Experimental Evaluation of an Open-Loop All-Optical Chaotic Communication System

A numerical investigation of the performance of an open-loop optical chaotic communication system for the isochronous synchronization solution has been carried out, under strong optical injection conditions achieved using antireflective coating at the input facet of the receiver laser in combination with an optical erbium-doped fiber amplifier (EDFA). Different message encoding techniques have been considered and tested at multigigabit rates and for different levels of optical injection to the receiver. The effects induced by the amplified spontaneous emission (ASE) noise of the EDFA to the performance of the chaotic communication system have also been studied. The performance of all the examined encryption methods for the 1 Gb/s bit-rate messages was quite satisfactory and was characterized by Q-factor values that exceeded 10, after synchronizing in the strong injection regime. For higher message bit rates, the Q-factor values for all methods decrease considerably due to the residual frequency components of the chaotic carrier that are now more significant in the message spectral region. The effect of the amplifier's ASE noise to the system's performance was deteriorated as long as the EDFA chaotic input was kept in relatively high power levels.

Bit error rate (BER) performances of DPSK are researched for space uplink optical communication system. Considering further phase fluctuation effect based on the traditional atmospheric turbulence model, BER performance versus transmission power, zenith angle, frequency deviation, divergence angle and transmission diameter are discussed for different wavelengths. Simulations, especially, indicate that considering the phase fluctuation effect, BER performance is sensitive for low frequency deviation. It also confirms that wavelength of 1550nm on communication system is still a good choice for the better BER performance. This work is helpful for enhancing transmission quality and the design of space optical communication system.

Performance of optical chaotic communication systems using multimode vertical cavity surface emitting lasers

<p>The transmission of high power inside the optical fiber, produce amplitude noise, phase noise and other transmission impairments that degrade the performance of optical communication system. The signal regeneration techniques are used to mitigate these nonlinear impairments in the electrical or in the optical domain. All-optical signal regeneration techniques are one of the solutions to mitigate these nonlinear transmission impairments in the optical domain without converting the signal from optical to electrical domain. The existing techniques are not capable enough to attain the Bit Error Rate (BER) less than 10<sup>-10</sup> with the power penalty less than – 9dBm. In this paper, a new all-optical signal regeneration technique is developed that mitigate amplitude and phase noises in the optical domain. The new optical signal regeneration technique is developed by combining the two existing technique one is 3R (Reshaping, Reamplification and Retiming) regeneration and other is Phase Sensitive Amplification (PSA). The 10Gb/s Differential Phase shift Keying (DPSK) noisy transmission system is used to verify the features of developed technique. The developed technique successfully mitigates the nonlinear impairments from the noisy DPSK system with significant improvement in BER at low power penalty with the additional feature of high Q-factor and an eye open response for the regenerated signal. It is determined that BER of 10<sup>-12</sup> is achieved at the power penalty of -14 dBm with Q-factor of 42 and an eye opened response. The developed technique in the DPSK system is realized using commercial software package Optisystem. The designed technique will be helpful to enhance the performance existing high-speed optical communication by achieving the minimum BER at low power penalty.</p>

Effects of source beam, link, and oceanic turbulence parameters on the scintillation index and bit error rate (BER) performance of cosine (cos) and cosine-hyperbolic (cosh) Gaussian light beams have been investigated in order to improve wireless optical communication link performance in oceanic turbulence. The Nikishov and Nikishov power spectrum of oceanic water and extended Huygens Fresnel principle were used in our evaluations; the results were obtained via MATLAB. The scintillation index and BER were examined versus oceanic turbulence parameters, which are the rate of dissipation of mean-square temperature, the ratio of temperature and salinity contributions to the refractive index spectrum, and the dissipation rate of kinetic energy per unit fluid mass of fluid. Further, the scintillation index and BER are investigated against the source size, propagation distance, and complex displacement parameters of cos- and cosh-Gaussian beams. This study aimed to select the suitable sinusoidal beam to be employed in order to increase the performance of underwater wireless optical communication systems operating in oceanic turbulence.

The performance of a free space optical (FSO) communication system is significantly affected by various atmospheric turbulence conditions and pointing errors (PEs) apart from the additive noise, which is assumed to be Gaussian. Optical pre-amplifiers are an essential component of FSO systems for improving the receiver sensitivity. However, optical pre-amplification results in amplified spontaneous emission (ASE), which dominates the receiver thermal and shot noises. The square law photodetection process at the receiver in a FSO system necessitates the consideration of chi-square statistics for the decision variable contrary to the Gaussian approximation that is widely used in the literature. In this paper, we evaluate the bit error rate (BER) performance of a FSO system assuming non-return-to-zero on–off keying modulation in the presence of ASE noise under weak, moderate to strong, and very strong atmospheric turbulence regimes and PEs. We also derive asymptotic BER expressions for the considered FSO system for large values of the signal-to-noise ratio in terms of simple elementary functions. Further insight into the system is provided by performing a diversity analysis.

Due to the light attenuation caused by absorption and scattering of sea water, the performance of underwater optical communication system is limited. Usually, the optical signals will be decayed severely in hundreds of meters and the waveforms are submerged in noise. To improve the signal-to-noise ratio (SNR), for traditional methods, most of the noise can be suppressed by filters based on classic linear theory. However, the signal will also be relatively attenuated by the filters. In this research, the nonlinear signal processing method, named as stochastic resonance (SR), is introduced to enhance the underwater laser communication signal. A SR system is simulated to evaluate the feasibility and effectiveness of weak signal detection in underwater laser communication. The influence of the noise to the bit-error-rate(BER) and the parameter optimization are simulated and discussed. It is proved that, the SR system has advantage over the low-pass filter(LPF) and has promising prospect in the signal enhancement in underwater laser communication.

In this paper, a new kind of method is developed to analyse the bit-error rate for a free-space optical communication system, which is based on the three most important parameters of scintillation statistics, i.e. fraction of time of fade and surge, mean frequency of level crossings, and mean duration of fade and surge. By using this method, the relationship between the bit-error rate and scintillation is clearly identified. The tip–tilt error deteriorates the performance of a free-space optical communication system. Fine tracking ability of adaptive optics (through tip–tilt compensation) can overcome this difficulty. The fade and surge statistical parameters with tip–tilt compensation are evaluated for the plane wave model. The bit-error rate as a function of the scintillation statistical parameters (with tip–tilt compensation) is developed. The results show that the bit-error rate is reduced notably through tip–tilt compensation for free-space optical communication.

The calculation of optical system performance for laser beam propagation in optical turbulence, such as bit error rate (BER), signal-to-noise ratio, and probability of fade, requires the knowledge of scintillation. In this paper, we show the analytical expressions of the aperture-averaged scintillation using a new recently introduced power spectrum of the refractive index fluctuations for underwater turbulence, the oceanic turbulence optical power spectrum (OTOPS). In addition, we use this main result to investigate the impact of weak oceanic turbulence on free-space optical system performance for a propagating Gaussian beam wave. Similar to the atmospheric turbulence case, results show that aperture averaging can reduce the mean BER and the probability of fade several orders of magnitude if the receiver aperture is chosen with a diameter larger than the Fresnel zone, L/k. Being valid for weak turbulence regime in any natural waters, results present the variations of irradiance fluctuations and the performance of underwater optical wireless communication systems depending on the practical values of average temperature and average salinity concentration that can be encountered in any world's waters.

The performance of free space optical communication system using multi-input multi-output orthogonal frequency division multiplexing (MIMO-OFDM) with a modified receiver structure is evaluated in this paper referred to as MIMO-OFDM-FSO with the modified receiver (MIMO-OFDM-FSO-MR). Utilizing equal gain combining the analysis is done by taking closed-form expression of average bit error rate and throughput. The simulation is performed to estimate various performance parameters such as throughput and bit error rate (BER) for the proposed MIMO-OFDM-FSO-MR model under different turbulence and weather conditions. Simulation reveals that the proposed model exhibits significant BER performance and provides better throughput and spectral efficiency as compared with conventional FSO systems, OFDM-FSO systems, MIMO-FSO systems and Low-density Parity Check (LDPC) coded MIMO-OFDM-FSO systems.

The efficient and accurate evaluation of the transmission performance of high-capacity optical communication systems has always attracted significant research attentions. The enhanced Gaussian noise (EGN) model is considered as an excellent solution to predict the system performance taking into account linear and nonlinear transmission impairments. Since the conventional form of the EGN model is complicated and intractable for a fast computation, the closed-form simplification has been regarded as a direction to significantly reduce the computational complexity. However, the accuracy of such a closed-form EGN model becomes a main concern in the application of ultra-wideband optical communication systems. In this work, we have investigated the accuracy of the closed-form EGN model for ultra-wideband optical fiber communication systems, where the performance of the system using electronic dispersion compensation, multi-channel nonlinearity compensation and full-field nonlinearity compensation has been evaluated in terms of symbol rate, number of channels and signal power. Our work will provide an insight on the application of the EGN model in next-generation ultra-wideband long-haul optical fiber communication networks.

This paper discusses the bit-error-rate (BER) performance of an aeronautical uplink optical wireless communication system (OWCS) when a Gaussian beam is employed and the M-ary pulse position modulation technique is used in an atmospheric turbulent medium. Weak turbulence conditions and log-normal distribution are utilized. The Gaussian beam is assumed to propagate on a slant path, the transmitter being ground-based, and the airborne receiver is on-axis positioned. Variations of BER are obtained against the variations in the link length, Gaussian beam source size, zenith angle, wind speed, wavelength, modulation order, data bit rate, equivalent load resistor, avalanche photodetector gain, and detector quantum efficiency. It is observed that the performance of the aeronautical uplink OWCS is affected from atmospheric turbulence significantly.

Timing jitter dependence on data format for ideal dispersion compensated 10 Gbps optical communication systems

This rsearch work presents an educational software interface tool for analyzing and estimating the bit error rate (BER) of an optical communication system. Currently BER estimation tool required expensive measurement equipment such as serial data analyzer (SDA) and BER Tester. In addition to cost all this equipment is also limited to BER estimation based on standard format and is not suitable for custom analysis because of time constraint to use equipment even during offline estimation. This educational software interface tool is developed using OPTISYSTEM software and built-in MATLAB command. MATLAB GUI is used as the software tool because it’s friendly user. OPTISYSTEM is used to design the PAM two levels, four levels, and eight levels system. MATLAB is used as an interface to build the BER estimation tool for measuring the PAM multilevel modulation technique. The MATLAB GUI system for measuring BER is design using Gaussian probability errors approximation method. The designed BER estimation tool simulation, is able to plot the eye diagram, BER diagram, Q-factor value, threshold value, and the most important function is to analysis the BER value for two levels, four levels and eight levels of a PAM optical communication systems.

Investigation of the phase fluctuation effect on the BER performance of DPSK space downlink optical communication system on fluctuation channel