Modeling of 2.5 Gbps-intersatellite link (ISL) in inter-satellite optical wireless communication (IsOWC) system

Free-space optics (FSO) has the combined features of most dominated telecommunication technologies: wireless and fiber optics. Many of the aspects of FSO are related to fiber optics with an important difference of transmission medium which is air/free space rather than the glass of the fiber-optic cable. Inter-satellite optical wireless communication systems (IsOWC), one of the important applications of FSO/WSO technology, will be deployed in space in the near future as such systems provide a high bandwidth, small size, light weight, low power and low cost alternative to present microwave satellite systems. In this paper, we have designed a model of IsOWC system using OPTI-SYSTEM™ simulator to establish an inter-satellite link (ISL) between two satellites estranged by a distance of 1000 km at data rate of 2.5 Gbps which is not reported in previous investigated works.     

Doppler effect performance for multiple hops optical connections in LEO satellite constellations

Low earth orbit satellite constellations using laser inter-satellite links are recognized to be capable to satisfy the increasing broadband communication demands. However, Doppler in inter-satellite laser communications can degrade the performance of the optical space network. It is crucial to study the Doppler performance on the high precision system. The expression of Doppler wavelength shift for multiple hops laser inter-satellite links is proposed in the paper. The calculation of Doppler wavelength shift in multiple hops ISL is studied with the consideration of location, motion and onboard characters of the satellites. Theoretical and numerical analysis show different routing way between two certain distant satellites will lead to different Doppler wavelength shift and signal transmitting time, and the variation of Doppler wavelength shift is mostly depend on the number of laser inter-satellite links hops; reasonable onboard time delay can augment signal transmitting time with little influence to the Doppler wavelength shift. It is hoped that the study can help the routing selection of the optical space network and system compensation.     

Continuous-Variable Quantum Secret Sharing Based on Thermal Terahertz Sources in Inter-Satellite Wireless Links

We propose a continuous-variable quantum secret sharing (CVQSS) scheme based on thermal terahertz (THz) sources in inter-satellite wireless links (THz-CVQSS). In this scheme, firstly, each player locally preforms Gaussian modulation to prepare a thermal THz state, and then couples it into a circulating spatiotemporal mode using a highly asymmetric beam splitter. At the end, the dealer measures the quadrature components of the received spatiotemporal mode through performing the heterodyne detection to share secure keys with all the players of a group. This design enables that the key can be recovered only by the whole group players’ knowledge in cooperation and neither a single player nor any subset of the players in the group can recover the key correctly. We analyze both the security and the performance of THz-CVQSS in inter-satellite links. Results show that a long-distance inter-satellite THz-CVQSS scheme with multiple players is feasible. This work will provide an effective way for building an inter-satellite quantum communication network.     

Enhancement of free space optical link in heavy rain attenuation using multiple beam concept

Free space optics (FSO) has attracted a lot of attention for a variety of applications in telecommunications area, and it is dream of every researcher and telecommunication society to make it a real alternative solution for the last mile problem, to replace fiber optics. FSO is much preferred because of its low maintenance cost and deployment time. FSO with single-beam system is vulnerable to atmospheric attenuation, so to overcome this, a multiple-beam FSO transceiver system has become prominent and is usually used. In this paper, average rain attenuation is evaluated from the collected rain intensity data which are collected for a period of seven months, and implemented in the study concerning results relating link distance, and received optical power of using multiple-beam FSO system in tropical rainy weather. Comparison is made in terms of received optical power, geometrical losses, atmospheric losses, and bit error rate (BER) on using different number of optical beams, based on simulation at data rate of 1 Gb/s. From the results it is clear that the quality of received power is improved by using up to four beams, along with link distance up to 1141.2 m as compared to one-beam, two-beam, and three-beam, with link distances 833.3 m, 991.0 m, 1075.4 m, respectively.     

Outage probability analysis of FSO system with Airy beam as carrier

Optical Review - Based on the scintillation index of Airy beam and exponentiated Weibull channel model, analytical expressions of outage probability for free-space optical (FSO) communication links...     

Millimeter-wave enabled PAM-4 data transmission over hybrid FSO-MMPOF link for access networks

Optical Review - In this paper, we propose a full duplex architecture based on a hybrid link composed of free space optics (FSO) and multimode plastic optical fiber (MMPOF) for short-range wireless...     

On the possible use of optical fiber Bragg gratings as strain sensors for geodynamical monitoring

Optical fiber sensors can be used to measure many different parameters including strain, temperature, pressure, displacement, electrical field, refractive index, rotation, position and vibrations. Among a variety of fiber sensors, fiber Bragg gratings (FBG) have numerous advantages over other optical fiber sensors. One of the major advantages of this type of sensors is attributed to wavelength-encoded information given by the Bragg grating. Since the wavelength is an absolute parameter, signal from FBG may be processed such that its information remains immune to power fluctuations along the optical path. This inherent characteristic makes the FBG sensors very attractive for application in harsh environments, “smart structures” and on-site measurements.This paper reviews the achievements about the FBG as a strain and temperature sensor and describes the potential applications of FBG sensors for applications in the field of geophysics and its expected development in the near future. The applications could include: rock deformation, fiber-optic geophone, optical based seismograph, vertical seismic profiling and structural monitoring of civil structures. Different techniques to detect strains and various applications will be reviewed and discussed. The problem of temperature–strain cross sensitivity, that is particularly difficult to eliminate, is addressed and approaches to overcome it are discussed.     

Simulation of Transmissions Through Optical Transport Networks

The introduction of optical technologies in the path layer of the transport network allows the network communication capacity and nodes throughput to be greatly increased. Optical networks covering large geographic areas and information super highways are coming in the not too distant future. For these reasons it is necessary to analyze the transmission of high-speed signals that transport high volumes of traffic throughout large-area networks. Simulation is an effective tool for this analysis, allowing one to take into account the complex nonlinear behavior of the long optical links and of some optical devices as wavelength converters. This article discusses two different approaches to the simulation of transmission through optical networks: the semi-analytical approach and the complete simulation. Advantages and disad vantages of each approach are considered, and the results obtained by different simulation software implementing the two approaches are compared.     

Analysis of free space optical link in turbulent atmosphere

Free space optical (FSO) communication is an upgraded supplement to the existing wireless technologies. FSO technology provides vast modulation bandwidth, unlicensed spectrum, cost effective deployment, low power consumption and less mass requirement. Today, researchers are preliminary focused to use the free space communication systems for inter satellites links. In this paper, the performance analysis of FSO communication link in weak atmospheric turbulence has been analyzed for different atmospheric transmission windows using OOK modulation. The analysis has been done using bit error rate as the performance metric. The effect of attenuation on the link performance has been investigated by varying distance between transmitter and receiver for a given power and data rate. Further, BER performance analysis has been carried out for varying data rate and transmitted power. Also, the effect of attenuation on received optical power has been studied. The work has been performed in OptSim environment.     

Parallel Microoptics for Interconnections Based on Vertical Cavity Surface Emitting Lasers Arrays

Low-cost vertical cavity surface emitting lasers (VCSELs) may allow the development of broadband optical networks. Designs suitable for microoptics and “jisso” (a Japanese terms which includes alignment, assembly, mounting and packaging) technologies are required for low-cost and small interconnection modules. Optical interconnections based on VCSEL arrays including both space and wavelength division multiplexing technologies are described.     

Physical layer security in mixed Rf/FSO system under multiple eavesdroppers collusion and non-collusion

Secure transmission in wireless networks is a big critical issue due to the broadcast nature of the wireless propagation environment. In this paper, the physical layer security performance in a mixed radio frequency (RF)/free space optical (FSO) system under multiple eavesdroppers is investigated. The RF links and FSO link within the system are assumed to respectively undergo Nakagami-m and Gamma–Gamma fading distributions. The two practical eavesdroppers scenarios considered includes: Colluding and Non-colluding in which their channel state information is unavailable at the source. The closed-form expressions for the lower bound security outage probability and the strictly positive secrecy capacity under both scenarios are derived by utilizing the system end-to-end cumulative distribution function and eavesdroppers’ probability density function. The results show that the increase in the number of eavesdroppers under both scenarios profoundly degrades the system secrecy performance. Moreover, it is demonstrated that both the atmospheric turbulence and pointing errors affect the concerned system secrecy and the impact of RF fading parameters is also presented. The accuracy of the numerical results obtained is validated by Montel-Carol simulations.     

Quantum-correlation-based free-space optical link with an active reflector

We present a quantum-correlation-based free-space optical(FSO) link over 250 m using an outdoor active reflector 125 m from the transceiver station. The performance of free-space optical communication can be significantly degraded by atmospheric turbulence effects, such as beam wander and signal fluctuations. We used a 660 nm tracking laser to reduce atmospheric effects, by analyzing the fast beam wander and slow temporal beam drift, using this information to correct the quantum channel alignment of the 810 nm signal photons. In this work, the active reflector consisted of a mirror, a 6-axis hexapod stage, and a long-range wireless bridge. The slow drift of the beam path due to outdoor temperature changes was steered and controlled using wireless optical feedback between the receiver units and the active reflector. Our work provides useful knowledge for improved control of beam paths in outdoor conditions, which can be developed to ensure high quality quantum information transfer in real-world scenarios, such as an unmanned FSO link for urban quantum communication or retro-reflective quantum communication links.     

Determination of rain attenuation parameters for free space optical link in tropical rain

Free space optics (FSO) is a promising communication technique for various types of services in the optical access network. Single beam FSO system in tropical rainy weather is vulnerable to atmospheric rain attenuation, so it is necessary to have precise power law parameters of rain attenuation in tropical regions. In this study, the power law parameters k, and α are estimated as 2.03 and 0.74, respectively for the FSO applications in tropical South-East Asian weather. These parameters were evaluated by using least square mean equation (LSME) method with Levenberg–Marquardt optimization based on the one year collected heavy rain data. The obtained parameter values for tropical weather are contributed to improve link performance for high-speed networks.     

Advanced modulation formats for delivery of heterogeneous wired and wireless access networks

It is believed that the integration of wired and wireless access networks (or heterogeneous network) will provide high bandwidth and flexibility for both fixed and mobile users in a single and cost-effective platform. Here, we propose and demonstrate a signal remodulated wired and wireless network with wireless signal broadcast. Dark-return-to-zero (DRZ) and polarization-shift-keying (PolSK) signals are used for the downstream wired and wireless applications respectively. At the remote antenna unit (RAU), the PolSK signal is demodulated to produce the binary-phase-shift-keying (BPSK) signal, which will be used for the wireless broadcast application. Signal remodulation is demonstrated using reflective semiconductor optical amplifier (RSOA) as a colorless reflective modulator in the optical networking unit (ONU)/RAU. The downstream signal is remodulated at the ONU/RAU to produce the non-return-to-zero (NRZ) upstream signal.     

Optical Entropy Network Mapped from Binary Feature Tree

The concept of a binary feature tree (BFT) and the principle of its formation are described. A pattern is divided into sub-parts by comparing its similarity with other patterns. The BFT is established by sub-parts of a group of patterns and mapped into a three layered neural network which Sethi called an entropy network. The interconnection pattern between the first and hidden layers is formed according to the “AND“ relationship of node feature patterns determined by BFT. The interconnection pattern between the hidden and last layers is obtained by training. The advantage of the proposed network is that the scale is small because a feature neuron is adopted and the interconnection is local instead of full; therefore, it is easily implemented by either hardware or software. Two simulation examples show the success of the entropy network for pattern recognition. A feature extraction by an optical inner product method is also described.Presented at 1996 International Topical Meeting on Optical Computing (OC ‘96), April 21-25, Sendai, Japan.     

Analysis of inter-satellite free-space optical link performance considering different system parameters

The welcome and adaptation of optical wireless technology by the modern era has brought forward the concept of an inter-satellite free-space optical communication system. In the present work, I study the combined effect of selection of different operating wavelengths and detector types along with the pointing errors at the transmitter and receiver side on the performance of an inter-satellite free-space optical link. The link performance has been optimized by measuring and analyzing the bit error rate and quality-factor of received signal under different scenarios. Performance of the inter-satellite link has also been investigated considering different modulation formats and data rates for LEO and MEO distances.     

K-dimensional protection structure (KDPS) for multi-link failure in data center optical networks

Currently, data center has become one of the most important application resources. Meanwhile, there is huge amount of data streams within a data center or among different data centers, which requires the transmission channel with high bandwidth and good reliability. Optical networks become the essential solution for the data center interconnection. Especially for intra data center networks, there are too many links for a limited number of nodes, which make the network so complex and vulnerable. A K-dimensional protection structure (KDPS) is proposed against multi-link failure in data center optical networks, and 3DPS is mainly introduced and analyzed in the paper. Two greedy algorithms are proposed to construct KDPS in static and dynamic optical networks respectively. Numerical results show that 3DPS can be constructed with more difficulty in dynamic optical networks, and the greedy algorithm can find the 3DPS much easier under three-link failures than under dual-link failures.     

Engineering implementation of a hybrid optical correlator using SLMs

Optical correlators have been widely used for such applications as automatic target identification, invariant pattern recognition and machine vision. In hybrid optical correlators, Spatial light modulators (SLMs) are used to dynamically update the input and the filter. However, implementation is difficult because of the interference of “ghost” images; rigorous requirements for filter registration, accurate and effective filter sizing and complex valued filtering functions. This paper proposes some practical approaches to handle these issues and provides engineering details of how to build a hybrid optical correlator, where a SLM serves as an updateable intensity filter for real-time pattern recognition.     

Analysis of Doppler-effeet on satellite constellations with wavelength division multiplexing architectures

With the development of optical space communications, a global space-based optical backbone network is currently proposed by using broadband laser inter-satellite links (ISLs) which enable routing traffic through the space. Satellite optical networking techniques based on wavelength division multiplexing (WDM) ISLs can transit significantly high data rates signals. In this letter, a new function of wavelength excursion due to Doppler-effect is developed for the ISLs, considering the conception of pointing ahead mechanism. The characteristic of wavelength excursion induced by Doppler-effect is examined in one of low earth orbit (LEO) satellite constellation networks named the next-generation LEO system (NeLS) with WDM ISLs assumed, and the influence on its communications caused by wavelength excursion is analyzed.     

Enabling Optical Network Test Bed for 5G Tests

In this work, we show some experimental approaches concerning optical network design dedicated to 5G infrastructures. In particular, we show some implementations of network slicing based on Carrier Ethernet forwarding, which will be very suitable in the context of 5G heterogeneous networks, especially looking at services for vertical enterprises. We also show how to adopt a central unit (orchestrator) to automatically manage such logical paths according to quality-of-service requirements, which can be monitored at the user location. We also illustrate how novel all-optical processes, such as the ones based on all-optical wavelength conversion, can be used for multicasting, enabling development of TV broadcasting based on 4G–5G terminals. These managing and forwarding techniques, operating on optical links, are tested in a wireless environment on Wi-Fi cells and emulating LTE and WiMAX systems by means of the NS-3 code.