Scalar off-resonant modulation instability in rare-earth-doped fiber amplifiers

Presents an analytical model which describes the dynamics of the modulation instability in a nonlinear, dispersive, homogeneously broadened and nonsaturable fiber amplifiers. The general case of arbitrary detuning between the laser frequency and the resonance frequency and arbitrary bandwidth of the amplifying transition is treated. The model accounts both for the gain dispersion and for the gain-induced, near resonant refractive index dispersion, Simple closed form expressions for the combined gain coefficients of the Stokes and anti-Stokes frequencies are obtained.     

The modulation instability laser. II. Theory

For pt.I see ibid., vol.25, no.9, p.2036-44 (1989). A general analysis of the modulation instability laser (MIL) in a nonlinear dispersive cavity is presented. The theory of the feedback-induced modulational instability is derived. By introducing the pump depletion within one circulation of the pump pulse, the steady-state MIL oscillation can be predicted. The ripple frequency is equal to the modulation instability frequency     

Modelocking and multimode instability in laser intracavity frequency modulation

Using the Maxwell-Bloch equations, we have studied dynamics associated with an electro-optically tunable laser modulated by a sinusoidal signal with a frequency near the cavity free spectral range. We find that frequency modulation (FM) modelocking may occur when a higher order FM mode acquires the lowest threshold. For short-cavity lasers, the pulse waveform in modelocking is complicated, and unlike the simple Gaussian shape suggested by previous studies. In order to explain instability observed in laser FM operation, we develop a linear stability analysis for the lasing FM mode. Our analysis shows that this type of instability is attributed to mode competition and to laser relaxation dynamics. We then confirm the analytic results with numerical simulations.     

Degenerate-cross-phase modulation of femtosecond laser pulses in a birefringent single-mode optical fiber

Degenerate-cross-phase modulation has been observed for femtosecond laser pulses propagating through a short birefringent single-mode optical fiber. The difference in the spectral broadening of the two output polarization components of a single laser pulse was attributed to the combination of self-phase modulation and degenerate-cross-phase modulation processes in the optical fiber. Theoretical simulations based on the solutions of the two coupled nonlinear Schrodinger equations are in good agreement with the measured results.     

保偏光纤中任意偏振方向矢量调制不稳定性

利用光脉冲在非线性双折射光纤中传播时所遵守的相干耦合非线性薛定谔方程,研究了保偏光纤中偏振方向与双折射轴成任意角度时,在反常色散区和正常色散区所产生的调制不稳定性。结果表明:在反常色散区对于任意的偏振角和任意输入功率的光脉冲都产生调制不稳定性;正常色散区的存在不稳定区域和稳定区域,对应不同的不稳定区域输入临界功率不同,脉冲有不同的增益谱。并且,给出了调制不稳定性增益谱随固有双折射和偏振角的变化关系。     

Pulse-amplitude equalization in a rational harmonic mode-locked fiber laser using nonlinear modulation

In this letter, a simple technique for the pulse-amplitude equalization of high repetition rate pulses generated from a rational harmonic mode-locked fiber ring laser was demonstrated. The principle is based on nonlinear modulation of the modulator and a theoretical explanation based on time-domain analysis was given. Amplitude equalized short pulses up to the seventh rational harmonic mode-locking were obtained with an optimum bias level and modulation depth of the modulator, which agrees well with the simulation result and demonstrates the efficiency of this method.     

利用多重尺度理论对光纤布拉格光栅调制不稳定性研究

利用激光脉冲在光纤光栅中传播时所遵守的相干耦合非线性薛定谔方程,通过多重尺度理论,主要研究了激光脉冲在高斯变迹布拉格光纤光栅中传输时,在反常色散区所产生的调制不稳定性和对应相关参量的关系;结果表明在反常色散区,当输入功率、传输距离一定时,当f=-1禁带之上能带底时,调制不稳定性增益的强度最强、宽度最窄;当远离能带底时强度减弱、宽度变宽;并且,增益谱都受到高斯变迹函数的制约。     

GHz pulse train generation in fiber lasers by cavity induced modulation instability

We report on the experimental generation of highly stable pulse trains with GHz level repetition rate in a ring cavity fiber laser. We show both theoretically and experimentally that the generation mechanism of the pulse trains was due to the cavity induced modulation instability (CIMI) lasing of the fiber laser. Coexistence of the conventional modulation instability (MI) and the CIMI in the same fiber laser were also experimentally observed. It shows that the two effects are independent of each other.     

Characteristics of a hemispherical microlens for coupling between a semiconductor laser and single-mode fiber

A hemispherical microlens is fabricated on the end of a single-mode fiber by an electric arc discharge technique. It improves coupling efficiency between InGaAsP lasers with buried heterostructure geometry and single-mode fiber. The lowest coupling loss of 2.9 dB is achieved with the optimum lens radius of 8.5 μm. This loss is 4.4 dB lower than that with a butt joint. Experimental results of coupling efficiency and alignment tolerances in coupling with different lens radii in the range of3.5-17 mum are discussed in detail. The results are in good agreement with theoretical values derived by Gaussian beam and paraxial ray approximations.     

Lifetime improvement of a visible multiline CO laser

The influence of charge capacitance, tube bore, and oxygen addition on the lifetime of a sealed-off visible carbon monoxide pulsed laser is reported. The results extend previous studies on the CW IR sealed-off CO laser.     

Bit correlation and memory effects in high-speed pump modulation ofa fiber laser

In the context of optical communications, we study experimentally the behavior of a pump-modulated fiber laser at frequencies close to the relaxation oscillation frequency. We show that correlations can appear between successive “1” bits in various situations. This “memory effect” can be interpreted using a simple deterministic model, and we show that this effect is related to the behavior of the population inversion, which does not follow adiabatically the photon number. Our results also suggest the existence of an optimum pump bias value for optical communications, slightly below threshold     

Characteristics of a semiconductor laser coupled with a fiber Bragg grating with arbitrary amount of feedback

Stationary characteristics (such as laser frequency at threshold, light-intensity curve, etc.) and relative intensity noise of laser diodes coupled with an external Bragg reflector are studied for arbitrary amount of optical feedback. We put the stress on the interplay between external and internal cavities when the feedback strength is increased. For strong feedback, new stationary solutions that do not exist in the case of conventional feedback appear, while the ellipse, which usually contains the modes and so-called antimodes, collapse in the plane frequency-gain. Finally, analytical expressions are compared with numerical results obtained through a new approach that uses Green functions.     

基于光纤环形镜的光纤激光器的优化设计

对基于光纤环形镜和光纤光栅的线形腔光纤激光器进行了优化设计.以光纤光栅作为激光器的输出端镜,分别将光纤环形镜和非线性放大环形镜与其构成激光器的谐振腔;在光纤光栅与光纤环形镜构成的谐振腔中引入偏振控制器,并以加入偏振控制器的环形镜作为激光输出端镜,对上述三种实验装置的激光输出特性进行了分析比较.     

IPG光纤激光发生器外部调制器调制激光强度和脉宽的实现

本文简述了IPG对调制信号的要求和下位机的工作原理,介绍了外部调制器调制激光强度和脉宽的实现过程。     

Low-threshold dye laser pumped by visible laser diodes

The author describes a continuous-wave (CW) dye laser has been pumped by laser diodes for the first time. Two 10-mW visible laser diodes were polarization-combined to pump a rhodamine 700 dye jet laser. The absorbed pump threshold power was 5.6 mW, and 0.28 mW of output power was produced at 758 nm. The resonator was scalable and generated over 360 mW with a slope efficiency of 57% when pumped with a DCM dye laser at 660 nm     

Interferometric signals in fiber optic methane sensors withwavelength modulation of the DFB laser source

We examine the performance limitations of a fiber optic methane sensor using microoptic GRIN lens cells in either transmission or reflective mode. We derive the worst case values of sensitivity due to interference effects caused by reflections within the cell as a function of the cell parameters. We also show both theoretically and experimentally how the interference signal may be minimized by suitable choice of the amplitude of the wavelength modulation. Although, theoretically, reflective cells could match the performance of transmission cells, in practice, transmission cells are superior in terms of interferometric noise levels. With reflective cells, two secondary reflections from the cell and secondary cavity effects in the system enhance the interference so that in practice their performance is inferior     

Experimental characterization of the bifurcation structure in an erbium-doped fiber laser with pump modulation

The bifurcation structure of phase space is investigated experimentally in an erbium-doped fiber laser with a sinusoidal pump modulation. We demonstrate a rich variety of bifurcations and dynamical states which appear in primary saddle-node bifurcations and discuss their relation to the main laser resonance. The systematic organization of coexisting attractors allows one to predict the behavior of the fiber laser, when initial conditions are allowed to evolve to their final states.     

An acousto-optical spectrometer with a visible laser diode source

An acousto-optical spectrometer has been constructed using a visible laser diode light source. The advantages of a visible laser diode in this application over the more prevalent infrared laser diodes are discussed. These include increased Bragg cell bandwidth and diffraction efficiency, and easier instrumental alignment, the latter allowing the attainment of much lower scattered light levels.