Dependence of ion-pair induced self-pulsing in Er-doped fiber lasers on emission to absorption ratio

We show theoretically that the ion-pair induced self-pulsing in Er-doped fiber lasers depends largely on the ratio of emission to absorption cross sections, and can be significantly suppressed as this ratio is increased. Our experimental results agree qualitatively with this prediction. This result is important for stabilizing Er-doped fiber lasers where short-cavities and high-gain fibers are required.     

Analysis of Er-doped fiber laser stability by suppressing relaxation oscillation

For Er-doped fiber lasers, we show that the fluctuation of lasing power caused by resonant pump-power perturbations is inversely proportional to the lifetime of photon in the laser cavity. Analysis shows that Er-doped fibers with high-gain coefficient are favorable for fiber lasers in the view of point of suppressing the lasing-power instability caused by the resonant pump perturbation. The results obtained are especially useful for single-frequency Er-doped fiber lasers which have a very short cavity length, i.e., a short lifetime of photon in the cavity.     

Polarization-maintaining fiber Bragg gratings for wavelengthselection in actively mode-locked Er-doped fiber lasers

Fiber Bragg gratings written in polarization-maintaining fiber are proposed for wavelength selection in actively mode-locked Er-doped fiber lasers. Combined with single-polarization optical circulator, they form unidirectional transmission filters that can be incorporated in polarization-maintaining laser cavities. We have fabricated such a grating in hydrogen-loaded PANDA fiber and we have incorporated it in a polarization-maintaining actively mode-locked Er-doped fiber laser designed to generate soliton-like pulses. Dependencies of pulse duration and spectral width on average intracavity power were measured. The power range over which soliton-like pulses were generated without pedestals was found to be ultimately limited by the grating's bandwidth     

Clad-pumped Yb,Er codoped fiber lasers

Double-clad and Yb,Er codoped fiber lasers emitting at eye-safe wavelengths (>1.5 μm) have been investigated by varying the codopant concentrations, core modifiers, fiber length, and the spectrum of the diode pump. With a proper composition, the laser output contains only one lasing wavelength, at 1.6 μm. Highest slope efficiency greater than 60% for this three-level system, emitting only at 1.6 μm, has been obtained by using a 20-m-long, double-clad and codoped fiber with the core and clad diameters of 6.3 and 300 μm, respectively. By tradeoff of slope efficiency fur higher output power, a 30-m-long fiber is considered to be the best choice     

Picosecond structure in self-pulsing GaAs injection lasers

Partial mode locking has been observed in self-pulsing GaAs injection lasers using an optical correlation technique. The lasers are operated at room temperature and the self-pulsing occurs near the end of the injection current pulse. The pulsewidths are about 4 ps, which are the shortest observed in an injection laser.     

Signal structure of continuously self-pulsing GaAs lasers

CW-excited GaAs lasers can emit self-induced pulses. To study these pulses we have used an intensity correlator involving phase-matched second-harmonic generation in LiIO3. Besides measuring the pulsewidth and the repetition rate we investigated the amplitude fluctuations within a pulse and the correlation between fluctuations of consecutive pulses.     

A simple model describing both self-mode locking and sustained self-pulsing in ytterbium-doped ring fiber lasers

This paper presents a model describing self-mode locking (SML) and sustained self-pulsing (SSP) in a unidirectional ring-fiber laser using only the interaction between the saturated population inversion and the optical signal circulating in the laser cavity. Gain saturation alone is used to explain SML behavior close to laser threshold and the sharp transition to an SSP regime. The model also describes self-pulsing inhibition to the profit of SML for a sufficiently high pump power. Experimental results agree with most model predictions, but the overestimation of the self-pulsing threshold suggests that the phenomenon is furthered by an effect other than gain saturation.     

Efficient and tunable Er/Yb fiber grating lasers

Efficient and tunable single-frequency fiber Bragg grating (FBG) lasers are demonstrated using a novel photosensitive Er/Yb fiber design. Both sub-mW threshold pump power, and high slope efficiencies of ~31% at 1536 nm and ~26.1% at 1562 nm were achieved. Wavelength tuning could be obtained over 11 and 25 nm in 1535 and 1550 nm wavelength regions, respectively, by cavity-length tuning     

Perturbation solution of self-pulsing in semiconductor lasers witha saturable absorber

We solve the three-component rate equations for semiconductor lasers with a saturable absorber or for multi-section semiconductor lasers by using a singular perturbation method. The effects of nonlinear gain and spontaneous emission are included in the rate equations. By transforming the rate equations to the generalized coordinates, we eliminate the most rapidly varying term adiabatically for the fast saturable absorber. Then, we solve the two-component nonlinear equations to obtain analytic expressions for parametric dependence of self-pulsing amplitude and self-pulsing frequency. the self-pulsing frequency shifts from the small-signal oscillation frequency to the lower-frequency side as we increase the self-pulsing amplitude. The square of the self-pulsing frequency does not linearly depend on the injection current, in agreement with experimental observations. We also derive an optimum saturable absorber recovery time for the shortest optical pulse generation     

Stability of self-pulsing due to Hopf bifurcation in semiconductor lasers

A formulation is given of the stability criterion for oscillations arising at Hopf bifurcations in semiconductor lasers. A second-order perturbation expansion is utilized to provide nonlinear rate equations for the laser. The rate equations contain terms whose second-order partial derivatives are required in the definition of stability parameters. Using these parameters, a simple statement of the stability criterion is possible. Numerical calculations are included, using typical device parameters, and show the existence of both stable and unstable Hopf oscillations.     

LD泵浦掺镱的双包层光纤激光器的研究

本文通过数值分析对线形腔LD泵浦掺镱的双包层光纤激光器进行研究,分析了不同泵浦方式下的泵浦光、激光输出功率和增益特性在光纤中的分布。结果表明,双端非对称泵浦比较适合高功率光纤激光器。进一步又研究双端非对称泵浦输出功率与光纤长度及腔镜反射率的影响,为提高光纤激光器的输出功率提供了理论和实验依据。     

Frequency instability in Er/Yb fiber grating lasers due to heatingby nonradiative transitions

Heating of the Er/Yb-codoped fiber lasers due to strong pump absorption was found to cause large frequency fluctuation in addition to lasing wavelength shift. Laser frequency fluctuation of up to 1.7 GHz was measured by using an absorption line of an acetylene gas cell. The large frequency fluctuation was reduced to less than 80 MHz with proper cooling of the laser     

Dynamic behavior of gain-clamped Er:Yb and high concentration Er-doped amplifier

All-optical gain-clamped erbium-ytterbium (Er : Yb)-doped amplifier dynamic response is modeled and investigated. The complex Er:Yb rate equation system is reduced to a single equation. This simplification gives a more intuitive understanding of relevant physical mechanisms of Er:Yb doping. Experiments confirm theoretical assumptions. Results also allow us to describe dynamics in highly doped Er devices such as waveguide amplifiers.     

损耗对掺镱双包层光纤激光器输出特性的影响

本文分析了损耗对线形腔掺镱双包层光纤激光器输出特性的影响。对有损耗的线形腔掺镱双包层光纤激光器输出特性进行了数值分析,(当考虑光纤损耗时)得出了泵浦功率和正反向激光功率在2 0米长光纤处有近2W降低(泵浦功率为2 0W时)的结论。同时,文中给出了有损耗时的输出功率与光纤长度、泵浦功率和后镜反射率R2 的关系曲线。     

Excellent initial guess functions for simple shooting method in Yb3+-doped fiber lasers

Excellent initial guess functions, providing for setting suitable initial estimates for simple shooting method, are developed to solve high power Yb³⁺-doped fiber lasers model with boundary conditions. When the guess value of slope efficiency is greater than or equal to the critical guess value of slope efficiency, the initial guess values of the forward signal power and backward pump power, generating from the excellent initial guess functions, are good initial guess values for the simple shooting method. Then, comparing the simulation results using our simple shooting method and the number sequence transition method based on MATLAB BVP solvers (NSTM-BVPs), the difference of the simulation results are less than given absolute error tolerance for different fiber length. Finally, we can conclude that the critical guess value of slope efficiency is less than 0.3 for all the fiber length, Yb³⁺-doped concentration, signal reflectivity and pump power.     

The influence of Er-doped fiber source under irradiation on fiber optic gyro

The relationship between the parameters of Er-doped fiber source (EDFS) and the performance of fiber optic gyro (FOG) is analyzed in theory firstly. Then, the irradiation resistance characterizations of FOG using EDFS with and without spectrum trimming are compared. Through the theory analysis and experimental research, it is confirmed that the mean wavelength of the EDFS with spectrum trimming varies less than the EDFS without spectrum trimming under irradiation, and the FOG used EDFS with spectrum trimming have more stable performance under irradiation. Therefore, to trim EDFS’s spectrum into a Gaussian-like spectrum is an effective manner to suppress the irradiation influence on FOG.     

Effects of ion-clusters on the intensity noise of heavilyerbium-doped fiber lasers

Using a modified ion-cluster model, we study the intensity noise of heavily erbium-doped fiber lasers in which some large ion-clusters may exist. Theoretical results show that the low-frequency noise is enhanced greatly when many erbium ions are in clusters. The fiber laser system is very sensitive to perturbations in the pump rate, and imposes a high demand on the stability of the pump source     

光纤外腔对半导体激光器发光特性的影响

1.半导体激光器的张弛振荡、自脉动等光强起伏现象,以及用于光通信系统时,由光纤端面或光盘反射所引起的噪声对高速光通信的应用影响较大。为了抑制光强起伏,近年来外腔半导体激光器得到了较大发展。许多实验证明:外腔不仅能抑制张弛振荡和自脉动等光强起伏现象,而且还有很好的选模作用。甚至用外腔还做出了可调谐的单频激光器。这里,我们将一段光纤耦合到激光器上,利用光纤端面的反射形成光反馈作成了光纤外腔。 2.实验用的激光器是GaAlAs DH激光器,波长约为820nm,结构是质子轰击条形。用作耦合的光纤是标准的多模梯度光纤,芯径为50μm,数值孔径为0.2。激光器被烧焊在一个梯形的热沉上,其出光面直接与光纤耦合(见图1)。光纤的耦合端做成了球面,而另一端则做成平面,光反馈就是由此面反射形成的。光纤耦合端距激光器的距离约为50μm,     

光纤损耗和自发辐射对掺镱双包层光纤激光器的影响

本文主要从速率方程出发,分析了光纤损耗和自发辐射对线形腔掺镱双包层光纤激光器的影响.通过数值模拟,结果表明光纤损耗对激光阈值、激光增益、输出功率都有影响,而自发辐射主要对激光输出功率产生一定的影响.从而为光纤激光器的优化设计提供理论依据.     

An optical power equalizer based on one Er-doped fiber amplifier

A device which exhibits zero or slightly negative differential optical gain over a broad input power range is demonstrated. The scheme is based upon saturation enhancement by bidirectional signal input in an Er-doped fiber amplifier. Power equalization of better than 1.2 dB over a 14-dB dynamic input power range is achieved at the 1530-nm signal wavelength. The noise figure penalty due to the equalization is below 3 dB as evaluated by a device simulation