Observation of dark pulse in a dispersion-managed fiber ring laser

The observation of dark pulse in a dispersion-managed fiber ring laser with net negative cavity group velocity dispersion (GVD) is reported. Both bright and dark pulses can be obtained in our fiber laser. When we appropriately adjust the cavity birefringence to achieve triple-wavelength mode-locked operation in the laser by rotating the polarization controller, the bright pulse could be switched to dark pulse. It is believed that the dark dispersion-managed (DM) pulse generation is caused by the linear and nonlinear intermodulation effects among the three wavelength pulses.     

Generation of domain-wall solitons in an anomalous dispersion fiber ring laser

We report experimental observations performed using a net anomalous dispersion Er-doped fiber ring laser without polarization-selective elements, highlighting the domain-wall solitary pulses generated under the incoherent polarization coupling. By adjusting the pump power and the polarization state appropriately, bright and dark solitons can stably co-exist in the cavity, both centered at 1562.16 nm with a 3-dB spectral width of ～ 0.15 nm and a repetition rate of 3.83 MHz. Moreover, the 0.8 mm long thulium-doped fiber (TDF) facilitated the mode-locking and self-starting of the laser. This is the first demonstration of a laser being used to generate bright and dark solitons synchronously while using TDF as the saturable absorber (SA). Except possessing the all-fiber structure, the laser exhibits good stability, which may have a significant influence on improvement of the pulse-laser design, and may broaden practical applications in optical sensing, optical communication, and soliton multiplexed systems.     

腔内相位调制全光纤脉冲激光器Ⅱ: 理论

针对低频腔内直接相位调制时全光纤激光器的脉冲现象,提出了合理的理论解释。基于光纤激光器自脉冲和固体激光器空间耦合的理论,对脉冲光产生的机理进行了分析,解释脉冲光产生的物理机制。假定光纤激光器中存在两个正交的偏振态,且两个偏振态以固体激光器空间耦合的模型耦合; 在相位调制作用下,两个耦合的偏振态之间相位差变化,导致两个偏振态的耦合特性发生变化,从而产生脉冲光输出。建立相应的数学模型,进行定性的理论分析。数值模拟表明,理论分析与实验结果符合得很好。     

Dark pulses with tunable repetition rate emission from fiber ring laser

We demonstrated the experimental observation of the dark pulses with tunable repetition rate from an erbium-doped fiber ring laser. A considerable length of high nonlinear fiber is incorporated into the fiber ring laser to enhance the nonlinear intensity. In our experiment, both bright and dark pulses can be observed under the conditions of appropriately setting of the device in the cavity. Further study showed that the dark pulse is formed due to the cross coupling between two different lasing wavelengths. Particularly, dark pulse-train with multiple repetition rates was observed from the laser cavity and the repetition rate switchable operation can be realized by simply adjusting the polarization controller (PC) in the cavity. The operation of multiple repetition rates of dark pulses was further experimentally investigated and detected as a result of pulse splitting of each component with different wavelength.     

Generation of cavity-birefringence-dependent multi-wavelength bright–dark pulse pair in a figure-eight thulium-doped fiber laser

We experimentally demonstrated a stable multi-wavelength bright–dark pulse pair in a mode-locked thulium-doped fiber laser(TDFL). The nonlinear polarization rotation(NPR) and nonlinear optical loop mirror(NOLM) were employed in a figure-eight cavity to allow for multi-wavelength mode-locking operation. By incorporating different lengths of high birefringence polarization-maintaining fiber(PMF), the fiber laser could operate stably in a multi-wavelength emission state. Compared with the absence of the PMF, the birefringence effect caused by PMF resulted in rich multi-wavelength optical spectra and better intensity symmetry and stability of the bright–dark pulse pair.     

High-energy dissipative soliton with MHz repetition rate from an all-fiber passively mode-locked laser

We experimentally demonstrate pulse energy enhancement in an all-fiber passively mode-locked laser operating in the large normal dispersion regime. By increasing the laser cavity length as well as its net cavity dispersion, the proposed laser, which is mode-locked by nonlinear polarization rotation, generates highly chirped dissipative solitons with pulse energies up to 9.4 nJ. The fundamental repetition rate is 2.3 MHz, and the pulse duration is 35 ps. Such low repetition rate as well as wide pulse width makes this mode-locked all-fiber laser a suitable oscillator to directly seed a fiber amplifier, which can be used as compact sources for high-power applications.     

Sub-100 kHz repetition rate erbium-doped fiber laser in anomalous dispersion regime

We propose and demonstrate a simple but efficient way to generate low repetition rate pulses in an erbium-doped fiber ring laser by using self-pulsing technique. About 2.25 km long single mode fiber is used to elongate in the cavity, providing large anomalous cavity dispersion in the wavelength region around 1550 nm. Self pulses at a repetition rate of 85.3 kHz with single pulse energy as high as 110 nJ are efficiently obtained on the nanosecond time scale. The experimental results demonstrate that the self-pulse fiber laser operating in the anomalous dispersion regime can also realize high-energy pulses at a very low pulse repetition rate.     

Experimental Observation of Bright and Dark Solitons Mode-Locked with Zirconia-Based Erbium-Doped Fiber Laser

We demonstrate the generation of dark and bright solitons with our homemade zirconia-based erbium-doped fiber and graphene oxide(GO) saturable absorber in anomalous dispersion region.The GO is fabricated using an abridged Hummer's method,which is combined with polyethylene oxide to produce a composite film.The film is sandwiched between two optical ferrules and embedded in the laser cavity to enhance its birefringence and nonlinearity.The self-starting bright soliton is easily generated at pump power of 78 mW with the whole length cavity of 14.7 m.The laser produces the bright pulse train with repetition rate,pulse width,pulse energy and central wavelength being 13.9 MHz,0.6 ps,2.74 p J and 1577.46 nm,respectively.Then,by adding the 10 m of single mode fiber into the laser cavity,dark soliton pulse is produced.For the formation of dark pulse train,the measured repetition rate,pulse width,pulse energy and central wavelength are 8.3 MHz,20 ns and 4.98 p J and1596.82 nm,respectively.Both pulses operate in the anomalous region.     

石墨烯被动锁模全正色散掺镱光纤激光器中的暗脉冲及其谐波

报道了一种基于石墨烯被动锁模的全正色散掺镱环形光纤激光器. 在激光器腔中应用激光诱导沉积法制备的石墨烯可饱和吸收体, 通过调节抽运光功率和偏振控制器的角度分别得到了明脉冲及其二阶谐波, 暗明脉冲对和暗脉冲及其二、三阶谐波这三类不同的脉冲. 其中, 暗明脉冲对和暗脉冲在基于石墨烯被动锁模的掺镱光纤激光器实验中都是第一次被观察到. 本文根据实验结果结合模拟分析了暗脉冲的产生机理, 并研究对比了明脉冲谐波和暗脉冲谐波产生的原因.     

Direct generation of 128-fs Gaussian pulses from a compensation-free fiber laser using dual mode-locking mechanisms

We have experimentally demonstrated the direct generation of 128-fs pulses in an all-anomalous-dispersion all-fiber mode-locked laser. The laser is free of dispersion compensation in the cavity based on standard single mode fiber (SMF). The time-bandwidth product is 0.536. The laser is achieved by using two mode-lockers, one is nonlinear polarization rotation (NPR), and the other is nonlinear amplifying loop mirror. The coexistence of dual mode-locking mechanisms can decrease the cavity length to 12-m, and also results in producing high-quality pulses with a Gaussian shape both on the pulse profile and spectrum, but without Kelly sidebands.     

All-fiber polarization locked vector soliton laser using carbon nanotubes

We report an all-fiber mode-locked erbium-doped fiber laser (EDFL) employing carbon nanotube (CNT) polymer composite film. By using only standard telecom grade components, without any complex polarization control elements in the laser cavity, we have demonstrated polarization locked vector solitons generation with duration of ~583 fs, average power of ~3 mW (pulse energy of 118 pJ) at the repetition rate of ~25.7 MHz.     

利用光谱滤波器实现自启动的全光纤超短脉冲掺Yb3+光纤激光器

讨论了利用光谱滤波器实现自启动的被动锁模掺Yb³⁺光纤环形激光器的锁模机理,并研制出全光纤结构超短脉冲掺Yb³⁺光纤环形激光器.使用980 nm二极管激光器作为抽运源,高掺杂浓度掺Yb³⁺光纤作为增益介质.在净群速度色散为正的环形腔中加入光谱滤波器,抑制Yb³⁺离子在1030 nm强发射峰的同时,通过对啁啾脉冲的光谱滤波实现脉冲压缩.光谱滤波器与光纤非线性偏振旋转效应相结合,实现了激光器在1053 nm可自启动、十分稳定的锁模运转.激光器锁模阈值功率300 mW,平均斜率效率18.3%,最大输出功率53.07 mW,对应最大输出脉冲能量3.2 nJ.锁模光脉冲中心波长1053.6 nm,3 dB带宽10.84 nm,重复频率16.45 MHz.锁模脉冲宽度为皮秒量级,经腔外光栅对压缩至188 fs. 关键词： 3+光纤激光器')" href="#">掺Yb³⁺光纤激光器 自启动锁模 全光纤     

Dark pulse generation in a dispersion-managed fiber laser

We report an experimental observation of dark pulse generation in a dispersion-managed erbium-doped fiber laser with net anomalous cavity group-velocity dispersion. It is found that apart from the bright soliton pulses, dark pulses with spectral sidebands could be obtained in the laser under appropriate operating conditions. The generation of dark pulses may be attributed to soliton shaping in the cavity.     

Tunable high energy giant chirped passively mode-locked Yb-doped fiber laser

A tunable, low-repetition rate, all-normal-dispersion Yb-doped fiber laser (YDFL) that is passively mode locked based on a phase shifted long period fiber grating (PS-LPFG) is demonstrated and proposed. The mode-locking mechanism of the laser is based on nonlinear polarization evolution (NPE). Using a PS-LPFG as the spectral filter in the laser cavity, the mode-locked output wavelength can be tuned continuously and smoothly over a spectral range of 10 nm, which is the first time implementation of a tunable giant chirped pulse with all-fiber format bandpass filter in YDFL. The maximum output pulse energy is 38.9 nJ at the repetition rate of 2.499 MHz.     

Wavelength tunable femtosecond laser based on short Er<Superscript>3+</Superscript>/Yb<Superscript>3+</Superscript> codoped phosphate fiber

A wavelength tunable laser system mode-locked by nonlinear polarization evolution based on a 3 cm-long homemade Er³⁺/Yb³⁺ codoped phosphate fiber has been reported. By simply adjusting the polarization controllers, the central wavelength of the mode-locked spectrum can be tuned over 1537.1–1563.3 nm continuously. Moreover, 264-fs pulse with 3-dB spectral width of 39.6 nm and peak power of 7.8 kW at a 7.55 MHz repetition rate is generated directly from the all-fiber ring cavity.     

Low-threshold single-wavelength all-fiber laser generating cylindrical vector beams using a few-mode fiber Bragg grating

We propose and demonstrate a low-threshold single-wavelength all-fiber laser generating cylindrical vector beams using a few-mode fiber Bragg grating. Both radially and azimuthally polarized beams have been generated with very good modal symmetry and polarization purity higher than 94%. The radially and azimuthally polarized modes can be switched by simply adjusting the polarization controllers built in the fiber laser cavity. This fiber laser operates at a single wavelength of 1053 nm with a 3 dB linewidth of less than 0.02 nm, signal-to-background ratio of more than 55 dB, and a threshold as low as 16 mW. A new method for the polarization purity measurement is also proposed.     

High-energy mode-locked all-fiber laser with ultralong resonator

The first experimental results on an all-fiber mode-locked ytterbium laser whose ultralong cavity has a length of 8 km are presented. An increase in the length of the laser cavity at a constant mean power of radiation makes it possible to increase the pulse energy by more than two orders of magnitude to a level of 4 μJ, which is record-high for the pulses generated by a fiber mode-locked master oscillator in the absence of Q-switching. A pulse repetition rate of 37 kHz is the record-low repetition rate for the mode-locked lasers. The numerical simulation of the lasing in the absence of extension fiber yields a possibility of a wide-range variation in the pulse duration due to the tuning of the intracavity polarization controllers. The simulation results are in qualitative agreement with the experimental data.     

All-fiber single polarized Yb-doped fiber laser with a high extinction ratio

We present an all-fiber design for a single polarization Yb-doped fiber laser with all-fiber connections spliced. Single polarization with a high extinction ratio was achieved by the design of a laser cavity consisting of a fiber Bragg grating inscribed on a single-polarization fiber as a high reflective mirror and a piece of end-cleaved single-polarization fiber as an output coupler. The fiber laser operates at 1063.25 nm with an output power of 1.7 W, an optical signal- to-noise ratio of 70 dB and a narrow bandwidth of 54 pm. The laser output has a polarization extinction ratio of 700:1 or 28 dB, and a very stable power output.     

2.1 μm可调谐多波长掺钬光纤激光器

为了实现2.1 μm波段光纤激光器输出多波长激光，设计了一种基于光纤Sagnac干涉仪的可调谐多波长掺钬光纤激光器。采用1.9 μm波段掺铥光纤激光器泵浦一段长3 m的掺钬石英光纤，获得2.1 μm波段的光放大；环形腔中，由保偏光纤和偏振控制器构成的光纤Sagnac干涉仪，实现2.1 μm波段周期滤波，获得了2.1 μm波段多波长激光，输出功率1 mW~15 mW可调谐，最多可观测到6个波长的激光输出。通过调节环形腔内偏振控制器，能够实现2.1 μm波段1~6个波长的调谐。     

利用啁啾脉冲光谱滤波和非线性偏振旋转技术实现高稳定性和开机自启动的全光纤掺Yb~(3+)光纤锁模激光器

建立理论模型,讨论了非线性偏振旋转全光纤锁模激光器的锁模过程、谐波过程以及导致激光器锁模运行难以稳定的影响因素.讨论了采用啁啾脉冲光谱滤波产生脉冲自振幅调制、增加激光器锁模稳定性和自启动能力的机理以及非线性偏振旋转与啁啾脉冲光谱滤波相结合实现锁模的物理过程和脉冲演化过程.研制出全光纤结构的超短脉冲掺Yb~(3+)光纤环形激光器,采用非线性偏振旋转和啁啾脉冲光谱滤波相结合的锁模技术,实现了激光器锁模的开机自启动和高稳定运行.对激光器进行了长期运行稳定性、锁模开机自启动能力、锁模输出参数可重复性监测.锁模脉冲中心波长1052.9 nm,谱宽9.1 nm,脉冲能量4.25 nJ,脉冲宽度17.8 ps.运行期间,各参数波动均小于0.3%.开机自启动能力和可重复性测试显示,激光器可实现一键自启动,启动后各参数可重复精度在0.55%以内.