Search

Accurate three-dimensional spatiotemporal distribution information on near-surface aerosols is of great significance for environmental research. In this study, a 3D scanning coaxial Mie lidar (3D-STML) was developed to achieve a fast three-dimensional scanning observation of aerosol diffusion processes in near-surface areas. 3D-STML generates high-spatiotemporal resolution images of aerosol extinction coefficient in real-time and captures the dynamic changes of aerosols in near real-time. By optimizing the design of the light guide mirror and the telescope sub-mirror, the system has a small overlap. Based on this, a highly stable and high-speed mechanical rotation mechanism was developed to enable three-dimensional observations. The integration of a solid-state high-repetition-rate pulsed laser and a coaxial, optical system for the transmitter and receiver ensures rapid tracking of aerosol plumes. To meet the observation requirements of near-surface aerosols, an aerosol inversion algorithm combining the Fernald and Klett methods was designed and developed. For aerosol plume monitoring needs, an aerosol plume-tracking algorithm based on Kalman filtering was developed to track the spatiotemporal evolution of aerosols automatically. Experimental results demonstrated that 3D-STML is capable of detecting aerosols in a range from 15 m to 4 km, with a distance resolution of 1.5 m and a time resolution of 0.083 s. It can effectively track and capture aerosol plumes. It can be used for large-scale, long-term observation of near-surface aerosols and for monitoring the spatiotemporal evolution of aerosol plumes. [ABSTRACT FROM AUTHOR]

The Cosmic Dawn was marked by the formation of the first stars, and preceded the Epoch of Reionization (EoR), when the Universe underwent a fundamental transformation caused by the radiation from these first stars and galaxies. Interferometric 21-cm experiments aim to probe redshifted neutral hydrogen signals from these periods, constraining the conditions of the early Universe. The SKA-Low instrument of the Square Kilometre Array (SKA) is envisaged to be the largest and most sensitive radio telescope at metre and centimetre wavelengths. The latest Aperture Array Verification Systems feature 7-m coaxial transmission lines connecting the low noise amplifiers to optical transmitters at the front of the analogue-receiving chain. An impedance mismatch between these components results in a partially reflected electromagnetic signal, introducing chromatic aberrations into the instrument bandpass. This causes power from the foreground signals to appear at higher delays, potentially contaminating the 'EoR window', a region in which the 21-cm signal should be detectable. We present an end-to-end simulation pipeline for SKA-Low using a composite sky model combining radio foregrounds from the Galactic and Extragalactic All-Sky MWA (GLEAM) Survey, Haslam 408 MHz, and a 1.5-cGpc 21-cm brightness temperature cube generated with the 21cm space simulator. We derive a model for the scattering parameters of a coaxial transmission line in terms of its specifications and bulk material properties. Assuming identical cables of length |$\le 15.0$|  m with impedance mismatch |$\le 10\, \Omega$|⁠ , the reflection is confined below the EoR window. However, we demonstrate that even a 0.1 per cent length tolerance introduces contamination with an absolute fractional difference of ~10 per cent across all accessible k-modes. [ABSTRACT FROM AUTHOR]

Visible light communication (VLC) has emerged as one promising candidate technique to improve the throughput performance in future sixth-generation (6G) mobile communication networks. Due to the limited battery capacity of VLC systems, light energy harvesting has been proposed and incorporated for achieving the simultaneous lightwave information and power transfer (SLIPT) function and for improving the overall energy efficiency. Nevertheless, almost all reported works are limited to SLIPT scenarios adopting a basic and well-discussed Lambertian optical transmitter, which definitely cannot characterize the potential and essential scenarios employing distinctive non-Lambertian optical transmitters with various spatial beam characteristics. For addressing this issue, in this work, SLIPT based on a distinct non-Lambertian optical beam configuration is investigated, and for further enhancing the harvested energy and the achievable data rate, the relevant flexible optical beam configuration method is presented as well. The numerical results show that, for a typical receiver position, compared with about 1.14 mJ harvested energy and a 31.2 Mbps achievable data rate of the baseline Lambertian configuration, a harvested energy gain of up to 1.55 mJ and an achievable data rate gain of 21.1 Mbps can be achieved by the non-Lambertian SLIPT scheme explored here. [ABSTRACT FROM AUTHOR]

We propose a novel family of codes comprising two mutually orthogonal states of polarization (SOPs) for the spectral encoding of one-dimensional (1D) Corite codes with two-code keying (TCK) for use in the spectral amplitude coding (SAC) of optical code-division multiple access (OCDMA) networks. We design these 1D Corite codes with TCK to create a specific code operation function, an encoding optical transmitter structure, and a decoding optical receiver structure, respectively. In the proposed system, multi-user interference (MUI) can occur due to interference from other simultaneous users. However, we have modified the cross-correlation to cancel out the MUI. Although the proposed system recovers bits successfully, it still suffers from phase-induced intensity noise (PIIN). Our numerical results demonstrate that the proposed system using 1D Corite codes with TCK can support a larger number of simultaneous users than other systems that use 1D CTP codes with TCK, 1D M3 sequence codes, 1D BIBD codes, and 1D BDS codes with TCK. Specifically, the proposed system can support up to 48 simultaneous users, which is a notable improvement. Our numerical results indicate that the proposed system using 1D Corite codes with TCK can achieve a data transmission rate of up to 2.5 Gbps, which is a significant improvement. [ABSTRACT FROM AUTHOR]

Thin‐film lithium niobate (TFLN)‐based electro‐optic modulators have extensive applications in broadband optical communications due to their broad bandwidth, high extinction ratio, and low optical loss. However, compared with their silicon and indium‐phosphide (InP)‐based counterparts, TFLN exhibits lower modulation efficiency. Simultaneously achieving low driving voltage and a wide modulating bandwidth poses a significant challenge. To address this limitation, this paper proposes a transparent conductive oxide film into the device, resulting in an ultra‐high modulation efficiency of 1.02 V cm. The fabricated composite electrode not only attains high modulation efficiency but also sustains a high electro‐optic bandwidth, as evidenced by the 3 dB roll‐off at 108 GHz and the transmission of PAM‐4 signals at 224 Gbit s−1. The fabricated device offers novel solutions for low‐cost, high‐performance modulators, thereby facilitating the downsizing of TFLN‐based multichannel optical transmitter chips. [ABSTRACT FROM AUTHOR]

In this study, we focus on the development of key processes towards wafer-scale 3-dimentional/vertical (3D) integration of Indium-Phosphide (InP) photonic membranes on InP electronics via adhesive bonding. First, we identified the most critical steps and optimized them to achieve high thermal and mechanical compatibility of components for the co-integration process. Next, we developed a strategy for InP-to-InP wafer bonding with high topology tolerance, and introduced hard benzocyclobutene (BCB) anchors to preserve the alignment and BCB thickness uniformity after bonding. The resulting bond layer is homogeneous in terms of physical and mechanical properties. Finally, we developed a novel method to selectively remove the InP substrate from the photonics side via wet etching while protecting the electronics carrier wafer with hermetic multi-layer coatings. The investigation of these key steps is essential for scalable 3D integration of photonics and electronics at ultra short distances (< $15 ~\mu \text{m}$). [ABSTRACT FROM AUTHOR]

This two-part work develops a comprehensive toolbox for the statistical characterization of nonlinear distortions of DAC-generated signal constellations to be transmitted over communication links, be they electronic (wireline, wireless) or photonic, Mach–Zehnder modulator (MZM)-based optical interconnects in particular. The all-analytic toolbox developed here delivers closed-form expressions for the second-order statistics (means, variances) of all relevant constellation metrics of the DACs' building blocks and of DAC-driven MZM-based optical transmitters, all the way to the slicer in the optical receivers over a linear channel with coherent detection. The key impairment targeted by the model is the random current mismatch of the ASIC devices implementing the DAC drivers. In particular the (skew-)centrosymmetry of the DAC metrics is formally derived and explored. A key applicative insight is that the conventional INL/DNL (Integral NonLinearity/Differential NonLinearity) constellation metrics, widely adopted in the electronic devices and circuits community, are not quite useful in the context of communication systems, since these metrics are ill-suited to predict communication link statistical performance. To rectify this deficiency of existing electronic DAC metrics, we introduce modified variants of the INL|DNL, namely the integral error vector (IEV) and the differential error vector (DEV) constellation metrics. The new IEV|DEV represent straightforward predictors of relevant communication-minded metrics: error vector magnitude (EVM) treated here in Part I, and Symbol/Bit Error-Rates (SER, BER) treated in the upcoming Part II of this paper. [ABSTRACT FROM AUTHOR]

In response to the problems of communication capacity and spectrum resource constraints, radio over fiber (ROF) technology has gained widespread adoption, and the quality and performance of the optical transmitter module also directly affect the transmission of the link. This paper presents the design of a direct modulation optical transmitter module in the frequency band ranging from 2.6 kHz to 206.8 MHz using OPA690 broadband voltage feedback op‐amp. The module features a tunable bias voltage range from 0 to 5 V to accommodate different threshold voltages for modulation power supply. It offers a gain of 12 dB and a signal‐to‐noise ratio exceeding 50 dB while demonstrating excellent stability, high signal purity, good spectral response characteristics, and compact size advantages. Based on this design, we further optimized the system circuit by adding a fourth‐order Butterworth filter structure, reducing the lower cut‐off frequency to about 500 Hz, increasing the gain by 6 dB, reducing the return loss to −26.91 dB, and the module's signal‐to‐noise ratio exceeding 90 dB. This optimization scheme improves the stability and signal purity of the optical transmitter module and improves the spectral response characteristics. In this paper, Multisim is used to analyze and verify the proposed optical transmitter circuit. In addition, a complete link experiment was carried out using an optical receiving module designed in the same laboratory to verify the feasibility of our proposed module. [ABSTRACT FROM AUTHOR]

A quantum well (QW) diode that is capable of emitting light is also capable of absorbing light. In particular, the QW diode has broad electroluminescence and responsivity spectra and thus, a distinct spectral overlap exists, enabling the establishment of light communication using two identical QW diodes, namely, one as the transmitter and the other as the receiver. Here, we demonstrate a time-division multiplexing (TDM) wireless light communication using two identical green QW diodes that are defined by software as transmitter or receiver to achieve real-time underwater data transmission via the same optical channel. To further exploit this dual emission-detection characteristics, we unite energy conservation, gravitational field and energy diagram theory to arrive the conclusion that the gravitational field may play a key role in the irreversibility between light emission and detection of the QW diode. [ABSTRACT FROM AUTHOR]

A Silicon Photonics modulator is a high-speed photonic integrated circuit for optical data transmission in high-capacity optical networks. Silicon Photonics modulators in the configuration of a Mach–Zehnder interferometer, in which a PN-junction rib-waveguide phase shifter is inserted in each arm of the interferometer, are studied in this paper because of their superior performance of high-quality optical data generation in a wide range of spectral bands and their simplicity in fabrication processes suitable to production in foundries. Design, fabrication, and fundamental characteristics of Silicon Photonics Mach–Zehnder modulators are reviewed as an introduction to these high-speed PICs on the Silicon Photonics platform. Modulation speed, or modulation bandwidth, is a key performance item, as well as optical loss, in the application to high-speed optical transmitters. Limiting factors on modulation speed are addressed in equations. Electrical resistance–capacitance coupling, which causes optical modulation bandwidth–optical loss trade-off, is the most challenging limiting factor that limits high-speed modulation. Expansion of modulation bandwidth is not possible without increasing optical loss in the conventional approaches. A new idea including quantum-mechanical effect in the design of Silicon Photonics modulators is proposed and proved in computational analysis to resolve the bandwidth loss trade-off. By adding high-mobility quantum-well overlayers to the side slab wings of the rib-waveguide phase shifter, the modulation bandwidth is doubled without increasing optical loss to achieve a 200 Gbaud modulation rate. [ABSTRACT FROM AUTHOR]

In the domain of the Internet of Things (IoT), Optical Camera Communication (OCC) has garnered significant attention. This wireless technology employs solid-state lamps as transmitters and image sensors as receivers, offering a promising avenue for reducing energy costs and simplifying electronics. Moreover, image sensors are prevalent in various applications today, enabling dual functionality: recording and communication. However, a challenge arises when optical transmitters are not in close proximity to the camera, leading to sub-pixel projections on the image sensor and introducing strong channel dependence. Previous approaches, such as modifying camera optics or adjusting image sensor parameters, not only limited the camera's utility for purposes beyond communication but also made it challenging to accommodate multiple transmitters. In this paper, a novel sub-pixel optical transmitter discovery algorithm that overcomes these limitations is presented. This algorithm enables the use of OCC in scenarios with static transmitters and receivers without the need for camera modifications. This allows increasing the number of transmitters in a given scenario and alleviates the proximity and size limitations of the transmitters. Implemented in Python with multiprocessing programming schemes for efficiency, the algorithm achieved a 100% detection rate in nighttime scenarios, while there was a 89% detection rate indoors and a 72% rate outdoors during daylight. Detection rates were strongly influenced by varying transmitter types and lighting conditions. False positives remained minimal, and processing times were consistently under 1 s. With these results, the algorithm is considered suitable for export as a web service or as an intermediary component for data conversion into other network technologies. [ABSTRACT FROM AUTHOR]

This paper presents an experimental evaluation of a wearable light-emitting diode (LED) transmitter in an optical camera communications (OCC) system. The evaluation is conducted under conditions of controlled user movement during indoor physical exercise, encompassing both mild and intense exercise scenarios. We introduce an image processing algorithm designed to identify a template signal transmitted by the LED and detected within the image. To enhance this process, we utilize the dynamics of controlled exercise-induced motion to limit the tracking process to a smaller region within the image. We demonstrate the feasibility of detecting the transmitting source within the frames, and thus limit the tracking process to a smaller region within the image, achieving an reduction of 87.3% for mild exercise and 79.0% for intense exercise. [ABSTRACT FROM AUTHOR]

The rapid evolution of passive optical network (PON) technologies has been driven by the necessity to accommodate 5th-generation system requirements. This research introduces a PON wavelength division multiplexing-based optical transmitter that is improved in both fiber link and bit rate. The transmitter is designed to connect many clients to a single-mode optical fiber. The optical transmitter under consideration is designed to provide an optimum data rate up to 20 Gbps per user. The data is modulated using a 2-bit per symbol Quadrature Phase Shift Keying (QPSK), and an M-array pulse coder. The R.F. signal is optically modulated during the optical system stage using a Mach–Zehnder external modulator supplied with an optical carrier generated by a vertical cavity surface emitting laser (VCSEL). Two PON configurations are devised in this context: initially, 16 VCSELs spanning 193.1–194.6 THz with a 10 GHz separation are utilized to modulate 16 data sources with 16 MZM. In contrast, in the second configuration, to reduce input laser power and system complexity, 16 data consumers share a single 193.1 THz VCSEL. Simulations of the performance measurements were conducted by Optisystem 19 for both configurations. The initial system configuration permits 20 Gbps transmission to 120 km with a Q-factor of at least 6. The power penalty of this configuration was reduced from − 970 to − 930 dB. The second configuration guarantees the dependability of data transmission over a distance of 100 km. The maximal Q-factors for the first and second configurations are 12 and 10, respectively, at a distance of 20 km. It has been established that the ideal input bias current for a VCSEL is 2 mA. The effects of the quadrature phase shift keying modulation QPSK is clearly appeared, as the current results are surpassed the peer publications regarding the utmost achievable fiber link length, Q-factor and supported data rate. [ABSTRACT FROM AUTHOR]

Currently, there are three types of optical communication networks based on the communication channel between the transmitter and receiver: the optical fiber channel, visible light channel, and optical wireless channel networks. The last type has several advantages for underwater communication, wireless sensors, and military communication networks. However, this type of optical network suffers from weather conditions in free-space communications and attenuation owing to the scattering and absorption mechanisms for underwater communication. In this study, we present a new transceiver architecture of a coherent optical code-division multiple-access (OCDMA) system based on a hybrid M-ary differential pulse position modulation scheme and a spreading code sequence called weighted modified prime code for underwater communication to minimize channel dispersion, increase the transmission rate per second, enhance the network bit error rate (BER) performance, and improve network security. Using an OCDMA system, we can simultaneously expand the network coverage area and increase the number of users sharing the network over the same channel bandwidth. The simulation results in this study proved that the proposed system can accommodate 1310 active users and a network throughput of 180 Gbps*user over a transmission distance of 930 m without any repeater at a 10−9 BER performance, compared to the 45 Gbps*user network throughput and 100 m transmission distance reported in the literature. [ABSTRACT FROM AUTHOR]

A photonics‐based terahertz (THz) wireless fronthaul is proposed, and its feasibility is investigated by real‐time demonstration. The proposed wireless fronthaul can be simply integrated into existing fiber‐optic fronthaul, to serve as a complementary or emergency network. An optical signal can be converted into a THz wireless signal by photonics‐based THz‐signal generation technology, utilizing a unitraveling carrier photo‐diode. Following wireless transmission, the THz wireless signal is reconverted to an optical signal by using a Schottky‐barrier diode and an optical transmitter. To investigate the feasibility of our proposed concept, real‐time transmission over a 100 m‐equivalent configuration is demonstrated with 24.33 Gb/s common public radio interface option 10 signals, at a carrier frequency of 275 GHz. The latency added by the proposed wireless fronthaul was measured to be few 100 ns, which is negligibly lower than the wireless transmission latency required by 6G key performance indicator. [ABSTRACT FROM AUTHOR]

Dual wavelength quantum cascade lasers (DW‐QCLs) are a type of semiconductor laser that can emit two different wavelengths of light simultaneously. They are constructed using quantum cascade structures, consisting of multiple layers of semiconductor materials carefully engineered to produce the desired wavelengths of light. This research article reports the numerical simulation and evaluation of the maximum capacity of free space optical (FSO) link employing novel coding schemes for DW‐QCL‐based pulsed optical transmitters. A 48‐stage DW‐QCL emitting at 10.5 and 8.9 μm wavelengths and a Quantum‐Well based Infrared Photodetector based receiver are considered for the study. The performance of the link is analyzed under short pulse transmission from the device at both wavelengths for various scenarios. Optical pulses are obtained either at a single wavelength or two different wavelengths by proper choice of electrical input current amplitude. This feature enables the implementation of four different coding schemes. Among the various coding approaches proposed, the scheme, which operates on symbols, performs the best, providing a maximum link length of 1700m, for a BER of 10−9. [ABSTRACT FROM AUTHOR]

To address the issues of signal waveform distortion and inter-symbol interference, both of which lead to performance degradation in airborne laser communication due to multipath transmission in airborne air-to-air channels, theoretical analysis and Monte Carlo ray tracing (MCRT) simulation methods were employed. Based on airborne application conditions, this research conducted numerical simulations of the Gaussian beam multipath transmission in an air-to-air channel, with a focus on analyzing the impact of meteorological conditions, communication distance, transmitter power, and initial pulse width on the pulse time spreading characteristics of received optical signals. In addition, an analysis of these parameters' impact on the inter-symbol interference (ISI) and bit error rate (BER) was conducted. The research findings can serve as a reference for the design of anti-interference techniques in airborne laser communication links. [ABSTRACT FROM AUTHOR]

Objective In recent years, there has been an explosive growth in data communication traffic. To address the demands for high-speed, high-capacity data transmission and the diversification of network application scenarios, 100 Gbit/s and Beyond (B100 Gbit/s) Dense Wavelength Division Multiplexing (DWDM) hybrid networking has gradually gained attention as an efficient solution. This paper conducts an analysis of the requirements, key technologies, and practical case studies of B100 Gbit/s DWDM hybrid networking to provide technical support and guidance for constructing high-capacity and efficient communication networks. Methods This paper first elucidates the requirements for the development of B100 Gbit/s DWDM hybrid networks, including the need for network capacity expansion and support for complex network architectures. Next, it focuses on introducing the key technologies of B100 Gbit/s DWDM hybrid networking, including constellation shaping, spectrum shaping, and flexible grid techniques. To support bitrate design in hybrid networking, a method for Optical Signal-to-Noise Ratio (OSNR) calculation in cascaded Erbium-Doped Fiber Amplifier (EDFA) communication systems is presented, utilizing parameters such as channel configuration information, signal optical power after transmitter, gain and noise parameters of EDFAs, to progressively calculate the output OSNR for each wavelength along the entire link. Finally, in conjunction with a foreign network case study and based on actual OSNR evaluation findings, a rational hybrid rate network design is performed, demonstrating the practical application of B100 Gbit/s DWDM hybrid networking in engineering projects. Results By employing B100 Gbit/s DWDM hybrid network, after flexibly configuring transmission rates and bandwidths according to OSNR evaluations, the deployment of hybrid rate networks at 200, 600 and 800 Gbit/s is achieved. This approach fulfills the high-capacity requirements of core sites while accommodating the long-distance, extensive span requirements of edge sites. Furthermore, network upgrades and expansion were smoothly accomplished within a three-year period. Conclusion Empirical evidence demonstrates that B100 Gbit/s DWDM networking effectively enhances network capacity, flexibility, and spectrum resource utilization. Moreover, it provides room for the continuous evolution of the networks, serving as a vital methods to advance the development of high-capacity optical transmission networks. [ABSTRACT FROM AUTHOR]

The study has outlined the performance evaluation of bidirectional wavelength division multiple access broadband optical passive elastic networks operation efficiency. Signal power level, Q coefficient parameter, and minimum data error rates are measured numerically in both downstream and upstream directions based on broadband passive optical networks (BPONs). The transmission data rate available in the downstream direction is 10 Gb/s, while its value in the upstream direction is 2 Gb/s. The suitable operating wavelength is selected in the near-infrared region around 1550 nm for minimum losses. The bits sequence length of the optical transmitter is taken in to account for testing the optical network performance efficiency. The proposed model has presented better performance than the previous model by 25.76 % in downstream direction and by 12.28 % in upstream direction. As well as the bidirectional wavelength division multiple access broadband passive optical elastic networks performance efficiency is measured. [ABSTRACT FROM AUTHOR]

We demonstrate the design and simulation of a long range four-channel wavelength division multiplexing-passive optical network (WDM-PON) operating at 40 Gb/s (4 × 10 Gb/s) in downstream transmission for undersea wireless optical communication. The proposed model consists of two separate subsections between the optical transmitter and receiver. The first subsection consists of the central office and 50 km long feeder fiber for transmitting the optical signal from a distant base station to the 1 × 4 optical demultiplexer located at the sea shore. The second subsection comprises 500 m distributed fiber from the 1 × 4 optical demultiplexer to the terminal point placed at the bottom of the sea and 15–20 m optical wireless channel inside sea water. Simulation results confirmed successful transmission of optical signals from the 50 km distant optical transmitter to the optical receiver located maximum 15 m inside the sea water with a signal-to-noise ratio of ∼20.96 dB, bit error rate of ∼1.55 × 10−8, and quality factor of ∼5.584. The eye diagram at the receiving end also exemplifies quality downstream data transmission at a rate of 10 Gb/s per channel. In addition, we compare the simulation results of the four-channel 40 Gb/s WDM-PON system with a four-channel WDM-PON system operating at 4 Gb/s (4 × 1 Gb/s). Simulation results confirm maximum reach of 17.5 m inside sea water at a cost of significant reduction in data rate. Furthermore, we analyze the system availability of the proposed WDM-PONs and find convincing results for high-speed secured data transmission under water. [ABSTRACT FROM AUTHOR]

This paper presents a novel approach to addressing the issue of temperature-induced instability in an optical, single-sideband transmitter based on a micro-ring resonator (MRR) suitable for millimeter-wave (mmW) radio-over-fiber (RoF) communications. We propose utilizing the drop port of the MRR to provide a feedback signal to the closed-loop control (CLC) system. The latter serves to maintain the optimal alignment between the laser's carrier and the MRR's resonant wavelength, thus mitigating the adverse effects of chromatic-dispersion-induced power fading at the receiving end. Since the feedback information is extracted from the otherwise-wasted resonant energy at the drop port, the control system does not compromise the delicate optical signal at the through port. A CLC was synthesized, designed, and prototyped to provide real-time wavelength tuning of the heat-pump-controlled laser based on the feedback signal. Experimental evaluations demonstrate that the wavelength of the laser could be successfully locked to the MRR's resonance with a wavelength dither of less than 0.004 nm (~491 MHz). This allowed us to limit the power-penalty deterioration to less than 2 dB for a RoF link with a 2.5-km standard telecommunication single-mode fiber (SMF), a modulation frequency of 37.8 GHz, and a carrier wavelength of 1563.97 nm (~191.820 THz). The proposed solution offers an alternative approach for the carrier and the MRR's resonant wavelength interlocking without the need for complex photonics like thermo-optic or electro-optic structures to control the temperature or phase velocity, respectively. [ABSTRACT FROM AUTHOR]

We present a 3-D ultrasound imaging system utilizing a light-based ultrasound transmitter. The system achieves high spatial resolution through a plain surface coated with a thin layer of carbon nanotubes (CNTs), which is optically scanned by a pulsed laser. The transmitter is fabricated by depositing a CNT-polydimethylsiloxane composite onto a glass substrate using techniques such as dip coating, dropping, and spin coating. The transmission characteristics are dependent on the laser beam width and CNT layer thickness, with the spin-coated layer demonstrating a center frequency of 9.08 MHz and bandwidth of 12.65 MHz. The imaging system boasts an axial resolution of 200 μm and lateral resolution of 190 μm. 3-D imaging was successfully performed on a chicken heart with a penetration depth up to 30 mm, providing a potential replacement for complex high voltage pulser circuits with a simple and manufacturable optical ultrasound transmitter. [ABSTRACT FROM AUTHOR]

This paper presents a real-time underwater wireless optical communication (UWOC) system. The transmitter of our UWOC system is equipped with four blue LEDs, and we have implemented pre-emphasis technology to extend the modulation bandwidth of these LEDs. At the receiver end, a 3 mm diameter APD is utilized. Both the transmitter and receiver are housed in watertight chassis and are submerged in a water pool to conduct real-time underwater experiments. Through these experiments, we have obtained impressive results. The data rate achieved by our system reaches up to 135 Mbps, with a BER of 5.9 × 10−3, at a distance of 10 m. Additionally, we have developed a convenient method for measuring the underwater attenuation coefficient, using which we have found the attenuation coefficient of the water in experiments to be 0.289 dB/m. Furthermore, we propose a technique to estimate the maximum communication distance of an on–off keying UWOC system with intersymbol interference, based on the Q factor. By applying this method, we conclude that under the same water quality conditions, our system can achieve a maximum communication distance of 25.4 m at 80 Mbps. Overall, our research showcases the successful implementation of a real-time UWOC system, along with novel methods for measuring the underwater attenuation coefficient and estimating the maximum communication distance. [ABSTRACT FROM AUTHOR]

This paper proposes a novel method to improve the anti-dispersion ability of the all-optical orthogonal frequency division multiplexing (AO-OFDM) system. By replacing the Sinc-shaped filter with a Gauss-shaped filter for sub-carrier generation and inserting a cyclic prefix (CP), the impact of dispersion on the system can be significantly mitigated. Formula derivation and numerical analysis of the pulse-shaping function of the AO-OFDM system in the time domain for each cycle indicated that the pulse-shaping function generated by the Gauss-shaped filter was less affected by the dispersion effect than that of the Sinc-shaped filter. Meanwhile, less inter-carrier crosstalk between carriers was also observed. After carrying out system transmission simulations employing these two different filters, we found that the AO-OFDM system based on the Gauss-shaped filter could greatly improve the anti-dispersion ability compared with the system based on a Sinc-shaped filter. When the parameter settings in both schemes were identical, that is, the number of subcarriers was 32 and the power of a single subcarrier was −13 dBm, the bit error rate (BER) of the system based on the proposed Gauss-shaped filter after 60 km SMF transmission was only 1.596 × 10−3, while the BER of the traditional Sinc-shaped filter based system scheme was as high as 8.545 × 10−2. [ABSTRACT FROM AUTHOR]

As one of the key technologies of the intelligent transportation system (ITS), vehicle-to-everything (V2X) communications have received increasing attention. Because of the broad and unlicensed spectrum, free space optical (FSO) communications have become a potential technology for V2X communications. In this article, the implementation of FSO communications is introduced first. Afterward, for the three advantages of FSO communications in ITS, the concrete principle and implementation approaches are illustrated in detail. First, based on the adaptive illumination schemes, the communication range is expanded without visual interference caused by illumination. Second, with the help of mode division multiplexing (MDM) and wavelength division multiplexing (WDM), the communication rate is further increased. Third, integrating sensing and communication enables vehicles to effectively obtain information and improve traffic efficiency and safety. In addition, applications of FSO communications in various communication scenarios in ITS are described. To satisfy the complex requirements of communication, illumination, and sensing in traffic scenarios, a deep learning-enabled heterogeneous system of FSO and radio frequency is proposed. Furthermore, future applications and open issues are provided for further investigation. [ABSTRACT FROM AUTHOR]

This work proposes a new paradigm for contactless vital sign sensing that adopts an integrated ultrawideband (UWB) radar and hybrid optical wireless communication (OWC) technologies. The proposed system is composed of a sensor node and a receiver node. The sensor node is responsible for detecting continuous vital sign signals and then transmitting these signals via the hybrid OWC transmitters, which are composed of a visible light communication transmitter and an infrared transmitter. The contactless UWB radar adopts low intermedium frequency demodulation rather than the conventional direct down conversion topology to avoid severe direct current (DC) offset issue. The advantages of this merged configuration do not only help reduce radar complexity but also provide the required modulated signal with vital signs for the subsequent OWC system. Moreover, the receiver node has an OWC receiver module for receiving vital signs that utilizes a photodiode-based receiver with an analog filter and digital signal processing mechanisms. The proposed architecture exhibits the potential to reduce radar complexity and provide new solutions to replace the conventional contact sensing system used in hospitals or nursing homes. [ABSTRACT FROM AUTHOR]

This article investigates the use of a visible light positioning system in an indoor environment to provide a three dimensional (3D) high‐accuracy solution. The proposed system leveraged the use of a single light‐emitting diode and an image sensor at the transmitter and the receiver (Rx) respectively. The proposed system can retrieve the 3D coordinate of the Rx using a combination of the angle of arrival and received signal strength (RSS). To mitigate the error induced by the lens at the Rx, a novel method is proposed and experimentally tested. The authors show that, the proposed method outperforms previously reported RSS under all circumstances and it is immune to varying exposure times within the standard range of 250 µs to 4 ms. The authors experimentally demonstrate that the proposed algorithm can achieve a 3D root mean squared error of 7.56 cm. [ABSTRACT FROM AUTHOR]

Spectrally efficient modulation formats become essential for optical network scaling as the demand for routed data streams exceeds the present wavelength-division multiplexing systems' throughput. However, achieving high spectral efficiency at high data rates requires complex and bandwidth-intensive electronics. In this study, we propose an all-optical aggregation scheme that combines multiple low spectral efficiency optical wavelength channels from an optical frequency comb based transmitter into fewer channels with higher spectral efficiency. Our method utilizes coherent spectral superposition and optical vector summation, eliminating the need for optical nonlinearities and relying on linear signal processing with an electro-optic modulator. By adjusting the phase of the radio frequency signal driving the modulator, we can easily achieve the required optical phase tuning for vector addition in the I-Q plane. Through experimental demonstrations, we show that the proposed approach enables the generation of 10 GBd PAM-4 and 10 GBd quadrature phase shift keying (QPSK) signals by aggregating two 10 GBd binary phase shift keying signals. Similarly, we aggregate two 10 GBd QPSK signals into one 10 GBd quadrature amplitude modulation-16 (QAM-16) signal. The experiments employ both conventional and sinc-shaped Nyquist signals. Our in-line, all-optical aggregation concept significantly enhances operational capacity while reducing complexity. It offers a promising solution for realizing flexible integrated optical transmitters for advanced modulation format signals using lower-quality electronics. Additionally, it aligns with the requirements of future dynamically reconfigurable optical networks that leverage spectral traffic aggregation. Given its reliance on linear signal processing with an electro-optic modulator, the integration of the method into any integrated photonic platform is straightforward. [ABSTRACT FROM AUTHOR]

Quantum key distribution (QKD) has evolved as a robust way of secret key distribution based on renowned modern physics concepts. To transmit sensitive information in the government, private, and personal sectors, high-security levels are now necessary. All conventional cryptographic algorithms applied in the communication models, which rely on mathematical models and conceptual assumptions, are unsecure. Thus, QKD systems are the best choice for protecting this information as a countermeasure since they provide unconditional security. In this paper, a design is proposed for the FSO channel using the CASCADE protocol under different atmospheric condition such as haze, rain and snow. The suggested framework's effectiveness and security in the context of QKD with two non-orthogonal photon states are assessed. Simulation results of this model show the percentage of original sequence recovery; the number of errors removed, optical spectrum at transmitter and receiver for a base frame length of 104 bits. Moreover, Error correction is calculated per iteration to improve signal quality at the receiver side and compared to previous work. The calculated value in this article shows a better result. Hence, both the sender and the receiver could achieve a security key using this method. [ABSTRACT FROM AUTHOR]

An operation scheme using electrical peaking and optical peaking to engineer the modulation band of a Si microring modulator is presented. By incorporating an inductor design at the metal traces of a Si microring modulator, the driving signal can be magnified near the peaking frequency. Although adjusting the wavelength detuning of a ring modulator also introduces optical peaking to extend the 3-dB roll-off frequency, using inductive peaking has no detrimental effect on the low-frequency response. By exploiting both effects, the modulation band can be tailored with more degrees of freedom. We accomplish a Si microring modulator design with a wide and flat transmission band over 95 GHz, which is potentially applied for a non-return-to-zero (NRZ) data transmission over 120 Gbit/s without extra signal post-compensation.

This work relates to the quality of the electrocardiogram (ECG) signal of an elderly person, transmitted using optical wireless links. The studied system uses infrared signals between an optical transmitter located on the person's wrist and optical receivers placed on the ceiling. As the elderly person moves inside a room, the optical channel is time-varying, affecting the received ECG signal. To assess the ECG quality, we use specific signal quality indexes (SQIs), allowing the evaluation of the spectral and statistical characteristics of the signal. Our main contribution is studying how the SQIs behave according to the optical transmission performance and the studied context in order to determine the conditions required to obtain excellent quality indexes. The approach is based on the simulation of the whole chain, from the raw ECG to the extraction process after transmission until the evaluation of SQIs. This technique was developed considering optical channel modeling, including the mobility of the elderly. The obtained results show the potential of optical wireless communication technologies for reliable ECG monitoring in such a context. It has been observed that excellent ECG quality can be obtained with a minimum SNR of 11 dB for on–off keying modulation. [ABSTRACT FROM AUTHOR]

This article discusses the application of a new type of modem with pseudo-noise coding and additional tone modulation, developed for the comparison of reference time scales over satellite communication channels. Experimental studies have compared the time scales of hydrogen masers from the composition of the State Primary Standard of Units of Time, Frequency, and the National Time Scale GET 1-2022 over an optical communication channel using the modems under consideration. As a communication channel, fiber-optic lines of different lengths were used, along which the two-way signal was transmitted. The output radio frequency signals of the modems, with the use of optical transmitters connected to the ends of the fiber lines, were transmitted counter-currently at an optical carrier frequency with a wavelength of 1.55 μm. The demodulation of optical signals into the radio frequency range was implemented at the ends of the fiber lines by optical receivers. The results of an experimental evaluation of type A indefiniteness by comparing time scales along fiber-optic lines of 50-km, 100-km, and 200-km lengths are presented. On a line 200-kmlong, the type A measurement uncertainty when comparing time scales does not exceed 3 ps in the daily measurement interval. The experiments revealed that implementing the method of comparing time scales with modems with pseudo-noise coding and additional tone modulation is possible over a 200-km-long fiber-optic line without intermediate optical amplifiers. This finding opens up the prospect of creating cascaded comparison systems for time scales of remote standards over fiber-optic communication lines with fewer intermediate optical amplifiers. [ABSTRACT FROM AUTHOR]

VCSEL can be used as the transmitter for optical interconnect applications especially for short reach communication. In this research paper, we proposed a VCSEL structure design which can generate the wavelength of 1160 nm. The VCSEL structure is proposed with the aim of small aperture diameter because for optical interconnects applications the size should reduce. Two distributed Bragg reflectors (DBR), i. e. top DBR and bottom DBR are used to confine the active cavity area and InGaAsP/InP material is used for the formation of active cavity region. Then, the performance of the proposed VCSEL is evaluated at various oxide aperture diameters in the range 2–7 µm for anode voltage, anode current and total power emitted is also calculated to achieve optimized performance. [ABSTRACT FROM AUTHOR]

The explosive growth of bandwidth demands of data center and super‐computing systems spur the appliance and development of optoelectronic‐based solutions such as micro‐ring modulator (MRM) transmitters, and advanced modulation schemes such as four‐level pulse‐amplitude modulation (PAM4). In this paper, a 4 × 25 Gb/s PAM4 MRM transmitter fabricated in 0.13 μm SiGe BiCMOS technology is presented. It consists of four‐channel MRM driver and thermal control loop. Capacitor and resistor degeneration techniques and inductor peaking techniques are adopted to expand channel bandwidth. Meanwhile, the predistortion technique is utilized to compensate for MRM nonlinearity, and auto gain control (AGC) circuits to enable the MRM driver to realize a fixed differential output swing of 3.5 Vpp. Furthermore, a thermal control method based on analog to digital converter, digital to analog converter, and logic control circuits is proposed to compensate for the temperature sensitivity of MRM. The measurement results show that the 25 Gb/s nonreturn‐to‐zero optical eye achieves an extinction ratio of 5.63 dB, and the PAM4 eye can be observed up to 40 Gb/s. [ABSTRACT FROM AUTHOR]

Vehicle-to-vehicle (V2V) communications are one of the most promising 6G scenarios. However, V2V communications demand high data rates and extremely low-latency requirements that are difficult to satisfy nowadays. Recently, vehicular visible light communications (V-VLC) have been proposed as a promising technology to guarantee such requirements. Multiple-input, multiple-output (MIMO) techniques can potentially achieve high data rates. However, when applied to V-VLC, they confront challenges such as the latency because of the need for closed-loop transmission or the correlation among optical channel responses. This article explains the use of blind interference alignment (BIA) for V-VLC based on the concept of a reconfigurable photodetector to provide linearly independent channel responses. It is shown that BIA solves the issues of MIMO techniques and may comply with the 6G V-VLC requirements. Besides, the vehicles are a convenient platform for implementing a reconfigurable photodetector. Finally, the open issues for BIA implementation in V-VLC are discussed to inspire future research. [ABSTRACT FROM AUTHOR]

Quantum key distribution (QKD) allows secret key exchange between two users with unconditional security. For QKD to be widely deployed, low cost and compactness are crucial requirements alongside high performance. Currently, the majority of QKD systems demonstrated rely on bulk intensity and phase modulators to generate optical pulses with precisely defined amplitude and relative phase difference—i.e., to encode information as signal states and decoy states. However, these modulators are expensive and bulky, thereby limiting the compactness of QKD systems. Here, we present and experimentally demonstrate a novel optical transmitter design to overcome this disadvantage by generating intensity- and phase-tunable pulses at GHz clock speeds. Our design removes the need for bulk modulators by employing directly modulated lasers in combination with optical injection locking and coherent interference. This scheme is, therefore, well suited to miniaturization and photonic integration, and we implement a proof-of-principle QKD demonstration to highlight potential applications. [ABSTRACT FROM AUTHOR]

In this study, a high-speed four-level pulse amplitude modulation (PAM-4) vertical-cavity surface-emitting laser (VCSEL) diode driver circuit is implemented in Taiwan Semiconductor Manufacturing Company 90-nm complementary metal–oxide–semiconductor technology. The laser diode driver (LDD) can input directly two non-return-to-zero signals to synthesize a PAM-4 current signal. In the LDD, the broadband techniques, including a de-emphasis technique, an equalizer, and a negative capacitor are used to enhance the circuit bandwidth. Through the eye diagram measurements, the performance of the PAM-4 VCSEL LDD chip on a printed circuit board is verified to be suitable in 25-Gb/s optical transmitters for short-reach transmissions. [ABSTRACT FROM AUTHOR]

This paper presents the potentials and challenges of programmable packet-optical nodes encompassing coherent pluggable modules applied in the context of optical metro networks. Two innovative applications of P4-based data plane programmability are then presented. The first targets the monitoring and processing of optical telemetry data/metadata directly in the forwarding plane. The second one focuses on the deployment of deep neural networks in P4 chipsets, effectively supporting in-network distributed cyber security functionalities in packet-optical nodes. [ABSTRACT FROM AUTHOR]

The study presents the average power model of optical Raman fiber amplifiers based on frequency spacing and amplifier section stage optimization technique. The amplifier section stage is taken from 25 to 75 km and frequency spacing is taken from 0.2 up to 1 nm. Input/output Raman signal variations are measured versus operating wavelength range and bit time period variations. The suitable input signal power for the optical transmitter is chosen to be −10 dBm and return to zero modulation code is applied with an available data rate of 10 Gb/s. Sixty-four channels are multiplexed to benefit a multi-number of users with suitable power levels. [ABSTRACT FROM AUTHOR]

Radars and lidars are two primary sensor modalities complementing optical cameras in active safety and autonomous driving applications. Radars and lidars operate at dramatically different frequency bands, experience different propagation effects, and are implemented using completely different technologies. Therefore, they also differ in operation, processing, and implementation challenges. Moreover, the lidar and radar communities have expertise in very disparate technologies and, therefore, are typically segregated and do not communicate. This work provides a fair comparison between lidars and radars, investigates similarities and differences between them, emphasizes their advantages, and summarizes their shortcomings. Lidar systems’ advantages are their high angular resolution and spatiotemporal consistency. Radar systems’ advantages are robustness to adverse weather and poor lighting conditions, long detection range, low cost, and the possibility for on-vehicle integration behind an optically nontransparent fascia. It is expected that 1) intensive research and development will enable future low-cost and long-range lidar technology, and 2) digital radars with a large number of transmit and receive channels will achieve lidar-like angular resolution and resolve mutual interferences while preserving other radar advantages. [ABSTRACT FROM AUTHOR]

As the demand for wireless capacity continues to grow, highly directional wireless communication technologies have the potential to provide massive gains in area spectral efficiency. However, novel challenges arise when considering bidirectional connectivity and multi-cell/multi-user systems with highly directional links. Some of these challenges can be alleviated with the introduction of asymmetric connectivity where the highly directional links are used solely for downlink transmission. As an example, we consider asymmetric links with an optical wireless communication (OWC) downlink and sub-6 GHz RF uplink. More specifically, we consider visible light communication as an instance of OWC, although the presented analysis and validation are applicable to alternative OWC technologies and other simplex downlink transmission technologies. While asymmetric connectivity has been previously demonstrated in scenarios like this, the impact of control-plane asymmetry has not been explored, to our knowledge. In this paper, we first introduce the novel challenges related to local handshaking in wireless networks with control-plane asymmetry. We then develop a theoretical framework for throughput analysis in a network where the sub-6 GHz RF channel is shared between a conventional RF link and an asymmetric RF/OWC link. This analysis is validated via simulation and verified in a testbed system using Mango WARP3 software defined radios and a commercially available RF access point. Finally, we use the derived throughput equations to analyze the impact of various protocol parameters and demonstrate one potential use of the derived equations to evaluate sum throughput in the presence of an unreliable OWC link. [ABSTRACT FROM AUTHOR]

This paper presents a real-time underwater wireless optical communication (UWOC) system. The transmitter of our UWOC system is equipped with four blue LEDs, and we have implemented pre-emphasis technology to extend the modulation bandwidth of these LEDs. At the receiver end, a 3 mm diameter APD is utilized. Both the transmitter and receiver are housed in watertight chassis and are submerged in a water pool to conduct real-time underwater experiments. Through these experiments, we have obtained impressive results. The data rate achieved by our system reaches up to 135 Mbps, with a BER of 5.9 × 10−3, at a distance of 10 m. Additionally, we have developed a convenient method for measuring the underwater attenuation coefficient, using which we have found the attenuation coefficient of the water in experiments to be 0.289 dB/m. Furthermore, we propose a technique to estimate the maximum communication distance of an on–off keying UWOC system with intersymbol interference, based on the Q factor. By applying this method, we conclude that under the same water quality conditions, our system can achieve a maximum communication distance of 25.4 m at 80 Mbps. Overall, our research showcases the successful implementation of a real-time UWOC system, along with novel methods for measuring the underwater attenuation coefficient and estimating the maximum communication distance.

Abstract Quantum illumination theoretically promises up to a 6 dB error‐exponent advantage in target detection over the best classical protocol. The advantage is maximised by a regime that includes a very high background, which occurs naturally when one considers microwave operation. Such a regime has well‐known practical limitations, though it is clear that, theoretically, knowledge of the associated classical benchmark in the microwave is lacking. The requirement of amplifiers for signal detection necessarily renders the optimal classical protocol here different to that which is traditionally used, and only applicable in the optical domain. This work outlines what is the true classical benchmark for the microwave Quantum illumination using coherent states, providing new bounds on error probability and closed formulae for the receiver operating characteristic, for both optimal (based on quantum relative entropy) and homodyne detection schemes. An alternative source generation procedure based on coherent states is also proposed, which demonstrates the potential to make classically optimal performances achievable in optical applications. The same bounds and measures for the performance of such a source are provided, and its potential utility in the future of room temperature quantum detection schemes in the microwave is discussed.

Summary: The bit error rate (BER) in optical communication systems is often get degraded due to various factors like launch power, dispersion, modal noise, and so on. Finding the most optimal launch power for a signal to provide acceptable BER is usually difficult on an installed link. Therefore, in this paper, an attempt has been made to use machine learning‐based linear regression technique for predicting the optimal signal quality for spatial division multiplexed (SDM)‐based fiber optical transmission system for a fixed distance. This technique helps in predicting the optimal value of continuous launch power. Therefore, to demonstrate the given concept in this research work, the generic setup of an SDM optical long‐haul system of 20 km in length has been designed and simulated in Optisystem‐14.0. The light sources in our experiments are two spatial optical transmitters with an emission wavelength of around 1550 nm. Abiding to the first step for the regression analysis, that is the data preparation, normality and correlation checks were performed. After this, a linear regression model is developed which was validated through a summary report, coefficients and diagnostic plots. Furthermore, the accuracy of the model is improved by employing Cook's distance. These tests help in dealing with the influence points that hinders the prediction ability of the proposed model. The results show that the R‐squared value is 0.9366, and value of adjusted R2 comes out to be around 0.9344; we therefore came to infer that the model explains nearly 94% variations in the dependent variables. [ABSTRACT FROM AUTHOR]

Since its early commercial deployment in the late 1980s, optical fiber has evolved to become the predominant carrier of the globe’s communications. Yet, after accommodating the world’s exponentially growing appetite for transmitted data for more than three decades, its ability to continue doing so is being challenged by fundamental factors. In this article, we review these factors and examine their consequences in terms of information capacity. In particular, we review the difficulties that are imposed by the nonlinear nature of fiber-optic transmission on the assessment of the capacity and on the definition of fundamental concepts, such as bandwidth and spectral efficiency. We discuss relevant approximations and regimes of operation in which bounds for the capacity can be effectively assessed while covering a broad range of applications ranging from interdatacenter communications to links spanning transoceanic distances. We relate to a broad variety of transmission schemes and discuss the potential benefits of spatial multiplexing with multimode and multicore fibers. State-of-the-art transmission experiments are also reviewed and compared with theoretical capacity bounds. [ABSTRACT FROM AUTHOR]