Amplitude-equalized dual-wavelength rational harmonic mode-locked fiber ring laser

We report a dual-wavelength amplitude-equalized rational harmonic mode-locked fiber laser operating at up to 40 GHz based on the technique of nonlinear polarization rotation (NPR) in a highly nonlinear fiber. A theoretical simulation shows that NPR structure can introduce a self-feedback mechanism to stabilize the two simultaneously lasing wavelengths. By carefully adjusting the polarization controllers (PCs) in the cavity, amplitude-equalized pulses at two different wavelengths have been obtained.     

Ultrahigh-repetition-rate bound-soliton harmonic passive mode-locked fiber lasers

On the basis of numerical simulation results, we put forward a way to realize harmonic passive mode locking of fiber lasers with an ultrahigh-repetition-rate pulse train. The equidistant distribution of ultrashort pulses filling the total laser cavity is due to bound-soliton mechanisms. In the case of large bound energy, such long soliton trains are very stable and have the ideal periodic structure as a soliton crystal.     

On the generation of high-quality Nyquist pulses in mode-locked fiber lasers

Nyquist pulses have wide applications in many areas, from electronics to optics. Mode-locked lasers are ideal platforms to generate such pulses. However, how to generate high-quality Nyquist pulses in mode-locked lasers remains elusive.We address this problem by managing different physical effects in mode-locked fiber lasers through extensive numerical simulations. We find that net dispersion, linear loss, gain and filter shaping can affect the quality of Nyquist pulses significantly. We also de...     

Pulse-amplitude-equalized output from a rational harmonic mode-locked fiber laser

We report, for the first time to our knowledge, the demonstration of amplitude equalization of high-repetition-rate pulses generated from a rational harmonic mode-locked Er-doped fiber laser. The output pulses are injected into another fiber laser with a nonlinear optical loop mirror. This scheme provides pulse-amplitude equalization up to the ninth rational harmonic mode-locked pulse train.     

Generation of picosecond optical phase conjugate pulses using cw mode-locked lasers

Low power picosecond optical phase conjugation has been demonstrated using cw mode-locked argon-ion and dye lasers via 4-wave mixing in ruby. Streak camera and power measurements show that the generated pulses are identical to the input pulses.     

皮秒光纤激光脉冲两个关键问题的研究

窄带耗散孤子锁模光纤激光器可以产生接近变换限制的皮秒脉冲,但受非线性相移的限制,输出脉冲重复频率不能通过增加腔长来降低,脉冲能量仅在0.1 nJ以下,严重制约着这类皮秒脉冲的实际应用。提出一种通过耦合器抽取腔内脉冲能量、抑制腔内非线性相移积累,进而允许增加腔长来降低窄带耗散孤子皮秒光纤激光脉冲重复频率的方法。运用该方法,成功地将激光器重复频率由35.2 MHz降低到了1.77 MHz,且脉冲时频特性保持不变。提出了一种基于级间FBG陷波滤波的抑制皮秒脉冲光纤放大中光谱展宽的方法。通过简单地使用级间陷波滤波器,既可窄化第一级光纤放大器后的输出脉冲谱宽,允许采用第二级光纤放大器进一步提升脉冲能量,而且,还可将脉冲重塑为近高斯形,利用高斯脉冲光谱展宽斜率小的特点,允许第二级光纤放大器将脉冲能量提升得更高。利用该方法,在RMS（均方值）谱宽保持0.4 nm以内的前提下,10 ps脉冲经标准单模光纤放大器后,能量可由0.2 nJ可提升到10 nJ以上。     

Numerical study of a harmonic mode-locked semiconductor optical amplifier fiber ring laser

An improved harmonic mode-locked Semiconductor optical amplifier (SOA) fiber ring lasers has been presented and numerically investigated based on the self-reproduction theory. The numerical result shows that a narrower optical pulse train with a more symmetrical-temporal shape can be obtained, when the modulation SOA is DC biased on high current, whereas the gain SOA is DC biased on the low current functions as a gain compensator in the experimental setup. Also, the system parameters effects on the characteristic of the harmonic mode-locked pulse have been investigated.     

Multi-soliton complexes in mode-locked fiber lasers

We numerically investigate the formation of soliton pairs (bound states) in mode-locked fiber ring lasers in the normal dispersion domain. In the distributed mathematical model (complex cubic-quintic Ginzburg–Landau equation), we observe a discrete family of soliton pairs with equidistantly increasing peak separation. We show that stabilization of previously unstable bound states can be achieved when the finite relaxation time of the saturable absorber is taken into account. The domain of stability can be controlled by varying this relaxation time. Furthermore, we investigate the parameter domain where the region of stable bound states does not shrink to zero for vanishing absorber recovery time corresponding to a laser with an instantaneous saturable absorber. For a certain domain of the small-signal gain, we obtain a robust first level bound state with almost constant separation where the phase of the two pulses evolves independently. Moreover, their phase difference can evolve either periodically or chaotically depending on the small signal gain. Interestingly, higher level bound states exhibit a fundamentally different dynamics. They represent oscillating solutions with a phase difference alternating between zero and π.     

Generation of bound solitons in actively phase modulation mode-locked fiber ring resonators

Bound solitons generated in actively mode-locked lasers enable new forms of pulse pairs and multiple pairs or groups of solitons in optical transmission or logics. In this paper, we present the generation of stable bound states of multiple solitons in an active mode-locked fiber laser using continuous phase modulation for wideband phase matching. Not only that dual-soliton bound states but also the triple- and quadruple-soliton pulses can be established. Simulation of the generated solitons are demonstrated. We have also prove by simulation that experimental relative phase difference and chirping caused by phase modulation of LiNbO₃ modulator in the fiber loop significantly influences the interaction between the solitons and hence their stability as they circulate in the anomalous path-averaged dispersion fiber loop.     

Long-cavity passively mode-locked fiber ring laser with high-energy rectangular-shape pulses in anomalous dispersion regime

We report on a long-cavity passively mode-locked fiber laser in the anomalous dispersion regime. The nonlinear polarization rotation technique is employed to achieve mode locking. The output pulse from the fiber laser has a rectangular shape and a corresponding gaussian-shape spectral profile. Stable mode-locked pulses at a repetition rate of 278 kHz with single pulse energy as high as 715 nJ are obtained under equal bidirectional pumping power of 500 mW in cavity. The experimental results demonstrate that the passively mode-locked fiber laser operating in the anomalous regime can also realize a high-energy pulse, which is different from the conventional low-energy soliton pulse.     

Dual-frequency pulses in fiber lasers

We analyze pulse propagation in a soliton fiber laser, modelled by the complex Schrödinger-Ginzburg-Landau equation. It is shown that this equation admits two previously unknown forms of stable stationary solutions. The first of them is a dual-frequency pulse, which propagates as a single unit, but has two symmetric peaks in the spectrum. The second one is a moving pulse, with the asymmetric double-hump spectrum.     

Generation of dual-wavelength domain-wall rectangular-shape pulses in HNLF-based fiber ring laser

The generation of dual-wavelength domain-wall rectangular-shape pulses in a highly nonlinear fiber (HNLF)-based fiber ring laser is experimentally demonstrated. The dual-wavelength lasing operation is realized by employing the intracavity birefringence-induced spectral filtering effect. An 85 m long HNLF is introduced into the fiber ring laser to enhance the nonlinear effect, which is favorable for the cross coupling between the two lasing beams. Experimentally, it was found that the interval of two domain walls in the time domain could be adjusted by simply tuning the linear cavity phase delay, which results in the achievement of different output pulse shapes. By properly rotating the polarization controller (PC), the dual-wavelength rectangular-shape pulses could be efficiently obtained. The proposed fiber laser provides a simple and efficient way to generate rectangular-shape pulse.     

Multiple pulses with broadband spectrum generation in passively mode-locked fiber ring laser incorporating a highly nonlinear fiber

Multiple pulses with broadband spectrum generation are experimentally obtained in passively mode-locked erbium-doped fiber ring lasers based on nonlinear polarization rotation, which is achieved by incorporating a length of highly nonlinear dispersion-shifted fiber in the laser cavity. The temporal and spectral dynamic behaviors of multipulse bunching states are demonstrated. The maximum spectral width and flatness are attained when the continuous-wave component is suppressed under appropriate polarization states and pump powers.     

Bound soliton pulses in passively mode-locked fiber laser

A passively mode-locked soliton fiber ring laser was successfully demonstrated, and bound soliton pulses with an FWHM pulsewidth of 326 fs and fixed separation of 938 fs were first observed. The number of bound soliton pairs in the cavity can be controlled under lower pump power. The transmission effects were investigated by injecting bound soliton pulses into a single mode fiber.     

Eighth-order rational harmonic mode-locked fiber laser with amplitude-equalized output operating at 80 Gbits/s

We report the generation of an 80 Gbit/s pulse train by an eighth-order rational harmonic mode-locking technique. Equalized pulse-train amplitude is achieved by proper adjustment of the dc bias point and the 10 GHz modulation strength applied to the cavity-loss modulator. A numerical model is developed to simulate the properties of the generated 80 Gbit/s pulse train. The simulated results are well supported by the experimental measurements.     

Chirped and chirp-free femtosecond pulses in passively mode-locked dye lasers

Femtosecond light pulse generation in a ring laser and its propagation properties are described. The basic principles and some theoretical aspects of the pulse generation process in dye lasers are summarized taking into account the influence of the amplifier, of the saturable absorber, of the glass path and of mirrors. Phase modulation arising from multilayer dielectric mirrors has been calculated and measured by determination of an equivalent intracavity glass path length. The main source of phase modulation (chirp) seems to be the saturable absorber.     

Generation of 10-GHz ultra-short pulses with low time jitter in an actively mode-locked fiber laser

We have experimentally achieved the 8.3-ps ultra-short pulse at 10 GHz repetition rate with the time jitter as low as 590 fs in an actively mode-locked fiber ring laser. The ring-cavity laser is mode-locked by a semiconductor optical amplifier based on cross-gain modulation. The external CW source is modulated with radio frequency signal by an amplitude modulator as the external optical pulses and, then, injected into the fiber ring cavity to achieve active mode locking. Further investigating the laser output characteristics, it indicates that the linewidth of employed CW source affects properties of the generated ultra-short pulse, such as phase noise and time jitter. Ultra-short pulse at high repetition rate with low time jitter can be generated by the optimization of CW laser source.     

被动锁模光纤激光器多孤子脉冲形成机理

基于非线性耦合薛定谔方程,在非线性偏振技术锁模的掺铒环形光纤激光器中,理论研究多孤子脉冲的形成和演化规律。研究结果表明:随着小信号增益不断增加,光纤激光器的锁模透过率函数影响多脉冲输出,多脉冲产生受色散波和脉冲分裂形成的峰值功率的限制效应和孤子能量量子化的影响,这是增益竞争和非线性偏振旋转引起的损耗之间动态平衡的最终结果。     

被动锁模光纤激光器多孤子脉冲形成机理

基于非线性耦合薛定谔方程,在非线性偏振技术锁模的掺铒环形光纤激光器中,理论研究多孤子脉冲的形成和演化规律。研究结果表明：随着小信号增益不断增加,光纤激光器的锁模透过率函数影响多脉冲输出,多脉冲产生受色散波和脉冲分裂形成的峰值功率的限制效应和孤子能量量子化的影响,这是增益竞争和非线性偏振旋转引起的损耗之间动态平衡的最终结果。     

Comments on “mode-locked pulses of homogeneous gain lasers”

Radmore's criticism of a paper by Piché and Bélanger concerned with the mode-locked pulses emitted by a loss modulated homogeneous gain laser is shown to be misleading.