Optical Input Research Articles

All-optical flip-flop by carbon/metal nanostructures in a multi-wave mixing

This work presents a design of a flip-flop controlled by the nonlinear optical response exhibited by a dynamic distribution of nanostructures in a liquid. Silver decorated carbon nanotubes suspended in ethanol were employed. The flip-flop proposed corresponds to a probabilistic NAND latch. The nonlinear nanofluids were studied by two-wave mixing experiments with nanosecond pulses at 532 nm wavelength. The behavior of the system is based on the Brownian motion with influence over the nonlinear transmittance of the nanostructures associated with a probabilistic optical bit. The optical response of the latch system output states was defined by the irradiance dependent on nonlinear optical absorption of the nanofluid. Specifically, the optical logical outputs depend on the state present at the optical inputs and the previous optical output states regulated by the feedback of the system. The nonlinear optical evolution of the effects in the nanofluids was explored as probabilistic phenomena governed by a concentration gradient of nanoparticles. The evaluation of the stability of a nanofluid defines the variables in the probabilistic system proposed. This work highlights the potential of nanohybrid materials for processing probabilistic functions, switching quantum effects, and for developing optical sensors.

Comparison of Target Refraction with Optical Vs. Immersion Biometry with Ladi Adjustment using Barrett Universal II Formula after Phacoemulsification with Premium IOLs

Purpose: The Barrett’s formula requires optical biometry inputs. The Ladi adjustment was designed to overcome this and use ultrasound (US) axial length (AXL) inputs into Barrett’s universal II formula. We compared the residual refractive error (RRE) with optical vs. ultrasound biometry with Ladi adjustment following phacoemulsification when all IOL powers were calculated using Barrett’s formula. Study Design: Prospective, randomised, double blinded study Methods: All adults undergoing routine phacoemulsification were recruited. The keratometry and AXL were randomly measured using either the IOL master 500 (IM500) or a combination of US biometry and Sirius topography. For the US measurements, 200 microns was added to the AXL (Ladi adjustment) and values were entered in the online Barrett’s calculator. The RRE (spherical equivalent – target refraction) was determined at 6 months. Results: We included 200 eyes of which 100 had IOL-power calculation using the IM500 and 100 using the Ladi adjustment of the US. The groups were comparable in baseline characteristics. The RRE was comparable in the two groups (-0.09+0.27D in US vs. -0.08+0.23D in IM500, p=0.90). The RRE was slightly higher in eyes with AXL>25mm (n=18 eyes, -0.21+0.33D in US vs. -0.07+0.17D in IM500), though this was not statistically significant (p=0.27). The preop BCVA (β= 0.06D, 95%CI= -0.5 to 0.13D, p=0.07) was the only factor marginally influencing RRE. Conclusion: The US biometry with the Ladi adjustment was as accurate as the IM500 and can be reliably used with the Barrett’s formula for IOL power calculations. Caution should be maintained at extremes of AXL.

67.5% Efficient InP-Based Laser Power Converters at 1470 nm at 77 K

Recent developments in long wavelength and cryogenic laser power converters have unlocked record performances in both areas. Here, devices for an optical input at ~1470 nm are studied for cryogenic applications, combining these cryogenic and long-wavelength attributes. Multijunction laser power converters are demonstrated to have a high-efficiency operation at 77 K. The photovoltaic-power-converting III-V semiconductor devices are designed with InGaAs-absorbing layers, here with 10 thin subcells (PT10), connected by transparent tunnel junctions. Unprecedented conversion efficiencies of up to 67.5% are measured at liquid nitrogen temperatures with an output power of Pmpp = 1.35 W at an average optical input intensity of ~62 W/cm2. A remarkably low bandgap voltage offset value of Woc~50 mV is obtained at an average optical input intensity of ~31 W/cm2.

2D van der Waals Heterostructure with Tellurene Floating-Gate for Wide Range and Multi-Bit Optoelectronic Memory.

Intensive research on optoelectronic memory (OEM) devices based on two-dimensional (2D) van der Waals heterostructures (vdWhs) is being conducted due to their distinctive advantages for electrical-optical writing and multilevel storage. These features make OEM a promising candidate for the logic of reconfigurable operations. However, the realization of nonvolatile OEM with broadband absorption (from visible to infrared) and a high switching ratio remains challenging. Herein, we report a nonvolatile OEM based on a heterostructure consisting of rhenium disulfide (ReS2), hexagonal boron nitride (hBN) and tellurene (2D Te). The 2D Te-based floating-gate (FG) device exhibits excellent performance metrics, including a high switching on/off ratio (∼106), significant endurance (>1000 cycles) and impressive retention (>104 s). In addition, the narrow band gap of 2D Te endows the device with broadband optical programmability from the visible to near-infrared regions at room temperature. Moreover, by applying different gate voltages, light wavelengths, and laser powers, multiple bits can be successfully generated. Additionally, the device is specifically designed to enable reconfigurable inverter logic circuits (including AND and OR gates) through controlled electrical and optical inputs. These significant findings demonstrate that the 2D vdWhs with a 2D Te FG are a valuable approach in the development of high-performance OEM devices.

Optimal Dirichlet boundary control by Fourier neural operators applied to nonlinear optics

We present an approach for solving optimal boundary control problems of nonlinear optics by using deep learning. For computing high resolution approximations of the solution to the nonlinear wave model, we propose higher order space-time finite element methods in combination with collocation techniques. Thereby, Cl-regularity in time of the global discrete solution is ensured. The simulation data is used to train solution operators that effectively leverage the higher regularity of the data. The solution operator is represented by Fourier Neural Operators and can be used as the forward solver in the optimal Dirichlet boundary control problem.The proposed algorithm is implemented and tested on high-performance computing platforms, with a focus on efficiency and scalability. The effectiveness of the approach is demonstrated on the problem of generating Terahertz radiation in periodically poled Lithium Niobate. The neural network is used as the solver in the optimal control setting to optimize the parametrization of the optical input pulse and maximize the yield of 0.3THz-frequency radiation.We exploit the periodic layering of the crystal to design the neural networks. The networks are trained to learn the propagation through one period of the layers. The recursive application of the network onto itself yields an approximation to the full problem. Our results indicate that the proposed method can achieve a speedup by a factor of 360 compared to classical methods. A comparison of our results to experimental data shows the potential to revolutionize the way we approach optimization problems in nonlinear optics.

Neuromorphic convolution with a spiking DFB-SA laser neuron based on rate coding.

We propose a neuromorphic convolution system using a photonic integrated distributed feedback laser with a saturable absorber (DFB-SA) as a photonic spiking neuron. The experiments reveal that the DFB-SA laser can encode different stimulus intensities at different frequencies, similar to biological neurons. Based on this property, optical inputs are encoded into rectangular pulses of varying intensities and injected into the DFB-SA laser, enabling the convolution results to be represented by the firing rate of the photonic spiking neuron. Both experimental and numerical results show that the binary convolution is successfully achieved based on the rate-encoding properties of a single DFB-SA laser neuron. Furthermore, we numerically predict 4-channel quadratic convolution and accomplish MNIST handwritten digit classification using a spiking DFB-SA laser neuron model with rate coding. This work provides a novel approach for convolution computation, indicating the potential of integrating DFB-SA laser into future photonics spiking neural networks.

Aboveground Forest Biomass Estimation Using Tent Mapping Atom Search Optimized Backpropagation Neural Network with Landsat 8 and Sentinel-1A Data

Accurate forest biomass estimation serves as the foundation of forest management and holds critical significance for a comprehensive understanding of forest carbon storage and balance. This study aimed to integrate Landsat 8 OLI and Sentinel-1A SAR satellite image data and selected a portion of the Shanxia Experimental Forest in Jiangxi Province as the study area to establish a biomass estimation model by screening influencing factors. Firstly, we extracted spectral information, vegetation indices, principal component features, and texture features within 3 × 3-pixel neighborhoods from Landsat 8 OLI. Moreover, we incorporated Sentinel-1’s VV (vertical transmit–vertical receive) and VH (vertical transmit–horizontal receive) polarizations. We proposed an ensemble AGB (aboveground biomass) model based on a neural network. In addition to the neural network model, namely the tent mapping atom search optimized BP neural network (Tent_ASO_BP) model, partial least squares regression (PLSR), support vector machine (SVR), and random forest (RF) regression prediction techniques were also employed to establish the relationship between multisource remote sensing data and forest biomass. Optical variables (Landsat 8 OLI), SAR variables (Sentinel-1A), and their combinations were input into the four prediction models. The results indicate that Tent_ ASO_ BP model can better estimate forest biomass. Compared to pure optical or single microwave data, the Tent_ASO_BP model with the optimal combination of optical and microwave input features achieved the highest accuracy. Its R2 was 0.74, root mean square error (RMSE) was 11.54 Mg/ha, and mean absolute error (MAE) was 9.06 Mg/ha. Following this, the RF model (R2 = 0.54, RMSE = 21.33 Mg/ha, MAE = 17.35 Mg/ha), SVR (R2 = 0.52, RMSE = 17.66 Mg/ha, MAE = 15.11 Mg/ha), and PLSR (R2 = 0.50, RMSE = 16.52 Mg/ha, MAE = 12.15 Mg/ha) models were employed. In conclusion, the BP neural network model improved by tent mapping atom search optimization algorithm significantly enhanced the accuracy of AGB estimation in biomass studies. This will provide a new avenue for large-scale forest resource surveys.

Integrated Bolometric Photodetectors Based on Transparent Conductive Oxides from Near‐ to Mid‐Infrared Wavelengths

On‐chip photodetectors are essential components in optical communications as they convert light into an electrical signal. Photobolometers are a type of photodetector that functions through a resistance change caused by electronic temperature fluctuations upon light absorption. They are widely used in the broad wavelength range from ultraviolet to mid‐infrared (MIR). In this work, a novel waveguide‐integrated bolometer that operates in a wide wavelength range from near‐infrared to MIR is introduced on the standard material platform with the transparent conductive oxides (TCOs) as the active material. This material platform enables the construction of both modulators and photodetectors using the same material, which is fully complementary metal–oxide–semiconductor compatible and easily integrated with passive on‐chip components. The photobolometers proposed here consist of a thin TCO layer placed inside the rib photonic waveguide to enhance light absorption and then heat the electrons in the TCO. This rise in electron temperature leads to decreasing electron mobility and consequential electrical resistance change. In consequence, a responsivity exceeding 10 A W−1 can be attained with a mere few microwatts of optical input power. Calculations suggest that further improvements can be expected with lower doping of the TCO, thus opening new doors in on‐chip photodetectors.

Adaptive polarization control for a fiber system based on the optimized AdamSPGD algorithm.

In this work, an adaptive control scheme based on the optimized AdamSPGD algorithm is proposed to maintain the stable state of polarization (SOP) of the optical signal in a fiber system. The search space can be reduced by half with the guidance of the physical equation of optical intensity that passes through a liner polarizer, leading to an increase in the speed and stability. Moreover, the robustness is guaranteed by the adoption of AdamSPGD as the optimization object. In the experiment, the input optical signals with random SOPs are successfully controlled to a stable output SOP. Compared to the original algorithm, the speed is increased by 44.73%, and the standard deviation of the required number of iterations is reduced by 21.27%.

Analysis of Effect of Input Power and RF Optical Signal Rate on Optical Communication System with OOK-NRZ Modulation

This study analyzed optical and RF signals in optical communication systems using the On-Off Keying Non-Return to Zero (OOK-NRZ) modulation method and the direct-detection receiver model with PIN photodiodes. In this study, a simulation was carried out using Python software. Changes in optical modulation input power and Symbol rate (Rs) were explored to understand their effect on signal characteristics. Models of ideal photodiodes (noiseless) and noisy photodiodes (considering thermal noise, shot noise, and bandwidth constraints) were used to compare receiver signals. The eye diagram analysis was employed to visualize receiver signal variation in a given time span. The results of this analysis provide a better understanding of the influence of changes in input power and symbol rate on optical communication systems through the OOK-NRZ method and insight into the characteristics of the receiving signal under realistic conditions. This study is able to provide guidance for the design and evaluation of optical communication systems using OOK-NRZ modulation and direct detection receivers.

Self-configuring programmable silicon photonic filter for integrated microwave photonic processors

Reconfigurable photonic filters show great promise as a potential solution to meet the evolving needs of future microwave communication systems. By integrating high-performance filters into programmable microwave photonic processors, they can provide significant benefits for signal processing applications. The development of an algorithm that can automatically characterize and reconfigure the filter using a single optical input and output port is essential for this purpose. This paper presents an optimization technique for a fully tunable ring-assisted Mach–Zehnder interferometer filter. The proposed filter design eliminates the need for monitoring components and employs a novel algorithm that operates independently in each ring by switching between the two arms of the filter. In addition, the filter can be configured to implement different filter architectures, allowing for flexible filtering requirements. Measurements were performed using the device as an interleaver, implementing different types of infinite impulse response filters in the optical and radio frequency domains. Side-coupled integrated spaced sequence of resonator filters were also implemented by reconfiguring the same device. These results demonstrate the exceptional reconfigurability of the filter design proposed herein in terms of bandwidth and central frequency.

High-performance laser power converts for wireless information transmission applications.

Laser Power Converters (LPCs) are components of the laser wireless power transmission (LWPT) system receiving laser power. This paper proposes a comprehensive test method that employs continuous, pulse-pause, and short-time techniques to evaluate the performance of six-junction GaAs LPCs operating with an optical input at 808 nm. Additionally, we investigate the performance of LPCs with different areas and achieve a conversion efficiency over 60%. Furthermore, we apply LPCs with varying areas to wireless information transmission and successfully achieve a response time of 1.7 µs.

On-chip all-optical second-order ordinary differential equation solver based on a single microdisk resonator.

This paper proposes an all-optical second-order ordinary differential equation (SODE) solver based on a single microdisk resonator. We validate the feasibility of our structure for constant and complex coefficient SODE solutions for Gaussian and super-Gaussian pulses. The results demonstrate a good agreement between the solutions obtained with the designed structure and those obtained through mathematical calculations for both constant and complex coefficient SODEs. We also discuss the influence of input optical signal pulse width on solution result deviations. Furthermore, we validate the capability of the designed structure to achieve tunable solutions for complex-coefficient SODEs with a tuning power of less than 10 mW. The device footprint is approximately 20×30 μm2, and it is 3-4 times smaller than the current smallest solving unit. The maximum Q-factor reaches 9.8×104. The proposed device avoids the traditional approach of cascading two resonators for SODE solving. Moreover, achieving mode alignment within the same resonator reduces the process challenges associated with aligning multiple devices in a cascade. Furthermore, it offers wider applicability for solving SODEs, namely, the ability to solve both constant and complex coefficient SODEs with complete derivative terms.

Quantum Dynamical Approach to Predicting the Optical Pumping Threshold for Lasing in Organic Materials.

The quantum dynamic (QD) study of organic lasing (OL) is a challenging issue in organic optoelectronics. Previously, the phenomenological method has achieved success in describing experimental observation. However, it cannot directly bridge the laser threshold (LT) with microscopic parameters, which is the advantage of the QD method. In this paper, we propose a microscopic OL model and apply time-dependent wave packet diffusion to reveal the microscopic QD process of optically pumped lasing. LT is obtained from the onset of output as a function of optical input pumping. We predict that the LT has an optimal value as a function of the cavity volume and depends linearly on the intracavity photon leakage rate. The calculated structure-property relationships between molecular parameters and the LT are in qualitative agreement with the experimental results, confirming the reliability of our approach. This work is beneficial for understanding the OL mechanism and optimizing the design of organic laser materials.

30.7 Tb/s Transmission over 400 km using 40 WDM channels of DP-16 QAM and Raman amplification without inline repeaters

Forty wavelength-division multiplexing (WDM) channels of 96 Gbaud (768 Gb/s) were transmitted over 400 km of SMF using only a Raman amplifier, which was accomplished through numerical simulations. Each WDM channel comprised eight electrical subcarriers of single sideband Nyquist-pulse-shaping. 16 quadrature amplitude modulation and dual polarization modulation were applied to each subcarrier channel and so one data symbol carried eight bits. The roll-off factor in the optical subcarrier spectrum was investigated from 2% to 11%, and the change in roll-off was analyzed according to the subcarrier channel in a single WDM channel. The spectral linewidth of the light source in the transmitter was changed up to 10 MHz, and the effect on the performance was examined for a coherent transmission system with constellation analysis. The optical input power per WDM channel was optimized and the wavelength spacing between WDM channels were analyzed using nonlinear effects from adjacent WDM channels. A transmission experiment for total 30.7 Tb/s over 400 km was performed using the obtained optimal values. BER evaluation was achieved by DSP algorithms including Kramers–Kronig detection and Nyquist filtering. All 40 WDM channels exhibited sufficient transmission performance using only the Raman backward pumping of the four pump wavelengths. The proposed system can be applied to unrepeatered metro‐networks or data-center interconnects.

All-optical wavelength and format conversion of DQPSK-to-PAM4 using DLI and pump assisted NOLM

An all-optical wavelength and format conversion scheme of 20 Gbps differential quadrature phase shift keying (DQPSK)-to-4-ary pulse amplitude modulation (PAM4) signals based on the delay line interferometer (DLI) and the pump assisted nonlinear optical loop mirror (NOLM) is proposed and numerically simulated. The input DQPSK signal is converted into two star-16-ary quadrature amplitude modulation (star-16QAM) signals (namely, star-16QAM-I and star-16QAM-Q) using DLI with the time delay of 1-symbol and different linear phase shifts of π/4 and −π/4, respectively. The star-16QAM signals are converted into the on-off keying (OOK) signals (namely, OOK-I and OOK-Q) using the pump assisted NOLM based on the self-phase modulation (SPM) and the cross-phase modulation (XPM) in the highly nonlinear fiber (HNLF). The two OOK signals can be aggregated into different types of PAM4 signals by adjusting their power ratio (PR) and relative phase shift (RPS) flexibly. Error vector magnitude (EVM) and bit error rate (BER) for the input and output optical signals are calculated to verify the scheme performance. Compared to the DQPSK signal with an input optical signal-to-noise ratio (OSNR) of 30 dB, there are about 2.5 dB penalty of receiver OSNR for the converted OOK-I and OOK-Q signals. For the corresponding aggregated equidistant PAM4 and equiamplitude PAM4 signals, they have about 6.3 dB and 12.1 dB penalty of receiver OSNR. The proposed scheme of DQPSK-to-PAM4 can be deployed at the all-optical gateway to bridge the long-hual and short-reach optical networks.

Optical MIMO Communication Based on Joint Control of Base Station and OPA-Type OIRS

As a new type of optical communication device, the optical intelligent reflecting surface (OIRS) can reflect, shape and split optical signals in real time, and is expected to expand the application scenarios of optical wireless communication. However, in the existing research, a single OIRS cannot support optical multiple input multiple output (MIMO) communication since OIRS performs the same modulation on all incident light. In this paper, we propose an optical MIMO communication system based on joint control of base station and optical phased array (OPA)-type OIRS. The communication system utilizes the OPA -type OIRS's characteristic of superimposing the input optical phase and the OIRS's phase to implement a joint beam control scheme of the base station and the OIRS, thereby realizing optical MIMO communication with a single OIRS. Considering the OIRS's physical model, pointing error, atmospheric turbulence and attenuation, our work establishes the mathematical model of the optical MIMO communication system, and derives the closed-form expression of the probability density function (PDF) of the channel fading, asymptotic outage probability and bit error rate (BER) for the first time. Experiments and simulations are built to verify the feasibility and accuracy of our system model and theoretical derivation, which proves that our results are consistent with the actual system.

Mutual influence of intermodal and fundamental four-wave mixing of 1.0 µm and 1.5 µm nanosecond pulses in a dual-wavelength fiber laser.

We introduce the experimental and theoretical investigation of the mutual influence of two four-wave mixing (FWM) processes during the propagation of high-power nanosecond pulses at 1030 nm and 1562 nm wavelengths in the few-mode optical fiber. Both fundamental mode FWM (FM FWM) of laser pulses at these wavelengths, and intermodal FWM (IM FWM) of 1030 nm pulses, have common anti-Stokes components at 1003 nm wavelength. This leads to the mutual influence of FWM effects. As a result, the decrease of optical power of the fundamental mode is observed at both 1030 nm and 1562 nm wavelengths. The method for the suppression of such an adverse effect is proposed. It is based on the attenuation of the 1030 nm higher LP11 mode at the few-mode optical fiber input.

Flexible Data Rate Allocation Using Non-Orthogonal Multiple Access (NOMA) in a Mode Division Multiplexing (MDM) Optical Power Splitter for System-on-Chip Networks.

We put forward and demonstrate a silicon photonics (SiPh)-based mode division multiplexed (MDM) optical power splitter that supports transverse-electric (TE) single-mode, dual-mode, and triple-mode (i.e., TE0, TE1, and TE2). An optical power splitter is needed for optical signal distribution and routing in optical interconnects. However, a traditional optical splitter only divides the power of the input optical signal. This means the same data information is received at all the output ports of the optical splitter. The powers at different output ports may change depending on the splitting ratio of the optical splitter. The main contributions of our proposed optical splitter are: (i) Different data information is received at different output ports of the optical splitter via the utilization of NOMA. By adjusting the power ratios of different channels in the digital domain (i.e., via software control) at the Tx, different channel data information can be received at different output ports of the splitter. It can increase the flexibility of optical signal distribution and routing. (ii) Besides, the proposed optical splitter can support the fundamental TE0 mode and the higher modes TE1, TE2, etc. Supporting mode-division multiplexing and multi-mode operation are important for future optical interconnects since the number of port counts is limited by the chip size. This can significantly increase the capacity besides wavelength division multiplexing (WDM) and spatial division multiplexing (SDM). The integrated SiPh MDM optical power splitter consists of a mode up-conversion section implemented by asymmetric directional couplers (ADCs) and a Y-branch structure for MDM power distribution. Here, we also propose and discuss the use of the Genetic algorithm (GA) for the MDM optical power splitter parameter optimization. Finally, to provide adjustable data rates at different output ports after the MDM optical power splitter, non-orthogonal multiple access-orthogonal frequency division multiplexing (NOMA-OFDM) is also employed. Experimental results validate that, in three modes (TE0, TE1, and TE2), user-1 and user-2 achieve data rates of (user-1: greater than 22 Gbit/s; user-2: greater than 12 Gbit/s) and (user-1: greater than 12 Gbit/s; user-2: 24 Gbit/s), respectively, at power-ratio (PR) = 2.0 or 3.0. Each channel meets the hard-decision forward-error-correction (HD-FEC, i.e., BER = 3.8 × 10-3) threshold. The proposed method allows flexible data rate allocation for multiple users for optical interconnects and system-on-chip networks.

Vertical Multi-Junction Laser Power Converters with 61% Efficiency at 30 W Output Power and with Tolerance to Beam Non-Uniformity, Partial Illumination, and Beam Displacement

Stable and reliable optical power converting devices are obtained using vertical multi-junction laser power converters. They are based on the GaAs and the InP material systems and are used for power-over-fiber or power-beaming applications. This study demonstrates that, in addition to providing the overall best conversion efficiencies with output voltages ideal for various applications, these semiconductor photovoltaic devices are very tolerant to beam non-uniformity, partial illumination, or beam displacement variations. Examples are given with two tight beams, each covering as little as ~7% of the cell area. An optical input power of 10 W was converted with still an efficiency of Eff ~59.4%. For an input power of 20 W, the illuminated area was set to ~22% without significantly affecting the conversion efficiency of Eff ~60%. Remarkably, for a beam diameter at ~65% of the chip length (i.e., covering ~35% of the chip area), a converted power of 29.5 W was obtained using a 12-junction GaAs device with a conversion efficiency of 61%. For a 10 junction InP-based device, an efficiency of Eff = 51.1% was obtained at an output voltage reaching as high as Voc = 5.954 V for an average optical intensity of 69 W/cm2 and an illumination area of ~57%.