Optical Filter Research Articles

Detection of Lygus Bugs in Strawberry Using Deep Learning

ABSTRACT Lygus bugs are significant insect pests of strawberries that cause substantial reduction in yield and quality of fruits. In California, tractor-mounted bug vacuums are used to mechanically control Lygus population in the field. Traditional methods to evaluate the performance of bug vacuum are tedious and time-consuming. Automated insect detection using machine learning is an effective approach for pest management which can overcome the drawbacks of conventional techniques and can be helpful to estimate the removed bugs by the vacuums. The objective of this research was to detect adult and nymph Lygus using deep learning in lab settings. A monochrome camera, an optical filter, and a light were used to capture videos of moving Lygus inside of a chamber. Two training models, MobileNet SSD v2 and Faster R-CNN ResNet-50 v1, were applied to recognize adult and nymph Lygus in images. The results showed that both models could accurately identify the Lygus classes (F1- score ≥ 0.80). This can be useful to assess the performance of bug vacuums and create a Lygus heatmap to monitor its population in the field.

Filtering-free complex-valued DSB-16QAM generation for a 100 G direct detection optical interconnection.

In this Letter, a complex-valued double-sideband 16QAM (CV-DSB-16QAM) signaling scheme is proposed and experimentally demonstrated in a 100-Gb/s intensity modulation/direct detection (IM/DD) interconnection system. Unlike the conventional real-valued double-sideband (DSB) quadrature amplitude modulation (QAM) of relatively lower spectral efficiency (SE) and single-sideband (SSB) QAM relying on sharp-edged optical filtering, the CV-DSB-16QAM signal is generated by combining two independent sideband modulated QPSK signals using a single intensity modulator with an optical filtering-free profile, which also saves one photodiode and one analog-to-digital-converter compared with the twin-SSB scheme. Compared to typical pulse amplitude modulation or SSB schemes, the proposed approach offers a compelling alternative for complex-valued DD systems' evolution, particularly in scenarios with high SE demands and controllable chromatic dispersion. The experimental demonstration evaluates a 25-GBaud CV-DSB-16QAM signal over a 2-km standard single-mode fiber (SSMF), achieving a net bit rate of 100 Gb/s and occupying only a 25.1-GHz electrical bandwidth with a 4% guard band.

Ultrathin, Wavelength‐Multiplexed and Integrated Holograms and Optical Neural Networks Based on 2D Perovskite Nanofilms

AbstractHolography, as a technique for coherent wavefront reconstruction, is extensively used in numerous optical applications such as optical imaging, 3D display, photolithography, and optical artificial intelligence. In order to achieve highly compact and functional integration with optoelectronic devices, the hologram needs to possess ultrathin thickness as well as multicolor functionality. However, its thickness is typically limited to optical wavelength ranges due to the requirement for pronounced amplitude or phase modulation, and it generally operates at a single wavelength band without wavelength‐multiplexed channels. Here, the hologram is decreased thickness to sub‐ten nanometers by exploiting the large refractive index and strong exciton absorption of 2D perovskites. Ultrathin perovskite holograms and holographic neural networks with high stability are successfully developed by using femtosecond laser direct writing, and their operation wavelength can be rationally tuned from 400–515 nm through halide anion engineering. Consequently, the wavelength can be multiplexed with low cross‐talks by stacked perovskite nanolayers for applications of holographic display and neural networks without the usages of complex optical structures or filters. This work provides a feasible and promising technical route for integrating ultrathin, high pixel density, and multiplexed holographic structures with flat optoelectronic devices for next‐generation integrated optical systems.

Dynamically Tunable Terahertz Multiple Plasmon‐Induced Transparency and Slow Light in Planar Metamaterials With Rectangular Interrupted Graphene

ABSTRACTA novel planar monolayer graphene metamaterial structure containing rectangular interrupted graphene is proposed. Dynamically tunable multiple plasmon‐induced transparency (PIT) and slow light are obtained within the terahertz band through destructive interference between continuous dark and interrupted bright modes. Two distinct graphene types function as the optical dark and bright modes, and continuous graphene array is the nonradiative dark mode, whereas interrupted graphene array is the broad linewidth bright mode, respectively. Given the existence of graphene structure in the continuous state, continuous graphene Fermi level is dynamic tuned through the simple use of the bias voltage. Expressions of n‐order coupled mode theory (CMT) are correctly deduced, with CMT fitting theoretical analysis being identical to finite‐difference time‐domain numerical simulation based on dual‐ and triple‐PIT results for n = 3 and n = 4 cases, respectively. The continuous graphene Fermi level increases within 0.7–1.1 eV; the group index of the dual‐PIT system is maintained within 475.1–801.6, while that of the triple‐PIT system is 583.3–886.3. Additionally, the maximal group index is as high as 886.3 at 1.1 eV, indicating that an outstanding slow light device is established. Consequently, these proposed structures and research outcomes can guide the design of multichannel optical filters, excellent slow light devices, and dynamically tunable optical modulators.

Design method for generating multiple colors with thickness-modulated thin-film optical filters for silicon solar cells

Design method for generating multiple colors with thickness-modulated thin-film optical filters for silicon solar cells

Third-order optical bandpass filters based on structures of alternating layers of quartz and silver

Designs of optical bandpass filters have been developed on planar structures, which were obtained by vacuum deposition onto quartz glass (SiO2) substrates of three layers also of quartz, which are half-wavelength resonators separated from each other, from free space, and from the substrate by four layers of silver (Ag). The thicknesses of the Ag and SiO2 layers were determined based on the given parameters of the filter passband by parametric synthesis of one-dimensional models using electrodynamic analysis. In this case, experimental frequency dependences of the real and imaginary parts of the permittivity of silver were used. The measured frequency responses of the manufactured prototypes of red, green and purple filters are in good agreement with the responses obtained during synthesis.

Miniaturized dual-photodiode sensor for simultaneous wavelength and irradiance measurement across the 500–1000 nm range

We introduce what we believe to be a novel chip-scale dual-photodiode sensor capable of simultaneously measuring centroid wavelength and irradiance within the 500–1000 nm range. The sensor employs a dual-photodiode design, where one photodiode is equipped with a coated filter layer to create differential responsivity, allowing for accurate spectral and intensity detection. Our sensor demonstrates high accuracy, with centroid wavelength and intensity measurements within a 5% margin of error for light sources with a full width at half maximum (FWHM) of 50 nm. This design supports the use of optional optical filters tailored to specific wavelength ranges, enhancing adaptability across diverse applications. Experimental validation confirms its practical potential in a variety of fields, including precision agriculture, horticulture, and environmental monitoring, especially for studies involving far-red and near-infrared light sources. The chip-scale fabrication of the sensor ensures cost-effective, portable, and scalable deployment, positioning it as a versatile solution for advancing optical sensing technologies in various scientific and industrial fields.

Linear and Nonlinear Optical Characteristics of Basic Fuchsin-Doped Polyvinyl Alcohol Films for Flexible Optoelectronics

Abstract Polyvinyl alcohol (PVA) containing different levels of basic fuchsine (BF) was prepared using the solution casting method. Characterization via Fourier-transform infrared spectroscopy detailed changes in functional groups within the PVA/BF composites, indicates the hydrogen bonding between OH group of PVA and BF molecules. Optical investigations spanning the 190-2500 nm range demonstrated UV blocking properties in prepared PVA/BF composites (fromn 2.05 to 2.56 eV and from 4.08 to 6.32 eV). Moreover, the studies on optical band gap indicated a decrease with increased BF concentrations, reflecting altered electronic transitions within the prepared composites. The study also employed the single oscillator model provided by Wemple-DiDomenico to elucidate refractive index variations. After incorporating BF dye into the PVA polymer, the values of the dielectric constant as the frequency approaches infinity (ε∞), the dielectric constant of lattice (εL), dispersion energy (Ed), and oscillator energy (Eo) in PVA/BF composite samples showed an increase. Moreover, the nonlinear optical properties, including optical susceptibility and nonlinear refractive index were investigated and discussed. These findings underscore the versatility of PVA doped with BF for various applications including optical filters, and solar cell devices.

Breaking the angular dispersion limit in thin film optics by ultra-strong light-matter coupling

Thin film interference is integral to modern photonics, e.g., allowing for precise design of high performance optical filters, photovoltaics and light-emitting devices. However, interference inevitably leads to a generally undesired change of spectral characteristics with angle. Here, we introduce a strategy to overcome this fundamental limit in optics by utilizing and tuning the exciton-polariton modes arising in ultra-strongly coupled microcavities. We demonstrate optical filters with narrow pass bands that shift by less than their half width (< 15 nm) even at extreme angles. By expanding this strategy to strong coupling with the photonic sidebands of dielectric multilayer stacks, we also obtain filters with high extinction ratios and up to 98% peak transmission. Finally, we apply this approach in flexible filters, organic photodiodes, and polarization-sensitive filtering. These results illustrate how strong coupling provides additional degrees of freedom in thin film optics that will enable exciting new applications in micro-optics, sensing, and biophotonics.

Tunable Optical Filter Based on Thin Film Lithium Niobate Photonic Crystals

In this paper, we propose a tunable optical filter with a high Q factor based on photonic crystal technology, achieving a Q factor of 442.85 using thin film lithium niobate technology. By proportionally adjusting the dimensions of the unit structure, this filter enables coarse tuning across the 1520–1570 nm range (C band). Furthermore, by utilizing the thermo-optic effect of lithium niobate, we can achieve fine-tuning of the optical filter within a temperature range of 300 K to 600 K, allowing for a center wavelength tuning capability of up to 3.7 nm. This design not only enhances the filter’s performance but also broadens its potential applications in optical communication and optical signal processing.

A Design Strategy for Low-Cost Single/Dual-Band Photodetector: Bulk Heterojunction and Interface Engineering.

Photodetectors (PDs) with band selection functions are highly desirable for the future complex environment. Currently, band-selective PDs are typically realized by integrating various optical filters with broadband PDs or constructing heterojunction with multi-photo-absorbing layers. However, these methods cause increased manufacturing costs and device integration complexity. Here, a novel solution-processed perovskite bulk heterojunction (BHJ) layer (MAPbI3:MA3Bi2I9) is developed as photo-absorbing layer, and an effective interface engineering is proposed to selectively shield photo-generated carriers in the BHJ. By regulating the bias voltage, the tunneling probability of photo-generated carrier of MAPbI3 in the BHJ layer can be easily controlled, enabling band-selective capability. The PD exhibits a superior photo-response in the visible and near-infrared region at the -0.3V, with responsivity of 26.5 and 70.2mAW-1 for 500 and 740nm, respectively. But, at the 0.1V, the PD responds only to the visible region with a photo-response of 3.7mAW-1 (500nm) and maintains a high rejection ratio (R500 nm/R740 nm) of 28.5. This PD also exhibits a fast response speed (rise time: 220µs, fall time: 240µs). This work provides a novel strategy to fabricate a cost-effective multifunctional photodetector for future advanced optoelectronic system.

Ultra-narrowband dual-cavity Bragg grating ring resonator optical filter

An optical filter utilizing a dual-cavity Bragg grating ring resonator is proposed to achieve narrowband transmission, high selectivity, and low insertion loss (IL). The design incorporates two Bragg grating-based Fabry–Perot cavities within a closed-loop configuration, merging the characteristics of Bragg grating and ring resonator optical filters. This configuration is particularly well-suited for applications in microwave photonic filtering, especially in dense wavelength division multiplexing and the heterodyne generation of millimeter-wave signals. The filter is designed with a focus on a silica optical fiber implementation but is also suitable as a proof of concept for silica-based integrated implementations, provided that the higher propagation losses of the latter are considered. To evaluate the filter’s performance, a model based on the transfer matrix method (TMM) is developed. This model provides numerical expressions for the filter’s transfer functions at its four ports and for the circulating fields inside the cavity at the waveguide-ring coupling point. The proposed dual-cavity Bragg grating ring resonator filter design achieves high performance with an ultra-narrow transmission band of approximately 3 MHz, an extinction ratio (ER) of 72 dB, a 3 dB slope of 25.4 dB/GHz, and an insertion loss of less than 0.1 dB.

Realizing high-performance four active plasmonic filters using a single structure

This research aims to contribute significantly to the field of plasmonic filtering technology within modern optical communication systems. By focusing on the development of a high-performance, more compact, and efficient design, this study explores the potential of hybrid plasmonic filters to revolutionize optical filtering applications. The approach leverages an innovative active material with electrically tunable permittivity, allowing for dynamic control over the filter’s optical properties. The research specifically examines four types of filters: low-pass filters (LPF), high-pass filters (HPF), band-pass filters (BPF), and band-reject filters (BRF). These filters are designed to operate effectively across a broad wavelength range of 1200–1800 nm, achieving a transmittance exceeding 98% at the output port, while maintaining isolation with transmittance below 2% at the isolated ports. The structure demonstrates a FWHM of approximately 216 nm for the band-pass filter and approximately 223 nm for the band-reject filter, which are considered moderate values, ensuring the versatility and multifunctionality of the design. The ultra-compact size, with a footprint of just 21 µm2, makes these filters particularly advantageous for integration into space-constrained optical communication systems.

Optimizing Na2EDTA concentration for enhanced properties of SILAR - deposited CTS thin films

Abstract This study investigates the impact of varying Na2EDTA concentrations on the properties of copper tin sulfide (CTS) thin films deposited on soda lime glass substrates using the successive ionic layer adsorption and reaction (SILAR) method. The aim is to optimize CTS thin film growth for photovoltaic technology applications. CTS thin films were prepared using SILAR with Na2EDTA concentrations of 0.01 M, 0.04 M, and 0.07 M, resulting in samples CTS01, CTS04, and CTS07. Characterization techniques included XRD, SEM, EDAX, FTIR, I-V curves, transmittance spectra, and Tauc plots. The results reveal significant variations in film properties with changing Na2EDTA concentration. XRD patterns indicate polycrystalline films with an orthorhombic CTS phase. SEM images show smooth, dense films with localized clusters. FTIR spectra detect hydrocarbon chains, aromatic rings, and hydroxyl or ether groups. The I-V curves of three samples (CTS01, CTS04, and CTS07) show a voltage-dependent transition from semiconducting to ohmic behavior. The CTS01 exhibits superior conductivity (3.13 × 10−5/Ωm), while the samples’ resistance and conductivity values show an inverse relationship. Transmittance curves display low UV transmittance and high visible transmittance,suggests that the samples are highly absorptive in the UV range and become more transparent in the visible range, indicating potential applications in optical filtering and photovoltaic devices. Tauc plots estimate band gap energies of 3.66, 3.89, and 3.23 eV, indicating high band gap energies suitable for buffer layers in solar cells. The correlation between band gap energy and crystallite size as a function of Na2EDTA concentration is also observed. The study demonstrates the importance of optimizing Na2EDTA concentration for achieving high-quality CTS thin films with desirable properties for photovoltaic applications. The findings highlight the potential of CTS thin films for solar cells, optical filtering, and photonic devices.

Real-time 60 Gb/s PS-64QAM SSB-DMT transceiver deploying a low-complexity distribution matcher in band-limited IM-DD system

In this work, we have implemented a low-complexity distribution matcher in real-time for bandwidth-limited intensity modulation and direct detection (IM/DD) system based on field programmable gate array (FPGA). For the hardware implementation of probabilistic shaping (PS), a simple and effective distribution matcher is the key to achieving the symbol of the target probability. Compared to traditional PS distribution matchers, our proposed distribution matcher has lower hardware implementation complexity and only requires a small amount of look-up table and registers to achieve target probability distribution. Meanwhile, an optical tunable filter is used to generate single sideband discrete multitone (SSB-DMT) signals for 50-km standard single-mode fiber (SSMF) transmission. By using PS technology and SSB modulation scheme, we successfully real-time realize 11-GHz PS-64QAM SSB-DMT signals over 25/50-km SSMF transmission in band-limited IM-DD system, achieving a line rate of approximately 65.7 Gbit/s.

Pressure effect on acoustical overtones in cubic Indium Antimonide

The influence of pressure on the light scattering properties of low-energy acoustical phonons in cubic Indium Antimonide (InSb) has been investigated by Raman spectroscopy. By implementing optical Bragg filters, the overtone scattering from transverse acoustical phonons near the X point of Brillouin zone (2TA(X)) could be measured in an explicit manner allowing for analysis of its lineshape. Accordingly, a significant line broadening was detected for this phonon mode corroborating our previous suggestion of considerable anharmonicity of the transverse lattice vibration upon compression at room temperature. Herein reported new results of density functional theory (DFT) calculations indicated similar pressure dependence for overtones of acoustical phonons near the X and the K critical points that plausibly accounted for the lack of energy discrimination between 2TA(X) and 2TA(K) modes in spectroscopic measurements under pressure.

Optimized scintillation imaging in low dose rate and bright room light conditions

Objective. To develop a robust method for non-contact surface dosimetry during Total Body Irradiation (TBI) that uses an optimally paired choice of scintillator material with camera photocathode and can work insensitively to the normal ambient room lighting conditions (∼500 Lux).Approach. This goal was approached by assessing the emission contrast of scintillator signal to background room ratio (SBR) detected by the camera, in the challening conditions of low dose rate TBI with high room lights. A total of 9 fast-response scintillators, 3 wavelength shifters, and 2 camera photocathodes were systematically tested to determine the optimal combination. The effects of room lights on the scintillator signal and the background signal were assessed to avoid signal saturation while retaining accurate dose measurement. A bandpass wavelength filter was then applied to reduce the effects on room lights and scintillator signal.Main Results. One scintillator (EJ262) combined with a blue-green sensitive photocathode camera and a 500 nm band pass filter produced the greatest available scintillator SBR of 95 with maximal room lights on. The caveat is that this design rejects all patient Cherenkov light, which can be useful for visualizing the patient treatment. Another option which retained the Cherenkov signal but produced less available scintillator signal was found with another scintillator (EJ-260) and a red photocathode camera with SBR of 35, but a narrow bandpass filter is required to make it work in ambient room lights, which addition will also remove most of the Cherenkov signal.Significance. Non-contact scintillator imaging can be used for surface dosimetry in TBI with appropriate pairing of scintillator emission spectrum and camera photocathode sensitivity or optical filtering range.

Integrated lithium niobate Vernier micro-ring filter with wide and fast tuning capabilities

Tunable optical micro-ring filters play significant roles in optical communications, microwave photonics, and photonic neural networks. Typical micro-ring filters are based on either a thermo-optic (TO) effect with microsecond timescales or an electro-optic (EO) effect with a limited tuning range. Here, we report a continuously tunable lithium niobate on insulator (LNOI) Vernier cascaded micro-ring filter with wire-bonded packaging integrated with both TO and EO tuning electrodes, featuring a 40-nm free spectral range (FSR), 2.3 GHz EO bandwidth, and a high sidelobe suppression ratio of 21.7 dB, simultaneously. Our high-performance optical micro-ring filter could become an important element in future LNOI photonic circuits with applications in high-capacity wavelength-division multiplexing (WDM) systems, broadband microwave photonics, fast-tunable external-cavity lasers, and high-speed photonic neural networks.

Polarization-independent topological corner states based on all-dielectric valley photonic crystals

Recently, topological edge states and corner states have provided new ways to manipulate light transmission and localization. Up to now, most works have focused on either transverse magnetic or transverse electric polarization. In contrast, dual-polarization photonic topological states have attracted extensive attention because of their potential applications in polarization-independent photonic devices. Previous study realizes the polarization-independent topological corner states by independently tuning the out-of-plane permittivity and the in-plane permittivity of the anisotropic elliptic metamaterial, which is difficult to realize in the optical regime. In this work, we achieve polarization-independent topological edge states and corner states based on all-dielectric fishnet photonic crystals made of isotropic material. Note that the frequencies of the topological edge states and corner states depend on the structure’s effective refractive index, which is related to the filling ratio of the dielectric material. By selecting a suitable filling ratio of the dielectric material, polarization-independent edge states and corner states are realized. In addition, we further construct a topological waveguide-cavity coupling system and demonstrate the function of a polarization-independent optical notch filter. Our work paves the way for the implementation of polarization-independent topological photonic devices.

Design of Magnetic Fluid-Enhanced Optical Fiber Polarization Filter.

In this paper, we demonstrated a method of filling the air holes of a photonic crystal fiber (PCF), coated with gold film, with magnetic fluid (MF) to enhance the Surface Plasmon Resonance (SPR). The simulation results show that at the wavelength of 1260-1675 nm, the minimum loss coefficient of the y-polarization mode is 4.7 times that before filling with MF, and the x-polarization mode is 0.45 times greater. Then, based on this method, we designed a polarizing filter with a core diameter of 9 µm. The numerical simulation results indicate that it not only maintains the same core diameter as the single-mode fiber, but also has a larger bandwidth and a higher extinction ratio (ER). Additionally, we can optimize its ER at a specific wavelength by adjusting the magnetic field.