Wavelength Discrimination Research Articles

High-fidelity surface reconstruction using complementary colorimetry-encoded fringe projection profilometry.

To solve the challenging issue of uneven reflectance of high-fidelity surface, this paper proposes a three-dimensional (3D) shape measurement method based on surface adaptation complementary colorimetry-encoded fringe projection profilometry. A complete complementary hue extraction method simulates the retina stimulation to establish the complementary conversion relationship between the projected and collected colors of the measurement system. On this basis, a surface reflectance adaptation fringe pattern encoding strategy is proposed to measure the high-fidelity surfaces. The experiments demonstrate that the proposed method is capable of efficiently balancing and adjusting the reflected light intensity of each fidelity surface, thereby suppressing the ambiguity reconstruction texture. The established complementary colorimetry relationship also improves the light wavelength discrimination, saturation avoidance, measurement accuracy and efficiency.

Filterless Bandpass Photodetectors Enabled by 2D/3D Perovskite Heterojunctions

AbstractBandpass photodetectors have tremendous applications in colorimetric analysis, light communication, imaging and machine vision systems. Compared to broadband photodetectors combined with external optical filters, solution‐processed filterless bandpass photodetectors enjoy high integration density and low cost, but suffer from broadened response edges and insufficient spectral rejection ratios (SRRs). Here, prototype filterless bandpass photodetectors with near square‐shape photoresponse are developed based on (CmH2m+1NH3)2PbI4/MAPbI3 (m = 4–8) and (CmH2m+1NH3)2PbBr4/MAPbBr3 (m = 2–8) perovskite heterojunctions. The strong and sharp excitonic absorption of 2D perovskites defines the ultranarrow response onset widths of 10 ± 1 nm. Besides, the strong photoluminescence (PL) self‐absorption of 2D perovskites suppresses the PL leakage from the front absorber to the back photoactive region, which is crucial to the achieved record high SRR of >2000. By integrating Br‐based 2D/3D perovskite photodetectors with onset edge wavelength discrimination of ≈20 nm, a multiple‐channel optical communication system with low spectral crosstalk is demonstrated.

Photogating-assisted tunneling boosts the responsivity and speed of heterogeneous WSe2/Ta2NiSe5 photodetectors

Photogating effect is the dominant mechanism of most high-responsivity two-dimensional (2D) material photodetectors. However, the ultrahigh responsivities in those devices are intrinsically at the cost of very slow response speed. In this work, we report a WSe2/Ta2NiSe5 heterostructure detector whose photodetection gain and response speed can be enhanced simultaneously, overcoming the trade-off between responsivity and speed. We reveal that photogating-assisted tunneling synergistically allows photocarrier multiplication and carrier acceleration through tunneling under an electrical field. The photogating effect in our device features low-power consumption (in the order of nW) and shows a dependence on the polarization states of incident light, which can be further tuned by source-drain voltages, allowing for wavelength discrimination with just a two-electrode planar structure. Our findings offer more opportunities for the long-sought next-generation photodetectors with high responsivity, fast speed, polarization detection, and multi-color sensing, simultaneously.

Selection on Visual Opsin Genes in Diurnal Neotropical Frogs and Loss of the SWS2 Opsin in Poison Frogs.

Amphibians are ideal for studying visual system evolution because their biphasic (aquatic and terrestrial) life history and ecological diversity expose them to a broad range of visual conditions. Here, we evaluate signatures of selection on visual opsin genes across Neotropical anurans and focus on three diurnal clades that are well-known for the concurrence of conspicuous colors and chemical defense (i.e., aposematism): poison frogs (Dendrobatidae), Harlequin toads (Bufonidae: Atelopus), and pumpkin toadlets (Brachycephalidae: Brachycephalus). We found evidence of positive selection on 44 amino acid sites in LWS, SWS1, SWS2, and RH1 opsin genes, of which one in LWS and two in RH1 have been previously identified as spectral tuning sites in other vertebrates. Given that anurans have mostly nocturnal habits, the patterns of selection revealed new sites that might be important in spectral tuning for frogs, potentially for adaptation to diurnal habits and for color-based intraspecific communication. Furthermore, we provide evidence that SWS2, normally expressed in rod cells in frogs and some salamanders, has likely been lost in the ancestor of Dendrobatidae, suggesting that under low-light levels, dendrobatids have inferior wavelength discrimination compared to other frogs. This loss might follow the origin of diurnal activity in dendrobatids and could have implications for their behavior. Our analyses show that assessments of opsin diversification in across taxa could expand our understanding of the role of sensory system evolution in ecological adaptation.

PbS QD-Coated Si Micro-Hole Array/Graphene vdW Schottky Near-Infrared Photodiode for PPG Heart Rate Measurement.

Near-infrared (NIR) photodetectors (PDs) have attracted much attention for use in noninvasive medical diagnosis and treatments. In particular, self-filtered NIR PDs are in high demand for a wide range of biomedical applications due to their ability for wavelength discrimination. In this work, we designed and then fabricated a Si micro-hole array/Graphene (Si MHA/Gr) van der Waals (vdW) Schottky NIR photodiode using a PbS quantum dot (QD) coating. The device exhibited a unique self-filtered NIR response with a responsivity of 0.7 A/W at -1 V and a response speed of 61 μs, which is higher than that seen without PbS QD coating and even in most previous Si/Gr Schottky photodiodes. The light trapping of the Si MHA and the PbS QD coating could be attributed to the high responsivity of the vdW photodiode. Furthermore, the presented NIR photodiode could also be integrated in photoplethysmography (PPG) for real-time heart rate (HR) monitoring. The extracted HR was in good accord with the values measured with the patient monitor-determined by analyzing the Fourier transform of the stable and reliable fingertip PPG waveform-suggesting its potential for practical applications.

Multi-dimensional wavefront sensing using volumetric meta-optics.

The ideal imaging system would efficiently capture information about the fundamental properties of light: propagation direction, wavelength, and polarization. Most common imaging systems only map the spatial degrees of freedom of light onto a two-dimensional image sensor, with some wavelength and/or polarization discrimination added at the expense of efficiency. Thus, one of the most intriguing problems in optics is how to group and classify multiple degrees of freedom and map them on a two-dimensional sensor space. Here we demonstrate through simulation that volumetric meta-optics consisting of a highly scattering, inverse-designed medium structured with subwavelength resolution can sort light simultaneously based on direction, wavelength, and polarization. This is done by mapping these properties to a distinct combination of pixels on the image sensor for compressed sensing applications, including wavefront sensing, beam profiling, and next-generation plenoptic sensors.

Oviposition behavior is not affected by ultraviolet light in a butterfly with sexually-dimorphic expression of a UV-sensitive opsin.

Animal vision is important for mediating multiple complex behaviors. In Heliconius butterflies, vision guides fundamental behaviors such as oviposition, foraging, and mate choice. Color vision in Heliconius involves ultraviolet (UV), blue and long-wavelength-sensitive photoreceptors (opsins). Additionally, Heliconius possess a duplicated UV opsin, and its expression varies widely within the genus. In Heliconius erato, opsin expression is sexually dimorphic; only females express both UV-sensitive opsins, enabling UV wavelength discrimination. However, the selective pressures responsible for sex-specific differences in opsin expression and visual perception remain unresolved. Female Heliconius invest heavily in finding suitable hostplants for oviposition, a behavior heavily dependent on visual cues. Here, we tested the hypothesis that UV vision is important for oviposition in H. erato and Heliconius himera females by manipulating the availability of UV in behavioral experiments under natural conditions. Our results indicate that UV does not influence the number of oviposition attempts or eggs laid, and the hostplant, Passiflora punctata, does not reflect UV wavelengths. Models of H. erato female vision suggest only minimal stimulation of the UV opsins. Overall, these findings suggest that UV wavelengths do not directly affect the ability of Heliconius females to find suitable oviposition sites. Alternatively, UV discrimination could be used in the context of foraging or mate choice, but this remains to be tested.

A Light-Programmed Rewritable Lattice-Mediated Multistate Memory for High-Density Data Storage.

Mainstream non-volatile memory (NVM) devices based on floating gate structures or phase-change/ferroelectric materials face inherent limitations that compromise their suitability for long-term data storage. To address this challenge, a novel memory device based on light-programmed lattice engineering of thin rhenium disulfide(ReS2 ) flakes is proposed. By inducing sulfur vacancies in the ReS2 channel through light illumination, the device's electrical conductivity is modified accordingly and multiple conductance states for data storage therefore are generated. The device exhibits more than 128 distinct states with linearly increasing conductance, corresponding to a sevenfold increase in storage density. Through further optimization to achieve atomic-level precision in defect creation, it is possible to achieve even higher storage densities. These states are extremely stable in vacuum or inert ambient showing long retention of >10 years, while they can be erased upon exposure to the air. The ReS2 memory device can maintain its stability over multiple program-erase operation cycles and shows superior wavelength discrimination capability for incident light in the range of 405-785nm. This device represents a significant contribution to NVM technology by offering the ability to store information in multistate memory and enabling filter-free color image recorder applications.

Mimicking evasive behavior in wavelength‐dependent reconfigurable phototransistors with ultralow power consumption

AbstractRetinal‐inspired synaptic phototransistors, which integrate light signal detection, preprocessing, and memory functions, show promising applications in artificial vision sensors. In recent years, it has been reported to construct heterojunction in phototransistors to realize positive photoconductance (PPC) and negative photoconductance (NPC) modulations, thereby achieving visible and infrared wavelength discrimination and various visual functions. However, relatively little attention has been paid to wavelength‐dependent switching and reconfigurability between two states (PPC and NPC), limiting further applications for complex simulations of biological visual functions. Here, a mixed organic–inorganic heterojunction synaptic phototransistor was constructed by integrating CsPbBr3 nanoplates (NPLs) with strong blue‐light absorption and poly(3‐hexylthiophene‐2,5‐diyl) (P3HT) with strong red‐light absorption. Compared with the three‐dimensional (3D) structure CsPbBr3 nanocubes (NCs), the two‐dimensional (2D) CsPbBr3 NPLs exhibited more efficient charge transfer with P3HT. Based on the individual optical absorption properties in organic–inorganic heterojunction, the device exhibited wavelength‐selective and reconfigurable behavior between PPC and NPC. A low power consumption of 0.053 fJ per synaptic event was achieved, which is comparable to a biological synapse. Finally, Drosophila's evasive behavior to food under red and blue light can be successfully demonstrated. This work demonstrates the future potential of synaptic phototransistors for visuomorphic computing.

Noise logic with an InGaN/SiNx/Si uniband diode photodetector

Noise logic is introduced by the wavelength dependent photocurrent noise of an InGaN/SiNx/Si uniband diode photodetector. A wavelength versus photocurrent noise discrimination map is constructed from the larger photocurrent noise for red light than that for green light. A minimum measurement time of four seconds is deduced from the standard deviation of the photocurrent noise for a safe wavelength distinction. A logic NOT gate is realized as representative with on or off red or green light as binary 1 or 0 inputs and the photocurrent noise above or below a defined threshold as binary 1 or 0 outputs.

Cortical-like colour-encoding neurons in the mushroom body of a butterfly

Colour is an important visual modality for many animals including insects. The flower-foraging swallowtail butterfly Papilio xuthus has spectrally acute chromatic vision using UV-, blue-, green- and red-sensitive photoreceptors1. The spectral organization of Papilio's retina is well understood but, as for other insects, how chromatic information is processed in higher order brain regions remains unclear. To identify neurons underlying color perception in Papilio, we have investigated the spectral properties of the visual inputs to the mushroom body (MB), a brain region implicated in learning and memory. By recording intracellular responses to a series of monochromatic lights, combined with dye injection, we have revealed a wide variety of spectral responses in three morphologically distinct neuron types. These heterogeneous responses are characterized by colour opponency and sharp tuning to particular wavelengths, which do not in general align with the sensitivities of the retinal photoreceptors, and presumably contribute to Papilio's acute wavelength discrimination. This finding provides new insights into the processing underlying insect colour vision.

Filter-free color pixel sensor using gated PIN photodiodes and machine learning techniques

This work addresses the possibility of light wavelength discrimination, using a specially designed Lateral PIN Gated Photodiode and Machine Learning signal processing techniques. The devices were designed at FEI University using IBM BiCMOS 8HP 0.13 μm technology. The terminal gate of the lateral PIN photodiode controls the vertical depletion layer, in order to modulate the capture of the electron-hole pairs generated by different wavelengths along the intrinsic region. The collected data were organized in optical power classes with the corresponding cathode currents. The experimental characterization shows that the terminal gate voltage can be used to discriminate different incident colors. The simulation results allowed the acquisition of a complete dataset to apply machine learning techniques and classify the photodetector captured color. This technique can be extended to photosensors arrays and eliminate the organic color filters. The best result was obtained using the “Linear and Quadratic Discriminant” algorithms, with the average accuracy of 92.46% and 96.82%, respectively.

Color Vision Deficits.

Color provides important information about the identity of the objects we encounter. After early processing stages in the retinal cones, thalamus, and occipital cortex, retinal signals reach the ventral temporal cortex for high-level color and object processing, which links color perception with top-down expectations and knowledge. In the language-dominant hemisphere, some of these regions communicate with the language systems; by assigning verbal labels to percepts, these circuits speed up stimulus categorization, and permit fast and accurate inter-individual communication. This paper provides a review of color processing deficits, from dysfunction of wavelength discrimination in the retinal photoreceptors to deficits of high-level processing in the ventral temporal cortex. Neuroimaging evidence defined the existence and localization of color-preferring domains in the ventral occipito-temporal cortex. Evidence from the performance of a brain-damaged patient with color anomia but preserved color categorization demonstrated the independence of color categorization from color naming in the adult brain. Evidence from patients with brain damage suggests that high-level color processing may be divided into at least three functional domains: perceptual color experience, color naming, and color knowledge.

Long wavelength infrared imaging under ambient thermal radiation via an all-silicon metalens

Further miniaturization of imaging systems is prevented by the prevalent, traditional bulky refractive optics today. Meta-optics have recently generated great interest in the visible wavelength as a replacement for refractive optics thanks to their low weight, small size, and amenability to high-throughput semiconductor manufacturing. Here, we extend these meta-optics to the long-wave infrared (LWIR) regime and demonstrate imaging with a 2 cm aperture f/1 all-silicon metalens under ambient thermal emission. We showed that even with the strongly chromatic nature of the metalenses, we can perform ambient light imaging, primarily due to the lack of wavelength discrimination in the sensor, as is the norm for an RGB-camera in the visible.

2D perovskite narrowband photodetector arrays

2D perovskite narrowband photodetector arrays have been fabricated in this work, which can realize optical imaging with the ability of wavelength discrimination.

Optical Grating Techniques for MEMS-Based Spectrometer—A Review

This paper examined the innovations of the spectrometers for the measurement of consistency based parameters of the handheld Micro Electronic Mechanical System (MEMS) Spectrometer. Fast, highly sensitive, miniature spectroscopy techniques empowered quick, savvy and effective measures for various applications. In the light spectroscopy-based identification and quantification, advances in the field of wavelength discrimination are significant and essential. The identification of grid parameters and limiting conditions are necessary for the design and fabrication of diffraction gratings, for the spectrometer. This work evaluates the emerging trends in Micro-Spectrometer's Grating Techniques, focusing on the aspects of grating parameters and the recent developments of grating. The main parameters for evaluating the performance of a grating have been reviewed and found that grating efficiency, groove density, free spectral range and resolving power play a significant part in the grating performance. The fabrication technique employed as well as the materials used in the fabrication process, play a significant role in the efficiency of the grating. Silicon, Silicon dioxide (SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ), Glass (Silica glass), Poly methyl methacrylate (PMMA), Chromium and Silicon nitride(Si <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> ) are the most used materials. The integration of new materials that are ideal for the state-of-the-art semiconductor industry techniques for MEMS fabrication along with a new blazing structure would increase the efficiency of the grating.

Retinal organization and visual abilities for flower foraging in swallowtail butterflies.

Papilio butterflies' ability to forage for flowers relies upon multiple visual cues such as color, brightness, and motion. Papilio learns the color of rewarding flowers and detects it at a distance. Its color vision is based on four photoreceptor classes: UV, blue, green, and red, providing sensitive wavelength discrimination. These four receptor classes also contribute to the perception of brightness and polarization. Papilio's motion vision is based on a different set of receptors: green, red, and broad band. This implies that two visual pathways exist in Papilio. The contribution of several receptor classes not only for chromatic vision but also achromatic vision likely enhances the butterfly's ability to detect flowers in complex visual environments.

Wavelength discrimination (WLD) detector optimization for time-of-flight positron emission tomography with depth of interaction information

Parallax error in positron emission tomography (PET) scanners degrades image quality away from the center of the field-of-view (FOV). Depth of interaction (DOI) encoding is a common method for mitigating this parallax error in PET scanners. A DOI encoding method based on wavelength discrimination (WLD) has recently been proposed, showing promising results in terms of figure of merit (FOM) values. This method employs an optical filter and a phoswich detector, comprising of LYSO (bottom layer) and GAGG (top layer) scintillators. The main idea behind this method is to place an optical filter between the phoswich detector and one of the two adjacent photodetectors that are used to acquire light photons emitted from the phoswich scintillators, thereby blocking the emission from one of the scintillators. This enables identification of the interacting scintillator, based on the signals detected by the two photodetectors. However, the method has a drawback: light photon loss due to the optical filter degrades the detector’s energy resolution. In this work, experiments were performed to optimize detector configuration of this WLD method. GFAG, a scintillator with a relatively short decay time, was chosen to replace GAGG to improve timing performance. The timing performances of the conventional setup (S50) were measured to be 276 ps and 216 ps for top (GFAG) and bottom (LYSO) layers, respectively. The coincidence resolving time (CRT) for each setup was acquired by using a 3 mm × 3 mm × 5 mm Ce:LYSO scintillator as reference detector. In terms of energy performance, GAGG provided better energy resolutions of 12.9% (top) and 12.6% (bottom) due to its higher light output, compared to 14.7% FWHM and 13.0% for GFAG. Further optimization was performed by reducing the area covered by the optical filter to 25% (S25) and 15% (S15) of the total detector area. The results for S25 were 249 ps (GFAG) and 213 ps (LYSO) for timing performance, and 11.8% and 11.9% for energy resolution of the top and bottom layers, respectively. For S15, the CRTs were 250 ps and 201 ps, while the energy resolutions were 11.2% and 10.8%. Thus, the combination of two fast scintillators (Ce:LYSO and GFAG) and better optical filter placement delivered improvements in timing and energy resolution while preserving WLD’s excellent DOI decoding capability.

The non-visual opsins expressed in deep brain neurons projecting to the retina in lampreys

In lower vertebrates, brain photoreceptor cells express vertebrate-specific non-visual opsins. We previously revealed that a pineal-related organ-specific opsin, parapinopsin, is UV-sensitive and allows pineal wavelength discrimination in lampreys and teleost. The Australian pouched lamprey was recently reported as having two parapinopsin-related genes. We demonstrate that a parapinopsin-like opsin from the Japanese river lamprey exhibits different molecular properties and distribution than parapinopsin. This opsin activates Gi-type G protein in a mammalian cell culture assay in a light-dependent manner. Heterologous action spectroscopy revealed that the opsin forms a violet to blue-sensitive pigment. Interestingly, the opsin is co-localised with green-sensitive P-opsin in the cells of the M5 nucleus of Schober (M5NS) in the mesencephalon of the river and brook lamprey. Some opsins-containing cells of the river lamprey have cilia and others an axon projecting to the retina. The opsins of the brook lamprey are co-localised in the cilia of centrifugal neurons projecting to the retina, suggesting that cells expressing the parapinopsin-like opsin and P-opsin are sensitive to violet to green light. Moreover, we found neural connections between M5NS cells expressing the opsins and the retina. These findings suggest that the retinal activity might be modulated by brain photoreception.

Ultrahigh-Resolution Fiber-Optic Sensing Based on High-Finesse, Meter-Long Fiber Fabry-Perot Resonators

Ultrahigh-resolution fiber-optic sensing has found a wide range of potential applications. However, the techniques reported so far are all based on highly specialized fiber structures and interrogation lasers, which are not widely available. In this paper, we report the demonstration of ultrahigh strain resolutions using only off-the-shelf commercial components. Our method leverages the high wavelength discrimination of long, high-finesse fiber Fabry-Perot interferometers (FFPI), using two 1 m-long FFPIs, one as the sensor and the other as a frequency reference. By locking the interrogation laser to the reference interferometer, which is co-packaged with the sensor interferometer, large, environment-induced sensing background is removed. This allows the laser to reliably probe the strains applied on the sensor with very high resolutions. A nominal, noise-limited strain resolution of 800 fε/√Hz has been achieved within 1-100 Hz. Strain resolution further improves to 75 fε/√Hz at 1 kHz, 60 fε/√Hz at 2 kHz and 40 fε/√Hz at 23 kHz, demonstrating better resolutions than proven techniques such as π-phase-shifted and slow-light fiber Bragg gratings. The work lays out a cost-effective scheme to achieve ultrahigh-resolution fiber-optic sensing.