47 research outputs found
Dynamical oscillations in nonlinear optical media
The spatial dynamics of pulses in Kerr media with parabolic index profile are
examined. It is found that when diffraction and graded-index have opposite
signs propagating pulses exhibit an oscillatory pattern, similar to a breathing
behavior. Furthermore, if the pulse and the index profile are not aligned the
pulse oscillates around the index origin with frequency that depends on the
values of the diffraction and index of refraction. These oscillations are not
observed when diffraction and graded-index share the same sign
Synchronization Phenomena in Coupled Birkhoff-Shaw Chaotic Systems Using Nonlinear Controllers
In this chapter, the well-known non-autonomous chaotic system, the Birkhoff-Shaw, which exhibits the structure of beaks and wings, typically observed in chaotic neuronal models, is used in a coupling scheme. The Birkhoff-Shaw system is a second-order non-autonomous dynamical system with rich dynamical behaviour, which has not been sufficiently studied. Furthermore, the master-slave (unidirectional) coupling scheme, which is used, is designed by using the nonlinear controllers to target synchronization states, such as complete synchronization and antisynchronization, with amplification or attenuation in chaotic oscillators. It is the first time that the specific method has been used in coupled non-autonomous chaotic systems. The stability of synchronization is ensured by using Lyapunov function stability theorem in the unidirectional mode of coupling. The simulation results from system’s numerical integration confirm the appearance of complete synchronization and antisynchronization phenomena depending on the signs of the parameters of the error functions. Electronic circuitry that models the coupling scheme is also reported to verify its feasibility
Underwater Optical Wireless Communication Systems: A Concise Review
Underwater optical wireless communications (UOWC) have gained a considerable interest during the last years as an alternative means for broadband inexpensive submarine communications. UOWC present numerous similarities compared to free space optical (FSO) communications or laser satellite links mainly due to the fact that they employ optical wavelengths to transfer secure information between dedicated point‐to‐point links. By using suitable wavelengths, high data rates can be attained. Some recent works showed that broadband links can be achieved over moderate ranges. Transmissions of several Mbps have been realized in laboratory experiments by employing a simulated aquatic medium with scattering characteristics similar to oceanic waters. It was also demonstrated that UOWC networks are feasible to operate at high data rates for medium distances up to a hundred meters. However, it is not currently available as an industrial product and mainly test‐bed measurements in water test tanks have been reported so far. Therefore, extensive research is expected in the near future, which is necessary in order to further reveal the “hidden” abilities of optical spectrum to transfer broadband signals at higher distances. The present work summarizes the recent advances in channel modeling and system analysis and design in the area of UOWC
Spatial Diversity for CDMA RoFSO Links over M Turbulence Channels with Nonzero Boresight Pointing Errors
A CDMA RoFSO link with receivers’ spatial diversity is studied. Turbulence-induced fading, modeled by the M(alaga) distribution, is considered that hamper the FSO link performance along with the nonzero boresight pointing errors effect. Novel, analytical closed-form expressions are extracted for the estimation of the average bit-error-rate and the outage probability of the CDMA RoFSO system for both directions of the forward and the reverse link. The numerical results show clearly the performance improvement of using spatial diversity, even in the most adverse atmospheric conditions with strong and saturated atmospheric turbulence with enhanced misalignment. Also, the effects of nonlinear distortion, multiple access interference and clipping noise aggravate the performance of the link, where cases with large number of users are taken into account
Statistical modeling of received signal strength for an FSO link over maritime environment
The article of record as published may be found at https://doi.org/10.1016/j.optcom.2021.126858Free space optical communications (FSO) have the potential to substantially improve communications technology in terms of channel capacity and offer an alternative to their RF counterpart. Additional characteristics
related to security, immunity, flexibility and low cost issues render FSO a reasonable candidate for military
applications. FSO technology does not come without challenges. Its major issue is the local meteorological
parameters that give rise to various atmospheric phenomena. The purpose of this work is to facilitate the
performance prediction of an FSO communication link over a maritime environment by utilizing macroscopic
meteorological parameters, i.e. air temperature, wind speed, relative humidity, air pressure, dew point, solar
radiation and sea temperature, obtained from point measurements. The received signal strength indicator
(RSSI) of the FSO receiver has been utilized as the performance metric of the channel and a closed form
expression has been deduced. The model has then been validated against real meteorological data and the
predicted RSSI values exhibited a reasonably strong correlation with the observed ones. Atmospheric turbulence
has been taken into account using the Navy Surface Layer Model (NAVSLaM) to estimate the structure index
parameter from the same meteorological data and thus allowed for a statistical correlation between the
refractive index structure parameter and RSSI
On the Outage Capacity of Transdermal Optical Wireless Links with Stochastic Spatial Jitter and Skin-Induced Attenuation
The tremendous development of both optical wireless communications (OWC) and implantable medical devices (IMDs) has recently enabled the establishment of transdermal optical wireless (TOW) links that utilize light waves to transfer information inside the living body to the outside world and conversely. Indeed, numerous emerging medical applications such as cortical recording and telemetry with cochlear implants require extremely high data rates along with low power consumption that only this new technology could accommodate. Thus, in this paper, a typical TOW link is investigated in terms of outage capacity which is a critical performance metric that has so far not been evaluated for such wireless systems in the open technical literature. More precisely, an outage capacity analysis is performed considering both skin-induced attenuation and stochastic spatial jitter, i.e., pointing error effects. Analytical expressions and results for the outage capacity are derived for a variety of skin channel conditions along with varying stochastic pointing errors which demonstrate the feasibility of this cross-field cooperation. Lastly, the corresponding simulation outcomes further validate our suggestions