Toward passive mode locking by nonlinear polarization evolution in a cascaded Raman fiber ring laser

We demonstrate a cascaded Raman fiber ring laser delivering a pulsed fourth-order Stokes component. Periodic emission of subnanosecond pulses is achieved from the interplay between nonlinear polarization evolution and Raman cascade process.     

Passive mode-locking of the Yb:CNGG laser

Passive mode-locking using a SESAM is demonstrated for the Yb-doped cubic non-stoichiometric crystal CNGG which exhibits local disorder. The pulse duration of 73 fs obtained is the shortest for an isotropic Yb-doped laser crystal while larger output coupling resulted in average output powers of 750 mW with 66% efficiency in the mode-locked regime.     

Mode-locked fiber laser based on an attenuation-imbalanced nonlinear optical loop mirror

We propose a mode-locked figure-eight fiber laser by utilizing an attenuation-imbalanced nonlinear optical loop mirror (AI-NOLM) for the first time. Stable self-starting passively mode-locked pulses as short as 296 fs are obtained. We have also confirmed that the pulse width of the laser can be varied by changing the amount of attenuation in the AI-NOLM.     

Dynamic sideband generation in soliton fiber lasers

We show numerically that when a soliton circulating in the laser cavity experiences dynamical bifurcations, extra sets of sidebands appear in the soliton spectrum. The new sidebands have clearly different characteristics to those of the conventional soliton sidebands, indicating that there exists a new mechanism of sideband generation in the lasers.     

4-W and 23-ps pulses from a lamp-pumped Nd:YAG laser passively mode-locked by polarization switching in a KTP crystal

Passive mode-locking of a cw lamp-pumped Nd:YAG laser using nonlinear polarization switching in a type-II SHG crystal is reported. Light pulses with more than 5 W of average power and pulse duration shorter than 25 ps have been obtained at 1064 nm. Received: 29 January 1999 / Revised version: 24 March 1999 / Published online: 1 July 1999     

Exponential recovery of low frequency fluctuations in a diode laser with optical feedback

We show that the recovery after each power drop on the chaotic low frequency fluctuations in a semiconductor laser with optical feedback follows an exponential envelope. The time constant for such exponential behavior was experimentally measured. This recovery time constant and the average time interval between consecutive drops have different dependences when measured as function of the pump current.     

Coexistence of single-mode and multi-longitudinal mode emission in the ring laser model

A homogeneously broadened unidirectional ring laser can emit in several longitudinal modes for large enough pump and cavity length because of Rabi splitting induced gain. This is the so called Risken-Nummedal-Graham-Haken (RNGH) instability. We investigate numerically the properties of the multi-mode solution. We show that this solution can coexist with the single-mode one, and its stability domain can extend to pump values smaller than the critical pump of the RNGH instability. Moreover, we show that the multi-mode solution for large pump values is affected by two different instabilities: a pitchfork bifurcation, which preserves phase-locking, and a Hopf bifurcation, which destroys it.     

Control of basins of attraction in a multistable fiber laser

We study how the basins of attraction of coexisting states can be controlled by either harmonic modulation or small noise applied to the pump parameter in a multistable erbium-doped fiber laser. The results of numerical simulations using the three-level laser model display good agreement with previously reported experimental studies on attractor annihilation by periodic modulation. In the laser with stochastic modulation, the attraction basins' volumes have a noise-dependent probabilistic character displaying some resonances for each of the coexisting attractors.     

Passively harmonic mode-locked erbium-doped fiber soliton laser with a nonlinear polarization rotation

Based on the nonlinear polarization rotation technique, we report on a stable passive 23rd harmonic mode-locked erbium-doped fiber soliton laser for the first time to the best of our knowledge. In this laser, 23 solitons are uniformly distributed in the cavity simultaneously, and all solitons have the same energy and duration. The increase of the coupler output enhances the dispersive radiation, and the longer cavity strengthens the interaction between solitons and dispersive waves. The two above factors play the key function to generate the 23rd harmonic mode-locked operation.     

SOA-based actively mode-locked fiber ring laser by forward injecting an external pulse train

An actively mode-locked fiber ring laser based on cross-gain modulation (XGM) in a semiconductor optical amplifier (SOA) is demonstrated to operate stably with a simple configuration. By forward injecting an easily-generated external pulse train, the mode-locked fiber laser can generate an optical-pulse sequence with pulsewidth about 6 ps and average output power about 7.9 mW. The output pulses show an ultra-low RMS jitter about 70.7 fs measured by a RF spectrum analyzer. The use of the proposed forward-injection configuration can realize the repetition-rate tunability from 1 to 15 GHz for the generated optical-pulse sequences. By employing a wavelength-tunable optical band-pass filter in the laser cavity, the operation wavelength of the designed SOA-based actively mode-locked fiber laser can be tuned continuously in a wide span between 1528 and 1565 nm. The parameters of external-injection optical pulses are studied experimentally to optimize the mode-locked fiber laser.     

Rapid infrared wavelength access with a picosecond PPLN OPO synchronously pumped by a mode-locked diode laser

We theoretically and experimentally investigate wavelength tuning of synchronously pumped optical parametric oscillators (OPOs) on changing the cavity length or the pump-repetition rate. Conditions for rapid and wide-range wavelength access are derived. Using an OPO pumped directly by a mode-locked diode-laser master-oscillator power-amplifier (MOPA) system, an all-electronically controlled access to near- and mid-infrared wavelengths is demonstrated. The singly (signal) resonant OPO is based on periodically poled lithium niobate (PPLN) and emits 8 ps idler pulses at a repetition rate of 2.5 GHz in the wavelength range 1986 to 2348 nm (signal: 1530 to 1737 nm). Wavelength tuning over 114 nm (signal) and 189 nm (idler) is achieved solely by electronically varying the repetition rate of the diode-laser oscillator over 720 kHz. By controlling the repetition rate with a programmable driver, an arbitrary emission sequence of the OPO on two wavelength channels is generated, with access times as short as 10 μs. 11 OPO wavelengths equally spaced in the range 1627–1689 nm (signal) or 2054–2154 nm (idler) could be addressed. Received: 6 September 2000 / Revised version: 16 March 2001 / Published online: 23 May 2001     

Passive mode locking with slow saturable absorbers

We give a comprehensive overview on passive mode locking of solid-state lasers with slow saturable absorbers, based on analytical and numerical calculations. For picosecond lasers, we present a simple equation to estimate the obtained pulse duration and compare the results to those for mode locking with fast saturable absorbers. We also discuss how much shorter the pulse duration can be compared to the absorber recovery time and present a simple rule. The effect of self-phase modulation is found to be qualitatively different compared to the case of a fast saturable absorber, and the effect of phase changes in the absorber is also discussed. Finally, we discuss various issues concerning soliton mode-locked lasers. Received: 20 July 2001 / Revised version: 28 September 2001 / Published online: 7 November 2001     

Q-switched mode-locking in an erbium-doped femtosecond fiber laser based on nonlinear polarization rotation

An erbium-doped fiber laser based on nonlinear polarization rotation (NPR) and negative group velocity dispersion (GVD) is built up. Two different Q-switched mode-locked (QML) operation states which can be distinguished by the properties in time and frequency domains are demonstrated. Besides the QML, stable continuous-wave mode-locked pulses centered at 1560 nm wavelength with pulse-width of 670 fs, harmonic mode-locking, Q-switching, and pulse splitting have been observed, respectively.     

Passively Q-switched mode-locking Erbium-doped fiber laser with net-normal dispersion using nonlinear polarization rotation technique

We experimentally demonstrate a passively Q-switched mode-locking (QML) operation in an Erbium-doped fiber ring laser with net normal dispersion by using nonlinear polarization rotation technique. A 2 m long section of dispersion compensating fiber (DCF) with extra large positive dispersion was inserted into the cavity to ensure the fiber laser working in the region of net positive dispersion. By carefully adjusting the polarization controller, both uniform dissipative mode-locking pulses with fundamental repetition rate and QML pulse trains with tunable repetition rate from 71.58 to 98.83 kHz are achieved. It is found that the QML operation is caused by the interaction between the polarization state of the pulse and the intracavity polarizer.     

Comparison of laser models via laser dynamics: The example of the Nd:YVO4 laser

Several models for the Nd³⁺:YVO₄ laser are compared in terms of their performance to describe the turn on transients of the laser. A blind search comparison performed using a genetic algorithm shows that the longitudinal hole burning effect must be included while Auger effect may be neglected.     

Broadly tunable femtosecond solid-state laser sources

The techniques of coupled-cavity modelocking and self-modelocking in which intensity-induced nonlinear effects are exploited have been reviewed for broad-band gain media. Particular emphases have been placed upon the archetypical colour-centre and titanium-sapphire laser configurations in which these techniques were first demonstrated and subsequent refinements are set in context. A femtosecond optical parametric oscillator pumped by a self-mode-locked titanium-sapphire laser has also been described as an exemplar of a practical means of extending the source tunability into the mid-infrared spectral region.     

Dynamics of helical-wave emission in a fiber-coupled diode end-pumped solid-state laser

We have generated TEM_0,l ^* modes in an end-pumped microchip laser using a standard fiber-coupled diode. A rich set of dynamic behaviors, such as periodic and quasi-periodic self-modulation, chaotic pulsing and frequency locking was observed in the generated TEM_0,l ^* modes. Experimental results confirm the theoretical predictions that the locking occurs as a subcritical bifurcation and that a region of coexisting locked and unlocked states exists. Received: 14 November 2000 / Revised version: 22 January 2001 / Published online: 23 May 2001     

Self-Q-switching and mode-locking in an all-fiber Er/Yb co-doped fiber ring laser

Using a section of un-pumped Er/Yb co-doped fiber (EYDF) as a saturable absorber, Self-Q-switching and self-mode-locking pulses have been obtained in an all-fiber EYDF ring laser. Such laser is with the self-Q-switched pulse threshold of 135.22 mW, the repetition rate of approximately 22.2 kHz, and the pulse duration of ∼2.8 μs, respectively. The self-mode-locked threshold is 591.8 mW. By incorporating the saturable absorption in an un-pumped EYDF and a Mach-Zehnder interferometer, when the pump power is increased to 1242.9 mW, the continuous-wave (CW) mode-locking with the pulse width of 26 ns has also been demonstrated experimentally for the first time.     

A tunable nonlinear optical loop mirror with feedback using linear highly birefringent fiber in the loop

The dynamics of a nonlinear optical loop mirror (NOLM) with feedback using a high birefringence fiber in the loop are investigated. The effect of rotating input polarization angle on the output power and polarization angle is numerically examined, illustrating the sensitivity of the NOLM with feedback to the input’s polarization state, as well as the polarization chaos present with sufficient input powers. The inclusion of a polarization-dependant loss in one or both arms of the coupler is also shown to change the output dynamical behaviour of the system.     

基于非线性偏振旋转锁模的高功率光子晶体光纤飞秒激光振荡器

为了探索大模场面积光子晶体光纤锁模激光器在全正色散锁模域内的耗散孤子锁模机理, 以获得更大的单脉冲能量和更高的峰值功率, 本文搭建了以掺镱大模场面积光子晶体光纤作为增益介质的耗散孤子锁模激光器. 激光器使用环形腔结构, 利用非线性偏振旋转以及滤光片提供的耗散作用实现了稳定的锁模运转. 实验中, 从激光器振荡级直接获得了平均功率10 W, 重复频率49.09 MHz(对应202 nJ的单脉冲能量), 脉冲宽度为1.03 ps的稳定锁模脉冲输出, 经过腔外色散补偿得到的脉冲宽度为95.5 fs.