Mode-locking of high power lasers by a combination of intensity and time dependent Q-switching

A new method for simultaneous mode-looking and Q-switching of high power lasers by a combination of intensity and time dependent Q-switching is described. The two Q-switching mechanisms are achieved by equipping the laser with a device, here called the “Electro-Opto-Optical Modulator” (EOOM). The modulator, which is driven by the optical field which it modulates in addition to an external electric field, contains nonlinear media which exhibit a large optical as well as dc Kerr effect. The advantages of this combined Q-switching compared with a pure intensity dependent Q-switching are that the generation of the model-locked pulses can be predetermined in time and that the length of the Kerr active medium can be decreased.     

Mode-locking of quasi-continuous lasers

A simple rate-equation theory is developed which indicates that the combination of nonlinear amplification and nonlinear absorption may be responsible for ultrashort pulse generation in a mode-locked quasi-continuous laser system in the absence of commensurately short relaxation times. It is tentatively proposed that this mechanism is responsible for picosecond pulse generation in the mode-locked dye laser.     

Mode-locking dynamics of synchronously-pumped colour-centre lasers

A theoretical model has been developed for studying the steady-state pulse shaping dynamics of a synchronously-pumped colour-centre laser. A wide range of results is presented detailing effects on the mode-locking process of pump pulse power and width, laser bandwidth, cavity mismatch and, stochastic noise. From the results, we identify conditions which lead to the formation of single and multiple pulses. We show this can be understood on the basis of a simple scaling law between the principal laser parameters.     

Mode-locking of diode laser-pumped solid-state lasers

Mode-locked diode-pumped solid state lasers have become important sources for efficient and reliable short pulse generation. We review techniques for active mode-locking of diode-pumped lasers, highlighting techniques which have produced much shorter pulse durations than previous technologies and extended operating repetition rates to the several gigahertz regime. To achieve even shorter pulse durations a series of nonlinear passive mode-locking techniques have been developed. Self-starting additive pulse mode-locking, resonant passive mode-locking and self-mode-locking of diode-pumped solid-state lasers are described.     

光纤激光器自成像腔相干组束研究

 探讨了3种不同自成像腔,即Talbot腔、自傅里叶变换腔(SF)和傅里叶变换自成像腔实现相干组束的机理和技术难点。介绍了利用光纤激光器,采用傅里叶变换自成像方法,实现1维2路和2维4路激光相干组束的实验情况,功率分别达到122 W以及26 W。     

Stability performance of short cavity Er-doped fiber lasers

An experimental study of stability between two types of short-cavity laser configurations is carried out. The short-cavity lasers are comprised of one or two pairs of wavelength-matched FBGs, encompassing a short length of highly-doped Er-fiber, to create effectively single- or dual-wavelength fiber lasers. The laser performance in terms of the laser output power and laser stability in relation to the gain medium length was investigated experimentally, analyzed and reported in this letter.     

Mode-locking of neodymium lasers by glasses doped with PbS nanocrystals

Nonlinear optical absorption properties of silicate glasses doped by the PbS nanocrystals were investigated by means of the picosecond pump-probe absorption spectroscopy and absorption bleaching technique. The glass samples were used as saturable absorbers for passive mode-locking of Nd:YAG and Nd:glass lasers. Application of the PbS doped glass together with the active mode-locking and laser cavity quality control enabled the stable of generation of 28 ps and 5 ps duration pulses in Nd:YAG and Nd:glass lasers respectively. PACS 42.60.Fc; 42.70.Hj; 78.47.+p     

Mode-locking S-band erbium fiber laser by employing alcohol-based saturable-absorber

Optical and Quantum Electronics - A novel reconfigurable photonic microwave mixer using an integrated dual-polarization binary phase shift keying modulator is proposed. In the modulator, one...     

PDLC-based VOA with a small polarization dependent loss

A polymer-dispersed liquid crystal (PDLC)-based variable optical attenuator (VOA) was demonstrated to exhibit a relatively small polarization dependent loss (PDL) in the optical communication C band. The influence of the PDLC characteristics, the temperature, as well as the wavelength of the laser irradiation, on the PDLC VOA performance was analyzed. The PDL, the insertion loss at saturated voltage, and the operating voltage of the PDLC-based VOA were reduced by optimizing the fabrication conditions and applying a bias voltage to the PDLC cells during polymerization-induced phase separation.     

Feedback coupling loss in single mode fiber lasers

Based on the expansion of the fundamental mode LP₀₁ in single mode fiber in terms of Laguerre-Gaussian free space modes, the feedback coupling losses for two different types of cavity mirror, i.e., a curvature mirror and a combing mirror of a lens and a plane mirror, are numerically calculated for the first time. The results show that, for the curvature mirror, the lowest coupling loss is obtained when its curvature radius matches the wavefront curvature. In particular, if a plane mirror is used as the cavity mirror, it has to be placed close to the fiber end to obtain the low coupling loss. For the combing mirror, the lowest coupling loss can be obtained when the plane mirror is placed at the back focal plane of the lens, and the variation of the coupling loss is insensitive to the mirror positions for the lens with longer focal length. Finally, the plane mirror and the combing mirror of a lens and a plane mirror are suggested to be the cavity mirror in the practical construction of the high power fiber lasers.     

Intensity noise of mode-locked fiber grating external cavity semiconductor lasers

The noise of hybrid soliton pulse source (HSPS) with linearly chirped Gaussian apodized fiber Bragg grating is analyzed by couple-mode equations including spontaneous emission noise when HSPS is mode-locked. Relative intensity noise (RIN) is calculated using numerical solutions of these equations. It is shown that transform-limited pulses are generated over a wide tuning range around the fundamental mode-locking frequency with low spontaneous noise. However, high noise level affects the operation of device, and therefore transform-limited pulses are not obtainable over a wide tuning range. Linewidth enhancement factor and spontaneous coupling factor are the most effective noise parameters and noise increases with increasing value of these parameters.     

Fundamental frequency noise properties of extended cavity erbium fiber lasers

A multimode linear cavity and a single-mode unidirectional ring cavity fiber laser with meter-long cavity lengths are shown to exhibit frequency noise limited by fundamental thermodynamic noise from 100?Hz to 100?kHz. Their measured spectra agree closely with theoretically derived thermodynamic noise and the characteristic dependence of the frequency noise power spectrum on the inverse of the cavity length is observed. The unidirectional ring laser exhibits a frequency noise of 2?Hz/Hz(1/2) at 1?kHz, one of the lowest published values to date from a free-running laser. The multimode linear cavity laser is shown to be a suitable candidate for thermal-noise-limited, meter-long fiber laser strain sensors with a strain resolution of 14?f?/Hz(1/2) at 1?kHz.     

Influence of the UV-induced fiber loss on the distributed feedback fiber lasers

It was found that the output power of the distributed feedback fiber lasers would be improved after annealing or left unused for several days after the laser had been fabricated, and the output of the fundamental mode would not increase but be clamped while the ±1 order modes would be predominant with the enhancement of the coupling coefficient during the fabrication. The paper discussed the influence of UV-induced fiber loss on the fiber phase-shifted DFB lasers. Due to the gain saturation and fiber internal loss, which included the temperament loss and permanent loss, there was an optimum coupling coefficient for the DFB fiber lasers that the higher internal fiber loss corresponded to the lower optimum values of coupling coefficient.     

Impact of polarization dependent loss on degree of polarization as feedback signal of polarization mode dispersion

Polarization dependent loss (PDL) has been recognized as a critical issue because various inline optical components may have nonnegligible PDL effect that interacts with polarization mode dispersion (PMD).We investigated the impact of PMD-PDL interaction on degree of polarization (DOP), which is the most commonly used feedback signal in PMD compensation. The simulation results of a 40-Gb/s NRZ code optical transmission system show that the maximum PMD increases from approximately 40 ps to more than 45 ps, while minimum DOP declines from approximately 0.6 to approximately 0.2. The interaction of PMD and PDL also induces residual PMD underestimation of 5-8 ps, which causes degradation of PMD compensation performance.     

Influence of light polarization on dynamics of continuous-wave-pumped Raman fiber lasers

The dynamical behavior of cw-pumped Raman fiber lasers is studied experimentally. Lasers made of standard single-mode fibers are found to present unstable behaviors depending on the states of polarization of the Stokes and pump fields. On the contrary, lasers made of polarization-maintaining fibers are found to be always stable. The observed behaviors suggest that birefringence- and Kerr-induced changes in polarization states dramatically affect Raman fiber lasers dynamics.     

Regenerative mode locking via superposition of higher-order cavity modes in composite cavity fiber lasers

We demonstrate a new method of optical pulse generation in regeneratively mode-locked fiber ring lasers (RML-FRLs). The method is based on generating dominant longitudinal modes in the fiber ring cavity by means of a composite cavity structure and their intermode beating at the photodetector incorporated in the regenerative feedback loop. The beat signal is then used as a modulation signal to generate optical pulses in a regenerative mode-locking scheme, thereby eliminating the requirement for a high-Q rf bandpass filter in a conventional RML-FRL. Optical pulses with a repetition frequency of 3.6 GHz have been generated successfully with a supermode noise suppression of more than 48 dB and a low phase noise of -85 dBc/Hz at 10 kHz offset from the carrier frequency.     

2 kW级光纤激光相干偏振合成

基于主动锁相相干偏振合成系统实现了四路500 W级全光纤窄线宽保偏放大器的共孔径合成输出。当相位控制系统处于闭环状态时, 整个合成系统的输出功率达2164 W, 合成效率为94.5%。实验中, 随着功率的提升, 合成效率未发生明显退化。这是目前相干偏振合成系统的最高输出功率。     

2 kW级光纤激光相干偏振合成

基于主动锁相相干偏振合成系统实现了四路500 W级全光纤窄线宽保偏放大器的共孔径合成输出。当相位控制系统处于闭环状态时, 整个合成系统的输出功率达2164 W, 合成效率为94.5%。实验中, 随着功率的提升, 合成效率未发生明显退化。这是目前相干偏振合成系统的最高输出功率。