Self-phase Modulation Effect Research Articles

Pulse Restoration for Long-Distance Transmission of Wavelength Division Multiplexed Signals Using Gain Saturable Erbium-Doped Fiber Amplifiers

In this article, the pulse restoration of different fibers is compared to obtain the optimum fiber. The dispersion-compensated fiber, having a high ability for pulse restoration, is optimized to reduce the self-phase modulation effect by taking the effective core area of the fiber. Then the optimized dispersion-compensated fibers are used in wavelength division multiplex transmission to increase the maximum distance of transmission. Here, 16 channels with a channel spacing of 200 GHz are modulated by an optical LiNbO3 phase modulator with non-return-to-zero format and transmitted over 1,050 km by using dispersion-compensated fibers with an effective core area of 30 pm2 and erbium-doped fiber amplifiers. The adequate quality factor and output power of different channels are observed at 70 km, 350 km, and 1,050 km. As the distance is increased, the quality factor falls.

Simulation investigation on supercontinuum generation and noise characteristics in the normal dispersion photonic crystal fiber with a flattened dispersion profile

The propagation of picosecond pulses in the normal dispersion photonic crystal fiber (PCF) with a flattened dispersion profile is numerically investigated. The characteristics of the amplitude and phase noise in the supercontinuum generation (SCG) are also analyzed through the coherent sliced supercontinuum (SC). The effects of self-phase modulation (SPM) and four-wave mixing (FWM) on broadening of the pulse spectrum are presented, and the best amplitude and phase noise performance with a specific fiber length is obtained. The SCG in the wavelength range of 1475 to 1625 nm has only fluctuation between ±1.5 dB, and both the amplitude and phase noise caused by the intensity noise of the input power is below 2.5% in the range of 1500 to 1600 nm.

Enhancement of chaotic carrier bandwidth in a semiconductor laser transmitter using self-phase modulation in an optical fiber external round cavity

A novel method to enhance the bandwidth of a chaotic carrier from a delayed feedback semiconductor laser transmitter is presented using self-phase modulation (SPM) in an optical fiber external round cavity. A physical model of the laser dynamics is established under the condition of optical feedback light with the SPM effect in the fiber path. A formula for frequency detuning of the optical dual-feedback under SPM is theoretically deduced. The results show that the nonlinear phase shift caused by SPM has an impact on the gain and bandwidth enhancement factor of the laser. The second-order nonlinear effect of the fiber enriches the variety of the amplitudes and phases of the laser while the nonlinear phase shift produces a number of new frequencies, which can spread the bandwidth. Numerical results reveal that with the SPM effect, the bandwidth can be enhanced 4 times more than the bandwidth without it, and the relaxation oscillation frequency of the chaotic laser is increased to 2.56 times more than that of the laser without the fiber path. The enhancement of the chaotic bandwidth can be extended by increasing the optical fiber length, the coupling-feedback ratio, the mirror reflectance and the second order nonlinear coefficient affect.

SPM Response of a Distributed coupling coefficient DFB-SOA All-Optical Flip-Flop

Deriving a dynamic model based on the coupled-mode and carrier rate equations, the effects of coupling coefficient and corrugation position on all-optical flip-flops (AOFF) we have analyzed in this paper. Also the self phase modulation (SPM) in the distributed coupling coefficient distributed feedback semiconductor optical amplifier (DCCDFB-SOA) has been implemented. Then the effects of SPM on the rise and fall times of the flip-flop DFB-SOA are investigated. It has been shown that the application of the optimized coupling coefficient and corrugation position improves the speed limitation in AOFF significantly. The transfer matrix method (TMM) time domain is utilized for the numerical simulations.

Soliton-like dispersion-free optical transmission based on optical time-domain fractional Fourier transform

In the present article, implementation of the optical time-domain fractional Fourier transform (FRFT) is achieved and a new method for soliton-like dispersion-free optical transmission is proposed. With this method, the pulses’ envelope will keep unchanged and non-broadened after transmission under the combined effects of chromatic dispersion and self-phase modulation in the fiber link without any dispersion compensation. Numerical analysis shows how a pulse evolves for different orders of FRFT.

Impact of the second order dispersion on compensation of SPM in an adaptive pulse pre-shaping quasi-CPA system

A model of quasi-CPA (chirped pulse amplification) system, in which the input is the transform-limited Gaussian pulses, is set up numerically to investigate the impact of the second order dispersion on the adaptive compensation of self-phase modulation (SPM) effect. The adaptive phase pre-shaping controlled by differential evolution algorithm is introduced to the input pulse before amplification and recompression. With maximizing the peak power of the output pulse, the simulation results show that the normal dispersion is really helpful to eliminate the side lobes of the output pulse and increase the pulse peak power.

Simple approach to picosecond pulse generation based on semiconductor optical amplifier

A simple optical pulse generator based on a semiconductor optical amplifier (SOA) is demonstrated with an easy-generated external optical pulse sequence. Using the cross-gain modulation and self-phase modulation effects inside an SOA, the simple optical pulse generator generates a 10 GHz 3.8 ps optical pulse train with an extremely low timing jitter of 60 fs.

Self-phase modulation effects and pulse propagation in gain-guided fibers

We present a theoretical analysis of pulse propagation and self-focusing in a gain-guided (GG) fiber amplifier. A weak pulse is launched in the GG fiber when the input pulse reaches a critical power the pulse begins to collapse in the transverse direction. By using different input powers the transmission characteristics are changed. We add coupling to a single-mode fiber at the output end and study pulse dispersion and energy.

Darboux Transformation and Soliton Solutions for Inhomogeneous Coupled Nonlinear Schrödinger Equations with Symbolic Computation

With the aid of computation, we consider the variable-coefficient coupled nonlinear Schrödinger equations with the effects of group-velocity dispersion, self-phase modulation and cross-phase modulation, which have potential applications in the long-distance communication of two-pulse propagation in inhomogeneous optical fibers. Based on the obtained nonisospectral linear eigenvalue problems (i.e. Lax pair), we construct the Darboux transformation for such a model to derive the optical soliton solutions. In addition, through the one- and two-soliton-like solutions, we graphically discuss the features of picosecond solitons in inhomogeneous optical fibers.

Variation of harmonic spectra in laser-produced plasmas at variable phase of femtosecond laser pulses of different bandwidth

The intensity enhancement of harmonics and change in harmonic profiles have been observed in a few plasma plumes (La, In, Mn) under variable phase modulation of Ti:sapphire laser pulses. It is seen that variation of relative harmonic intensities in the plateau region could be achieved by chirp variation of narrowband (~10 nm bandwidth) radiation. The effect of the self-phase modulation (SPM) of broadband (~20 nm bandwidth) laser radiation on the harmonic emission from nanoparticles, C60, and Ag plasma while passing through a glass slab is also studied. The observation of broadband harmonic emission and redshift in harmonic wavelengths for an unchirped laser pulse are explained in terms of SPM. The observation of blueshift of harmonic radiation with both positively and negatively chirped pulses was attributed to the different effects of SPM on the chirped pulses.

Effect of self-phase-modulation on dispersion compensated absolute polar duty cycle division multiplexing transmission

The effect of self-phase modulation (SPM) on 40 Gb/s absolute polar duty cycle division multiplexing (AP-DCDM) is investigated and reported. The study includes the influence of launched power, number of channels and dispersion compensation method. Dispersion post-compensation and combination of dispersion pre- and post-compensation are used to manage the transmission links. At high powers, SPM degrades the pulse recompression process and provides an upper bound on the AP-DCDM transmitted pulse energy. It is demonstrated that the 40 Gb/s AP-DCDM system shows a 4.1 dB improvement and less than 1 dB penalty in terms of SPM tolerance in comparison to 40 Gb/s 4-ary and on off-keying (OOK) systems, respectively. The SPM effect is stronger in the 100 post-compensated link than that in the combination of pre- and post-compensated links. Dispersion pre-compensation of 18 22 is found as the optimum range of pre-compensation ratio for AP-DCDM system, which makes optimisation of the launched power possible.

Effect of wakefields on the propagation of a short laser pulse in a plasma channel

The effect of electric wakefields (generated inside the pulse) on the propagation of a short, asymmetric laser pulse in a plasma channel is analyzed. A nonlinear wave equation governing the propagation dynamics of a moderately intense laser pulse in a plasma channel along with equations describing the generation of wakefields is set up. The simultaneous evolution describing the pulse length and spot size in the presence of wakefields is derived using a variational technique. Using numerical methods the evolution of spot size, pulse length and intensity is graphically analyzed. The frequency chirp induced due to the combined effects of group velocity dispersion and self-phase modulation is also obtained. A comparative study of the propagation characteristics of two pulses, one having a fast rise and slow fall time while the other with a slow rise and fast fall time, has been presented.

Fine structure in spatial self-phase modulation patterns: at a glance determination of the sign of optical nonlinearity in highly nonlinear films

We present a fast and simple method to determine the sign of the nonlinear coefficient n2 in films with high nonlinearity. The method exploits the effect of spatial self-phase modulation and the role of wavefront curvature that leads to a specific far field pattern that is dependent on the sign of n2 and on the sample position. The method can be considered a 'visualization' of the Z-scan for highly nonlinear films. Application to nematic liquid crystals under different experimental conditions confirms the results expected from the theory.

Compensation of Gain Narrowing by Self-Phase Modulation in High-Energy Ultrafast Fiber Chirped-Pulse Amplifiers

We propose a method to compensate gain narrowing by use of the self-phase modulation effect in a femtosecond fiber chirped-pulse amplifier (CPA). An engineering rule is derived to determine the stretched pulse duration that allows this compensation. Simulations are carried out to validate this idea. A tradeoff is found between achievable pulse duration and output energy, but we show that this technique allows the generation of 100 fs pulses even for high-gain systems, with output energies of the order of 100 ? J. An experimental proof of principle demonstrates the generation of 112 fs, 10 ?J pulses, the shortest high-energy pulse, to our knowledge, generated by a fiber CPA system.

Link Performance Monitoring Technique for Measuring Residual Chromatic Dispersion of Optical Links

We propose a simple technique for measuring the residual chromatic dispersion (CD) of optical links based on two single-sideband tones. The residual CD was measured with an accuracy of +/- 10 ps/nm, regardless of the effect of self-phase modulation.

Influence of the Channel Number on the Optimal Dispersion Map Due to XPM in WDM Links

The influence of the channel number on the optimal dispersion map (ODM) due to cross-phase modulation (XPM) in wavelength division multiplexed links is assessed using an analytical method. The analytical method is validated by comparison with numerical simulation using two different methods: the pump-probe method and a realistic method in which all channels are digitally modulated carriers. It is shown that there are usually, at least, two local ODMs due to XPM: one characterized by negative residual dispersion per span (RDPS) and another characterized by positive RDPS. These two local ODMs due to XPM lead to similar XPM-induced degradation. However, the local ODM with negative RDPS shows always much higher tolerance to the dispersion map (DM) variation. Furthermore, as the ODM due to the combined effect of self-phase modulation and group-velocity dispersion is characterized by negative RDPS when reduced and moderate power levels are used, the use of the local ODM due to XPM with negative RDPS is recommended. This local ODM due to XPM remains approximately the same as long as, at least, 8 channels are transmitted when 100 or 50 GHz channel spacings are used and 12 channels are transmitted when 25 GHz channel spacing is used. However, the high XPM tolerance to the DM variation for 25 GHz channel spacing leads to the conclusion that the ODM for 8 channels is the recommended DM in case of an arbitrary number of channels, independently of the channel spacing. These outcomes are independent of the power level, number and length of spans and transmission fiber type.

Experimental investigation of SPM in long-haul direct-detection OFDM systems

We experimentally investigate the effect of self-phase modulation on direct-detection orthogonal frequency division multiplexed (OFDM) transmission at 11.1 Gb/s over 960km and 1600km uncompensated standard single-mode fiber links. We show that for long-haul systems, the penalties due to nonlinear distortion in OFDM systems are comparable to those in links employing electronic predistortion.

Optical wave breaking of high-intensity femtosecond pulses in silicon optical waveguides

We have investigated numerically the propagation of high-intensity femtosecond optical pulses with pulsewidth of 100 fs (half width at 1/ e maximum) on the silicon-on-insulator (SOI) optical waveguide when the central wavelength of the pulse locates in the normal dispersion region. Results show that the combined effects of group-velocity dispersion (GVD), third-order dispersion (TOD), self-phase modulation (SPM), and free-carrier dispersion (FCD) can lead to the phenomenon of optical wave breaking that manifests as an asymmetric profile and oscillation near the trailing edge of the pulse. Moreover, the optical wave breaking will be experienced from generation to disappearance during propagation.

Mitigation of the effects of self phase modulation and group-velocity dispersion in fiber optic communications: dispersion- and power-map cooptimization using the genetic algorithm

We show that co-optimization of dispersion and power maps in long-haul fiber optic communications can significantly mitigate the effects of group-velocity dispersion (GVD) and self phase modulation (SPM). A genetic algorithm is used for arriving at the optimal (or a near-optimal) link design in reasonable time, since exhaustive search is almost impossible for this intractable problem. Design of a 20-span×80 km/span link that can recover an input Gaussian pulse almost in its original form is presented. This design provides near-optimum values of the required net dispersion, dispersion map, and power map to mitigate the effects of SPM and GVD

Operation properties of a reconfigurable photonic logic gate based on cross phase modulation in highly nonlinear fibers

The operation features of a 160 Gb / s reconfigurable all-optical logic gate based on cross phase modulation in highly nonlinear fibers are numerically investigated for six logic functions (XOR, OR, NAND, NOR, NOT, and AND). High bit rate operation is numerically demonstrated for a wide input signal wavelength range ( > 20 nm ). Performance enhancement of the proposed setup operating at 160 Gb / s for different signal wavelengths is exhibited by using a 2R regenerator based on the self-phase modulation effect in highly nonlinear fibers at the gate's output. The operation of the multi-functional logic gate is investigated considering either a pulsed or a continuous wave probe.