contrast signals, but differ in the stage at which the contrast signal is calculated. In one, chromatic contrast is determined at the cone receptor level, the dominant procedure in literature. In the other model, it is determined at a postreceptoral level, that is, after cone signals have been transformed into chromatic-opponent channels. We applied Akaike's Information Criterion to compare the performance of the models and calculated their relative probabilities and evidence ratios. We found evidence in favor of the second model and conclude that postreceptoral contrast is the most accurate determinant for chromatic contrast sensitivity.

Up-conversion emission color tuning in NaLa(MoO4)2: Nd3+/Yb3+/Ho3+ excited at 808 nm

As alternatives to Yb3+-sensitized up-conversion (UC) materials excited at 980nm, Nd3+-sensitized UC phosphors irradiated by 808nm have been used to decrease the absorption of water and alleviate the overheating effect in vivo biological application. Intense red and green UC emissions from 5F5→5I8 and 5F4/5S2→5I8 transitions of Ho3+ appeared in Nd3+/Yb3+/Ho3+ tri-doped NaLa(MoO4)2 through successive energy transfer Nd3+→Yb3+→Ho3+ under 808nm excitation, in which Yb3+ ions were proven to be the energy transfer bridge between Nd3+ and Ho3+ by lifetime measurement. The variable emission color and intensity ratios of red to green emissions were realized by adjusting the doping concentration of Yb3+, pulse width of the excitation laser and the addition of Ce3+ ion, which depends on the different population pathways to the green and red emitting states of Ho3+. The chromaticity modulation mechanisms of these approaches were proposed, which provides a feasible strategy to tune the UC emission color.

Chromaticity modulation of upconversion luminescence in CaSnO3:Yb3+, Er3+, Li+ phosphors through Yb3+ concentration, pumping power and temperature

CaSnO3:Yb3+, Er3+, Li+ upconverting phosphors are synthesized by a simple solid state method. The doping concentration of Li+ ions is optimized by comparatively studying upconversion luminescence of samples with various Li+ content. The effects of Yb3+ concentration, pumping power and temperature on chromaticity of upconversion luminescence in CaSnO3:Yb3+, Er3+, Li+ phosphors are investigated, the related mechanisms are discussed and the abilities to modulate chromaticity are evaluated.

The effect of harmonization on cortical magnetic responses evoked by music of rapidly changing tonalities

The act of shifting from one key to another is termed tonal modulation, which has been used to articulate emotion expressions and formal structures in Western music. The present study recorded cortical activity to examine how the auditory-evoked magnetic fields are affected by harmonizing music of rapidly changing tonalities. Participants were asked to covertly sing the pitch names of well-learned modulating melodies along with the harmonized or unharmonized melodies. In our musical stimuli, three flats were added to the key signature for every four beats. Such a rapid modulation is achieved by a chromatic inflection of the submediant tone between the third and fourth beats. Tonal modulations with such chromatic progressions are termed chromatic modulations. A major finding was that the amplitude of N1m (neuromagnetic response at approximately 110 ms after the onset of a stimulus) was significantly reduced by harmonization only when a modulation occurred. We also observed that harmonization enhanced the P2m (neuromagnetic response at approximately 200 ms after the onset of a stimulus) amplitude. The results provide evidence of the impacts of harmonization on attention efforts and pitch categorization.

Dystrophin Is Required for Proper Functioning of Luminance and Red–Green Cone Opponent Mechanisms in the Human Retina

Visual information is processed in parallel pathways in the visual system. Parallel processing begins at the synapse between the photoreceptors and their postreceptoral neurons in the human retina. The integrity of this first neural connection is vital for normal visual processing downstream. Of the numerous elements necessary for proper functioning of this synaptic contact, dystrophin proteins in the eye play an important role. Deficiency of muscle dystrophin causes Duchenne muscular dystrophy (DMD), an X-linked disease that affects muscle function and leads to decreased life expectancy. In DMD patients, postreceptoral retinal mechanisms underlying scotopic and photopic vision and ON- and OFF-pathway responses are also altered. In this study, we recorded the electroretinogram (ERG) while preferentially activating the (red-green) opponent or the luminance pathway, and compared data from healthy participants (n = 16) with those of DMD patients (n = 10). The stimuli were heterochromatic sinusoidal modulations at a mean luminance of 200 cd/m2. The recordings allowed us also to analyze ON and OFF cone-driven retinal responses. We found significant differences in 12-Hz response amplitudes and phases between controls and DMD patients, with conditions with large luminance content resulting in larger response amplitudes in DMD patients compared to controls, whereas responses of DMD patients were smaller when pure chromatic modulation was given. The results suggest that dystrophin is required for the proper function of luminance and red-green cone opponent mechanisms in the human retina.

Dependence of chromatic responses in V1 on visual field eccentricity and spatial frequency: an fMRI study

Psychophysical sensitivity to red-green chromatic modulation decreases with visual eccentricity, compared to sensitivity to luminance modulation, even after appropriate stimulus scaling. This is likely to occur at a central, rather than a retinal, site. Blood-oxygenation-level-dependent (BOLD) functional magnetic resonance imaging (fMRI) responses to stimuli designed to separately stimulate different afferent channels' [red-green, luminance, and short-wavelength (S)-cone] circular gratings were recorded as a function of visual eccentricity (±10 deg) and spatial frequency (SF) in human primary visual cortex (V1) and further visual areas (V2v, V3v). In V1, the SF tuning of BOLD fMRI responses became coarser with eccentricity. For red-green and luminance gratings, similar SF tuning curves were found at all eccentricities. The pattern for S-cone modulation differed, with SF tuning changing more slowly with eccentricity than for the other two modalities. This may be due to the different retinal distribution with eccentricity of this receptor type. A similar pattern held in V2v and V3v. This would suggest that transformation or spatial filtering of the chromatic (red-green) signal occurs beyond these areas.

Design and synthesis of luminescent porous coordination polymers for chromaticity modulation, sensing of nitrobenzene and iodine encapsulation

A family of porous coordination polymers constructed from C2v symmetry ligands with increased conjugation moieties was systematically designed and prepared, which is highly promising for chromaticity modulation, sensing of nitrobenzene, and I2 encapsulation.

Alouatta trichromatic color vision: cone spectra and physiological responses studied with microspectrophotometry and single unit retinal electrophysiology.

The howler monkeys (Alouatta sp.) are the only New World primates to exhibit routine trichromacy. Both males and females have three cone photopigments. However, in contrast to Old World monkeys, Alouatta has a locus control region upstream of each opsin gene on the X-chromosome and this might influence the retinal organization underlying its color vision. Post-mortem microspectrophotometry (MSP) was performed on the retinae of two male Alouatta to obtain rod and cone spectral sensitivities. The MSP data were consistent with only a single opsin being expressed in each cone and electrophysiological data were consistent with this primate expressing full trichromacy. To study the physiological organization of the retina underlying Alouatta trichromacy, we recorded from retinal ganglion cells of the same animals used for MSP measurements with a variety of achromatic and chromatic stimulus protocols. We found MC cells and PC cells in the Alouatta retina with similar properties to those previously found in the retina of other trichromatic primates. MC cells showed strong phasic responses to luminance changes and little response to chromatic pulses. PC cells showed strong tonic response to chromatic changes and small tonic response to luminance changes. Responses to other stimulus protocols (flicker photometry; changing the relative phase of red and green modulated lights; temporal modulation transfer functions) were also similar to those recorded in other trichromatic primates. MC cells also showed a pronounced frequency double response to chromatic modulation, and with luminance modulation response saturation accompanied by a phase advance between 10–20 Hz, characteristic of a contrast gain mechanism. This indicates a very similar retinal organization to Old-World monkeys. Cone-specific opsin expression in the presence of a locus control region for each opsin may call into question the hypothesis that this region exclusively controls opsin expression.

Achromatic luminance contrast sensitivity in X-linked color-deficient observers: An addition to the debate

It is a matter of debate whether X-linked dichromacy is accompanied by enhanced achromatic processing. In the present study, we used sinusoidally modulated achromatic gratings under photopic conditions to compare the contrast sensitivity (CS) of protanopes, deuteranopes, and normal trichromats. 36 male volunteers were examined. CS was tested in static and dynamic conditions at nine different spatial frequencies. The results support the assumption that X-linked color-defective observers are at an advantage in terms of achromatic processing. Both protanopes and deuteranopes had significantly better CS than controls in both the static and the dynamic conditions. In the static condition, the advantage was observed especially at higher spatial frequencies, whereas in the dynamic condition, it was seen also at lower frequencies. The results are interpreted in terms of decreased chromatic modulation of the luminance channel and the early plasticity of the parvocellular system.