Linewidth analysis of 40-GHz passively mode-locked multi-mode semiconductor lasers

An experimental analysis on the quality of 40-GHz radio-frequency signals generated by various passively mode-locked semiconductor lasers is addressed. The analysis is performed considering the frequency linewidth of 40-GHz optically generated signals and the number of longitudinal modes selected by the cavity of each laser under study. Four of these devices are multi-quantum wells InAlGaAs Fabry-Pérot lasers. They have been engineered to exhibit a specific number of longitudinal modes: 4, 5, 10, and 22 modes, respectively. Another device under test is a bulk distributed Bragg reflector laser exhibiting 3 lasing modes. The last device under study is a quantum-dash Fabry-Pérot laser characterized by 40 lasing modes. From our experimental results it appears that, regardless the nature of the device cavity and active media, the strength of the passively mode-locked mechanism might be enhanced with the number of longitudinal modes oscillating into the laser cavity, allowing a reduction in the frequency linewidth.     

Dual-wavelength dissipative soliton operation of an erbium-doped fibre laser using a nonlinear polarization rotation technique

We report on the generation of dual-wavelength dissipative solitons in a passively mode-locked fibre laser with a net normal dispersion using the nonlinear polarization rotation (NPR) technique. Taking the intrinsic advantage of the intracavity birefringence-induced spectral filtering effect in the NPR-based ring laser cavity, the dual-wavelength dissipative solitons are obtained. In addition, the wavelength separation and the lasing location of the dual-wavelength solitons can be flexibly tuned by changing the orientation of the polarization controller.     

Compact,temperature-stable multi-gigahertz passively modelocked semiconductor disk laser

We present a compact passively mode-locked semiconductor disk laser at 1045 nm. The gain chip without any post processing consists of 16 compressively strained In Ga As symmetrical step quantum wells in the active region. 3-GHz repetition rate, 4.9-ps pulse duration, and 30-mW average output power are obtained with 1.4 W of 808-nm incident pump power. The temperature stability of the laser is demonstrated to have an ideal shift rate of 0.035 nm/K of the lasing wavelength.     

Tunable and switchable dual-wavelength passively mode-locked fiber ring laser with high-energy pulses at a sub-100 kHz repetition rate

We demonstrate a tunable and switchable dual-wavelength passively mode-locked fiber ring laser in the anomalous dispersion regime that generates high-energy pulses at a sub-100 kHz repetition rate. The nonlinear polarization rotation (NPR) technique is employed in this configuration to allow for passively mode-locked operation. By exploiting the intensity-dependent loss caused by NPR, the mode competition could be efficiently alleviated. Moreover, taking advantage of the intrinsic spectral filter induced by the intracavity birefringence, the dual-wavelength separations as well as the wavelength lasing locations could be flexibly tuned by properly rotating the polarization controller. With a repetition rate of 85.8 kHz, the laser delivers the single pulse energy of 198 nJ at a pump power of 250 mW. The combination of high per-pulse energy and flexible tunability in this fiber laser is useful for practical applications.     

连续锁模Nd：YVO4激光器实现1 GHz高频输出

LD抽运全固体Nd:YVO4激光器在连续锁模状态运转下获得了高达1 GHz的重复频率.实验中采用半导体可饱和吸收镜作为锁模元件.利用透过率只有0.8%的输出镜以及可获得较小抽运光斑的2 W LD作为抽运源来优化激光器设计,有效地抑制了调Q锁模状态的运转.低的激光器振荡阈值（35 mW）和连续锁模阈值(0.8 W)显示了饱和吸收体低的插入损耗和激光器合理的设计.在最大抽运1.6 W时获得了210 mW的平均输出功率.     

连续锁模Nd∶YVO4激光器实现1 GHz高频输出

LD抽运全固体Nd∶YVO4激光器在连续锁模状态运转下获得了高达1 GHz的重复频率.实验中采用半导体可饱和吸收镜作为锁模元件.利用透过率只有0.8%的输出镜以及可获得较小抽运光斑的2 WLD作为抽运源来优化激光器设计,有效地抑制了调Q锁模状态的运转.低的激光器振荡阈值(35 mW)和连续锁模阈值(0.8 W)显示了饱和吸收体低的插入损耗和激光器合理的设计.在最大抽运1.6 W 时获得了210 mW的平均输出功率.     

Modulation instability induced by cross-phase modulation in a dual-wavelength dispersion-managed soliton fiber ring laser

We report on the observation of the modulation instability induced by cross-phase modulation in a dual-wavelength operation dispersion-managed soliton fiber ring laser with net negative cavity dispersion. The passively mode-locked operation is achieved by using a nonlinear polarization rotation technique. A new type of dual-wavelength operation, where one is femtosecond pulse and the other is picosecond pulse operation, is obtained by properly rotating the polarization controllers. When the dual-wavelength pulses are simultaneously circulating in the laser ring cavity, a series of stable modulation sidebands appears in the picosecond pulse spectrum at longer wavelength with lower peak power due to modulation instability induced by cross-phase modulation between the two lasing wavelengths. Moreover, the intensities and wavelength shifts of the modulation sidebands can be tuned by varying the power of the femtosecond pulse or the lasing central wavelengths of the dual-wavelength pulses. The theoretical analysis of the modulation instability induced by cross-phase modulation in our fiber laser is also presented.     

Diode array pumped, non-linear mirror Q-switched and mode-locked Nd : YVO4 laser — a good tool for powder SHG measurement

A non-linear mirror consisting of a lithium triborate crystal and a dichroic output coupler are used to mode-lock (passively) an Nd : YVO₄ laser, pumped by a diode laser array. The laser can operate both in cw mode-locked and simultaneously Q-switched and mode-locked (QML) regime. The peak power of the laser while operating in QML regime is much higher but pulses suffers from poor amplitude stability. The incorporation of an acousto-optic modulator as an active Q-switch enhances the stability of the QML pulse envelope. The second-order non-linearity of powdered crystalline urea is conclusively measured with respect to KDP while the laser is operating in passively Q-switched and passively mode-locked regime as well as in actively Q-switched and passively mode-locked regime.     

High power passively mode-locked Nd:YVO<Subscript>4</Subscript> laser using graphene oxide as a saturable absorber

We report on a passively mode-locked Nd:YVO₄ laser using a novel graphene oxide saturable absorber fabricated by vertical evaporation method. An 880 nm LD pump source was used to reduce the thermal load of the laser crystal. At the pump power of 7.4 W, 1.2 W average output power of continuous wave mode-locked laser with optical conversion efficiency of 16.2% was achieved. To the best of our knowledge, this is the highest output power of passively mode-locked solid-state laser using graphene oxide saturable absorber. The repetition rate of passively mode-locked pulse was 88 MHz with the pulse energy of 13.6 nJ.     

Stable multiwavelength and passively mode-locked Yb-doped fiber laser based on nonlinear polarization rotation

Based on the nonlinear polarization rotation (NPR) technique and a fiber Mach–Zehnder interferometer (MZI), a fiber laser which can work in two different modes has been demonstrated. In one mode, it works as a continuous wave (CW) multiwavelength laser, and stable dual-, triple- and tetra-wavelength lasing with the wavelength spacing of 1.1 nm are obtained. In the other mode, it works as a passively mode-locked fiber laser, and the generated pulses have a repetition rate of 10.6 MHz, an FWHM width of 800 ps and the largest energy of 1 nJ. The multi-functional property makes this fiber laser a very convenient, cost effective and multi-purpose laser source.     

All-fiber wavelength tunable passively mode-locked erbium-doped ring laser

An all-fiber, wavelength-tunable, passively mode-locked erbium-doped ring laser is presented. Erbium-doped fibers (EDF) are used as the gain media because of their large gain bandwidth. Nonlinear polarization rotation (NPR) plays the dual role of realizing mode-locking and effectively adjusting the intensity-dependent loss of the cavity. An unbalanced Mach-Zehnder interferometer (UMZI) is used as a tunable optical beam filter. By using the UMZI and adjusting the polarization controllers (PCs), a sub-picosecond mode-locking laser is realized that is self-starting with central lasing wavelengths that can be accurately tuned over a range of about ~ \sim 30 nm and also has controllable spacings between different tunable wavelengths.     

Single output LD end-pumped passively mode-locked Nd:YVO4 laser with semiconductor saturable absorber mirror

A quarter-wave plate and the thin film polarizer(TFP) are used for the LD end-pumped passively mode-locked Nd:YVO4 laser with semiconductor saturable absorber mirror(SESAM) to obtain a single beam output with a total power of 4.8 W.An optical-optical efficiency is achieved to be 24% for a stable CW mode-locking operation at 1064 nm,with a pulse repetition rate of 70 MHz and pulse width of 16 ps.The multipulse in the pulse sequence is eliminated for reaching a peak power as high as 4 kW.     

Raman continuum generation at 1.0–1.3 μm in passively mode-locked fiber laser based on nonlinear polarization rotation

We experimentally demonstrate cascaded Raman scattering continuum generation at 1.0–1.3 μm with pulse energy of 47 nJ by utilizing a commercially available all-normal-dispersion single-mode fiber (SMF) with a low threshold pump power. We achieve passively mode-locked all-fiber lasing by nonlinear polarization rotation technique. Continuous Raman gain is obtained by the same SMF in every roundtrip because of the ring-cavity configuration, which makes it possible to achieve high-order Raman Stokes waves by a short fiber length. Limited by the pump power, the maximum output average power and peak power are 87.4 and 339 mW, but it has great potential to be improved. These make it an ideal continuum source for many applications, such as optical coherence tomography.     

Widely tunable passively mode-locked fiber laser with carbon nanotube films

In this paper, we demonstrate a widely tunable passively mode-locked fiber laser covering the C or L band with carbon nanotube films. Our results show that the saturable absorber incorporating nanotubes (SAINT) has potential for constructing widely tunable passively mode-locked fiber laser.     

Environmentally stable ytterbium figure-of-eight fiber laser producing 177-fs pulses

Pulses of 177 fs and 1035 nm, with average power of 1.2 mW, have been generated directly from a passively mode-locked Yb-doped figure-of-eight fiber laser, with a nonlinear optical loop mirror for mode-locking and pairs of diffraction gratings for intracavity dispersion compensation. To our knowledge, these are the shortest pulses ever to come from a passively mode-locked Yb-doped figure-of-eight fiber laser. This represents a 5-fold reduction in pulse duration compared with that of previously reported passively mode-locked Yb-doped figure-of-eight fiber lasers. Stable pulse trains are produced at the fundamental repetition rate of the resonator, 24.0 MHz.     

Passively Q-Switched and mode-locked Nd:YVO<Subscript>4</Subscript> laser with sandwich structured wallpaper graphene oxide absorber

We report on a passively Q-switched and mode-locked Nd:YVO₄ laser using a novel low-cost wall-paper graphene oxide absorber. Sandwich structured wallpaper graphene oxide absorber was constructed by a high transmission mirror, a piece of wallpaper graphene oxide absorber and a reflective mirror. The average output power of 310 mW of passively Q-switched and mode-locked laser was successfully achieved. The repetition rate and pulse width of the Q-switched envelope were 213 kHz and 770 ns, respectively. The repetition rate of passively mode-locked pulse within the Q-switched envelope was 81.3 MHz with the pulse energy of 3.8 nJ.     

Impacts of operational parameters on nonlinear polarization rotation-based passively mode-locked fiber laser

The operational parameters including the polarization controlling and the pump power in a nonlinear polarization rotation-based passively mode-locked fiber laser are studied in this paper.The carrier rate equations of the activated erbium-doped fiber are first employed together with the nonlinear Shro¨dinger equations to reveal the relation between the operational parameters and the output state of the passively mode-locked fiber laser.The numerical and experimental results demonstrate that the output state of the mode-locked laser varies with the polarization controlling and the pump power.The periodicity of the polarization controlling is observed.With given pump power,there exists a set of polarization controlling under which the ultra-short pulse can be generated.With given polarization controlling,the mode-locked state can be maintained generally except for some particular values of pump power.Three shapes of the output optical spectra from the fiber cavity can be identified when the pump power changes.The results in this paper provide a comprehensive insight into the operation of the nonlinear polarization rotation-based passively mode-locked fiber laser.     

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.     

基于石墨烯的1 064 nm连续锁模超短脉冲激光器

介绍了利用沉积在增透镜上的石墨烯薄膜作为可饱和吸收体、808 nm激光二极管端面泵浦Nd∶YVO4晶体的1 064 nm连续锁模激光输出特性。采用W型折叠谐振腔结构,在808 nm泵浦功率为8.0 W时,有稳定的连续锁模脉冲输出,平均输出功率达到185 mW;当抽运功率增加到16.0 W时,获得了中心波长1 063.4 nm、脉冲宽度为518 fs、重复频率为66.7 MHz、最大平均输出功率为323 mW的百飞秒量级超短脉冲激光输出。实验结果表明:石墨烯具有优良的可饱和吸收性,在1 064 nm波段能够实现高功率、百飞秒量级连续锁模脉冲激光输出。     

Diode-pumped passively Q-switched mode-locked Nd:LuVO4 laser with a semiconductor saturable absorber mirror

We present a compact passively Q-switched mode-locked Nd:LuVO₄ laser run in a Z-type folded cavity with semiconductor saturable absorber mirror (SESAM). The repetition rates of the passively Q-switched pulse envelope ranges from 22.99 to 141.18 kHz as the pump power increased from 2.372 to 8.960 W. The repetition rates of mode-locked laser pulses in the Q-switched pulse envelope has 111 MHz determined by the cavity length and the mode-locked pulse duration is evaluated to be 257 ps. An average output power of 823.5 mW is achieved at the pump power of 8.96 W, corresponding to an optical conversion efficiency of 9.2%.