Low Crosstalk Research Articles

High-Density LED Array Based on Epitaxial Slice Damage-Free Process and Its Single-Contact Operation Mode With Low Crosstalk

High-Density LED Array Based on Epitaxial Slice Damage-Free Process and Its Single-Contact Operation Mode With Low Crosstalk

A 3.06 μm Single-Photon Avalanche Diode Pixel with Embedded Metal Contact and Power Grid on Deep Trench Pixel Isolation for High-Resolution Photon Counting.

In this study, a 3.06 μm pitch single-photon avalanche diode (SPAD) pixel with an embedded metal contact and power grid on two-step deep trench isolation in the pixel is presented. The embedded metal contact can suppress edge breakdown and reduce the dark count rate to 15.8 cps with the optimized potential design. The embedded metal for the contact is also used as an optical shield and a low crosstalk probability of 0.4% is achieved, while the photon detection efficiency is as high as 57%. In addition, the integration of a power grid and the polysilicon resistor on SPAD pixels can help to reduce the voltage drop in anode power supply and reduce the power consumption with SPAD multiplication, respectively, in a large SPAD pixel array for a high-resolution photon-counting image sensor.

Design of a multi-core photonic crystal fiber supporting 518 OAM modes

A multi-ring core photonic crystal fiber (PCF) with seven high-index ring regions is designed for the transmission of multiple orbital angular momentum (OAM) modes. The new structure which has an optimized air hole arrangement shows improved transmission quantity and number of OAM modes. Numerical analysis reveals that the PCF can transmit 518 OAM modes in the range of 1.4–1.75 µm stably while avoiding cross talk from the adjacent ring core resulting in a low cross talk of merely −208.5dB, confinement loss less than 10−9dB/m, as well as mode quality greater than 0.925. The results disclose a new method to increase the communication capacity and suggest that the PCF has great application potential.

A cascade splicing-based multimode fiber-tapered single-mode fiber structure for pressure sensing

Pressure sensing holds immense significance in the realm of fiber optic sensors, particularly in the context of industrial and environmental safety monitoring. In this paper, we propose and experimentally validate an optical fiber structural sensor based on Mach-Zehnder interferometer (MZI) for pressure measurement. The sensor adopts a cascaded spliced single-mode-multimode-tapered single-mode fiber (SMF-MMFTapered SMF, SMTS) structure, taking advantage of the mode mismatch effect between different fiber types and the high sensitivity of the evanescent field surrounding the tapered single-mode fiber. A segment of multimode fiber (MMF) is incorporated as the mode coupler to enhance the multimode interference (MMI). Experimental results demonstrated the sensor's robustness to pressure and temperature changes, with measurement sensitivities of the interference wavelengths Dip A and Dip B at 5.751 nm/KPa and 1.394 nm/KPa, respectively, within the pressure range of 0 ∼ 4410 Pa. The sensor also exhibited a response of 1.113 nm/°C and 0.857 nm/°C in the temperature range of 27.5 °C ∼ 41 °C. The sensor indicates a low temperature crosstalk of only 0.194 KPa/°C. By applying temperature compensation to correct pressure measurements, the accuracy of pressure sensing can be significantly improved. The sensor offers distinct advantages, including high sensitivity, low temperature crosstalk, compact structure, and simple fabrication, making it a promising candidate for applications in biochemistry and industrial production.

Inverse design of asymmetric Y-junctions for ultra-compact, broadband, and low crosstalk mode (de)multiplexers.

Asymmetric Y-junctions, compared with mode coupling-based devices, possess considerably smaller wavelength dependence and thus are more promising for ultra-broadband mode (de)multiplexing in integrated optics. However, these devices also feature relatively high mode crosstalk and insertion loss. Here, we show that the mode crosstalk and loss of an asymmetric Y-junction can be significantly reduced by optimizing the waveguide shape of the Y-junction using an adjoint-based inverse design. Based on such inverse-designed asymmetric Y-junctions, we realize ultra-compact, broadband, and low crosstalk silicon photonic TE00 & TE1 and TE0 & TE2 mode (de)multiplexers with sizes of only 4.5 × 1.2 µm2 and 6 × 1.4 µm2, respectively. From simulations it is shown that the TE0 & TE1 and TE0 & TE2 mode (de)multiplexers contain wide bandwidths of 160 nm (1460-1620 nm) and 140 nm (1460-1600 nm), respectively, over which the mode crosstalks are below about -20 dB, and the losses are <0.41 dB and <0.88 dB, respectively. The experimental results show that in the corresponding TE0 & TE1 and TE0 & TE2 mode division multiplexing systems, the crosstalks are less than -15.5 dB and -15 dB over the spectral ranges of 1453-1580 nm and 1460-1566 nm, respectively, and the losses are <1.7 dB at 1520 nm and <8.24 dB over the entire measured wavelength range.

Multiplexed fiber-optic photoacoustic sensors for simultaneous detection of multi-point gases

A multiplexing scheme of fiber-optic photoacoustic (PA) gas sensors is demonstrated for simultaneous detection of multi-point gases. By sharing the PA demodulation device, the average cost of single point measurement can be significantly reduced. The passive fiber-optic PA gas sensing probe is integrated by a PA tube and a Fabry-Perot (F-P) interferometric (FPI) cantilever. The laser excited the PA signals is simultaneously incident into two sensing probes. The superimposed F-P interference spectrum containing multi-point gas concentration information is received by a high-speed spectrometer. For synchronous measurement of multi-point gases, a white-light interferometry (WLI) based frequency division multiplexing (FDM) spectral demodulation method is exploited. A multi-point acetylene gas remote monitoring system is established by two PA gas sensing probes with 3 km fiber cable. The experimental results show that the sensing probes have achieved the detection limit of sub-ppm. The crosstalk between the two sensors is characterized by the gas concentrations at the two points, indicating a crosstalk of about − 35 dB. This multiplexing scheme of fiber-optic PA sensing probes has the merits of remote monitoring, low crosstalk, high sensitivity, intrinsic safety and low cost. It can be applied for coal spontaneous combustion monitoring, dissolved gas analysis and gas micro-leakage monitoring.

Optimizations of Double Titanium Nitride Thermo-Optic Phase-Shifter Heaters Using SOI Technology.

A commercial thermo-optic phase shifter (TOPS) is an efficient solution to the imbalance problem in the fabrication process of Mach-Zehnder modulator (MZM) arms. The TOPS consumes electrical power and transforms it into thermal energy, which changes the real part of the effective refractive index at the waveguide and adjusts the MZM transfer function to work in the linear region. The common model being used today is constructed with only one heater; however, this solution requires more electrical power, which can increase the transmitter system cost. To reduce the system energy cost, we propose a pioneering optimal double titanium nitride heater model under forward biasing at 1550 nm wavelength using the standard silicon-on-insulator technology. Numerical investigations were carried out on the key relative geometrical parameters, heat distribution at the silicon layer, thermal crosstalk, and laser wavelength drift. Results show that the optimal TOPS design can function with a low electrical power of 19.1 mW to achieve a π-phase shift, with a low thermal crosstalk of 0.404 and very low optical losses over 1 mm length. Thus, the proposed device can be used for improving the imbalance problem in MZMs with low electrical power consumption and low losses. This functionality can be utilized to obtain better performances in transmitter systems for data centers and long-range optical communication system applications.

Dual-Core Ce: YAG-Derived Silicate Scintillation Fiber for Real-Time X-Ray Detection

A dual-core Ce:YAG-derived scintillation fiber (DCSF) was proposed conceptually, simulated numerically, and prepared experimentally by the modified molten core method (MCM) for the first time, of which, the core material is amorphous yttrium aluminosilicate glasses and the cladding material SiO2. Theoretically, it is found that such kind of DCSF exhibits very low inter-core crosstalk with the help of finite element simulation analysis, which may result from the high index difference of ∼0.097 between core and cladding. The average decay lifetime of the prepared DCSF are 31.4 ns and 36 ns at 350 nm and 500 nm, which are shorter than those of its Ce:YAG bulk crystal counterpart. Radiation monitoring was demonstrated by an all-fiber detection system. The radiation response of the DCSF bundle was also investigated, whose radio-luminescence response intensity is ∼1.66 and ∼1.12 times higher than that of the single-core fiber bundles with similar core-diameter and with similar core-area, respectively. In conclusion, with radiation detection performance improvement enabled by space division multiplexing capability, the DCSF not only provides a solution for the dilemma between low transmission loss and high optical yield, but also makes a substantial step towards the development of practical and reliable radiation detectors.

Optical division scheme for binary number by 2[formula omitted]

In this paper, we propose a circuit for binary number division by 2n utilizing data shifting technology. The circuit design incorporates electro-optic Mach–Zehnder interferometers and S-bent waveguides. Notably, no arithmetic operations are involved. We simulate the circuit using the 2D-beam propagation method and observe low cross talk (ranging from ∼−4.04 dB to −14.65 dB) and a high contrast ratio (∼12.32 dB) based on simulation results. Additionally, we present a quantum realization of the proposed circuit employing the SWAP gate and provide experimental outcomes from a real quantum computer.

High-sensitivity fiber SPR strain sensor based on n-type structure.

At present, fiber strain sensors are mainly of the grating type and interference type, while there is relatively little research on fiber surface plasmon resonance (SPR) strain sensors. In this Letter, we propose a highly sensitive fiber SPR strain sensor based on an n-type structure. The strain changes the shape of the fiber n-type structure, causing the transmission mode of light in the fiber to change, thereby changing the SPR incidence angle and causing the SPR resonance valley wavelength to shift, achieving highly sensitive SPR strain sensing. The test results indicate that the strain sensing sensitivity of the proposed sensor reaches 21.33 pm/µε, and two n-type structures are connected in series to obtain a double n-type structure, further enhancing the strain sensing sensitivity to 33.44 pm/µε. This fiber strain sensor has advantages of high sensitivity, low temperature cross talk, strong structural stability, and low production cost, and is expected to become a new solution for wearable intelligent monitoring equipment and strain sensors in the aerospace field.

Power-efficient polarization-insensitive tunable microring filter on a multi-layer Si3N4-on-SOI platform.

We develop and demonstrate a non-duplicate polarization-diversity tunable bandpass optical filter by leveraging the bi-directional transmission of add-drop dual-coupled microring resonators (MRRs) on a multi-layer Si3N4-on-silicon-on-insulator (SOI) platform. By using Euler-bends, we implement compact and low-loss Si3N4 MRRs with an equivalent bending radius of ∼38 µm. Fiber-to-fiber (on-chip) insertion loss of 4.3 dB (1.7 dB) with a low polarization-dependent loss of <0.5 dB and low differential group delay of <2.5 ps is achieved. The extinction ratio is more than 30 dB. The thermo-optic tuning efficiency of the Si3N4 MRRs is improved with a suspended micro-heater design. As a result, a wavelength tuning range of ∼2 nm and a 3-dB bandwidth tuning range of 20 GHz are experimentally demonstrated. The tuning efficiency is 33 pm/mW, which is ∼7.5 times higher than the previous design. This reconfigurable polarization-insensitive filter, with low loss, low cross talk, and high power efficiency, is highly promising for practical applications in optical communication and signal processing.

Light-stimulated long-term potentiation behavior enhanced in a HfO2/InGaZnO photonic synapse

Photonic-based neuromorphic systems offer numerous advantages, including low crosstalk, high bandwidth, and low power consumption, making them an ideal choice for ultrafast neuromorphic systems. Although these neuromorphic systems promote the utilization of amorphous oxide semiconductors (AOSs) for promising photonic synapses, precise control of their unique persistent photoconductivity to mimic synaptic plasticity using an external light stimulus has rarely been studied. This study investigates the significant enhancement of the long-term potentiation (LTP) behavior in an InGaZnO (IGZO) photonic synapse through facile HfO2 passivation. In HfO2/IGZO synapses, the HfO2 layer is crucial in enhancing the LTP characteristics. The improvement in the persistent photocurrent behavior of the HfO2/IGZO synapse was attributed to the higher activation energy required for the neutralization of ionized oxygen vacancies, facilitating the LTP behavior. The LTP was dynamically modulated depending on external light pulse conditions. A large number of multilevel states (1024 states) were enabled by consecutive light simulations. Furthermore, HfO2/IGZO synapses exhibit different learning capacities depending on the external stimuli configuration. These findings demonstrate our ability to manipulate synaptic functionality in AOS-based artificial photonic synapses, paving the way for multifunctional photonic synapse circuitry. This advancement holds the potential for realizing an artificial vision system in the future.

Low fluorescence crosstalk patterning of quantum dots based on laser drilling and micropore filling

In this study, a dual-color patterned perovskite quantum dot color conversion layer with a light-blocking matrix was created by combining laser drilling with micropore filling technology. When the blue micro-LED and the quantum dot color conversion layer make contact, the fluorescence crosstalk effect can be simulated to be near zero. The color conversion layers with high color gamut (111.2% of the National Television System Commission) were further confirmed to have outstanding optical isolation performance through experimental observations. This work may have significant advantages for its applications in photonic integration, micro-LED, and near-field displays due to simple operation process, maskless, harmlessness to quantum dots, short process period, and low crosstalk effect.

Adaptive readout approaches of resistive sensor array for wearable electronics applications

Sensor arrays are widely used to extract the distribution of variables in large sensing areas or collect multi-degree-of-freedom data. In this paper, we propose adaptive resistance matrix approaches, which can get rid of additional electrical components such as diodes, transistors, multiplexers, op-amps, switches, and current sources. By eliminating the power supply parameters, these approaches can show great advantages and application potential when they are used to measure wearable flexible sensor arrays or other low-cost sensor arrays. Experimental results have shown that the proposed approaches achieved a high accuracy (99.45% and 99.80%), large measurement range (0.5 ∼ 1.5 times the reference resistance value), and relatively low crosstalk error (0.066% and 0.128%). The approach was then applied to a flexible strain sensor array to estimate the three-degree-of-freedom lumbar spine motion, and the results have shown that the resistance distribution of the sensor array can clearly show the strain distribution under different lumbar movements.

Assessing crosstalk in simultaneous multicolor single-molecule localization microscopy

Single-molecule localization microscopy (SMLM) can reach sub-50nm resolution using techniques such as stochastic optical reconstruction microscopy (STORM) or DNA-point accumulation for imaging in nanoscale topography (PAINT). Here we implement two approaches for faster multicolor SMLM by splitting the emitted fluorescence toward two cameras: simultaneous two-color DNA-PAINT (S2C-DNA-PAINT) that images spectrally separated red and far-red imager strands on each camera, and spectral demixing dSTORM (SD-dSTORM) where spectrally close far-red fluorophores appear on both cameras before being identified by demixing. Using S2C-DNA-PAINT as a reference for low crosstalk, we evaluate SD-dSTORM crosstalk using three types of samples: DNA origami nanorulers of different sizes, single-target labeled cells, or cells labeled for multiple targets. We then assess if crosstalk can affect the detection of biologically relevant subdiffraction patterns. Extending these approaches to three-dimensional acquisition and SD-dSTORM to three-color imaging, we show that spectral demixing is an attractive option for robust and versatile multicolor SMLM investigations.

Low-loss and power-efficient phase shifter based on an optimized multimode spiral silicon waveguide.

Low-loss and energy-efficient phase shifters are an effective tool to reduce the power consumption of large-scale photonic integrated circuits. In this work, a low-loss and power-efficient thermo-optic phase shifter has been demonstrated on the silicon-on-insulator platform. The multimode spiral waveguide is optimized to obtain lower power consumption and low cross talk. The waveguide width is beyond the single-mode region in consideration of low propagation loss. The optimized ultra-low loss 180° Bezier bends are used to further reduce the bending loss. The experimental results show that the excess loss of the phase shifter is only 0.36 dB at 1550-nm wavelength and the power consumption is 4.87 mW/π.

Deep focus light-field camera for handheld 3D intraoral scanning using crosstalk-free solid immersion microlens arrays.

3D in vivo imaging techniques facilitate disease tracking and treatment, but bulky configurations and motion artifacts limit practical clinical applications. Compact light-field cameras with microlens arrays offer a feasible option for rapid volumetric imaging, yet their utilization in clinical practice necessitates an increased depth-of-field for handheld operation. Here, we report deep focus light-field camera (DF-LFC) with crosstalk-free solid immersion microlens arrays (siMLAs), allowing large depth-of-field and high-resolution imaging for handheld 3D intraoral scanning. The siMLAs consist of thin PDMS-coated microlens arrays and a metal-insulator-metal absorber to extend the focal length with low optical crosstalk and specular reflection. The experimental results show that the immersion of MLAs in PDMS increases the focal length by a factor of 2.7 and the transmittance by 5.6%-27%. Unlike conventional MLAs, the siMLAs exhibit exceptionally high f-numbers up to f/6, resulting in a large depth-of-field for light-field imaging. The siMLAs were fully integrated into an intraoral scanner to reconstruct a 3D dental phantom with a distance measurement error of 82 ± 41 μm during handheld operation. The DF-LFC offers a new direction not only for digital dental impressions with high accuracy, simplified workflow, reduced waste, and digital compatibility but also for assorted clinical endoscopy and microscopy.

Machine learning assisted hybrid transduction nanocomposite based flexible pressure sensor matrix for human gait analysis

Human gait analysis strongly correlates with critical health metrics and provides significant information about physiological well-being. Therefore, accurate, fast, and cost-effective gait monitoring is required for intelligent healthcare systems. This paper reports the development of a flexible hybrid transduction Barium Titanate (BTO)/SU-8 nanocomposite-based, individually addressable pressure sensor matrix. The proposed sensor is highly suitable for wearables compared to the conventional pressure sensors due to its speedy and cost-effective design flow and ease of operation. The hybrid (piezoelectric/triboelectric), photo-patternable active layer enables strain and contact electrification-based sensing that convolves into a highly sensitive, lower cross talk and large area pressure sensing. The reported sensor is incorporated with a solder-free modular data acquisition setup for a straightforward design integration. A pressure sensitivity of 34 mV kPa-1 for the deep linear region and 2.7 mV kPa-1 for the linear region over a pressure range of 0–170 kPa is reported. The sensor shows excellent reliability and negligible hysteresis with an average deviation of 2.7 %. Furthermore, the 36 pressure cells with hybrid transduction deliver rich feature extraction to machine learning algorithms compared to single transducer-based systems for an accurate gait and grip strength monitoring. The developed convolution neural network (CNN)-2D model gives a model accuracy of 98.5 % and 98.3 % for two different gait characterizations, while delivering a model accuracy of 93.75 % for grip strength assessment. The combination of hybrid sensor design, development, and use of machine learning offers a novel approach to tackle the issues associated with sensors that are incompatible with rapidly developing smart healthcare technology.

Two fiber-bundle-type FI/FO devices of low insertion loss and cross talk applied for connecting 13-core 5-mode fiber.

Two fiber-bundle-typed fan-in/fan-out (FI/FO) devices, "wavy hexagon-shaped silhouette" type (W-FI/FO) and "tortoise-shaped silhouette" type (T-FI/FO), have been proposed and manufactured based on tapering glass tubes for docking with a self-made 13-core 5-mode fiber. The W-FI/FO device consists of 19 5-mode fibers and has an extended layout based on the 13-core 5-mode fiber structure. It could dock multiple fibers with 19 or 13 cores of the same size standards. When connecting it with 13-core 5-mode, the average losses (ILs) of its five modes are 1.07 dB, 2.95 dB, 3.42 dB, 3.65 dB, and 4.38 dB. The cross talks of the five linearly polarized (LP) modes are -69.1 dB, -64.7 dB, -44.2 dB, -43.9 dB, and -39.1 dB. The T-FI/FO device has a similar core arrangement to the 13-core 5-mode fiber and its average ILs of the five LP modes are 0.23 dB, 1.31 dB, 2.09 dB, 2.66 dB, and 3.03 dB. The cross talks of its five LP modes between adjacent cores are -72.8 dB, -67.8 dB, -43.6 dB, -40.0 dB, and -35.3 dB. The IL and cross talk of the LP01 mode are of satisfactory values, which are 0.23 dB and -72.8 dB, respectively. These two proposed FI/FO devices are expected to be used for high-speed optical interconnection and fiber communication.

Light manipulation for all-fiber devices with VCSEL and graphene-based metasurface.

Light manipulation for all-fiber devices has played a vital role in controllable photonic devices. A graphene-based metasurface is proposed to realize light manipulation. A row of VCSEL-based optical engines with low crosstalk is used as the control light to modulate the signal transmitted in the microstructured fiber. In this configuration, the proposed device can work independently of the wavelength division multiplexing (WDM) system. With an insertion loss of only 0.28 dB, evanescent wave coupling to graphene layers is polarisation-insensitive. The device could be effectively manipulated for a few days (not less than 72 hours), which possesses the capacity to dynamically modulate the signal light with both low-temperature sensitivity and low-wavelength sensitivity. The 35 nm wavelength interval results in a change of only about 0.1 dB in the output light intensity of the microstructured fiber when the wavelength changes from 1530 nm to 1565 nm. Moreover, the modulation depth is approximately 2 dB when the modulating voltage is 2.2 V, which may open avenues for channel detection techniques and have deep implications in top tuning applications.