Optical Communication Channels Research Articles

Near-field formation of the UCA-based OAM EM fields and short-range EM power flux profiles

Orbital angular momentum (OAM) multiplexing is a recently considered solution for enhancing wireless and free-space optical communications channel capacity, whether implemented separately or in combination with existing multiplexing techniques. The theoretically infinite number of paraxially propagating and mutually orthogonal OAM modes is expected to increase the channel capacity. However, the orthogonality for different OAM modes has been shown to decrease for far link range distances, and the paraxiality of the OAM beams is not very good for small radiating sources. Based on the current knowledge, OAM beams are most likely to be used for short-range communications. Many models of the electromagnetic (EM) fields carrying the OAM neglect the fact that the OAM beam sources could be electrically large or introduce other approximations that are appropriate for far-field analysis only. An in-depth analysis of the short-range properties of OAM EM fields is still lacking. To address this problem, we propose the use of the infinitesimal (Hertz) dipole method customized for the analysis of the OAM EM fields. This technique can model the positioning and basic radiation properties of separate antennas or antenna sub-arrays that are the building blocks of OAM arrays exactly and efficiently. Similar modeling can represent the OAM sources for free-space optical communications. We focus here on the uniform circular antenna arrays and provide an in-depth analysis of what can and cannot be expected, in the best case, in their utilization. We assume low losses, which is a common assumption for many methods, except for computationally much more demanding full-wave simulations. The obtained results indicate the need to simultaneously optimize the transmission of all planned OAM modes and allow estimates of the link distances that could provide adequate OAM wave reception in various cases.

Non-line-of-sight multiple reflection underwater wireless optical communications channel model based on a capillary waves rough sea surface.

In a non-line-of sight reflective underwater wireless optical communications (UWOC) link, the transmitted beam relies on reflections from the sea surface to propagate to the underwater receiver. Most previous research on reflective channels has sufficiently considered single reflections from a smooth or rough surface, while ignoring the effect of multiple reflections. In fact, a rough sea surface may cause the reflected photons to hit the sea surface again, which is referred as a multiple reflection process. To make up for deficiencies in the existing literature, we first construct a capillary waves rough sea surface model, and then present a multiple reflection channel model with the help of the Monte Carlo ray tracing approach. The path loss and channel impulse response (CIR) were further evaluated based on the model for different communications scenarios. Numerical results suggest that multiple reflections increase the path loss by more than about 5dB, and reduce the CIR amplitude to less than one-third compared to a single reflection. The work done in this paper aims to provide theoretical support for UWOC system design.

Speckle-based structured light shift-keying for non-line-of-sight optical communication.

We report an experimental proof of concept for speckle-based one-to-three non-line-of-sight (NLOS) free space optical (FSO) communication channels employing structured light shift-keying. A 3-bit gray image of resolution 100×100 pixels is encoded in Laguerre-Gaussian or Hermite-Gaussian beams and decoded using their respective intensity speckle patterns via trained 1D convolutional neural network. We have achieved an average classification accuracy of 96% and 93% using L G ml and H G pq beams, respectively, among all three channels. It demonstrates the directional independence and broadcasting capability of speckle-based decoding (SBD) in FSO communication using structured light. Further, we have extended the study from 2D to 1D SBD in one-to-three NLOS FSO communication channels to decrease the computational cost and to emphasize the importance of the 1D SBD approach.

Simulation analysis of underwater wireless optical communication based on Monte Carlo method and experimental research in complex hydrological environment

This paper aims to address the challenges of short optical communication distances and high Bit Error Rates (BERs) caused by seawater absorption, scattering, and underwater turbulence. This paper establishes an optical communication channel model based on the Monte Carlo method and simulates and analyzes the process of received optical power attenuation when light is transmitted underwater due to absorption and scattering. The simulation model focuses on the influence of seawater type, transmission distance, receiver position, and angle on the received optical power attenuation. The results of this simulation will provide theoretical support for the development of prototype underwater optical communication systems and experiments in complex environments. To solve the long-range weak signal reception and processing issues in underwater optical wireless communication systems, this paper proposes the design and implementation of an underwater optical wireless communication system using optimized on-off keying high-power light-emitting diode/laser diode modulation technology and avalanche photodiode (APD)/photomultiplier (PMT) receiver modules. In addition, this paper describes the design of the underwater optical communication host computer software, which provides functions such as mode selection, BER monitoring, and file transfer. To test the performance of the proposed system, this paper conducts experiments in a 35 m long pool, fixed platform, and underwater mobile platform, as well as cross-air-water interface optical communication performance test experiments in a complex hydrological environment. The results show that the system achieved a 35 m underwater medium communication distance, transmission rate of 5–20 Mbps, and cross-domain wireless optical communication function under the condition of a BER of less than 10−6. The experiments also revealed that the communication distance decreases as the turbidity of the water body increases and the PMT receiver module selected at the receiver end has a longer communication distance than the APD receiver module. Overall, this paper demonstrates the feasibility of the proposed technology for underwater optical communication systems in complex waters, providing theoretical and data support for the next engineering practice.

On off keying line coding based optical transmitter for various both optical fiber communication and OWC channels

Abstract This paper demonstrated the on off keying line based optical line transmitter for different fiber communication and wireless lighted channels. The max Q form and min BER values after PIN receiver based optical fiber base band channel, linear multi-mode fiber channel and OWC at optimum length is clarified. Lighted power variations after light fiber channel, linear multi-mode fiber channel and OWC versus spectral base band wavelength variations at optimum length is demonstrated. Lighted power form variations after lighted base band fiber channel, linear multi-mode fiber channel and OWC versus time variations at optimum length is indicated. Total lighted power after optical fiber base band channel, linear multi-mode fiber channel and OWC at optimum length is clarified. Total electrical power after PIN receiver based optical fiber channel, linear multi-mode fiber channel and OWC at optimum length.

Statistical channel modeling of intensity fluctuations in a turbulent underwater wireless optical communication system

Subject of study. The statistical modeling of received intensity fluctuations due to temperature-induced turbulence and the random presence of air bubbles in an underwater wireless optical communication channel is presented. Aim of study. Temperature-induced turbulence and air bubbles induce severe intensity fluctuations in the received optical signal, which degrade the underwater wireless optical communication link performance. Method. Therefore, to characterize the turbulent water channel, an experimental setup has been designed in the laboratory that considers uniform and gradient-based temperature variations along with variable-sized bubble populations. To estimate the effect of these random variations in the water channel, a statistical approach has been followed, which characterizes the nature of the recorded observations. Main results. It is observed that the behavior of random irradiance fluctuations due to uniform and gradient-based temperature variations in the underwater wireless optical communication link follows a single-lobe Gaussian distribution. Moreover, with the incorporation of air bubbles, the received irradiance fluctuations no longer follow a single-lobe Gaussian distribution but follow a multi-lobe Gaussian distribution, i.e., the Gaussian mixture model, which is the weighted sum of the Gaussian distribution. The accuracy of the proposed underwater wireless optical communication link models is verified by conducting the goodness of fit test; the observed confidence interval of 95% authenticates the proposed model. Also, the performance of the Gaussian-mixture-model-based underwater wireless optical communication link has been evaluated in terms of bit error rate, and the acceptable bit error rate levels between 1014 and 1010 have been observed. The proposed underwater wireless optical communication with Gaussian mixture model completely depicts thermally uniform, gradient-based nonuniform, and variable air bubble populations in the ocean. Practical significance. The Gaussian mixture model can further be utilized by the researchers to estimate numerous performance parameters of the turbulent underwater wireless optical communication links using advanced modulation schemes and diversity techniques and paves a valuable way to address the future aspects of research in this area.

Beam Divergence Loss Mitigation in Free Space Optical Communication Channel Using Field of View Technique

A rapid advancement in the electronics and telecommunications industries has been observed. As a result, Communication gadgets are becoming more powerful and are more widely adopted. The demand for high data rate transmission is increasing. This has led to spectrum scarcity in Radio Frequency (RF) systems. Consequently, it is necessary to explore other technical means to meet the increasing demand for higher data rates. Free Space Optical Communication (FSOC) is a promising technology that offers one of such means. However, the major technical challenge in the FSOC systems is that, their performance is limited by atmospheric impairments such as: absorption, scattering and turbulence caused by rain, cloud, snow, wind, dust, aerosol, and fog. This research is aimed to addressed beam divergence challenge due to fog and raindrop in a tropical climate using wider field of view technique (FoV). The result showed that, for the fog measurement using mini solar panel at the receiver, the system achieved higher SNR of 60 dB at corresponding BER of 10-4. While, with the photodiode, the system achieved an SNR of 38 dB at same BER. For the rain measurement the same procedure was adopted and the system achieved higher SNR of 90 dB and 58 dB at same BER utilizing both solar panel and photodiode respectively. The result showed that, the fog impairment attenuates optical signal more than of rain by 34 % averagely

Design and Performance Evaluation of Free Space Optical Communication Link in Zaria, Nigeria

Free Space Optical Communication (FSOC) is an optical technology with a great chance to complement traditional wireless communication technologies. It offers essential advantages compared to Radio Frequency (RF), such as low power consumption, no frequency restrictions, no electromagnetic interference, security, and a significant increase in bandwidth. Similarly, they have proven a worthy substitute for fiber optics with notable advantages. FSOC systems are usually installed above ground level and are therefore exposed to prevailing weather conditions such as haze, fog, rain, etc. which negatively affect the optical signal transmission. There is a shortage of research on using FSO systems in tropical regions. For this reason, accurate free space optical communication channel modeling helps telecommunication operators to engineer and appropriately manage their networks. Therefore, this research work developed Free Space Optical Communication Channel Model to mitigate the effects of atmospheric attenuations by estimating the specifically induced attenuation caused by both haze and rainfall rates on the FSOC link in the Zaria geographical area using two years of measured visibility data and rainfall rates data of the study location obtained from Nigerian Meteorological (NIMET) agency, Zaria station, locatedat the Nigeria College of Aviation Technology (NCAT) Zaria and Center for Energy Research and Training (CERT), Ahmadu Bello University (ABU), Zaria. The performance of the FSOC system is analyzed and evaluated through Link Margin (LM) analysis by using the design specifications of a commercial optical transceiver (TereScope 5000). The haze-induced attenuation obtained at 850nm, 950nm, and 1550nm is 5.934dB, 6.402dB, and 3.152dB respectively. Therefore, the result shows that the 1550 nm wavelength has minimum haze-induced attenuation compared to 850nm and 950nm at a propagation link distance of 6km. Furthermore, from the results of the performance evaluation of the LM analysis for the combined effects of Geometrical Attenuation (Gatt), Haze-Induced Attenuation (HIA), and Rain-Induced Attenuation (RIA), the result shows that operating a 1550nm wavelength in transmission power greatly improves optical transmission when compared with 850nm and 950nm wavelengths. Generally, the overall outcome of the research concludes that the free space optical communication system has the robustness to handle successful wireless communication during the worst weather conditions in Zaria throughout the year for a link range of up to 6km

Efficient employment of optical sources integrated with both light detectors and free space communication modulated channel under ambient conditions effects

Abstract The paper simulates the efficient employment of light sources integrated with both light detectors and free space communication channel under ambient condition effects. The modified duobinary non return to zero line coding system based optical wireless communication channel under light or dense fog level effects. Max. Q factor against OWC reach is simulated at light and dense fog level for the suggested with the previous model. The study emphasis that the OWC length has been reached to 65 km at light fog level and the OWC length has been reached to 5 km at dense Fog level with acceptable signal power. The total light power and total electrical power are illustrated at light and dense fog levels. Max. Q factor and min. BER after receiver based OWC are clarified at light and dense fog levels.

Investigation of the Optical Communication Channel Throughput of an Information Receiver in the Form of a Silicon Photomultiplier Tube under Conditions of Background Illumination

Investigation of the Optical Communication Channel Throughput of an Information Receiver in the Form of a Silicon Photomultiplier Tube under Conditions of Background Illumination

Effect of bioluminescence on the performance of an underwater optical wireless communication channel

The performance of an underwater wireless optical communication channel (UWOC) is affected by the ambient noise in the water medium. However, no major studies have estimated the spectral bioluminescence upwelling radiance (BLu) numerically with the inputs of measured bioluminescence potential (BP) in oceanic conditions. This study presents a numerical model to estimate the BLu in open ocean and coastal waters and to investigate the UWOC channel performance in terms of the bit error rate (BER) in presence of bioluminescence using Monte Carlo numerical technique. The simulation results suggested that the BER performance degrades in the presence of bioluminescence and can be improved with a narrower receiver FOV. Further, the impact of bioluminescence on the BER performance of the UWOC system at different operational depths is investigated under typical system specifications (APD/PMT, FOV, and receiver aperture). The simulation results showed that BER at different operational depths is more sensitive in open ocean waters than in coastal turbid water with the bioluminescence signal. The results demonstrate that the PMT improves the UWOC channel performance better than the APD. Besides, these results revealed that the BP stimulation at multiple depths deteriorates the BER performance heavily in comparison to the BP stimulation at single depth in the real sea environment. The results presented in this study provide valuable insights and information for accurate design and development of the UWOC system for the enhanced bioluminescence background noise conditions.

Robust structured light in atmospheric turbulence

Structured light is routinely used in free-space optical communication channels, both classical and quantum, where information is encoded in the spatial structure of the mode for increased bandwidth. Both real-world and experimentally simulated turbulence conditions have revealed that free-space structured light modes are perturbed in some manner by turbulence, resulting in both amplitude and phase distortions, and consequently, much attention has focused on whether one mode type is more robust than another, but with seemingly inconclusive and contradictory results. We present complex forms of structured light that are invariant under propagation through the atmosphere: the true eigenmodes of atmospheric turbulence. We provide a theoretical procedure for obtaining these eigenmodes and confirm their invariance both numerically and experimentally. Although we have demonstrated the approach on atmospheric turbulence, its generality allows it to be extended to other channels too, such as aberrated paths, underwater, and in optical fiber.

Performance Comparison of Different Rotated QAM Based DMT Schemes in Underwater Optical Wireless Communication

In the paper, different rotated QAM-based DMT schemes are proposed and experimentally demonstrated. To overcome the severe high-frequency fading in the underwater optical wireless communication (UOWC) channel, a deviation correction-based maximum likelihood detection (DC-MLD) is introduced into the rotated-QAM scheme. It can improve the precision of the de-rotated process and achieve a better performance than the MLD. Besides, other rotated-QAM schemes using machine learning, including k-means clustering, support vector machine (SVM), and logistic regression (LR), are investigated. These schemes do not need channel state information to achieve the de-rotated process. Meanwhile, the training overhead and execution time of SVM and LR are compared. The experimental results show that, after 5-m air and 4.2-m water channel, compared with the 16QAM DMT, the rotated-16QAM DMT can improve more than 2.5dB received optical power (ROP) sensitivity at the bit error rate (BER) of 1e-3 under the data rate of 3 Gb/s. Meanwhile, the proposed rotated-16QAM scheme with DC-MLD can save more 0.8dB ROP than that with MLD at BER of 2e-4. Besides, it has better performance than the rotated-16QAM DMT with k-means, LR, and SVM.

Near-Infrared Optical Transmitting Module for Service Channel of Atmospheric Quantum Communication Line

This work presents an optical transmitting module operating in the near-infrared wavelength range for the organization of a wireless service channel in an atmospheric optical quantum communication channel. The main characteristics were measured to demonstrate the functionality of the module and to assess the quality of the transmitted signal, such as the values of the error vector magnitude and the eye diagram opening level. It was determined that the transmitting module can operate at symbol rates up to 5 GBaud. In addition, the optimal signal modulation parameters were found and the possible bit rate of data transmission in the atmospheric optical communication channel was estimated: a QPSK-modulated signal with a carrier frequency of 80 MHz and a symbol rate of 50 MBaud allowed to get a bit rate of 100 Mbit/s with an EVM value of 14%.

Corrections to “On the Capacity of Intensity-Modulation Direct-Detection Gaussian Optical Wireless Communication Channels: A Tutorial”

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Assessment of quality of signal transmission process in focs with DWDM

The power of a group DWDM signal increases nonlinear interference in the optical path, especially the value of the interference of the FWM. These interfering factors degrade signal transmission quality and can completely disable the WDM system. Therefore, when designing a DWDM system, it is necessary to optimize the power of the transmitted signal to minimize the probability of error in the optical channel. The article presents the research results and analysis of factors affecting the quality of fiber-optic communication systems with wave separation of channels. Selecting the optimal power level of the group signal and evaluating the transmission quality of optical communication channels in WDM allows us to solve the problem of science-based design, implementation, and effective operation of advanced optical communication systems with wave division of channels.

Visible-light wireless communication system performance signature improvement for high bit rate transmission system

Abstract This paper deals with the visible-light communication (VLC) network system improvement for high bit rate transmission system. The previous model use the visualizer analyzer for the estimate of bit error rate in which the maxi. Q factor is reached to 2.51. The previous study is used free space channel over along length of 200 km by the optical wireless communication (OWC) channel with available data rates of 4 Gb/s. This presented model has a transmission rate of 10 Gb/s which has a maximum Q factor of 6.34 at the same operating parameters by using CW laser as an optical source and Mach–Zehnder modulator with two cascades optical wireless communication (OWC) channel.

Statistical Simulation of Characteristics of an Optical Communication Channel Based on Scattered Radiation with an Unmanned Aerial Vehicle

Statistical Simulation of Characteristics of an Optical Communication Channel Based on Scattered Radiation with an Unmanned Aerial Vehicle

Investigation of the Optical Communication Channel Throughput with an Information Receiver in the Form of a Silicon Photomultiplier

Investigation of the Optical Communication Channel Throughput with an Information Receiver in the Form of a Silicon Photomultiplier

Signal quality enhancement in multiplexed communication systems based on the simulation model of the optimum technical specifications of Raman fiber optical amplifiers

Abstract Raman optical amplifiers have more reliability than the repeater in the optical communication networks. In the optical amplifier, the transmission equals the gain bandwidth of the amplifiers. The optical amplifier has functionalities such as WDM amplification (gain equalization), gain control (rapidly variation of the gain), inter-stage access (compensation in the dispersion rate). This paper presents the optimum technical specifications of fiber Raman optical amplifiers (FROAs) with average power system for signal quality improvement in multiplexed systems. The signal has upgraded to a max. Q-factor of 11.47 applied along 1000 m as a range through the free-space optical (FSO) communication channel that has an attenuation rate of 10 dB/km. Our suggested system has clarified the best Q-factor that is greatly increased to reach 49.36 in the presence of the pump laser. The multiplexed communication systems signal quality is enhanced by the percentage ratio of 39.65%.