optical communication
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<span>The continuous development of internet of things (IoT) technology enables many devices to be interconnected through the external environment. Meanwhile, 5G technology provides an enhanced quality of services with high data transmission rates, requiring IoT implementation in the 5G architecture. Free-space optical communication (FSO) is considered a promising technique that can provide high-speed communication links, so FSO is an optimal choice for wireless networks to fulfill the full potential of 5G technology, providing speeds of 100 Gb/s or more. By implementing 5G features in IoT, IoT coverage and performance will be enhanced by using FSO models. Therefore, the paper proposed and investigated the multiple-input and multiple-output/free-space optical communication (MIMO/FSO) model using subcarrier quadrature amplitude modulation (SC-QAM) and relay stations over atmospheric turbulence channels by log-normal and gamma-gamma distribution under different turbulence conditions. The performance is examined based on the average channel capacity (ACC), which is expressed in terms of average spectral efficiency (ASE) parameters while changing the different parameters of the model. The mathematical formulas of ACC for atmospheric turbulence cases are calculated and discussed the influence of turbulence strength, the different number of relay stations, misalignment effects, and different MIMO configurations.</span>

Abstract In this study, we propose an application scheme of free space optical communication technology in INMARSAT, and propose a 1.12 Tbit/s coherent free-space optical (FSO) communication system based on wavelength division multiplexing (WDM) and polarization-multiplexing quadrature phase shift keying (PM-QPSK) modulation technology. Based on optisystem software platform, the spectrum, bit error rate (BER), received power, error vector magnitude (EVM), and receiver sensitivity of the edge and middle channels of the system are analyzed. The simulation results show that the transmission rate and channel capacity of INMARSAT communication system are greatly improved by selecting the channel spacing and transmission environment reasonably.

Photodetectors converting optical signals into electrical signals have been widely utilized and have received more and more attention in scientific research and industrial fields including optical interconnection, optical communication, and environmental monitoring. Herein, we summarize the latest development of photodetectors with different micro-nano structures and different materials and the performance indicators of photodetectors. Several photodetectors, such as flexible, ultraviolet two-dimensional (2D) microscale, and dual-band photodetectors, are listed in this minireview. Meanwhile, the current bottleneck and future development prospects of the photodetector are discussed.

Over the years, the overdependence on Wireless Fidelity (Wi-Fi) for data transmission necessitated the need for an alternate and more reliable means of communication, hence, Light Fidelity (Li-Fi). It involves the use of Light Emitting Diode to transmit data by blinking (i.e. switching them on and off) at a speed not noticeable to the eye. This paper proposed the development of the Li-Fi system using off the shelf electronic components. This would make the system an indispensable means of communication in the nearest future. This data transmission system is different from those in existence because expensive components were not in the design, invariably reducing the overall cost of the implementation. Keywords: Light Fidelity (Li-Fi), Wireless Fidelity (Wi-Fi) Optical communication, Telecommunication

With the rapid development of optical communication systems, more advanced techniques conventionally used in long-haul transmissions have gradually entered systems covering shorter distances below 100 km, where higher-speed connections are required in various applications, such as the optical access networks, inter- and intra-data center interconnects, mobile fronthaul, and in-building and indoor communications. One of the techniques that has attracted intensive interests in short-reach optical communications is machine learning (ML). Due to its robust problem-solving, decision-making, and pattern recognition capabilities, ML techniques have become an essential solution for many challenging aspects. In particular, taking advantage of their high accuracy, adaptability, and implementation efficiency, ML has been widely studied in short-reach optical communications for optical performance monitoring (OPM), modulation format identification (MFI), signal processing and in-building/indoor optical wireless communications. Compared with long-reach communications, the ML techniques used in short-reach communications have more stringent complexity and cost requirements, and also need to be more sensitive. In this paper, a comprehensive review of various ML methods and their applications in short-reach optical communications are presented and discussed, focusing on existing and potential advantages, limitations and prospective trends.

Abstract The present research realises a controllable optical memory using one dimensional indium phosphate (InP) photonic structures at three optical communication windows (850 nm, 1310 nm and 1550 nm). The photonic structures comprise 21 layers of InP and air material. The memory applications are realised at both single and dual signals of the communication windows. The physics of the research deals with the materials property including the variation of the refractive indices with respect to the input signal. Similarly, mathematics of the works relies on the analysis of reflectance, transmittance and absorbance phenomena. Further, the light from visible spectrum acts as triggering signal to realise optical memory applications. Finally, it is revealed that InP based photonic structures are suitable for controllable memory applications pertaining to the single wavelength (850 nm, 1310 nm, 1550 nm) or dual wavelengths (850 nm and 1310 nm, 1310 nm and 1550 nm, 1550 nm and 850 nm).