Cadmium selenide (CdSe) belongs to the binary II-VI group semiconductor with a direct bandgap of ~1.7 eV. The suitable bandgap, high stability, and low manufacturing cost make CdSe an extraordinary candidate as the top cell material in silicon-based tandem solar cells. However, only a few studies have focused on CdSe thin-film solar cells in the past decades. With the advantages of a high deposition rate (~2 µm/min) and high uniformity, rapid thermal evaporation (RTE) was used to maximize the use efficiency of CdSe source material. A stable and pure hexagonal phase CdSe thin film with a large grain size was achieved. The CdSe film demonstrated a 1.72 eV bandgap, narrow photoluminescence peak, and fast photoresponse. With the optimal device structure and film thickness, we finally achieved a preliminary efficiency of 1.88% for CdSe thin-film solar cells, suggesting the applicability of CdSe thin-film solar cells.
To demonstrate the existence of singular parity-time symmetry (PT-symmetry) broken point in optics system, we designed a one-dimensional PT symmetric structure including N unit-cell with loss and gain materials in half. We performed an analytical deduction to obtain the transmittance and reflectance of the structure basing on Maxwell’s equations. We found that with the exact structure unit-cell number and the imaginary part of refraction index, the transmittance and reflectance are both close to infinite. Such strict condition is called the singular point in this study. At the singular point position, both the transmission and reflection are direction-independent. Away from the singular point, the transmittance and reflectance become finite. In light of classical wave optics, the single unit and total structure both become the resonance units. The infinite transmittance and reflectance result from the resonance matching of single unit and total structure. In light of quantum theory, the singular point corresponds to the single eigenvalue of electromagnetic scattering matrix. The infinite transmittance and reflectance mean a huge energy transformation from pumping source to light waves. Numerical calculation and software simulation both demonstrate the result.
Here we present a graphene photodetector of which the graphene and structural system infrared absorptions are enhanced by interface phonon polariton (IPhP) coupling. IPhPs are supported at the SiC/AlN interface of device structure and used to excite interband transitions of the intrinsic graphene under gated-field tuning. The simulation results show that at normal incidence the absorbance of graphene or system reaches up to 43% or closes to unity in a mid-infrared frequency range. In addition, we found the peak-absorption frequency is mainly decided by the AlN thickness, and it has a red-shift as the thickness decreases. This structure has great application potential in graphene infrared detection technology.
The broad emission and high photoluminescence quantum yield of self-trapped exciton (STE) radiative recombination emitters make them an ideal solution for single-substrate, white, solid-state lighting sources. Unlike impurities and defects in semiconductors, the formation of STEs requires a lattice distortion, along with strong electron–phonon coupling, in low electron-dimensional materials. The photoluminescence of inorganic copper(I) metal halides with low electron-dimensionality has been found to be the result of STEs. These materials were of significant interest because of their lead-free, all-inorganic structures, and high luminous efficiencies. In this paper, we summarize the luminescence characteristics of zero- and one-dimensional inorganic copper(I) metal halides with STEs to provide an overview of future research opportunities.
Upcoming generations of coherent intra/inter data center interconnects currently lack a clear path toward a reduction of cost and power consumption, which are the driving factors for these data links. In this work, the trade-offs associated with a transition from coherent C-band to O-band silicon photonics are addressed and evaluated. The discussion includes the fundamental components of coherent data links, namely the optical components, fiber link and transceivers. As a major component of these links, a monolithic silicon photonic BiCMOS O-band coherent receiver is evaluated for its potential performance and compared to an analogous C-band device.
Semiconductor optoelectronic fiber technology has seen rapid development in recent years thanks to advancements in fabrication and post-processing techniques. Integrating the optical and electronic functionality of semiconductor materials into a fiber geometry has opened up many possibilities, such as in-fiber frequency generation, signal modulation, photodetection, and solar energy harvesting. This review provides an overview of the state-of-the-art in semiconductor optoelectronic fibers, including fabrication and post-processing methods, materials and their optical properties. The applications in nonlinear optics, optical-electrical conversion, lasers and multimaterial functional fibers will also be highlighted.
With the benefits of low latency, wide transmission bandwidth, and large mode field area, hollow-core antiresonant fiber (HC-ARF) has been a research hotspot in the past decade. In this paper, a hollow core step-index antiresonant fiber (HC-SARF), with stepped refractive indices cladding, is proposed and numerically demonstrated with the benefits of loss reduction and bending improvement. Glass-based capillaries with both high (n = 1.45) and low (as low as n = 1.36) refractive indices layers are introduced and formatted in the cladding air holes. Using the finite element method to perform numerical analysis of the designed fiber, results show that at the laser wavelengths of 980 and 1064 nm, the confinement loss is favorably reduced by about 6 dB/km compared with the conventional uniform cladding HC-ARF. The bending loss, around 15 cm bending radius of this fiber, is also reduced by 2 dB/km. The cladding air hole radius in this fiber is further investigated to optimize the confinement loss and the mode field diameter with single-mode transmission behavior. This proposed HC-SARF has great potential in optical fiber transmission and high energy delivery.
Optical traps have emerged as powerful tools for immobilizing and manipulating small particles in three dimensions. Fiber-based optical traps (FOTs) significantly simplify optical setup by creating trapping centers with single or multiple pieces of optical fibers. In addition, they inherit the flexibility and robustness of fiber-optic systems. However, trapping 10-nm-diameter nanoparticles (NPs) using FOTs remains challenging. In this study, we model a coaxial waveguide that works in the optical regime and supports a transverse electromagnetic (TEM)-like mode for NP trapping. Single NPs at waveguide front-end break the symmetry of TEM-like guided mode and lead to high transmission efficiency at far-field, thereby strongly altering light momentum and inducing a large-scale back-action on the particle. We demonstrate, via finite-difference time-domain (FDTD) simulations, that this FOT allows for trapping single 10-nm-diameter NPs at low power.
X-ray detection is of great significance in biomedical, nondestructive, and scientific research. Lead halide perovskites have recently emerged as one of the most promising materials for direct X-ray detection. However, the lead toxicity remains a worrisome concern for further commercial application. Great efforts have been made to search for lead-free perovskites with similar optoelectronic properties. Here, we present a lead-free oxide double perovskite material Ba2AgIO6 for X-ray detection. The lead-free, all-inorganic nature, as well as the high density of Ba2AgIO6, promises excellent prospects in X-ray applications. By employing the hydrothermal method, we successfully synthesized highly crystalline Ba2AgIO6 powder with pure phase. Furthermore, we prepared Ba2AgIO6 wafers through isostatic pressure and built X-ray detectors with Au/Ba2AgIO6 wafer/Au photoconductive structure. The as-prepared X-ray detectors showed a sensitivity of 18.9 μC/(Gyair·cm2) at 5 V/mm, similar to commercial α-Se detectors showcasing their advantages for X-ray detection.
Optical directed logic (DL) is a novel logic operation scheme that employs electrical signals as operands to control the working states of optical switches to perform the logic functions. This review first provides an overview of the concept and working principle of DL. The developing trends of DL computing are then discussed in detail, including the fundamental optical DL gates, combinational optical DL operations, reconfigurable logic computing, low power optical logic computing, and programmable photonic network. The concluding remarks provide an outlook on the DL future development and its impacts in optical computing.
As an important computing operation, photonic matrix–vector multiplication is widely used in photonic neutral networks and signal processing. However, conventional incoherent matrix–vector multiplication focuses on real-valued operations, which cannot work well in complex-valued neural networks and discrete Fourier transform. In this paper, we propose a systematic solution to extend the matrix computation of microring arrays from the real-valued field to the complex-valued field, and from small-scale (i.e., 4 × 4) to large-scale matrix computation (i.e., 16 × 16). Combining matrix decomposition and matrix partition, our photonic complex matrix–vector multiplier chip can support arbitrary large-scale and complex-valued matrix computation. We further demonstrate Walsh-Hardmard transform, discrete cosine transform, discrete Fourier transform, and image convolutional processing. Our scheme provides a path towards breaking the limits of complex-valued computing accelerator in conventional incoherent optical architecture. More importantly, our results reveal that an integrated photonic platform is of huge potential for large-scale, complex-valued, artificial intelligence computing and signal processing.
In this paper, we proposed a quality of transmission (QoT) prediction technique for the quality of service (QoS) link setup based on machine learning classifiers, with synthetic data generated using the transmission equations instead of the Gaussian noise (GN) model. The proposed technique uses some link and signal characteristics as input features. The bit error rate (BER) of the signals was compared with the forward error correction threshold BER, and the comparison results were employed as labels. The transmission equations approach is a better alternative to the GN model (or other similar margin-based models) in the absence of real data (i.e., at the deployment stage of a network) or the case that real data are scarce (i.e., for enriching the dataset/reducing probing lightpaths); furthermore, the three classifiers trained using the data of the transmission equations are more reliable and practical than those trained using the data of the GN model. Meanwhile, we noted that the priority of the three classifiers should be support vector machine (SVM)>K nearest neighbor (KNN)>logistic regression (LR) as shown in the results obtained by the transmission equations, instead of SVM>LR>KNN as in the results of the GN model.
Integrated waveguides with slot structures have attracted increasing attention due to their advantages of tight mode confinement and strong light-matter interaction. Although extensively studied, the issue of mode mismatch with other strip waveguide-based optical devices is a huge challenge that prevents integrated waveguides from being widely utilized in large-scale photonic-based circuits. In this paper, we demonstrate an ultra-compact low-loss slot-strip converter with polarization insensitivity based on the multimode interference (MMI) effect. Sleek sinusoidal profiles are adopted to allow for smooth connection between the slot and strip waveguide, resulting reflection reduction. By manipulating the MMI effect with structure optimization, the self-imaging positions of the TE0 and TM0 modes are aligned with minimized footprint, leading to low-loss transmission for both polarizations. The measurement results show that high coupling efficiencies of − 0.40 and − 0.64 dB are achieved for TE0 and TM0 polarizations, respectively. The device has dimensions as small as 1.1 μm × 1.2 μm and composed of factory-available structures. The above characteristics of our proposed compact slot-strip converter makes it a promising device for future deployment in multi-functional integrated photonics systems.
In this paper, we reported an integrated method to generate ultra-wideband (UWB) pulses of different orders based on a reconfigurable silicon micro-ring resonator-coupled Mach–Zehnder interferometer. Under proper operating conditions, the device can produce Fano resonances with a peak-to-valley extinction ratio of above 20 dB. UWB monocycle and doublet signals with picosecond pulse widths are produced when the micro-ring resonator is modulated by square and Gaussian electrical pulses, respectively. With our Fano resonance modulator on silicon photonics, it is promising to foresee versatile on-chip microwave signal generation.
A near-infrared femtosecond laser is focused by a 100 mm-focal-length plano-convex lens to form a laser filament, which is employed to drill holes on copper targets. By shifting or rotating the focusing lens, additional aberration is imposed on the focused laser beam, and significant influence is produced on the aspect ratio and cross-sectional shape of the micro-holes. Experimental results show that when proper aberration is introduced, the copper plate with a thickness of 3 mm can be drilled through with an aspect ratio of 30, while no through-holes can be drilled on 3-mm-thickness copper plates by femtosecond laser with minimized aberration. In addition, when femtosecond laser filament with large astigmatism is used, micro-holes that had a length to width ratio up to 3.3 on the cross-section are obtained. Therefore, the method proposed here can be used to fabricate long oval holes with high aspect ratios.
Silicon photonic platforms offer relevance to large markets in many applications, such as optical phased arrays, photonic neural networks, programmable photonic integrated circuits, and quantum computation devices. As one of the basic tuning devices, the thermo-optic phase shifter (TOPS) plays an important role in all these applications. A TOPS with the merits of easy fabrication, low power consumption, small thermal time constant, low insertion loss, small footprint, and low crosstalk, is needed to improve the performance and lower the cost of the above applications. To meet these demands, various TOPS have been proposed and experimentally demonstrated on different foundry platforms In this paper, we review the state-of-the-art of TOPS, including metal heater, doped silicon, silicide, with silicon substrate undercut for heat insulation, folded waveguide structure, and multi-pass waveguide structure. We further compare these TOPSs and propose the directions of the future developments on TOPS.
Thin-film solar cells show considerable application potential as alternative photovoltaic technologies. Cuprous antimony chalcogen materials and their derivatives, represented as CuSbS2 and CuPbSbS3, respectively, exhibit the advantages of low cost, massive elemental abundance, stability, and good photoelectric properties, including a suitable bandgap and large optical absorption coefficient. These advantages demonstrate that they can be used as light absorbers in photovoltaic applications. In this study, we review the major properties, fabrication methods, and recent progress of the performance of the devices containing CuSbS2 and CuPbSbS3. Furthermore, the limitations and future development prospects with respect to the CuSbS2 and CuPbSbS3 solar cells are discussed.
Integrated photonics is widely regarded as an important post-Moore’s law research direction. However, it suffers from intrinsic limitations, such as lack of control and satisfactory photonic memory, that cannot be solved in the optical domain and must be combined with electronics for practical use. Inevitably, electronics and photonics will converge. The photonic fabrication and integration technology is gradually maturing and electronics-photonics convergence (EPC) is experiencing a transition from device integration to circuit design. We derive a conceptual framework consisting of regulator, oscillator, and memory for scalable integrated circuits based on the fundamental concepts of purposeful behavior in cybernetics, entropy in information theory, and symmetry breaking in physics. Leveraging this framework and emulating the successes experienced by electronic integrated circuits, we identify the key building blocks for the integrated circuits for EPC and review the recent advances.
Thermally activated delayed fluorescence (TADF) organic light-emitting diodes (OLEDs) have been demonstrated in applications such as displays and solid-state lightings. However, weak stability and inefficient emission of blue TADF OLEDs are two key bottlenecks limiting the development of solution processable displays and white light sources. This work presents a solution-processed OLED using a blue-emitting TADF small molecule bis[4-(9,9-dimethyl-9,10-dihydroacridine)phenyl]sulfone (DMAC-DPS) as an emitter. We comparatively investigated the effects of single host poly(N-vinylcarbazole) (PVK) and a co-host of 60% PVK and 30% 2,2′-(1,3-phenylene)-bis[5-(4-tert-butylphenyl)-1,3,4-oxadiazole] (OXD-7) on the device performance (the last 10% is emitter DMAC-DPS). The co-host device shows lower turn-on voltage, similar maximum luminance, and much slower external quantum efficiency (EQE) roll-off. In other words, device stability improved by doping OXD-7 into PVK, and the device impedance simultaneously and significantly reduced from 8.6 × 103 to 4.2 × 103 W at 1000 Hz. Finally, the electroluminescent stability of the co-host device was significantly enhanced by adjusting the annealing temperature.
Embedded data are used to retrieve phases quicker with high accuracy in phase-modulated holographic data storage (HDS). We propose a method to design an embedded data distribution using iterations to enhance the intensity of the high-frequency signal in the Fourier spectrum. The proposed method increases the anti-noise performance and signal-to-noise ratio (SNR) of the Fourier spectrum distribution, realizing a more efficient phase retrieval. Experiments indicate that the bit error rate (BER) of this method can be reduced by a factor of one after 10 iterations.
Indium Gallium Nitride based blue light-emitting diodes (LEDs) suffer from insufficient crystal quality and serious efficiency droop in large forward current. In this paper, the InGaN-based blue LEDs are grown on sputtered aluminum nitride (AlN) films to improve the device light power and weaken the efficiency droop. The effects of oxygen flow rate on the sputtering of AlN films on sapphire and device performance of blue LEDs are studied in detail. The mechanism of external quantum efficiency improvement is related to the change of V-pits density in multiple quantum wells. The external quantum efficiency of 66% and 3-V operating voltage are measured at a 40-mA forward current of with the optimal oxygen flow rate of 4 SCCM.
A light-emitting organic solar cell (LE-OSC) with electroluminescence (EL) and photovoltaic (PV) properties is successfully fabricated by connecting the EL and PV units using a MoO3:Al co-evaporation interfacial layer, which has suitable work function and good transmittance. PV and EL units are fabricated based on poly(3-hexylthiophene) (P3HT)-indene-C60 bisadduct (IC60BA) blends, and 4,4′-bis (N-carbazolyl) biphenyl-fac-tris (2-phenylpyridine) iridium (Ir(ppy)3), respectively. The work function and the transmittance of the MoO3:Al co-evaporation are measured and adjusted by the ultraviolet photoelectron spectroscopy and the optical spectrophotometer to obtain the better bi-functional device performance. The forward- and reverse-biased current density-voltage characteristics in dark and under illumination are evaluated to better understand the operational mechanism of the LE-OSCs. A maximum luminance of 1550 cd/m2 under forward bias and a power conversion efficiency of 0.24% under illumination (100 mW/cm2) are achieved in optimized LE-OSCs. The proposed device structure is expected to provide valuable information in the film conditions for understanding the polymer blends internal conditions and meliorating the film qualities.
Photonics is poised to play a unique role in quantum technology for computation, communications and sensing. Meanwhile, integrated photonic circuits—with their intrinsic phase stability and high-performance, nanoscale components—offer a route to scaling. However, each integrated platform has a unique set of advantages and pitfalls, which can limit their power. So far, the most advanced demonstrations of quantum photonic circuitry has been in silicon photonics. However, thin-film lithium niobate (TFLN) is emerging as a powerful platform with unique capabilities; advances in fabrication have yielded loss metrics competitive with any integrated photonics platform, while its large second-order nonlinearity provides efficient nonlinear processing and ultra-fast modulation. In this short review, we explore the prospects of dynamic quantum circuits—such as multiplexed photon sources and entanglement generation—on hybrid TFLN on silicon (TFLN/Si) photonics and argue that hybrid TFLN/Si photonics may have the capability to deliver the photonic quantum technology of tomorrow.
The slab effective index difference between the transverse-electric (TE) and transverse-magnetic (TM) polarizations was utilized to obtain complete photonic bandgap (CPBG) in a silicon nitride ( SixNy) photonic crystal slab. For this, coincident frequency range in the TE photonic bandgap (PBG) and TM PBG, which denotes the CPBGs of the slab, must be found with the same structure. Through adjusting the effective index pair of TE and TM polarizations by changing the thickness of the SixNy core layer, and also optimizing the structure parameters within the photonic crystal plane, a large normalized CPBG of 5.62% was theoretically obtained in a slab of SixNy with a refractive index of 2.5. Moreover, based on the obtained CPBG, a microcavity which could support both TE and TM polarization was theoretically demonstrated. The cavity modes for different polarizations were both well confined, which proved the reliability of the CPBG. In addition, using the same method, the lowest refractive index of SixNy on silica slab for a CPBG could be extended to as low as 2. The results indicate that there is potential for development of various high-performance CPBG devices based on SixNy slab technology.
Energy harvesting and light detection are key technologies in various emerging optoelectronic applications. The high absorption capability and bandgap tunability of organic semiconductors make them promising candidates for such applications. Herein, a poly(3-hexylthiophene-2,5-diyl) (P3HT):indene-C60 bisadduct (ICBA) bulk heterojunction-based organic photodiode (OPD) was reported, demonstrating dual functionality as an indoor photovoltaic (PV) and as a high-speed photodetector. This OPD demonstrated decent indoor PV performance with a power conversion efficiency (PCE) of (11.6 ± 0.5)% under a light emitting diode (LED) lamp with a luminance of 1000 lx. As a photodetector, this device exhibited a decent photoresponsivity of 0.15 A/W (green light) with an excellent linear dynamic range (LDR) of over 127 dB within the optical power range of 3.74 × 10-7 to 9.6 × 10-2 W/cm2. Furthermore, fast photoswitching behaviors could be observed with the rising/falling times of 14.5/10.4 µs and a cutoff (3 dB) frequency of 37 kHz. These results might pave the way for further development of organic optoelectronic applications.
Windows are critically important components in building envelopes that have a significant effect on the integral energy budget. For energy saving, here we propose a novel design of hydrogel-glass which consists of a layer of hydrogel and a layer of normal glass. Compared with traditional glass, the hydrogel-glass possesses a higher level of visible light transmission, stronger near-infrared light blocking, and higher mid-infrared thermal emittance. With these properties, hydrogel-glass based windows can enhance indoor illumination and reduce the temperature, reducing energy use for both lighting and cooling. Energy savings ranging from 2.37 to 10.45 MJ/m2 per year can be achieved for typical school buildings located in different cities around the world according to our simulations. With broadband light management covering the visible and thermal infrared regions of the spectrum, hydrogel-glass shows great potential for application in energy-saving windows.
With the rapid growth of computer science and big data, the traditional von Neumann architecture suffers the aggravating data communication costs due to the separated structure of the processing units and memories. Memristive in-memory computing paradigm is considered as a prominent candidate to address these issues, and plentiful applications have been demonstrated and verified. These applications can be broadly categorized into two major types: soft computing that can tolerant uncertain and imprecise results, and hard computing that emphasizes explicit and precise numerical results for each task, leading to different requirements on the computational accuracies and the corresponding hardware solutions. In this review, we conduct a thorough survey of the recent advances of memristive in-memory computing applications, both on the soft computing type that focuses on artificial neural networks and other machine learning algorithms, and the hard computing type that includes scientific computing and digital image processing. At the end of the review, we discuss the remaining challenges and future opportunities of memristive in-memory computing in the incoming Artificial Intelligence of Things era.
Metasurfaces, also known as 2D artificial metamaterials, are attracting great attention due to their unprecedented performances and functionalities that are hard to achieve by conventional diffractive or refractive elements. With their sub-wave-length optical scatterers, metasurfaces have been utilized to freely modify different characteristics of incident light such as amplitude, polarization, phase, and frequency. Compared to traditional bulky lenses, metasurface lenses possess the advantages of flatness, light weight, and compatibility with semiconductor manufacture technology. They have been widely applied to a range of scenarios including imaging, solar energy harvesting, optoelectronic detection, etc. In this review, we will first introduce the fundamental design principles for metalens, and then report recent theoretical and experimental progress with emphasis on methods to correct chromatic and monochromatic aberrations. Finally, typical applications of metalenses and corresponding design rules will be presented, followed by a brief outlook on the prospects and challenges of this field.
Sodium metal batteries (SMBs) are receiving broad attention due to the high specific capacity of sodium metal anodes and the material abundance on earth. However, the growth of dendrites results in poor battery performance and severe safety problems, inhibiting the commercial application of SMBs. To stabilize sodium metal anodes, various methods have been developed to optimize the solid electrolyte interphase (SEI) layer and adjust the electroplating/stripping behavior of sodium. Among the methods, developing anode host materials and adding electrolyte additives to build a protective layer are promising and convenient. However, the understanding of the interaction process between sodium metal and those organic materials is still limited, but is essential for the rational design of advanced anode hosts and electrolyte additives. In this study, we use copper(II) hexadecafluorophthalocyanine (F16CuPc), and copper(II) phthalocyanine (CuPc), as model systems to unravel the sodium interaction with polar functional groups by in-situ photoelectron spectroscopy and density functional theory (DFT) calculations. It is found that sodium atoms prefer to interact with the inner pyrrolic nitrogen sites of CuPc, while they prefer to interact with the outer aza bridge nitrogen atoms, owing to Na-F interaction at the Na/F16CuPc interface. Besides, for the both organic molecules, the central Cu(II) ions are reduced to Cu(I) ions by charge transfer from deposited sodium. The fluorine-containing groups are proven to promote the interaction process of sodium in organic materials, which sheds light on the design of functional interfaces in host materials and anode protective layers for sodium metal anodes.