Recently, data have proliferated rapidly with social network services, artificial intelligence (AI), and metaverse technologies. Concomitantly, conventional computer technology has reached its limits in terms of energy density and latency 1. To enable the advent of a more innovative world, new alternatives are required for computing systems to store and process abundant data in a compact form using less energy. Optoelectronic synapses are strong candidates for overcoming these limitations owing to their parallel communication, wavelength-division multiplexing, and hyperconnectivity 2, 3. In particular, photonic neuromorphic devices have facilitated low-power computing by mimicking both volatile and nonvolatile properties of biological synapses 4, 5. The use of circularly polarized light enables more nuanced modulation of synaptic weights within optoelectronic synapses. By manipulating the angular momentum of light, finer and more distinct gradations of synaptic strength can be created. This capability is pivotal for mimicking the complexity of biological synapses, allowing a broader range of synaptic weights to be generated within a finite system 6. In essence, the incorporation of circularly polarized light empowers photonic synapses to achieve not only the benefits of parallel communication and wavelength multiplexing, but also the ability to finely tune and diversify synaptic weights. This advancement has the potential to drive low-power computing further by enhancing the degrees of freedom within the system, thus addressing the pressing need for innovative computing solutions capable of efficiently managing vast and expanding volumes of data in our technologically advanced world.
Recently, significant progress has been made in optoelectronic devices, with considerable efforts from numerous researchers. Interestingly, chiral materials can serve as effective circularly polarized light (CPL) sensing media. CPL detectors using such materials show a selective response to circularly polarized light, which presents a compelling avenue rich with potential advantages 6, 7, 8, 9 Especially, chiral gold and perovskite materials exhibit tunable optical properties, allowing for customization to match specific wavelength ranges, thereby broadening the scope of applications 10, 11. Despite their promise for detecting circularly polarized light, there is still a high demand for a new type of CPL sensing medium that possesses the following features to overcome conventional limitations: (1) high stability and durability for reliable long-term performance, (2) multiple transition bands for higher integration, and (3) a simple and eco-friendly fabrication process to reduce manufacturing costs and avoid technical hurdles. To meet these requirements, a CPL sensing medium is expected to show (1) strong resistance against air, humidity, and heat; (2) negligible optical losses into heat or vibrations; (3) sufficient chiroptical activity; (4) effective photoelectronic properties; (5) multiple transition band structures; and (6) a mild and simple synthesis procedure. Addressing these limitations can improve the feasibility and effectiveness of chiral circularly polarized light detectors, paving the way for their enhanced utility in various technological fields.
Semiconducting quantum dots (QDs) are suitable materials for optical neuromorphic hardware because their discrete energy band structure provides accurate conversion between optical and electronic properties with excellent structural stability 12. QDs offer a unique opportunity for engineering defect states because of their high surface-to-volume ratio and surface tension 13, which make them attractive for producing multiple exciton transition states with differential CPL absorption behaviors. However, their practical use in CPL detectors is challenging because semiconductors generally possess a low dissymmetry g-factor owing to the small dynamic polarizability in exciton transition bands 14, 15, despite several efforts to enhance the optical activity by engineering the shape, dimension, and shell thickness of QDs 16, 17, 18. Thus, the left-circularly polarized (LCP) and right-circularly polarized (RCP) light show negligible differences in exciton generation, thereby significantly limiting their practical use in chiral photonic devices 19, 20. However, it has recently been reported that the magnetic properties of chiral nanomaterials can significantly boost the optical activity because the transient magnetic dipole moments of the materials contribute equally to the rotational strength, R0a, along with the electric moment 21. Based on this information, we hypothesized that engineering the magnetic properties of semiconducting QDs could be a solution to amplify the chiroptical activity, enabling practical applications.
In this study, for the first time, we propose the use of chiroferromagnetic quantum dots (CFQDs) to develop a chiroptical synaptic device (ChiropS) (Scheme 1a). By creating amorphization defects in QDs using chiral molecules, we successfully induced the following significant features: (1) atomic structural chirality, inducing chiroptical activities; (2) ferromagnetic properties, amplifying chiroptical activities; (3) multiple exciton transition bands and concurrent circular dichroism (CD) peaks, providing wavelength-division multiplexing with higher degrees of freedom in modulating synaptic weights; and (4) nonlinear long-term plastic properties with linear optical input, which function as a noise filter. The multichannel ChiropS developed using the synthesized CFQDs successfully detected circular polarization information as well as the wavelengths of the incoming light (Scheme 1b). We also confirmed that the amplification process can be used as the low-level preprocessing unit of the optical noise filter for energy-efficient neuromorphic computing (Scheme 1c). This study forms the cornerstone of next-generation computing systems.
Chiral Ag2S CFQDs were synthesized using a facile one-pot method in an aqueous solution containing cysteine (Cys) and Ag precursors under a basic pH environment at 70°C. The Cys molecules serve as chirality-inducing agents, stabilizers, and sulfur sources for the Ag2S CFQDs, enabling the transfer of the chirality of the molecules to the Ag2S CFQDs (Fig. 1a). Consequently, a dynamic light scattering analysis indicated the surface charge of Ag2S with a negative zeta-potential value (-36.5 mV) and a hydrodynamic diameter of 3.08 nm (Fig. S1). The average diameter of the inorganic core of the Ag2S CFQD was measured to be 2.6 \(\:\pm\:\) 0.4 nm using transmission electron microscopy (TEM). To determine the atomic structure of the inorganic core, we obtained atomic-resolution scanning TEM (STEM)high-angle annular dark-field (HAADF) images with double-aberration-corrected TEM. The atomic-resolution STEM-HAADF image and its fast Fourier transform (FFT) pattern shown in Fig. 1b and 1c present a distorted atomic arrangement pointing in multiple directions, which implies that the Ag2S CFQDs potentially have multiple trap states owing to the amorphization defects caused by the atomic distortion (Fig. S2). The X-ray diffraction (XRD) patterns of L-Cys-Ag2S CFQDs coincided with the STEM result, showing a huge peak broadening yielded by the amorphous defects and small diameter of the CFQDs while the overall appearance of the XRD patterns matched with the monoclinic α-Ag2S (P21/c) phase (Fig. S2).
The chiroptical activity induced by structural distortion of the chiral Ag2S CFQDs was investigated using circular dichroism (CD) spectroscopy. The CD spectra of the L- and D-Cys Ag2S CFQDs showed nearly perfect mirror symmetry, whereas Ag2S CFQDs made with racemic Cys molecules were chiroptically silent (Fig. 1d). In addition, the anisotropic g-factor of L- and D-Cys Ag2S CFQDs was noticeably strong, up to 0.003, which is approximately 10–100 times higher than that of previously reported QDs with similar dimensions (Fig. 1e) 22, 23. The strong chiroptical activity and multiple signs of the CD peaks enabled the Ag2S CFQDs to respond differently to LCP and RCP light. The multiple exciton transition bands and concurrent CD peaks throughout the visible range provided wavelength-division multiplexing, enabling multichannel perception for sensory and neuromorphic devices that respond to various ellipticities and wavelengths of light.
For the sensitive detection of CPL depending on handedness, it is important to maximize the chiroptical activity of the QDs. Chiroptical activity can be calculated quantum chemically using rotational strength:
$$\:{R}_{0a}=\text{I}\text{m}\left[<{{\Psi\:}}_{0}\left|\widehat{\text{E}}\right|{{\Psi\:}}_{a}>\bullet\:<{{\Psi\:}}_{a}\left|\widehat{\text{M}}\right|{{\Psi\:}}_{0}>\right]$$
,
where \(\:{{\Psi\:}}_{0}\) and \(\:{{\Psi\:}}_{a}\) are the wave functions for the ground state (0) and excited state (a), and+ \(\:\widehat{\text{E}}\) and \(\:\widehat{\text{M}}\) are the corresponding electric and magnetic moment operators
$$\:\widehat{\text{M}}=\frac{-e\hslash\:}{2mc}\left(\widehat{L}\:+{g}_{S}\widehat{S}\right)$$
with the orbital (\(\:\widehat{L}\)) and spin (\(\:\widehat{S}\)) angular momentum operators for the direction of the magnetic field.
Here, to increase the transient magnetic dipole moment, the number of unpaired electrons and their spin-polarized density must be increased.
Based on this theory, we hypothesized that the defects induced by lattice distortion using a chiral ligand would increase the number of unpaired electrons and subsequently enhance the magnetic and chiroptical properties of Ag2S CFQDs. The magnetic hysteresis curve measured at 300 K indicated that the synthesized Ag2S CFQDs possessed ferromagnetic properties, as intended (Fig. 1f). The saturation magnetization of L-Cys-Ag2S was approximately 0.016 emu/g, which is one order of magnitude higher than that of CdTe QDs 24. This ferromagnetic behavior of the chiral Ag2S CFQDs can be attributed to both chiral atomic distortion and the intrinsic sulfur antisite defects originating from the S 3p and Ag 4d orbitals under S-rich conditions at the nanoscale. To confirm this, defect-free CFQDs were synthesized using a racemic mixture of L- and D- Cys. As expected, there was no resultant spin polarization or magnetic moment in defect-free Ag2S because of the symmetric total spin-polarized density of states (Fig. S2, S3) 25, 26, 27, 28, 29.
To address the effect of the external magnetic field on the chiroptical properties of the CFQDs, we measured the magnetic CD (MCD) spectra under an external magnetic field of 1.6 T parallel and antiparallel to light propagation (Fig. S4). The total CD spectra of the chiral nanomaterials under a magnetic field contained both pure CD and MCD signals, therefore, we subtracted the pure CD signal from the total CD signal to obtain the correct MCD spectra 30. The results demonstrated that the MCD peak appeared in the ultraviolet region and shifted in the direction of the magnetic field, which was attributed to ligand-to-metal charge transfer on the surface layers of the chiral Ag2S CFQDs 30, 31. No significant perturbation of the electronic state occurred owing to an external magnetic field in this system, indicating that the intrinsic chiral distribution of electric charges was dominant in the chiral Ag2S CFQDs.
Computational investigations confirmed that defects generate unpaired electrons that possess spin polarization, which significantly contributes to strong chiroptical activities. We calculated the electronic excitation and CD spectra using density functional tight binding theory (DFTB) and the simplified Tamm–Dancoff approximation (sTDA). In our model, we constructed a low-symmetry CFQD belonging to the chiral C1 point group with an acanthite structure 32 with (103), (121), and (\(\:\stackrel{\text{-}}{\text{1}}\)23) faces, which is consistent with the XRD and TEM results. The placement of the Cys molecules followed the chiral pattern of sulfur atoms along the surface. The resulting nanoparticles had a diameter of 2.0 nm and a composition of Ag60S30. This model serves as a representative example of hierarchical chirality, encompassing chirality information from the ceramic cores, ligands, and surface-decoration patterns. The Cys molecules were in a negative state, yielding an overall negatively charged structure, which is consistent with the experimental zeta potential results. The innermost part of the CFQD core displayed a negligible density of unpaired electrons, whereas an excess of unpaired electrons with a spin-up orientation accumulated near the surface. These electrons arise mostly from the delocalized s-orbitals of the ligands and d-type orbitals of the silver atoms, as illustrated in the inset of Fig. 2a. The isosurfaces representing the spin density exhibited pronounced chiral symmetry. Spin polarization can affect the transport and recombination of carriers by inhibiting electron-hole recombination 33. Thus, they can enhance the utilization efficiency of photogenerated carriers, prolong their lifetimes, and reduce complex losses, which are beneficial for photonic device applications 34, 35, 36, 37.
The calculated CD spectrum derived from the model matched the alternating pattern of the experimentally observed positive and negative bands for both L-Cys-Ag2S and D-Cys-Ag2S (Fig. 2b, c). To assess the average particle and hole localization for each CD band, we included the transitions with the largest rotational strength (the vertical lines depicted in Fig. 2a-b) and two additional transitions adjacent to the one with the largest rotational strength to compute the average of the natural transition orbitals (NTOs) at each CD band. As shown in Fig. 2d-g both the particles and holes are located on the CFQD surface, indicating that these selected transitions are mostly charge transfers on the CFQD surface, where the unpaired electrons are situated. These results indicate that the underlying cause of the optical activity exhibited by the Ag2S CFQDs predominantly arises from the spin-polarized wave function, a consequence of the ferromagnetic property of the system, a property rooted in the chiral crystal defects of the CFQDs.
We also experimentally examined the multiband electrical structure of the CFQDs. Compared to the absorbance spectra, in which the bands were hidden by the absorption of the ligands (Fig. 3a and Fig. S5), the photoluminescence excitation (PLE) spectrum revealed multiple exciton transition bands from 400 to 700 nm (Fig. 3b). The multiple distinctive bands in both the photoluminescence (PL) and PLE spectra of the Ag2S CFQDs were expected to originate from chiral lattice defects 38, 39. To examine the dependence of the differential emission intensity on the handedness of the excitation light, we analyzed fluorescence-detected circular dichroism (FDCD) spectra of the dispersion of the chiral Ag2S CFQDs. This measurement collected information on the circular differential excitation-induced emission intensity of the fluorescent samples. The FDCD spectral bands at the corresponding CD peak positions confirmed their ability to generate different numbers of electron–hole pairs depending on the handedness of the incident light (Fig. 3c). These results confirm that our chiral Ag2S CFQDs are suitable materials for ChiropS as a sensing medium because they cannot only readily detect and distinguish circular polarization but also convert optical information to electronic signals with sensitivity. Together with the Gaussian-fitted PLE spectrum, CD and FDCD confirmed the four distinctive excitonic transition bands of the L-Cys-Ag2S CFQDs at 407, 464, 556, and 637 nm (Fig. 3d and 3e), indicating that our CFQDs are a superior sensing medium for multichannel devices responding to different synaptic weights depending on the polarization and wavelength of the light that significantly increase the degree of integration.
To demonstrate this multiplexing property, we fabricated ChiropS with a bottom-gate top-contact field-effect transistor (FET) structure. A 100-nm-thick SiO2 was synthesized by thermal oxidation on a highly doped Si substrate, where SiO2 and Si served as the gate oxide and electrode, respectively. A 30-nm-thick photoactive layer comprising a Ag2S/carboxymethyl cellulose (CMC) layer was formed by spin coating, and 50-nm-thick p-type pentacene was thermally evaporated as a semiconductor channel. The CMC polymer provided adequate viscosity to the aqueous solution to generate a film during spin-coating. The cross-sectional scanning electron microscopy (SEM) images show the device stacks (Fig. 3f). The charge-transfer efficiency from Ag2S to pentacene was investigated using the steady-state PL spectra of the Ag2S/CMC and Ag2S/CMC/pentacene films (Fig. 3g). Under light illumination at a wavelength of 514 nm, the Ag2S/CMC film exhibited PL over a wide emission wavelength range, with a peak at 650 nm. However, the PL disappeared completely with an additional pentacene layer on the Ag2S/CMC layer because of the radiative transfer between Ag2S/CMC and pentacene, thereby indicating the effective splitting of excitons 40. The energy band diagram of the Si/SiO2/Ag2S/CMC/pentacene device is shown in Fig. 3h, based on ultraviolet photoelectron spectroscopy (UPS) and the Tauc plot from the PLE spectrum of L-Cys-Ag2S CFQDs (Fig. S6). The major band gap was determined to be 2.34 eV using a Tauc plot 41. The secondary electron cut-off was situated at 17.03 eV, indicating the work function value of 4.17 eV, and the valence band maximum was at 1.16 eV below the Fermi level.
The device exhibited photonic programming (i.e., potentiation), which was electrically erasable (Fig. 3i). During programming (left panel of Fig. 3i), charge carriers were generated in the pentacene layer by UV illumination. Photogenerated holes could readily escape from Ag2S to pentacene through Ohmic contact. Conversely, the photogenerated electrons remain in the conduction band of Ag2S and act as space charges, thereby inducing an additional internal electric field. This accelerated the swept holes into the semiconductor channel. Consequently, more electrons remain in the active layer, resulting in a shift in the threshold voltage of the device. The trapped electrons were maintained by the potential well for a long time even after the light was turned off. However, they can be removed by applying a positive potential to the channel (right panel of Fig. 3i), confirming that the device is electrically erasable.
We investigated the basic memory characteristics of the integrated 1-channel ChiropS, with the pentacene channel of a width of 150 µm and a length of 1,000 µm (optical microscope image in Fig. S7). The device exhibited distinct transfer behaviors in the programmed state (2 mW, 405 nm light for 30 s) and the erased state (gate voltage (VGS) of -30 V for 3 s), as shown in Fig. 4a. Under a VGS of -4 V for data sensing, the on/off current window was about 15.8 (Ierase = 82.84 ± 9.86 pA, Ipgm = 1.31 ± 0.13 nA) at a drain voltage (VDS), and source voltage (yellow circles) of -5 and 0 V, respectively. Both the programming and erasing states showed a retention stability of more than 104 s at 22°C, suggesting its non-volatile memory characteristics (Fig. 4b). In addition, the device showed a higher current at the IDS-VDS characteristics under illumination (Fig. 4c) because the generated electrons in the chiral Ag2S layer formed a negative electric field and enhanced the gate potential. In the absence of the chiral Ag2S layer, the Au/Pentacene/SiO2/Si device did not respond to illumination, confirming the role of the Ag2S layer (Fig. S8).
The device also exhibited photonic synaptic behavior, that is, a gradual conductance change (Fig. 4d). For this investigation, the device was illuminated with a lower-power photonic pulse (0.8 mW/cm2) for 30 s, and the drain current was concurrently measured at an interval of 50 ms under VGS = -4 V and VDS = -5 V (Fig. 4e). The readout current gradually increased during exposure, corresponding to the photonic potentiation characteristics. After the completion of photonic potentiation (t = 40 s in Fig. 4d), the drain current partially decreased as soon as the light was turned off, suggesting that some electron carriers recombined and disappeared spontaneously. This corresponds to short-term plasticity (STP) of synapses. Meanwhile, some electrons remain in a programmed state, providing long-term plasticity (LTP). Then, the persistent electrons could be completely erasable electrically using a negative gate voltage of -30 V for 3 s.
When the illumination was repeated at regular time intervals, the previously programmed state became the initial state of the subsequent illumination, thereby increasing the channel conductivity (Fig. 4f). During the lights-on period (blue), the output current jumped followed by gradually increased. During the light-off period (white), STP was observed, followed by LTP. The readout currents under constant light-on (red) and off (black) conditions are shown for reference purposes. The number of electron carriers and residual electric carriers is proportional to the illumination time. Therefore, the output currents of both STP and LTP increased with increasing illumination time from 5 s to 50 s (Fig. 4g). The drain current decreased gradually in the light-off period, which could be fitted with an exponential decay function (\(\:I\left(t\right)=\:{I}_{\text{o}}\:+\:{I}_{\text{A}}\bullet\:{e}^{-\text{t}/{\tau\:}}\)), where \(\:I\left(t\right)\) is the drain current at time t after light-off, \(\:{I}_{o}\) is the maximum programmed current at t = 0, \(\:{I}_{\text{A}}\) is the fitting constant, and τ is the time constant (the fitting curves in black color, Fig. 4g) 42, 43. The fitting result showed that the τ increased linearly as the device was illuminated for a longer time. (Fig. 4h) This implies that the rate of current decrease slowed as more electrons were trapped. Consequently, the optical input can be converted into electrical output in a nonlinear manner. The inset of Fig. 4g shows the current loss ratio obtained after 10 s of lights-off, indicating that the current loss was more prominent at a shorter pulse width.
This behavior suggests that the device can be used as a noise filter or signal amplifier at the sensor level, such as a low-level image preprocessing unit for image recognition (Fig. 4i and Fig. S9). ChiropS exhibited nonlinear LTP behavior with respect to the linear optical input (inset of Fig. 4g), suggesting its possible use as in situ noise filter (or signal amplifier). A schematic of the proposed system demonstrating its optical noise filtering ability is shown in Fig. S11. For the demonstration, we generated a Gaussian random noise (σ)-added handwritten MNIST dataset, where the strength of noise was controlled from 0.1 to 0.9. The first panel shows one of the examples of a noise-added dataset of index 5 with σ = 0.2. When the datasets were exposed to the ChiropS array and left for a sufficient time until the LTP regime was reached, the optical input could be converted to the LTP conductance of the device. The conductance can be read electrically and then sent to an artificial neural network for training and recognition. A detailed histogram of the pixel intensities in the MNIST dataset is shown in Fig. S10. It was confirmed that the random noise was decreased after tau fitting with a pixel intensity below 40% for MNIST handwritten values, and a pixel intensity above 80%, containing valuable numerical information, was relatively maintained.
We examined the benefit of preprocessing units in ChiropS using 784 × 10 single-layer perceptron-based artificial neural networks (ANN) for MNIST pattern recognition. Fig. S11a and b compare the MNIST dataset recognition rates for the normal sensor case and the noise-filtered case using ChiropS, respectively. As the standard deviation of Gaussian noise increases from 0.1 (red) to 0.9 (dark grey), both cases showed similar recognition accuracy and tendency from 0.91 to 0.71 at 165 epochs. In addition, the estimated total normalized energy consumption between the optical input images and the electrical output images was reduced by 21% on average with the ChiropS by filtering unnecessary energy consumption by the noise signals after the data pretreatment with the Gaussian noise in simulations. (Fig. 4j). Because more electrons are trapped by high optical stimulation, causing asymmetric LTP behavior with slow current reduction rates, it is possible to preserve the variable numerical information while maintaining the recognition accuracy on MNIST. The characteristics of random noise are reduced using the STP filter for small noises with low pixel intensity. In addition, the electrical erasing process can be made gradual by precisely controlling the electrical pulse conditions, thereby allowing for electrical depression. Therefore, the device showed photonic potentiation and electrical depression behaviors upon appropriate manipulation of the photonic and electric pulses (Fig. S12).
Based on its well-proven neuromorphic performance, we built a 2 × 3 ChiropS multiarray device. To demonstrate the chiral optoelectronic performance with multiplexing, the device was operated using three types of polarization (linear polarization and left- and right-handed circular polarization) at three different wavelengths: 405, 488, and 532 nm. Figure 5a shows a structural schematic of the 2 × 3 chiral L-Cys-Ag2S CFQDs-based synaptic array. To demonstrate the capabilities of the six channels, the devices were exposed to wavelengths of 405, 488, and 532 nm in each row, and the LCP and RCP lasers were exposed in the first and second columns, respectively. The intensity of light passing through the polarizer was 2 mW/cm2. The anisotropic g-factor of L-Cys Ag2S CFQDs-based ChiropS was 0.0005 at 405 nm, -0.001 at 488 nm, and 0.0007 at 532 nm (Fig. 1e). The IDS-VDS output curves were evaluated and compared under LCP and RCP laser illumination conditions for each wavelength (Fig. 5b). The results confirmed that the six devices responded well, as expected. The device responded strongly to the LCP at 405 nm, to the RCP at 488 nm, and evenly at 532 nm. Furthermore, the transfer characteristics on a linear scale of the L-Cys, D-Cys, and DL-Cys Ag2S ChiropS corresponded well with the CD spectra obtained at laser wavelengths of 405, 488, and 532 nm (Fig. S13).
The dynamic photocurrent response of each device was monitored during four illumination and erasure cycles to confirm repeatability. For each cycle, the corresponding pulsed laser (2 mW/cm2) for programming was exposed for 20 s, and the electric pulse for erasing (VGS = -30 V) was applied for 3 s (Fig. 5c). The drain current was read at the initial state before illumination (1), at programmed states after 10 s of illumination (2–5) when the STP decay time had passed after the end of the photonic pulse, and at the final state after the erasure (6). The mapping results are shown in Fig. 5d. The initial and final current values of all devices (points 1 and 6) were identical (~ 0.34 nA, suggesting that the residual signals could be effectively erased; therefore, independent programming was possible at every cycle. Moreover, the devices responded uniformly during the cycles (Points 2–5), confirming that accurate signal detection is possible. Figure 5e summarizes the average and deviation of the reading currents from each channel. To quantitatively show the degree of dissymmetric responsivity of ChiropS to LCP and RCP, we calculated the anisotropy factor of responsivity (\(\:{g}_{\text{r}\text{e}\text{s}}\)) using \(\:{g}_{\text{r}\text{e}\text{s}}=2\left({I}_{\text{D}\text{S},\text{L}}-{I}_{\text{D}\text{S},\text{R}}\right)/({I}_{\text{D}\text{S},\text{L}}+{I}_{\text{D}\text{S},\text{R}})\), where \(\:{I}_{\text{D}\text{S},\text{L}}\) and \(\:{I}_{\text{D}\text{S},\text{R}}\:\)are the drain current responsivity under LCP and RCP illumination, respectively (Fig. 5f). The \(\:{g}_{\text{r}\text{e}\text{s}}\) values were plotted along with the g-factor spectra of L-Cys-Ag2S CFQDs to show a correlation between the CPL responsivity of the device and the g-factor of the Ag2S CFQDs, where a successful operation of ChiropS to distinguish the angular momentum of photons at wavelengths of 405, 488, and 532 nm was observed, following a trend similar to g-factor spectra.
Because the suggested ChiropS processor can intrinsically distinguish three types of polarization (linear polarization, left- and right-handed circular polarization) and three different wavelengths (405, 488, and 532 nm) owing to the chiral-induced amorphous defects of Ag2S CFQDs, at least nine times more information can be processed in a single ChiropS channel. Furthermore, the arrayed processor with six channels further diversified the produced synaptic weights together with the synaptic properties of STP and LTP that can be operated at nano-level current with reduced noise. Therefore, it possesses the potential to solve the bottleneck in which a large amount of redundant data is exchanged between the sensor and processing units by integrating ChiropS neuromorphic systems and becomes a key component of high-dimensional visualization applications in machine vision.
