Effect Of Group Velocity Dispersion Research Articles

SMF 길이와 RDPS의 분포 패턴에 따른 왜곡된 WDM 신호의 보상 특성

고품질 초고속 광 신호 전송을 위해서는 그룹 속도 분산과 비선형 현상에 의한 왜곡을 억제하거나 줄여주는 기술이 필요하다. 가장 대표적인 기술로 분산 제어 (DM; dispersion management), 광 위상 공액 기술과 이 둘을 결합한 기술이 있다. 하지만 이러한 기술들에서 현재 사용되고 있는 단일 모드 광섬유의 고정 길이와 중계 구간 당 잉여 분산 (RDPS; residual dispersion per span)의 고정값은 유연한 링크 구성을 제한하고 있다. 본 연구의 목적은 광전송 링크를 구성하는 모든 중계 구간의 SMF 길이와 RDPS의 인위적 분포와 랜덤 분포를 통한 초고속 장거리 광전송 시스템의 유연한 구성 가능성을 살펴보는 것이다. 전송 링크 전체의 평균 RDPS와 입사 전력과 같은 링크 파라미터에 의존하지만 제안한 링크 구조들이 유연한 광전송 시스템 구성에 유용하다는 것을 확인하였다. For transmitting the ultra-high speed optical signals with better performance, the techniques to suppress or mitigate the signal distortion due to group velocity dispersion and optical Kerr effects are required. Dispersion management (DM), optical phase conjugation, and the combination of these two are promising techniques to compensate for the signal distortion. However, the fixed length of single mode fiber (SMF) and the fixed residual dispersion per span (RDPS) usually used in these optical links restricts flexible link configuration. The goal of this paper is to investigate the possibility of the flexible configurations of the ultra-high and long-haul optical transmission systems by using the artificial and the random distribution of SMF length and RDPS of each fiber spans consisted of the optical link. It is confirmed that the proposed link configurations should be one of the methods suitable for implementing the flexible optical transmission systems, however which depend on other link parameters, such as the averaged RDPS, and the launch power.

Influence of group-velocity-dispersion effects on the propagation of femtosecond laser pulses in air at different pressures

The influence of group-velocity-dispersion (GVD) effects on the propagation of femtosecond laser pulses in air at different pressures is investigated by numerically solving the extended nonlinear Schr\"odinger equation. It is observed that GVD has a great influence on the collapse distance ${L}_{\mathrm{c}}$ of the self-focusing short laser pulses when the pressure is relatively high (e.g., 10 atm), in which case the semiempirical formula describing the collapse distance of self-focusing laser pulse [Dawes and Marburger, Phys. Rev. 179, 862 (1969)] is no longer applicable, while GVD has little influence on the self-focusing process of longer laser pulses. Through the results of numerical simulations as well as analytical analysis, we find that the initial duration of the laser pulse is the main factor that determines the GVD effect on the propagation and the increase of the pressure and pulse compression during the propagation enhance this effect. The spectral data show that GVD also influences the spectrum broadening in high-pressure cases.

Dispersion Managed Optical Links with Optical Phase Conjugator Placed at the Various Positions

The needs of ultra-high optical backbone systems are currently increased to transmit the high-quality multimedia services. For transmitting the ultra-high speed optical signals with better performance, the techniques to suppress or mitigate the optical signal distortion due to group velocity dispersion and optical Kerr effects are required. Dispersion management (DM), optical phase conjugation, and the combination of these two are promising techniques to compensate for the signal distortion. The goal of this paper is to investigate the possibility of the flexible configurations of the ultra-high and long-haul optical backbone systems using optical links with the random distribution of residual dispersion per span (RDPS) and optical phase conjugator (OPC) placed at the various positions. We confirm that the proposed link configurations should be one of the methods suitable for implementing the flexible optical backbone systems, also, the possibility is more available to longer backbone.

High Contrast Optical “OR” Logic Gates Using a Photonic Crystal Fiber Modulated by PAM-ASK

In this work, we present a numerical study of an all-optical logical gate based in a symmetric nonlinear directional coupler (NLDC) in Photonic Fiber Crystals (PCFs) PCFs operating with two ultrashort fundamental soliton pulses of 100 fs, modulated by PAM-ASK with binary amplitude modulation to represent the logical level 1 and 0. The performance of a symmetric dual core NLDCPCF to execute two-input logical functions is examined. We evaluate the effect resulting from an increment in the PAM coding parameter offset (ε), considering the anomalous Group Velocity Dispersion (GVD), third-order dispersion (β3) and nonlinear effects Self Phase Modulation (SPM), Self-Steepening (SS), lntrapulse Raman Scattering (IRS) in a lossless configuration. Our results indicate that is possible to get logical operations for the cores 1 or 2 using a phase control to the input pulse in one of the fibers.

Particle swarm optimization in WDM/OCDM networks with physical impairments

In this paper, optimization procedures based on particle swarm optimization (PSO) are investigated, aiming to efficiently solve the optimal resource allocation for signal-to-noise plus interference ratio (SNIR) optimization of optical code paths (OCPs) from wavelength division multiplexing/optical code division multiplexing (WDM/OCDM) considering imperfections on physical layer. The characteristic of the PSO is attractive due their performance-complexity tradeoff and fairness regarding the optimization methods that use numerical methods, matrix inversion and other heuristics. The SNIR model considers multiple access interference (MAI) between the OCP based on 2-D codes (time/wavelength), amplifier spontaneous emission (ASE) at cascaded amplified spans, and group velocity dispersion (GVD) and polarization mode dispersion (PMD) dispersion effects. The numerical results have revealed the viability of the PSO algorithm considering solution quality and convergence. Besides, the numerical results have shown a penalty when the ASE, GVD and PMD effects are considered.

Modeling of Single-Section Quantum Dot Mode-Locked Lasers: Impact of Group Velocity Dispersion and Self Phase Modulation

A short pulse train with pulsewidth was generated in a quantum dot mode-locked laser (QD MLL). Due to the short dispersion length, it is required to include group-velocity dispersion (GVD) in modeling pulse train generation and evolution from QD MLLs. On the other hand, Kerr effect is also required to consider due to high peak power density in the laser cavity, and its induced self-phase modulation (SPM) also contributes to the pulse evolution. In this paper, a time domain traveling wave model, including the effect of GVD and SPM, combined with rate equations, is established to model the pulse evolution in a single-section QD MLL. It is shown that the pulse evolution calculated by this model is in reasonable agreement with the experiments. The contribution to the pulse evolution by the GVD and SPM impact is discussed.

Effect of group-velocity dispersion on the stability of quantum-cascade lasers

As the effect of group-velocity dispersion (GVD) on the stability of midinfrared quantum-cascade lasers (QCLs) has not been explored so far, both amplitude and phase instabilities of QCLs were analyzed in the presence of a background saturable absorber in the lasing medium. The investigation was carried out through the linearization of the Maxwell–Bloch formalism for the lasing medium by including second-order dispersion of group velocity and intensity-dependent loss accounting for the saturable absorber. The effect of the GVD on laser instability was found to be strongly related to the strength of the saturable absorber and pumping. The effect of the GVD is more significant at lower pumping levels and with weaker saturable absorbers.

랜덤하게 분포하는 RDPS의 분산 제어 광전송 링크에서의 시스템 성능 특성

Optical phase conjugation combining with dispersion management (DM) is promising technique to compensate for signal distortion due to group velocity dispersion (GVD) and nonlinear Kerr effects in optical communication systems. However the fixed residual dispersion per span (RDPS) usually used in the optical links with OPC and DM restricts the flexible link configuration. In this paper, OPC links combining DM of the randomly distributed RDPS is proposed for implementing the flexible optical transmission network. It is confirmed that the excellent compensation in the optical links with the randomly distributed RDPS is obtained, limiting the launch power of WDM channels to the relatively low. It is also confirmed that the relatively high launch power WDM channels are effectively transmitted through the optical links with the randomly distributed RDPS of averaged 50 - 100 ps/nm.

Group velocity dispersion and relativistic effects on the wakefield induced by chirped laser pulse in parabolic plasma channel

The excitation of wake field plasma waves by a short laser pulse propagating through a parabolic plasma channel is studied. The laser pulse is assumed to be initially chirped. In this regard, the effects of initial and induced chirp on the plasma wake field as well as the laser pulse parameters are investigated. The group velocity dispersion and nonlinear relativistic effects were taken into account to evaluate the excited wake field in two dimension using source dependent expansion method. Positive, negative, and un-chirped laser pulses were employed in numerical code to evaluate the effectiveness of the initial chirp on 2-D wake field excitation. Numerical results showed that for laser irradiances exceeding 1018W/cm2, an intense laser pulse with initial positive chirp generates larger wake field compared to negatively and un-chirped pulses.

Dispersion Management and Optical Phase Conjugation in Optical Transmission Links with a Randomly Distributed Single-Mode Fiber Length

Suppressing or mitigating signal distortion due to group velocity dispersion and optical Kerr effects is necessary in ultra-high speed and long-haul wavelength division multiplexing (WDM) transmission systems. Dispersion management (DM), optical phase conjugation (OPC), and the combination of these two are promising techniques to compensate for signal distortion. In this paper, to implement a flexible optical WDM network, a new optical link configuration with a randomly distributed single-mode fiber (SMF) length and fixed residual dispersion per span in the combination of DM and OPC is proposed and investigated. The simulation results show that the best net residual dispersion (NRD) in the proposed optical links is +10 ps/nm, which is independent of pre- and postcompensation. The effective launch power of the WDM channel is increased more in the optical links with NRD = +10 ps/nm controlled by only precompensation. Furthermore, the system performance difference between the proposed optical link configuration with the best NRD and the conventional optical link with uniform distribution of the SMF length had little significance. Consequently, it is confirmed that the proposed optical link configuration with the best NRD is effective and useful for implementing a reconfigurable long-haul WDM network.

분산 보상 광섬유의 분산 계수와 중계 구간 당 잉여 분산에 따른 WDM 신호의 보상 특성

단일 모드 광섬유의 그룹 속도 분산과 비선형 효과에 의해 왜곡되는 960 Gbps 파장 분할 다중 신호의 보상을 위해 분산 제어 기술이 적용된 광전송 링크에서 분산 보상 광섬유 (DCF; dispersion compensating fiber)의 분산 계수와 중계 구간 당 잉여 분산량 (RDPS; residual dispersion per span)이 왜곡 보상에 미치는 영향을 분석하였다. 우선 왜곡 보상에 큰 영향을 미치는 최적 전체 잉여 분산량 (NRD; net residual dispersion)은 고려한 모든 DCF의 분산 계수와 RDPS에 관계없이 큰 입사 전력에서 구해야 한다는 것을 확인하였다. 중계 구간의 RDPS는 매우 작게, 반면 DCF의 분산 계수는 크게 하여야 시스템 성능이 현저하게 개선되는 것을 확인하였다. The effects of dispersion coefficient of dispersion compensating fiber (DCF) and residual dispersion per span (RDPS) on in the dispersion managed optical links for compensating the distorted 960 Gbps wavelength division multiplexd (WDM) signals due to group velocity dispersion (GVD) and optical nonlinear effects of single mode fiber (SMF) are investigated. It is confirmed that optimal net residual dispersion (NRD), which greatly affects compensating for optical signals, should be induced under the large launch power condition, irrelevant on the considered dispersion coefficient of DCF and RDPS. It is also confirmed that system performances are greatly improved by selecting the very small RDPS and very large dispersion coefficient of DCF.

Slow light in photonic crystal with combinations of gradient dielectric constant

A line defect waveguide formed by a new kind of two-dimensional photonic crystal with combinations of gradient varied dielectric was designed and the properties of slow light will been studied by using the Plane Wave expansion Method (PWM). The result shows that the group velocity is slower when the corresponding combination of gradient dielectric constants are with higher dielectric constant and lower interval. In our new structure of photonic crystal, the corresponding group velocity can reach as low as 0.06c (c: light velocity in vacuum), two orders magnitude lower than light velocity. Meanwhile, the group velocity dispersion effect is relatively small.

The Generation Mechanism of Airy—Bessel Wave Packets in Free Space

Localized optical Airy—Bessel configuration wave packets were first generated on the basis of a grating-telescope combination [Nat. Photon. 4(2010) 103]. By studying the spatially induced group velocity dispersion effect of ultrashort pulsed Bessel beams during propagation, we find the universal physical foundation of generating Airy—Bessel wave packets (ABWs) in free space. The research results are expected to open up more common channels for generating stable linear localized ABWs.

Optical pulse compression on a silicon chip—Effect of group velocity dispersion and free carriers

The effect of group velocity dispersion and free carrier lifetime on pulse quality and nonlinear phase acquisition is studied in a two-stage pulse compressor on a silicon chip. Appropriately, designing the dispersion in the nonlinear medium enables compressed pulses with more than 90% of the pulse energy confined in the main lobe to be generated. Free carrier lifetime is observed to impact nonlinear phase acquisition in the single pulse regime. The pulse compression factor decreases monotonically as the pulse repetition rate increases. Conditions for efficient compression at high repetition rates in the absence of free carrier quenching techniques are discussed.

중계 구간의 SMF 길이와 RDPS 분포가 일정하지 않은 분산 제어 광전송 링크를 통한 왜곡된 WDM 신호의 보상

분산 제어 (DM; dispersion management)은 파장 분할 다중 (WDM; wavelength division multiplexed) 채널의 고품질 전송을 위해 광섬유의 그룹 속도 분산 (GVD; group velocity dispersion)과 비선형 효과의 상호 작용에 의해 왜곡되는 신호의 보상할 수 있는 대표적 기술이다. DM이 적용된 광전송 링크의 유연한 구성에 필요한 중계 구간 (fiber span)을 구성하는 단일 모드 광섬유 (SMF; single mode fiber)의 길이와 중계 구간 당 잉여 분산 (RDPS; residual dispersion per span)을 랜덤하게 분포시키는 구조와 인위적으로 분포시키는 구조에서의 최적 전체 잉여 분산 (NRD; net residual dispersion)의 최적치와 유효 입사 전력 범위를 도출하였다. 고려한 SMF의 길이와 RDPS 분포 패턴 모두 precompensation으로 NRD를 조절하는 경우에서는 +10 ps/nm, postcompensation으로 NRD를 조절하는 경우에서는 -10 ps/nm이 최적 NRD라는 것을 알 수 있었다. 그리고 NRD가 상기 값으로 설정된 경우 중계 구간이 증가할수록 SMF 길이를 감소시키고, RDPS를 증가시키는 인위적인 분포의 전송 링크에서의 시스템 성능이 가장 양호하여 균일한 분포의 링크에 비해 유효 입사 전력 범위가 2 dB 정도 신장되는 것을 확인하였다. Dispersion management (DM) is the typical technique compensating for the distorted signals due to interaction of group velocity dispersion (GVD) and optical nonlinear effects for transmitting wavelength division multiplexed (WDM) channel with the excellent performance. Optimal net residual dispersion (NRD) and effective launching power range of optical transmission links with random distribution and artificial distribution of single mode fiber (SMF) length and residual dispersion per span (RDPS) required to flexibly design of optical links in DM. It is confirmed that optimal net residual dispersion (NRD) are +10 ps/nm and -10 ps/nm controlled by precompensation and postcompensation, respectively, in both of the considered distribution patterns of SMF length and RDPS. And, in optimal NRD, system performance in optical links with the descending distribution of SMF length and the ascending distribution of RDPS among the artificial distribution patterns are more improved, consequently, effective launching power range is expanded by almost 2 dB than those in optical links with the uniform distribution.

Numerical study on pulse contrast enhancement in a short-pulse-pumped optical parametric amplifier

We investigate pulse cleaning behaviors in short-pulse-pumped optical parametric amplifiers (OPA). We theoretically study the contrast enhancement of amplified signal pulse and generated idler pulse, and reveal their dependence on the parametric gain in both the regimes of small signal and saturated amplifications. The signal contrast enhancement is nearly equal to the parametric gain, while the idler contrast is approximately equal to the product of the contrasts of the pump and signal pulses in a low gain OPA and increases with the gain. The effects of group-velocity mismatch and group-velocity dispersion on the contrast enhancement are also investigated. The results presented in this paper are of value for pulse cleaning.

전송 반 구획에서만 중계 구간 당 분산이 랜덤하게 분포하는 광 링크에서의 WDM 신호의 성능

그룹 속도 분산 (GVD; group velocity dispersion)과 비선형 효과의 상호 작용에 의해 왜곡되는 파장 분할 다중 (WDM; wavelength division multiplexing) 신호를 보상하기 위해 광 위상 공액기 (OPC; optical phase conjugator)와 분사 제어 (DM; dispersion management)가 적용된 광전송 링크에서의 전체 잉여 분산 (NRD; net residual dispersion)의 최적치와 유효 입사 전력 범위를 도출하였다. 실제 광전송 시스템의 융통적 설계를 위해 한 쪽 반 전송 구획에서의 단일 모드 광섬유 (SMF; single mode fiber) 중계 구간(span) 당 잉여 분산 (RDPS; residual dispersion per span)이 랜덤하게 분포하는 광전송 링크를 고려하였다. precompensation으로 전체 분산을 조절하는 링크의 최적 NRD는 10 ps/nm이고 이 경우 유효 입사 전력 범위는 -8~1 dBm인 것을 확인하였다. 또한 postcompensation으로 전체 분산을 조절하는 링크의 최적 NRD는 -10 ps/nm이고, 유효 입사 전력 범위는 -7.5~1 dBm인 것을 확인하였다. Optimal net residual dispersion (NRD) and effective launching power range of optical transmission links with optical phase conjugator (OPC) and dispersion management (DM) for compensating the distorted wavelength division multiplexing (WDM) signals due to interaction of group velocity dispersion (GVD) and optical nonlinear effects. WDM systems considered in this research have optical links with the random distribution of residual dispersion per span (RDPS) in each single mode fiber (SMF) spans of only one half transmission section for designing the adaptive optical transmission system configurations. It is confirmed that optimal NRD is 10 ps/nm and effective launching power range is obtained to be -8~1 dBm under NRD = 10 ps/nm in optical links with total dispersion controlled by precompensation. And, it is also confirmed that optimal NRD is -10 ps/nm and effective launching power range is obtained to be -7.5~1 dBm under NRD = -10 ps/nm in optical links with total dispersion controlled by postcompensation.

Temporal coherence in mirrorless optical parametric oscillators

One of the unique features of mirrorless optical parametric oscillators based on counterpropagating three-wave interactions is the narrow spectral width of the wave generated in the backward direction. In this work, we investigate experimentally and numerically the influence that a strong phase modulation in the pump has on the spectral bandwidths of the parametric waves and on the efficiency of the nonlinear interaction. The effects of group-velocity mismatch and group-velocity dispersion are elucidated. In particular, it is shown that the substantial increase in temporal coherence of the backward-generated wave can be obtained even for pumping with a temporally incoherent pump. A configuration of a mirrorless optical parametric oscillator is proposed where this gain in spectral coherence is maximized without a penalty in conversion efficiency by employing group-velocity matching of the pump and the forward-generated parametric wave.

Common approach for compensation of axial motion artifacts in swept-source OCT and dispersion in Fourier-domain OCT

Swept-source optical coherence tomography (SS-OCT) is sensitive to sample motion during the wavelength sweep, which leads to image blurring and image artifacts. In line-field and full-field SS-OCT parallelization is achieved by using a line or area detector, respectively. Thus, approximately 1000 lines or images at different wavenumbers are acquired. The sweep duration is identically with the acquisition time of a complete B-scan or volume, rendering parallel SS-OCT more sensitive to motion artifacts than scanning OCT. The effect of axial motion on the measured spectra is similar to the effect of non-balanced group velocity dispersion (GVD) in the interferometer arms. It causes the apparent optical path lengths in the sample arm to vary with the wavenumber. Here we propose the cross-correlation of sub-bandwidth reconstructions (CCSBR) as a new algorithm that is capable of detecting and correcting the artifacts induced by axial motion in line-field or full-field SS-OCT as well as GVD mismatch in any Fourier-domain OCT (FD-OCT) setup. By cross-correlating images which were reconstructed from a limited spectral range of the interference signal, a phase error is determined which is used to correct the spectral modulation prior to the calculation of the A-scans. Performance of the algorithm is demonstrated on in vivo full-field SS-OCT images of skin and scanning FD-OCT of skin and retina.

Analysis of the nonlinear optical switching in a Sagnac interferometer with non-instantaneous Kerr effect

In this work we present a study of the performance of nonlinear switching in a Sagnac interferometer under the action of a relaxed Kerr nonlinearity, using ultrashort optical pulses. Soliton and quasi-soliton pulses have been used as initial conditions. We include the effect of GVD (Group Velocity Dispersion) and consider that losses are negligible. The transmission, compression factor (C) and extinction ratio [XRatio (tr)] curves versus input energy were analyzed for two lengths of the loop (1Z 0 and 2Z 0) of the Sagnac interferometer, where Z 0 is one soliton period. It was verified that an increase of the response time (τ) of the relaxed Kerr nonlinearity leads to a degradation of the nonlinear switching, transmission, compression factor and extinction ratio curves. For instance, in the quasi-soliton propagation regime with loop of length 1Z 0 and input energy 1.83 pJ, the extinction ratio (XRatio (tr)) decreases from + 8.13 dB, at the instantaneous nonlinear medium, to − 0.83 dB, − 2.50 dB, − 5.95 dB, − 8.63 dB, − 10.11 dB and − 12.10 dB, at the relaxed medium with τ = 1 ps, τ = 2 ps, τ = 5 ps, for τ = 10 ps, τ = 15 ps and τ = 30 ps, respectively. In the soliton propagation regime with loop of length 2Z 0 and time duration of 10 ps, for the input pulse (pump power of 0.34 W), one can observe that for the non-instantaneous nonlinear medium, as τ increases, the transmitted output pulses are delayed to longer times (21.49 ps, 23.9 ps and 25 ps) and the pulse envelope starts presenting broadening effects (14.7 ps and 29 ps) for τ = 2 ps and 5 ps, respectively. In our analysis, for the Sagnac interferometer with ring of length 2 Zo = 5.06 km, the chirp distribution has revealed that the spectral profile of the output pulses are smoother for the non-instantaneous medium with τ = 2 ps and 5 ps. In this sense, these two last situations are more suitable for switching applications in WDM systems. These studies are crucial for the analysis of the behavior of the Sagnac interferometers based in non-instantaneous Kerr response fibers, applied in telecommunication systems, in optical signal processing, optoelectronics instrumentation and in several related fields.