Free Space Optical Wireless Communication Research Articles

Orientation-based solar noise impact on underwater and free-space optical wireless communication systems: experimental investigations

Solar noise, when it interferes with the received signal at the system receiver (Rx) of an optical wireless communication (OWC) system, degrades the system’s performance. The detrimental effect of solar noise on OWC systems has been well established in the literature. This work experimentally demonstrates solar noise interference in the OWC system by pointing the system Rx in various orientations in air and water mediums, e.g., 0° (Rx pointing horizontally leftward), 45°, 90° (Rx pointing vertically downward), 135°, 180° (Rx pointing horizontally rightward), 225°, 270° (Rx pointing vertically upward), and 315°. The experimental outcomes depict the signal’s noise content, spectral leakage, and roll-off rate variation at multiple Rx orientations. We also demonstrate the solar noise interference in transmitting an image through the outdoor underwater OWC link by pointing the system Rx in various orientations. Experimental demonstration confirms that the same OWC system never behaves identically in the presence of solar noise if the system Rx keeps changing its orientation during the maneuver.

Performance Analysis of Hybrid Radio Frequency and Free Space Optical Communication Networks with Cooperative Spectrum Sharing

This paper investigates the impact of cooperative spectrum sharing policy on the performance of hybrid radio frequency and free space optical wireless communication networks, where primary users and secondary users develop a band of the same spectrum resource. The radio frequency links obey Nakagami-m distribution with arbitrary fading parameter m, while the free space optical link follows gamma-gamma distributed atmospheric turbulence with nonzero pointing error. Because the secondary users access the spectrum band without payment, their behavior needs to be restricted. Specifically, the power of the secondary users is dominated by the tolerable threshold of the primary users. Considering both heterodyne and intensity modulation/direct detection strategies in optical receiver, the performance of optical relaying networks is completely different from that of traditional networks. With the help of bivariable Fox’s H function, new expressions for cumulative distribution function of equivalent signal to noise ratio at destination, probability density function, outage probability, ergodic capacity and symbol error probability are built in closed forms.

Stable and Highly Efficient Free-Space Optical Wireless Communication System Based on Polarization Modulation and In-Fiber Diffraction

The performance of free-space optical data transmission is severely deteriorated by the fluctuation of optical signal intensity, which is resulted from the bias drift of electro-optical modulation devices. In order to improve the performance of free-space optical communication systems, a bias-drift avoiding, beam steered free-space optical wireless communication system is presented based on polarization modulation for the first time to the best of our knowledge. An in-fiber diffraction device based on a 45° tilted fiber grating (TFG) serves simultaneously as an in-fiber polarizer, free-space light emitter, and beam steerer in the proposed communication system, which endows the proposed system with the merits of highly efficient, compact, stable and bias-drift free. The usage of 45° TFG has three benefits: 1), it realizes polarization modulation preventing bias-drift due to its polarization sensitive feature; 2), it enables stable and highly efficient in-fiber compact free-space light emitter; and 3) it accomplishes free-space beam steering due to its wavelength-depending diffraction characteristic. A 2.1 m free-space optical wireless data transmission has been demonstrated with a data rate of 4.8 Gbps per beam using 1.2 GHz bandwidth OFDM signals. This proposal prevents the bias drift issue and maintains high stability. Hence, it can be applied in some harsh situations and confidential data transmission fields.

10Gbps 2D MGC OCDMA Code over FSO Communication System

Currently, wide bandwidth signal dissemination along with low latency is a leading requisite in various applications. Free space optical wireless communication has introduced as a realistic technology for bridging the gap in present high data transmission fiber connectivity and as a provisional backbone for rapidly deployable wireless communication infrastructure. The manuscript highlights on the implementation of 10Gbps SAC-OCDMA FSO communications using modified two dimensional Golomb code (2D MGC) that possesses better auto correlation, minimum cross correlation and high cardinality. A comparison based on pseudo orthogonal (PSO) matrix code and modified two dimensional Golomb code (2D MGC) is developed in the proposed SAC OCDMA-FSO communication module taking different parameters into account. The simulative outcome signifies that the communication radius is bounded by the multiple access interference (MAI). In this work, a comparison is made in terms of bit error rate (BER), and quality factor (Q) based on modified two dimensional Golomb code (2D MGC) and PSO matrix code. It is observed that the 2D MGC yields better results compared to the PSO matrix code. The simulation results are validated using optisystem version 14.

Effects of oceanic turbulence on the propagation of four-petal Gaussian model beams

The evolution of average intensity for four-petal Gaussian model (FPGM) laser beams propagating through the oceanic turbulence is investigated. The analytical expressions of the average intensity at any receiver plane are derived based on the extended Huygens-Fresnel principle. Our results indicate that with the propagation distance increasing long enough in far field area, the initial profile of FPGM laser beams gradually disappears, and finally the profile converts into Gauss-like beam with several small petals. We also find that the spreading of the FPGM laser beam increases with the increasing of waist width of the Gaussian beam and equivalent temperature structure constant. The beam spreading decreases with the increasing of the dissipation rate of temperature variance and the inner scale of turbulence. The salinity fluctuation has a greater contribution to the spreading of the FPGM beam than that of the temperature fluctuation. Our results can be helpful for the design of the free space optical wireless communication and underwater imaging systems operating in oceanic environment.

Spreading and wandering of Gaussian–Schell model laser beams in an anisotropic turbulent ocean

The effect of anisotropic turbulence on the spreading and wandering of Gaussian–Schell model (GSM) laser beams propagating in an ocean is studied. The long-term spreading of a GSM beam propagating through the paraxial channel of a turbulent ocean is also developed. Expressions of random wander for such laser beams are derived in an anisotropic turbulent ocean based on the extended Huygens–Fresnel principle. We investigate the influence of parameters in a turbulent ocean on the beam wander and spreading. Our results indicate that beam spreading and random beam wandering are smaller without considering the anisotropy of turbulence in the oceanic channel. Salinity fluctuation has a greater contribution to both the beam spreading and beam wander than that of temperature fluctuations in a turbulent ocean. Our results could be helpful for designing a free-space optical wireless communication system in an oceanic environment.

Free Space Optical Wireless Communications under Turbulence Channel Effect

This article is focused on the turbulence attenuation and their effect on optical beam in free space. Analysis has been done for comparison the atmospheric turbulence effect between two classical methods, Rytov approximation and Andrews's method. The SNR was calculated for not weak turbulence employing Tailor series at different strength of scintillation. These calculations run for communications of wavelengths 850nm and 1550nm. The distance between the transmitter and receiver o horizontal link set to value range (0-2000) m. Keywords: Rytov variance, Atmospheric turbulence, Rytov approximation, Andrews's method. Signal to noise ratio.

Free Space Communications With Beam Steering a Two-Electrode Tapered Laser Diode Using Liquid-Crystal SLM

A free space optical wireless communication system with 3 degree angular coverage and 1.25 GHz modulation bandwidth is reported, in which relatively narrow laser beam of a simultaneous high power, high modulation speed and ultra high modulation efficiency directly modulated two-electrode tapered laser diode is steered using a nematic phase-only Liquid-Crystal On Silicon Spatial Light Modulator (LCOS SLM) by displaying reconfigurable 256 phase level gratings.

Free space optical wireless communications using directly modulated two-electrode high brightness tapered laser diode

A two-electrode tapered laser uses a separate excitation to achieve high output modulation depth with a small input current swing that can be provided with existing standard optical communication components, making it a novel source for optical wireless communications. Presented is a 1.25 Gbit/s free-space optical wireless communication system over a distance of 60 m, with a high power and high modulation efficiency two-electrode tapered laser. The system exhibits a 6.5 dB power penalty.

Modeling and simulation of heterojunction photovoltaic detector based on InAs0 .15Sb0.85 for free space optical communication

In this paper we report a theoretical model of InAs1−xSbx based photovoltaic detector for characterising the device in respect of RA product, voltage responsivity, quantum efficiency, detectivity and noise equivalent power. The model takes into account all the dominant dark current components e.g., diffusion, generation-recombination and tunneling (both band-to-band and trap-assisted) of the detector. The life-time of the carriers has been modeled by considering the three dominant recombination mechanisms e.g., radiative (band-to-band), Shockley-Read-Hall (SRH) and Auger recombination. The detector is expected to find application in free space optical communication system in 8–11 μm bands. Several researchers have already proposed that infrared region is best suited for free space optical wireless communication. The noise equivalent power (NEP) has been estimated to 3.35 × 10−11 WHz1/2 for an equivalent load resistance of 1 MΩ for operation at 77 K.

Flexible optical wireless links and networks

The worldwide demand for broadband communications is being met in many places by installed single-mode fiber networks. However, there is still a significant "first-mile" problem, which seriously limits the availability of broadband Internet access. Free-space optical wireless communications has emerged as a viable technology for bridging gaps in existing high-data-rate communications networks, and as a temporary backbone for rapidly deployable mobile wireless communication infrastructure. In this article we describe research designed to improve the performance of such networks along terrestrial paths, including the effects of atmospheric turbulence, obscuration, transmitter and receiver design, and topology control.