Wave Mixing Effect Research Articles

Optical waveform monitoring based on a free-running mode-locked femtosecond fibre laser and four-wave mixing in a highly nonlinear fibre

AbstractOptical sampling based on ultrafast optical nonlinearities is a useful technique to monitor the waveforms of ultrashort optical pulses. In this paper, we present a new implementation of optical waveform sampling systems by employing our newly constructed free–running mode–locked fibre laser with a tunable repetition rate and a low timing jitter, an all–optical waveform sampler with a highly nonlinear fibre (HNLF), and our developed computer algorithm for optical waveform display and measurement, respectively. Using a femtosecond fibre laser to generate the highly stable optical sampling pulses and exploiting the four–wave mixing effect in a 100m–long HNLF, we successfully demonstrate the all–optical waveform sampling of a 10GHz optical clock pulse sequence with a pulse width of 1.8 ps and a 80Gbit/s optical data signal, respectively. The experimental results show that waveforms of the tested optical pulse signals are accurately reproduced with a pulse width of 2.0 ps. This corresponds to a temporal resolution of 0.87 ps for optical waveform measurement. Moreover, the optical eye diagram of a 10Gbit/s optical data signal with a 1.8 ps pulse width is also accurately measured by employing our developed optical sampling system.

The effect of dispersed Petrobaltic oil droplet size on photosynthetically active radiation in marine environment.

Oil pollution in seawater, primarily visible on sea surface, becomes dispersed as an effect of wave mixing as well as chemical dispersant treatment, and forms spherical oil droplets. In this study, we examined the influence of oil droplet size of highly dispersed Petrobaltic crude on the underwater visible light flux and the inherent optical properties (IOPs) of seawater, including absorption, scattering, backscattering and attenuation coefficients. On the basis of measured data and Mie theory, we calculated the IOPs of dispersed Petrobaltic crude oil in constant concentration, but different log-normal size distributions. We also performed a radiative transfer analysis, in order to evaluate the influence on the downwelling irradiance Ed, remote sensing reflectance Rrs and diffuse reflectance R, using in situ data from the Baltic Sea. We found that during dispersion, there occurs a boundary size distribution characterized by a peak diameter d0 = 0.3 μm causing a maximum E d increase of 40% within 0.5-m depth, and the maximum Ed decrease of 100% at depths below 5 m. Moreover, we showed that the impact of size distribution on the "blue to green" ratios of Rrs and R varies from 24% increase to 27% decrease at the same crude oil concentration.

Investigation of Four Wave Mixing Effect at Different Transmission Power Levels and Channel Spacing

There is an incredible focus on broadband fiber optical transmission system as it offers many advantages over other communication systems such as large bandwidth and significantly low losses [1]. This high bandwidth in optical communication networks is further increased by using Wavelength Division Multiplexing. In WDM based fiber optical communication systems nonlinearities in fiber are a limiting factor which degrade the system performance and limit the data rate and bandwidth of the system [3]. As we increase the transmission power levels so as to transmit data for long-haul communications systems these non linear effects tend to accumulate. Due to these non linear effects, all input signals may interact with each other in a complicated way which degrades overall performance of optical communication system. In WDM systems, the interaction of input signals with each other adversely affects the performance of the system. Hence it is of great importance to understand fiber non linear effects and its effect on optical fiber communication system. The main objective of this paper is to study non linear effects in fiber optic communication system mainly Four Wave Mixing (FWM) and to analyze to effect of increasing optical transmission powers and channels spacing in a wave division multiplexing system. The results show that as the transmission power is increased, the efficiency of four wave mixing effect increases. Also if the channel spacing in a WDM system is kept uneven, the power levels of mix frequencies produced as a result of FWM effects is reduced to a considerable amount. General Terms Investigation, Four Wave Mixing, Wave Division Multiplexing

Analysis of Wave Length Conversion using Four Wave Mixing Effect in an Optical Fiber

Analysis of Wave Length Conversion using Four Wave Mixing Effect in an Optical Fiber

Investigation on four wave mixing effect in various optical Fibers for different spectral efficient orthogonal modulation Formats

The paper analyzes the four wave mixing (FWM) effect in different spectral efficient orthognal modulation formats at equal channel spacing of 100GHz and 50GHz to design long haul wavelength division multiplexing (WDM) optical system. Further, the comparison of reduction of FWM for existing and proposed modulation format have been analyzed by varying the laser input power from −10dBm to 10dBm.

Utilizing the plasmonic resonance to enhance three wave mixing effects in nano-scale cut-wire

In this paper, quantitative study of the enhanced three wave mixing effects from periodic array of nano-scale golden cut-wires embedded in nonlinear dielectric is performed. Geometrical parameters of the considered structure are chosen so that the plasmonic resonance occurs in the wavelength 1.5 μm. Plasmonic resonance of this structure gives rise to the localization factor significantly larger than that of the cut-wire structures with no plasmonic resonance. Considering the surrounding medium of the cut-wire a typical second-order nonlinear optical medium, enhancement of the nonlinearity of this nonlinear medium is illustrated. Since the mentioned structure can be considered a homogeneous nonlinear medium with the effective nonlinear susceptibility, nonlinear retrieval method is used to determine the effective nonlinear susceptibility for all four frequency combinations. Maximum enhancement of the effective susceptibility is obtained for the second harmonic generation of the applied wave with the frequency corresponding to the plasmonic resonance, with the enhancement up to two orders of magnitude. Efficiency of the second harmonic generation in this resonant structure surrounded with nonlinear dielectric is calculated to be 30 times more than that of the nonlinear dielectric with the same dimensions.

Wavelength Assignment Considering Four Wave Mixing Using Genetic Algorithm DOI: 10.14209/jcis.2007.1

This article presents a new estrategy to assign wavelengths in a optical link considering the four wave mixing effect in the optical fiber. The four wave mixing effect in taken into account by using a formulation that calculates the fiber noise figure for each wavelenght. We analyze the assignments when there are additions and droppings of wavelengths, considering the best and satisfactory assignments using the exhaustive and genetic algorithms, respectively. We obtain the distributions o wavelengthms from a genetic algorithm, which considers the quality of service criterion based on bit error rate. We show that our strategy is capable of determining assignments of wavelength, the maximum number of wavelengths and their positions in the grid to minimize the impact of the four wave mixing effect.

Role of Laser Linewidth in High Speed DWDM System by Incorporating Duobinary Modulation Scheme

This work is focused on realization of DWDM system of 1.6 Tb/s ultra high capacity using duobinary return to zero modulation scheme with EDFA and dispersion compensation scheme.Duo binary format is used as it is suitable for high spectral efficiency at large transmission distance.40 channels having capacity of 40 Gbps data rate each are multiplexed with channel spacing of 100 GHz to realize 1.6 Tbps as total transmission over optical span of 60 Km by using pre and post compensation technique.The comparison of parameters is observed in terms of Q value and eye opening keeping BER in acceptable range Moreover, the role of laser line-width is also investigated to minimize the non linearity and four wave mixing effect.

Total date rate of multi-wavelength 2R regenerators for time-interleaved RZ-OOK signals.

Multi-wavelength regeneration free of inter-channel crosstalk is desirable for wavelength division multiplexing (WDM) systems, especially from the cost-effectiveness point of view. This paper presents the design rules of time-interleaved multi-wavelength 2R regeneration systems based on data-pump four wave mixing (FWM) effect, and several key factors, such as FWM bandwidth, wavelength assignment, and duty cycle, are comprehensively taken into account. The total data rate of time-interleaved WDM regeneration systems along with polarization multiplexing or bidirectional transmission are discussed, which are mainly determined by temporal overlap, spectral broadening and FWM bandwidth. As two examples, an eight-wavelength unidirectional regenerator using polarization multiplexing is designed by optimizing the fiber birefringence, and a six-wavelength bidirectional regenerator is demonstrated by experiment. Each is expected to have a total data rate of about 200 Gb/s for the optical RZ-OOK signals, and the wavelength number is increased at the expense of spectral efficiency.

To Investigate the Characteristics Parameters of Semiconductor Optical Amplifier based on Wavelength Converters for all Optical Networks

optical wavelength converters are key devices for all optical networks. Wavelength conversion employing semiconductor optical amplifiers (SOAs) has become an important component in WDM networks. This paper investigates the performance of a 20 Gb/s SOA-based FWM wavelength converter system. For this we have optimized the SOA parameters to achieve adequate quality factor and enhancement in four wave mixing effect so as to improve the converted signal power. This will be done in such a manner that the SOA never saturates and generate maximum four-wave mixing signals with minimum gain fluctuations. Performance is analyzed in terms of converted signal power, converted optical signal-to-noise ratio (OSNR) and Q factor for both up and down conversions with respect to wavelength shifted up to 10nm. It was found that the conversion efficiency and OSNR of the converted signal are 1dB and 45 dBm resp. Keywordslength converter, WDM, SOA, FWM

Optimization of fiber Raman amplifier by reduction of four wave mixing effect

We analyzed the four wave mixing (FWM) effect by propagating two channels through the same backward pumped fiber Raman amplifier (FRA) with variations in FRA parameters. It is observed that FWM increases with increase in signal input power as well as pump power. The FWM effect is also analyzed for Raman constant $$({f}_{\text{ r }})$$ ( f r ) to obtain the optimum value of $$({f}_{\text{ r }})$$ ( f r ) , and it is found that to have minimum FWM, the optimum value of Raman constant comes out to be 0.18. This Raman amplifier can be used for wavelength division multiplexed application with constant broadband gain.

Analytical characterization of four wave mixing effect in direct-detection double-sideband OFDM optical transmission systems

A closed-form expression for the variance of the four-wave mixing (FWM) induced in each subcarrier of a double sideband orthogonal frequency division multiplexing (OFDM) system employing direct detection is proposed and validated. Particularly, using a small signal analysis, equivalent transfer functions that characterize the frequency response of the FWM effect are derived taking into account the walkoff effect between the modulated pump waves and the FWM wave. The accuracy of the variance estimates provided by the closed-form expression is assessed for different sets of system parameters. The closed-form expression provides good variance estimates of the FWM-induced degradation caused by degenerate and nonsymmetric nondegenerate FWM components. For symmetric non-degenerate FWM components, the proposed expression provides reliable but pessimistic variance estimates, not exceeding the actual FWM variance in 1.5 dB for modulation indexes of interest.

40 Gb/s NRZ-DQPSK Data All-Optical Wavelength Conversion Using Four Wave Mixing in a Bulk SOA

Differential quadrature phase shift keying (DQPSK) modulation has become particularly attractive in high-speed optical communications because of its resistance to fiber nonlinearities and its more efficient use of fiber bandwidth. Because of its wavelength conversion ability, semiconductor optical amplifier (SOA) four wave mixing effect has attracted much attention. We experimentally study the FWM wavelength conversion of 40 Gb/s (20 GBd) NRZ-DQPSK data. A bulk SOA with 21 dB gain and 10 dBm output saturation power is used. The Q-factors of the input and wavelength converted signal are measured. Some signal regeneration properties are shown. A Q-factor improvement up to 1.7 dB is observed.

All-optical circular shift register based on semiconductor optical amplifiers

We present a new and potentially integrable scheme to realize an all-optical circulating shift register consisting of a fiber-loop based optical buffer (OB) and an optical AND gate. The OB is implemented using semiconductor optical amplifier as a nonlinear element and the AND gate is realized by means of four wave mixing effect in a semiconductor optical amplifier. The operation of the shift register has been verified for a 10-bit input sequence at a sequence bit rate of 2.5 GHz and 10 GHz respectively. The simulation results show that \(\hbox {BER}=10^{-9}\) is achieved at optical signal-to-noise (OSNR) ratio of 16dB at the shift register output. The dependence of the output quality factor (\(Q\)-factor) on SOA parameters is also investigated and discussed.

Comparison Among Different Types of Advanced Modulation Formats Under Four Wave Mixing Effects

Comparison Among Different Types of Advanced Modulation Formats Under Four Wave Mixing Effects

Investigation of four wave mixing effect with different number of input channels at various channel spacing

In this paper the design, implementation and performance analysis of four wave mixing (FWM) in optical communication system for different number of input channels is presented using various values of channel spacing. Here, all the input channels have been spaced evenly at various values like 6.25GHz, 12.5GHz, 25GHz, 40GHz, 50GHz with the different number of channels at the input i.e. with 2, 4, 6, 8, 12 input channels. The simulation results reveal that the four wave mixing is minimum when the channel spacing is maximum i.e. 50GHz with minimum number of channels i.e. 2 input channels. It is observed that on increasing the channel spacing, the interference between the input frequencies decreases and hence the four wave mixing also decreases. Also, on increasing the number of input channels/users, the interference between the input frequencies increases and thus, the four wave mixing also increases.

Multi-wavelength generation by self-seeded four-wave mixing

A cost effective method of generating multi-wavelength based on the cascaded four wave mixing effect is experimentally demonstrated. The proposed scheme is free from external tunable laser sources and pump modulators, resulting from the use of a broadened linewidth tunable dual wavelength erbium-doped fiber laser as intracavity pump. In this configuration, the number of four wave mixing cascades becomes larger in tandem with the increment of erbium-doped fiber amplifier output power. When its output power is set at 20.57 dBm, six waves having optical signal to noise ratio larger than 10 dB are generated. The six waves are stable with peak power fluctuations less than 1 dB within 30 minutes period and tunable with wavelength spacing ranging from 1.03 nm to 11.31 nm.

Effect of transmission fiber on dense wavelength division multiplexed (DWDM) chaos synchronization

A comprehensive investigation on the nonlinearities of transmission fiber affecting the synchronization of transmitters and receivers in eight channel dense wavelength division multiplexing (DWDM) chaotic communication system is presented. Very much like conventional DWDM systems, four wave mixing (FWM) and Raman effects are numerically found to be the two main limiting factors in DWDM chaos propagation also with latter being more dominant. The deterioration of chaos signal on eight wavelengths after propagation through fiber is measured by respective sync diagrams. A novel hybrid scheme based on polarization interleaving with unequal channel spacing is discovered here to offset the negative effects of both above limiting factors.

The preliminary study of the high chlorophyll in the central Bohai Sea in summer

In the central Bohai Sea, both historical data and in situ observations show that the distribution of high chlorophyll concentration is consistent with warm water. The previous studies confirm that the warm water is caused by a joint effect of wave and tidal mixing. In this paper, the authors have coupled the Princeton ocean model (POM) with a biochemical model to further investigate the formation of the high chlorophyll concentration. When the wave mixing is excluded, the water temperature is lower and the chlorophyll concentration is also lower than the observation. However, if the wave mixing is included, strong wave mixing in the upper layer brings the warm water downward and nutrients upward so that both temperature and nutrients tend to be uniformly high from the surface to the bottom. This provides an environment which is favorable for the growth of the phytoplankton. Therefore the chlorophyll concentration, as a symbol of phytoplankton, shows high value in the central Bohai Sea. In conclusion, the wave mixing plays an important role in the formation of high chlorophyll concentration in the central Bohai Sea.

Wave mixing effects on minor chemical constituents in the MLT region: Results from a global CTM driven by high-resolution dynamics

[1] The dynamical fields of a high-resolution mechanistic general circulation model (GCM) with resolved gravity waves (GWs) are used to drive a chemistry-transport model (CTM) of the mesosphere-lower thermosphere (MLT). Both models have been used in previous studies and are coupled in off-line mode in order to study the explicit effects of GWs on the transport and photochemistry of minor constituents of the MLT. This is done on the basis of a sensitivity experiment. In our control simulation the CTM is driven with the full dynamical fields from an annual cycle simulated with the GCM, where mid-frequency GWs down to horizontal wavelengths of 350 km are resolved and their wave-mean flow interaction is self-consistently induced by an advanced turbulence model. A perturbation simulation with the CTM is defined by eliminating all meso-scale variations with horizontal wavelengths shorter than 1000 km from the dynamical fields by means of spectral filtering before running the CTM. The response of the CTM to GWs perturbations reveals strong effects on the trace-gas concentrations. In particular, minor chemical constituents with large photochemical life-time are strongly affected by vertical wave mixing, while constituents with short life-time reflect the dependence of their reaction rates on meso-scale temperature perturbations and on the changed distributions of long-lived constituents. The mean model response is strongest around the mesopause. We present detailed discussions of the simulated gravity-wave mixing effects on the photochemistry and highlight the consequences for our understanding of the general circulation of the MLT.