Objective Utilizing actively Qswitched fiber lasers to generate high-energy narrow-linewidth nanosecond laser pulses is a mainstream technology. Various types of active Qswitches have been developed based on different principles. Among them, fiber- pigtailed acousto-optic modulators (AOMs) and electro-optic modulators (EOMs) have garnered wide attention owing to their nanosecond- level switching time and high extinction ratios spanning tens of decibels. However, the output of Qswitched fiber lasers based on fast switches, such as AOMs and EOMs, typically exhibits a typical multipeak structure. Researchers have proposed various methods to address this issue; however, they present certain limitations. Therefore, obtaining high- power narrow-linewidth lasers with smooth pulses from actively Qswitched fiber lasers is crucial. In this study, a novel Qswitch is designed based on the linear electro-optic effect of a beta-BaB2O4 (BBO) crystal with a high damage threshold. Moreover, to eliminate the multipeak phenomenon caused by the short rise time of the Qswitch, a fiber coupler is used to form a coupling ring (CR), which enables a gradual release of the initial signal energy and successfully realizes a smooth pulse output. Methods To construct an intensity modulator suitable for high- power lasers, a pair of single- mode fiber collimators (COLs) is used for spatial optical- path coupling. A high- damage- threshold BBO uniaxial crystal is placed between orthogonal polarization devices. The intensity of the transmitted laser can be modulated by applying a periodic half- wave voltage to the BBO crystal. Additionally, to obtain a smooth Qswitched pulse output, a smooth and long- rise waveform is required. The longer the circulation time within the fiber CR, the longer the rise time. However, this implies that the precision of the input pulse segmentation decreases, thereby reducing the smoothness of the rise- time waveform. Therefore, a fiber CR comprising optical coupler is inserted, with the ring length set to 0.5 m. Results and Discussions First, the performance of the constructed intensity modulator is tested (Fig. 2). The measured rise time is approximately 8 ns, with an insertion loss and extinction ratio of approximately 2 dB and 20 dB, respectively, thus satisfying the requirements of a high- gain double- cladding fiber laser for Q- switching. As the pump power increases [Fig. 3(a)], the repetition frequency of the pulse sequence gradually transitions from 1/4 to 1/3 and 1/2 of the modulation frequency, before eventually exhibiting a regular pulse sequence. This occurs because, after the laser pulse depletes inverted ions during cavity circulation, the gain generated in the doped fiber during the subsequent Q- switch closed period is insufficient to establish a pulse within the limited open time. By gradually increasing the pump power, the gain within a single cycle increases accordingly. When increased to a certain value, the accumulated gain within a single cycle is sufficient to support pulse establishment during the subsequent Q- switch open time, thus resulting in a pulse- sequence repetition frequency that matches the modulation frequency. The pulse- waveform details before and after the insertion of the fiber CR are shown in Fig. 3(b). After the Q- switch is activated, the waveform exhibits the typical multipeak characteristics before the insertion of the CR. After inserting the fiber CR, the multipeak structure on the pulse completely disappears and the temporal waveform becomes extremely smooth. The principle by which the fiber CR smooths the temporal waveform of the pulse is explained as follows: Considering the evolution process of a rectangular pulse passing through the fiber CR (Fig. 4), the analysis results summarized based on Equations (1) and (2) indicate that the original rectangular pulse, after transmission through the CR, evolves into a series of equally spaced delayed subpulses with different amplitudes, thus effectively altering the Q- switch rise time. Consequently, the temporal multipeak structure is completely eliminated, thus resulting in a smooth laser pulse. Additionally, the average power increases almost linearly with the pump power without any saturation effect [Fig. 5(a)]. As the damage threshold of the fiber devices and the pump power cannot be further increased to compress the pulse width, the duty cycle should be reduced to increase the gain. The width of the output pulse can be further compressed by reducing the duty cycle to increase the gain recovery time. When the duty cycle is reduced from 50 degrees o to 3 degrees o, the pulse width is compressed to 35 ns, and the pulse is extremely smooth with no multipeak structures. The laser output linewidth narrows to 0.08 nm with a signal-to-noise ratio of 60 dB [Fig. 5(b)]. Conclusions In this study, a highly doped large- mode- area double- cladding fiber is used as the gain medium. Simultaneously, a novel intensity modulator based on the linear electro-optic effect of a high- damage- threshold BBO crystal is designed as a Q- switch. Furthermore, to eliminate multipeaks in the output pulse caused by the rapid opening of the Q- switch, a fiber CR is introduced to allow the initial signal energy to be released gradually, thereby resulting in smooth laser pulses. The principles of pulse temporal evolution are analyzed comprehensively. The laser yields a smooth pulse output with an average power exceeding 1 W, a linewidth as narrow as 0.08 nm, and a pulse width of 35 ns.

-The role of injection seeding power on the operation and output characteristics of a single-longitudinal-mode (SLM) injection seeded Q-switched fiber laser is investigated. The mode coupling between seeding laser and the potential longitudinal-modes of the oscillator changes as the injection seeding power increase. So the Qswitched laser may operate at different regimes which can be distinguished by the pulse features. Only with a proper range of injection seeding power that is not too larger or too small, the operation of injection seeded Qswitched fiber laser with narrow-linewidth, high peak power and narrow pulsewidth laser pulses is possible. The Q-switched fiber laser linewidth is narrowed through inserting a dual-OCs oscillator into the laser cavity. 200-ns, 1-W peak power SLM Q-switched laser pulse with nearly transform-limited linewidth is obtained when the pump power is 300 mW.

With a fiber pigtailed electro-optic modulator as the active Q-switch, mode-hopping-free single-longitudinal-mode pulses are generated by a ring cavity fiber laser based on the injection seeding technique. The experimental results show that the single-longitudinal-mode oscillating properties of the laser may be determined by the power and the center frequency of the injection seed rather than the ...

With a fiber pigtailed electro-optic modulator as the active Q-switch, mode-hopping-free single-longitudinal-mode pulses are generated by a ring cavity fiber laser based on the injection seeding technique. The experimental results show that the single-longitudinal-mode oscillating properties of the laser may be determined by the power and the center frequency of the injection seed rather than the Q-switch waveform and modulation frequency. With the injected seed power of 200 μW, single-longitudinal-mode Q-switched pulses with the repetition rate and the pulse width from 1 to 100 kHz, and 50 to 400 ns are achieved with the laser. The output pulse linewidth can be narrowed effectively by reducing the coupling ratio of the output coupler of the laser. A stable single-longitudinal-mode pulse stream with a linewidth of 1.5 MHz is obtained with our laser, which may be the narrowest linewidth for a Q-switched fiber laser so far to our best knowledge.

Aiming at the application requirements of spectral calibration at 2.04 μm channel of the spatial heterodyne spectrometer used for spaceborne CO2 remote sensing detection,a narrow-linewidth,tunable and highly-stable Tm/Ho co-doped fiber laser (THDFL) is developed.The effective longitudinal mode spacing is expanded by using Wiener effect of the linear compound resonant cavity.The multi-mode laser oscillation is effectively suppressed,and the output laser linewidth reaches 7.5 MHz.By axially stretching the FBG packaged with temperature compensation and vibration isolation techniques,the THDFL can be tuned from 2040 nm to 2042.5 nm,and the output wavelength uncertainty is less than 5 × 10-3 nm.The output power of THDFL reaches 192 mW with the developed 1565 nm fiber laser pumping source.Using the output laser provided by the tunable THDFL,spectral calibration of the spatial heterodyne spectrometer at 2.04 μm channel is realized after being originated to a wavelength standard,and the calibration accuracy is better than the set index requirements.

The operation mechanism and the pulse property of an actively Q-switched erbium-doped fiber laser based on an acousto-optic modulator (AOM) switch with the injection seeding technique are investigated. Our results show that the Q-switched pulses can be locked to oscillate near a fixed frequency higher than that of the seed laser, though the frequency-shift effect of the AOM impedes stable cavity mode oscillations. The operation mechanism of such Q-switch fiber lasers can be explained by the mutual locking-in among the shifted frequency components originated from the injected coherence seed with the help of the gain dynamics of the Q-switch cavity. Moreover, narrow-linewidth Q-switched pulses with different repetition rates can be obtained with different cavity lengths for incredibly stable output pulses without any use of cavity-stabilized techniques.

研究了一种结构新颖、光谱特性可精确控制的Sagnac环滤波器,此滤波器通过在传统Sagnac环中插入两段高双折射光纤和一个偏振控制器构成.利用等效光路和传输矩阵法理论研究了该滤波器的滤波特性.研究结果表明:固定两段高双折射光纤参数,仅通过调整偏振控制器的状态,便可精确控制Sagnac环滤波器的滤波光谱特性.将Sagnac环滤波器用于掺铒光纤(EDF)放大自发辐射(ASE)光源的光谱平坦滤波,通过调节偏振控制器三个波片的倾斜角度,实验获得了光谱平坦的宽带ASE激光.

提出了一种He气辅助熔接的全光纤型空芯光子晶体光纤(HC-PCF)低压气体腔的制备方法.通过用高压待充气体冲洗HC-PCF,确保了腔内的气体纯度;通过利用光谱监测系统监测HC-PCF降压过程及He气辅助熔接过程中CO2吸收光谱的变化,研究了HC-PCF中气体动力学运动过程;通过利用He气辅助熔接方法,制备得到压强为7 kPa、插入损耗小于2 dB、长度为10m的全光纤型HC-PCF低压CO2气体腔.该方法也适用于更低压强的HC-PCF气体腔的研制,且制备的气体腔具有良好的气密性和长期稳定性.

单纵模调Q激光光源广泛应用于精密测量等领域,光纤激光器是一种性能优良的新一代固体激光器,近年来,光纤激光器的单纵模调Q技术发展迅速.对单纵模光纤激光器中引入Q开关和单纵模种子注入调Q光纤激光器这两种光纤激光器的单纵模调Q技术的工作原理、发展现状以及未来可能的发展趋势进行了综合述评.

研究了基于级联单光纤耦合器(OC)和双OC光纤环的复合环形腔光纤激光器的单纵模运转特性.通过对级联单OC和双OC光纤环辅腔的谐振通带特性进行分析,给出了优化双OC环的谐振通带特性以实现稳定单纵模运转的依据.利用构建的这种复合环形腔光纤激光器,实验验证了该理论依据的正确性.当主腔腔长为6.8 m,单OC环环长为0.45 m,双OC环环长约为0.56 m时,选取双OC的耦合比为0.7,单纵模运转的稳定性相对最好,实验与理论分析结果相吻合.

A widely tunable single longitudinal mode (SLM) fiber laser with cascaded Type I and Type II fiber ring secondary cavities, which uses a tunable fiber Bragg grating (FBG) as the mode-restricting and wavelength-tuning element, is proposed and demonstrated. Since the cascaded fiber rings can effectively expand the pass-band spacing to make the mode selection with the FBG easier, the stability of SLM oscillation can be improved by suitably optimizing the coupling ratio of optical couplers in Type II fiber ring to ensure that at least one and only one longitudinal mode dominates in the selected pass-band. When the fiber ring lengths are designed to make their expanded pass-band spacing be a value from 0.5 to 1 times of the 3-dB bandwidth of the FBG, the mode competitions between both neighboring pass-bands and main cavity modes, may be effectively eliminated, making the laser maintain mode-hop-free SLM oscillations while it is widely tuned.