Optical Signal Power Research Articles

Adaptive Control for Underwater Simultaneous Lightwave Information and Power Transfer: A Hierarchical Deep-Reinforcement Approach

In this work, we consider a point-to-point underwater optical wireless communication scenario where an underwater sensor (US) transmits its sensing data to a remotely operated vehicle (ROV). Before the US transmits its data to the ROV, the ROV performs simultaneous lightwave information and power transfer (SLIPT), delivering both control data and lightwave power to the US. Under the considered scenario, our objective is to maximize energy harvesting at the US while supporting predetermined communication performance between the two nodes. To achieve this objective, we develop a hierarchical deep Q-network (DQN)–deep deterministic policy gradient (DDPG)-based online algorithm. This algorithm involves two reinforcement learning agents: the ROV and US. The role of the ROV agent is to determine an optimal beam-divergence angle that maximizes the received optical signal power at the US while ensuring a seamless optical link. Meanwhile, the US agent, which is influenced by the decision of the ROV agent, is responsible for determining the time-switching and power-splitting ratios to maximize energy harvesting without compromising the required communication performance. Unlike existing studies that do not account for adaptive parameter control in underwater SLIPT, the proposed algorithm’s adaptive nature allows for the dynamic fine-tuning of optimization parameters in response to varying underwater environmental conditions and diverse user requirements.

High-performance optical dialogue for power electronic system

High-accuracy signal and high-quality power transmissions play an essential role in power electronics systems. Nowadays, the severe electromagnetic interference (EMI) by the switching converter threatens the stable operation of conventional signal and power transmissions. To mitigate the effects of EMI, optical fiber is a better solution due to its unmatched isolation properties. Here, we perform a transmission configuration, named optical dialogue, based on a single fiber for simultaneous bidirectional analog optical signal (AOS) and analog optical power (AOP) transmission, to ensure EMI immunity. This optical dialogue transmission not only utilizes AOS to achieve high-accuracy signal transmission, but also utilizes AOP to achieve high-quality power transmission. We validate the proposed optical dialogue transmission using discrete off-the-shelf components, demonstrating the high frequency signal transmission and high efficiency power transmission. Our proposed optical dialogue transmission offers a high-performance optical solution for signal and power transmission, which is significant step forward in the development of more accurate, reliable, and safer power electronic systems.

Comparing the Performance of Optical Communication Links using G.652 and G.655 Fiber in Python Packages

This study investigates and compares the performance of a 10 Gbps optical communication link utilizing two prevalent single-mode fibers: G.652 and G.655. The analysis employs both theoretical calculations and Python-based simulations to assess the effectiveness of each fiber type in this high-speed transmission scenario. With the ever-growing demand for bandwidth in communication networks, 10 Gbps transmission systems are becoming increasingly commonplace. Single-mode fibers like G.652 and G.655 play a vital role in these systems, offering low signal attenuation for long-distance data transmission. However, each fiber type exhibits distinct dispersion characteristics, which can impact signal integrity over extended distances. This investigation adopts a two method for performance evaluation. Firstly, link power budget calculations are performed to determine the optical signal power before and after propagating through a 50-kilometer fiber span. The received power serves as the foundation for subsequent Q-factor and Bit Error Rate (BER) analysis. These calculations establish the theoretical limitations of the system based on well-defined formulas. Secondly, Python-based simulations are conducted to corroborate the theoretical findings and provide a more comprehensive performance assessment. This approach leverages the capabilities of two prominent Python packages: Opticomlib and OpticommPy. Opticomlib excels at analyzing the behavior of individual optical pulses within the system, enabling an understanding of the signal propagation. On the other hand, OpticommPy specializes in parameter sweep analysis, allowing for the investigation of how critical parameters like received power influence the Q-factor. By combining these functionalities, the simulations provide a detailed picture of the system's performance under various conditions. The calculated BER and Q-factor values for both G.652 and G.655 fiber links surpass the industry-accepted performance standards. These results demonstrate the effectiveness of using Python-based tools for comprehensive performance analysis of optical communication systems. However, it's important to note that slight discrepancies exist between the calculated and simulated results.

Optically biased and controlled signal processing in silicon photonics.

Optically biased and controlled signal processing is demonstrated in a commercial foundry silicon photonics integrated circuit process. Data and control signals are carried by different wavelengths in a WDM format. Optical signals on bias and control channels are converted to electrical voltages using series stacked photodiodes operating in photoconductive mode. Two examples of this scheme, namely, an amplitude modulator and a two-tap sequence detector capable of supporting different modulation formats, are experimentally demonstrated. The amplitude modulator requires 0.25 mW of optical control signal power to tune its optical output power by 15 dB. The two-tap sequence detector maps the consecutive symbols of a modulated signal such as OOK, PAM-3, and PAM-4, to distinct levels. A maximum control signal power of 5 mW is needed to calibrate and bias the sequence detector. This latter scheme may be extended to detect longer sequences and other modulation formats.

Analysis of Changes in Modulation Parameters on Optical Communication System

This study aims to analyze the NRZ-OOK modulation format in free-space optical communication. Simulations were conducted to examine the influence of the SpS parameter and optical signal power at the input modulator on the average power of the modulated optical signal. The research employed a computer simulation approach, where the optical signal was transmitted through an optical path without cables, enabling fast data transmission and longer distances compared to wired media. The method used specifically uses a machine learning-based application, Python. The simulation results indicate that higher SpS values result in a more accurate and smoother optical signal representation. Furthermore, an increase in the optical signal power at the input modulator increases the average power of the modulated optical signal. However, negative optical power values do not hold any relevant physical meaning. The magnitude of the Pi_dBm value also affects the optical signal spectrum, with higher optical power generating more robust frequency components. Graphs with negative optical power exhibit significant noise due to distortion and non-linearity. The findings of this study provide a better understanding of the influence of these parameters in the NRZ-OOK modulation format for free-space optical communication.

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.

Deep-Learning-Enabled Direct Detection With Reduced Computational Complexity and High Electrical-Spectral-Efficiency

Complex-valued double-sideband (CV-DSB) direct detection (DD) is a promising solution for high capacity and cost-sensitive data center interconnects, since it can reconstruct the optical field as a homodyne coherent receiver while does not require a costly local oscillator laser. In a carrier-assisted CV-DSB DD system, the carrier occupies a large proportion of the total optical signal power but bears no information. Reducing the carrier to signal power ratio (CSPR) can improve the information-bearing signal power and thus maximize the achievable system performance. Recently, we have proposed and demonstrated a deep-learning-enabled DD (DLEDD) scheme to reconstruct the full-field of the CV-DSB signal. In the DLEDD scheme, the optical CV-DSB signal was detected by a dispersion-diversity receiver and then recovered by a deep convolutional neural network (CNN). Nevertheless, the computational complexity of the deep CNN is the main obstacle to the application of the DLEDD scheme. In this paper, we demonstrate a 50-GBaud CV-DSB 32-ary quadrature amplitude modulation (32-QAM) signal transmission over 80-km single-mode fiber with ∼64% computational-budget reduction in the field reconstruction. This is achieved by using 1×1 convolutions to attain a sparse dimensionality (in particular the number of channels) of the deep CNN. To the best of our knowledge, we achieve the highest electrical spectral efficiency of 7.07 b/s/Hz per polarization per wavelength for a CV-DSB DD receiver without requiring a sharp-roll-off optical filter.

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.

Power limits with adjustable 10G receiver parameters for A-RoF transmission

Current paper characterizes the performance of the three-radio-frequency-channels, orthogonal-frequency-division-multiplexed (OFDM) radio-over-fiber (RoF) transmission system in terms of error-vector-magnitude and received optical signal power for a typical 10 GHz receiver obtained by the comprehensive simulations. The impact of the transmitted OFDM channels' signal-to-noise ratio (SNR) is also considered. We demonstrate that the SNR decrease from 40 dB to 25 dB results in an error vector magnitude (EVM) increase of up to 4 %. Furthermore, we propose the approach for allowing adjusting these results to other receiver sensitivity and responsivity values by introducing a delta in received optical signal power eliminating additional simulation or complicated calculations. The feasibility of the adjustments with a precision of up to 0.001% of the EVM is proved.

Design and Implementation of Wireless Optical Access System for VLC-IoT Networks

With the development of information technology, the Era of the Internet of Everything led by the Internet of Things (IoT) has arrived. The development of traditional Internet of Things based on radio frequency (RF) communication is increasingly perfect, but it is difficult to apply in electromagnetic sensitive industries such as nuclear power plants, engine rooms, hospitals, and industrial control. Under the background of limited spectrum resources, crowded space is filled with a lot of RF communication waves, and the electromagnetic environment is extremely complex. Traditional IoT is also difficult to apply in the high secrecy industries. In these special scenarios, the development of the IoT based on visible light communication (VLC) is particularly important. To realize the VLC-IoT, in this paper, the crosstalk phenomenon in the full-duplex real-time VLC is studied, and the crosstalk phenomenon is suppressed by reducing beam angle and field angle, power isolation, and ground plane segmentation. And the transmitter and receiver in the full-duplex VLC system are integrated on a single printed circuit board (PCB). Combined with the existing mature network, a full-duplex real-time VLC system based on fast Ethernet is implemented, which can be also considered as the wireless optical access system for VLC-IoT networks. Among them, the combination of a red LED and APD430A/M (optical receiver designed by Thorlabs) can achieve 100 Mbps Ethernet transmission of 30 m, and the combination of a white LED with the same optical power and the receiver with a blue light filter designed in this paper can achieve 100 Mbps Ethernet transmission of 4 m. The change of communication distance is because the latter only uses the blue light component to transmit information, which leads to the decrease of signal optical power and the low responsivity of the optical receiver at short-wave strength. All the above wireless optical access systems for VLC-IoT networks have been tested for packet loss rate and communication rate. In the daily lighting environment, the above systems can realize the transmission of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">8</sup> packets with zero packet loss and 94.9 Mbps transmission rate, in line with the characteristics of Fast Ethernet transmission rate, fully meeting the platinum user standard in the Carrier Ethernet. Based on this experiment, the key performance of the receivers is quantified in this paper. The noise equivalent power (NEP) of the receiver designed in this paper at peak response wavelength is 3.7 nW, which is better than the 5.5 nW of APD430A/M. With the help of the wireless optical access systems designed in this paper, a VLC-IoT networks experiment is realized, and multiple terminal devices can access the VLC-IoT networks at the same time by the wireless optical.

Optical differential phase shift keying transceiver systems performance efficiency at high data rate optical systems in the presence of Pr doped amplifiers

Abstract This work has been clarified the optical differential phase shift keying transceiver systems performance efficiency at high data rate optical systems in the presence of pr doped amplifiers. The Max optical signal power variations after fiber link versus wavelength variations at various system data rates are demonstrated. The total optical power within optical fiber at data rates from 10 to 100 Gbps are indicated. The Max electrical signal power variations against frequency after receiver variations at various system data rates are clarified. The total electrical power after receiver at various system data rates are demonstrated. The light/electrical power received, OSNR and SNR variations in relation to data rate variations are also studied.

A self-locking Rydberg atom electric field sensor

A crucial step toward enabling real-world applications for quantum sensing devices such as Rydberg atom electric field sensors is reducing their size, weight, power, and cost (SWaP-C) requirements without significantly reducing performance. Laser frequency stabilization is a key part of many quantum sensing devices and, when used for exciting non-ground state atomic transitions, is currently limited to techniques that require either large SWaP-C optical cavities and electronics or use significant optical power solely for frequency stabilization. Here, we describe a laser frequency stabilization technique for exciting non-ground state atomic transitions that solves these challenges and requires only a small amount of additional electronics. We describe the operation, capabilities, and limitations of this frequency stabilization technique and quantitatively characterize its performance. We show experimentally that Rydberg electric field sensors using this technique are capable of data collection while sacrificing only 0.1% of available bandwidth for frequency stabilization of noise up to 900 Hz.

OCDMA Codeword Switching Technique to Avoid Interference of Time-of-Flight LiDAR System for Autonomous Vehicles

The direct time-of-flight (d-ToF) technique is the most promising method for light detection and ranging (LiDAR) systems in long-range autonomous applications. However, the receiver cannot distinguish its own pulse signal from those of other LiDAR systems. This causes mutual interference between LiDAR systems, which degrades object recognition. The optical code division multiple access (OCDMA) modulation technique can be used to avoid mutual interference. However, it is difficult to secure sufficient orthogonal codes, because each laser channel uses a designated codeword. In addition, when interference occurs in a specific direction, it can occur continuously. Adversarial attacks on a LiDAR system can trick a vehicle to perform false object recognition without physical contact. This can endanger passengers, pedestrians, and other vehicles. Therefore, we propose an OCDMA codeword switching technique that can effectively solve these problems in driving environments. First, we analyzed the characteristics of optical orthogonal codes (OOC) and defined the interference generated in LiDAR systems. The proposed technique exhibits interference robustness by using a code index buffer based on differences in the received optical signal power. In addition, verification of the hardware implementation and its complexity was analyzed using LiDAR testbench and an FPGA. The interference and continuous interference of the proposed technique in various driving environments were verified using simulation model. Compared with using only a designated codeword, the proposed technique reduces interference by 82.59% and 85.51%, and continuous interference by 92.24% and 96.94% in straight-line and curved driving, respectively.

A Novel Microstructure of 2‐Bit Optical Analog to Digital Converter Based on Kerr Effect Nonlinear Nanocavities in 2D Photonic Crystal

In this paper, an all‐optical analog‐to‐digital converter based on nonlinear with silicon materials is designed and simulated. The proposed structure consists of three nonlinear nanocavity that control the optical signal power intensity. The nonlinear material used is aluminum gallium arsenide (AlGaAs). Aluminum gallium arsenide (AlGaAs) with a linear refractive index of n0 = 1.4 and a nonlinear refractive index of n2 = 1.5 × 10−17. Due to the small path length of the waveguides, the optical signals move a short distance and as a result, the power optical losses along the path are reduced and on the other hand, the speed of the structure is increased. The transmission percentage is between 90% and 100%. The overall dimensions of the structure are 324 μm2. The plane wave expansion (PWE) method is used to calculate the band structure. The two‐dimensional finite difference time domain (2D‐FDTD) method is used to calculate the transmission power spectrum and the simulation results.

Nonlinear wavelength conversion cross phase modulation in fiber systems based on directly modulated laser measured

Abstract This study has clarified the simulation of the nonlinear cross phase modulation (CPM) performance signature in optical fiber telecommunication systems. We have been clarified the max Q factor in relation to Cross phase shift modulation for the previous models and proposed model. The optimum optical power varied with spectral time and wavelength variation that is simulated for 90° cross phase shift modulation. Optimum total optical and electrical signal power is demonstrated for 90° Cross phase shift modulation. The max signal quality factor and min BER are assured for various degrees based on cross phase shift modulation. In addition to the optimum signal quality factor is emphasized for 90° Cross phase shift modulation.

Silicon photonic receiver for satellite laser communication terminals.

We report the optical performance of a photonic receiver for laser communication applications. The receiver is composed of 14 × 12 grating coupler arrays. The received optical signal power will be combined electrically via germanium photodiodes. The photonic receiver is designed for 20-µm to 30-µm mode field diameter (MFD) input sources. To maximize the fill factor of the 200 µm × 200 µm light-receiving area, a design strategy has been proposed. (1) Grating couplers are customized for compactness. (2) Periods of grating couplers are designed to work as end-fire and back-fire grating couplers for the same incident angle of the input laser source. (3) Different widths of waveguides are routed to minimize cross talk. The photonic receiver is evaluated with a 10-µm MFD source. As a result of the evaluation, the receiving area considering the minimum efficiency of -10.5 dB is 95% of the designed area when illuminating 20-µm to 300-µm MFD laser sources.

Stimulated Brillouin Scattering Based Image-Reject Microwave Signal Harmonic Down-Converter

We propose and demonstrate a photonic microwave signal harmonic down-converter with image rejection capability via stimulated Brillouin scattering (SBS). A dual-polarization dual-parallel Mach–Zehnder modulator (DP-DPMZM) is driven by a radio frequency/image (RF/IM) signal and a local oscillation (LO) signal to realize equivalent phase modulation and 4th-order double sideband modulation respectively. The optical carriers from the two arms of the DP-DPMZM can cancel out each other after polarization combining, thereby increasing the useful optical signal power in photodetection. Since the beating notes between the IM-modulated signals and LO-modulated 4th-order sidebands interfere destructively, the down-converted IM signals disappear naturally, which makes the down-converted image parts be suppressed in optical domain. By using an SBS-based dual-band microwave photonic filter to suppress the RF modulated -1st-order sideband and amplify the +1st-order sideband, destructive interference can be broken. Therefore, the RF signal over frequency range of 21-28 GHz can be down-converted to intermediate frequency (IF) band, and the image rejection ratio (IRR) can be also improved to more than 55 dB. Under -160 dBm/Hz noise floor, the SFDR is 105.1 dB·Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2/3</sup> .

100 Gb/s NRZ OOK signal regeneration using four-wave mixing in a silicon waveguide with reverse-biased p-i-n junction.

A silicon waveguide with reverse-biased p-i-n junction is used to experimentally demonstrate all-optical regeneration of non-return-to-zero (NRZ) on-off keying (OOK) signal based on four-wave mixing. The silicon waveguide allows a high conversion efficiency of -12 dB. The 0.22 dB (1.1 dB) quality (Q) factor and 0.74 dB (6.3 dB) extinction ratio (ER) improvements on average are achieved for 100 Gb/s (50 Gb/s) NRZ OOK signal regeneration at different receiving powers via the optimal match between the input signal optical power and input-output transfer curve. To the best of our knowledge, this silicon-based all-optical regenerator exhibits superior regeneration performance, including large ER and Q factor improvements, and the highest regeneration speed of NRZ OOK signal, and it has wide applications in 5 G/6 G networks.

Coherent combining of low-power optical signals based on optically amplified error feedback.

In free-space optical communication links, the combining of optical signals from multiple apertures is a well-known method to collect more power for improved sensitivity or mitigation of atmospheric disturbances. However, for analog optical combining no detailed analysis has been made in cases when the optical signal power is very low (<-60 dBm) as would be the case in very long-haul free-space links. We present a theoretical and experimental study of analog coherent combining of noise-limited signals from multiple independent apertures by applying low frequency optical phase dithering to actively compensate the relative phases. It is experimentally demonstrated that a 97% combining efficiency of four 10 GBaud QPSK signals is possible with a signal power per aperture exceeding -80 dBm, in fair agreement with theory. We also discuss the scaling aspects to many apertures.

Deep learning-based real-time analysis of lightpath optical constellations [Invited

Optical network automation requires accurate physical layer models, not only for provisioning but also for real-time analysis. In particular, in-phase (I) and quadrature (Q) constellation analysis enables deep understanding of the characteristics of optical connections (lightpaths), e.g., their length. In this paper, we present methods for modeling lightpaths based on deep learning. Specifically, we propose using autoencoders (AEs) and deep neural networks. Models are trained and composed in a sandbox domain with the information received from the network controller and sent to the node agent that uses them to compare the features extracted from the received signal and the expected features returned by the models. We investigate two different use cases for lightpath analysis focused on lightpath length and optical signal power. The results show a remarkable accuracy for the lightpath modeling and length prediction and a noticeable performance of the AEs for unsupervised IQ constellation feature extraction and relevance analysis.