Stable operating region in a harmonically actively mode-locked fiber laser

We theoretically study the recovery of a harmonically actively mode-locked soliton fiber laser from pulse dropout. In such lasers, a large number of pulses propagate simultaneously in the cavity. In order to obtain stable operation, pulses that are dropped due to changes in environmental conditions should recover, while other pulses that propagate in the cavity should remain stable. Soliton perturbation theory is used to find stability conditions for the noise in a time slot where a steady state pulse exists and in a time slot where a pulse is dropped. In the stable operating region of the laser, noise is stable in the presence of a pulse while noise becomes unstable in time slots where a pulse is dropped. Such a stability condition ensures that the laser can recover from accidental pulse dropout. A good agreement between the results of a reduced model and the results of a comprehensive numerical simulation was obtained. The results of this paper may enable to improve the stability of actively mode-locked fiber lasers.     

Performance characterization of a harmonically mode-locked erbiumfiber ring laser

We describe the performance of a harmonically mode-locked, erbium fiber ring laser. Transform-limited pulses with durations of 20-50 ps at 5.044 GHz repetition rate are obtained. The modulation frequency can be detuned by up to ±70 kHz and the lasing wavelength can be varied over the entire erbium gain bandwidth. Pulsewidths and pulse bandwidths are measured as a function of modulation power and frequency detuning. The laser is actively stabilized by locking intra-cavity Fabry-Perot etalon passbands to the laser modes     

Electrically wavelength-tunable picosecond pulses generated from aself-seeded laser diode using a compensated dispersion-tuning approach

We developed a compensated dispersion-tuning approach to generate electrically wavelength-tunable short pulses from a self-seeded Fabry-Perot laser diode. Single-mode pulses with a sidemode-suppression ratio over 30 dB are obtained across most of the 18.5-nm tuning range in the fiber configuration. The use of both dispersion-compensating fiber and standard single-mode fiber with equal and opposite group velocity dispersion allows electrical tuning to be performed at a constant repetition rate     

Ultrastable harmonically and regeneratively modelockedpolarisation-maintaining erbium fibre ring laser

The authors report the operation of a harmonically and regeneratively modelocked erbium fibre ring laser at 1.55 μm for the first time. Harmonic regenerative modelocking was achieved by feeding back the harmonic longitudinal beat signal which was detected with a high speed photodetector and a high Q dielectric filter. The repetition rate was 10 GHz and the soliton effect shortened-the pulse width from 7.0 to 2.7 ps     

Wavelength-tunable 40-GHz picosecond harmonically mode-locked fiber laser source

We demonstrate a novel 40-GHz mode-locked fiber laser that utilizes a single active device to provide both gain and mode-locking. The laser produces pulses as short as 2.2 ps, is tunable over a 27-nm band centered at 1553 nm, and exhibits long-term stability without cavity-length feedback control. The pulse train at 1556 nm was used in a 40-Gb/s transmission experiment over 45 km with a low 0.4-dB power penalty.     

Pulse stabilisation in harmonically FM modelocked erbium fibre ring laser with DFBLD

A new pulse stabilisation scheme for a harmonically frequency modulated (FM) modelocked erbium fibre ring laser using a distributed feedback laser diode (DFBLD) is presented. More than 65 dB supermode noise suppression in the RF spectrum was obtained with the proposed method. Effective reduction of supermode noise can be accomplished as the DFBLD in the fibre laser acts not only as a fast-gain saturated medium but also as an optical bandpass filter for suppressing supermode noise in a harmonically modelocked laser system.     

Smoothly wavelength-tunable picosecond pulse generation using a harmonically mode-locked fiber ring laser

A simple design of a stable, smoothly wavelength-tunable picosecond pulse generator has been demonstrated using a dispersion-tuned, harmonically mode-locked fiber ring laser with a directly modulated semiconductor optical amplifier (SOA). The SOA functions as both a polarization-insensitive mode locker and a supermode noise suppressor. Near-linearly chirped pulses are generated and compressed to less than 4 ps when the intracavity dispersion is anomalous while 11-ps, near-transform-limited pulses are generated without compression when the dispersion is normal. Smooth wavelength tuning is achieved over more than 11 nm by only tuning the modulation frequency and pulse characteristics are stable over the entire tuning span. A simple numerical model successively simulates the operation principle of the system. The tuning range is determined by both the gain profile and the total intracavity dispersion. The dispersion and the SOA ensure the long-term stability of the system.     

Alternate and simultaneous generation of 1-GHz dual-wavelengthpulses from an electrically tunable harmonically mode-locked fiber laser

A new scheme of producing dual-wavelength mode-locked pulses from a fiber laser is proposed and experimentally demonstrated. In addition to the simultaneous generation of two selected wavelength components, the scheme also allows the alternate generation of mode-locked pulses at different wavelengths. The alternate switching of wavelengths is demonstrated at 1 GHz, and has been achieved over an electrical tuning range of 13.1 nm using the dispersion-tuning approach. A constant mode spacing of 7.1 nm is maintained during the tuning process     

Relaxation-free harmonically mode-locked semiconductor-fiber ringlaser

A 10-Gb/s semiconductor-fiber ring laser is proposed and demonstrated. The performance of a harmonically mode-locked semiconductor-fiber ring laser was described in detail. A long cavity length configuration in semiconductor optical amplifier is found to eliminate the relaxation oscillation, and improved short-term amplitude stability. The laser output has a pulsewidth of 18.4 ps and a spectral width of 0.3 nm     

Pulse dropout in harmonically mode-locked fiber lasers

We have studied theoretically and experimentally supermode competition in an actively mode-locked Er-fiber laser that operates in a high harmonic mode. Using an innovative numerical technique that allows us to properly account for the complex interaction of multiple pulses with the gain media, we could study the dynamics that leads to supermode competition, pulse dropouts, and pulse pair generation, and to accurately predict the limits of the stable operating regime     

A novel configuration for multiwavelength actively mode-lockedfiber lasers using cascaded fiber Bragg gratings

A novel scheme for multiwavelength and wavelength-switching operations in an actively mode locked fiber laser using a cascaded sequence of fiber Bragg gratings in the laser cavity is presented. In this scheme, the cavity lengths for all wavelengths selected by the gratings are intrinsically identical, Generation of simultaneous dual-wavelength picosecond pulses with a wavelength separation of 3.5 or 20.1 nm was demonstrated. The interchange between dual- and single-wavelength operations and wavelength switching from one single-wavelength to another were simply achieved by polarization adjustment     

Characteristics of the optical-frequency conversion in asemiconductor laser

A small signal analysis is presented for optical-frequency conversion using nearly degenerated four-wave mixing (FWM) in a semiconductor laser. The nearly degenerate FWM is mainly introduced by the carrier beating at the detuning frequency of the pump and the probe waves. Generally speaking, the influence of the nonlinear gain saturation on the frequency conversion efficiency is very small compared with that of the carrier density beating. However, the conversion efficiency is damped by the nonlinear gain saturation at higher bias current. The frequency conversion efficiency and the probe transmissivity are almost symmetrical with respect to the zero detuning frequency. The bandwidth of the converted signal is governed by the relaxation resonance frequency of the laser. A definition of the conversion. The theoretical results agree with experiments     

Characteristics of the dispersive free-electron laser

The dispersive free-electron laser (DFEL) was previously introduced as an optical klystron (OK) superimposed upon a free-electron laser (FEL). In this paper it is shown that with proper design this device provides a gain increase of the order of 4 over the gain of the OK (for equal lengths) with a gain-energy acceptance product approaching that of the FEL. Even when the transverse excursion of the electron beam exceeds the optical beam dimension, there is only a slight reduction in gain from the above value.     

Characteristics of a gas laser amplifier

Characteristics of a gas laser amplifier are theoretically analyzed by employing Lamb's model. A wave equation in the time domain is obtained when traveling waves in the positive and negative directions are present simultaneously in the nonlinear active medium. The wave equation which contains linear and third-order nonlinear terms is applicable to any spectral construction of the incident signal, such as discrete, continuous, and mixed. An approximate solution of the wave equation is obtained in the frequency domain. Some characteristics of a kernel which appears in the frequency-domain representation are discussed. As an application of the theory, characteristics of one- and two-frequency amplifiers are calculated and compared to previous analysis.     

GaN基激光器的特性

GaN基激光器具有广泛的应用.如何获得平整腔面是蓝宝石衬底上制作GaN激光器的困难之一.通过对解理面的分析和不同衬底厚度时腔面形貌的比较,发现减薄衬底可以有效降低腔面粗糙度.当外延片厚度减薄至50μm时,获得近似镜面的腔面.激光器的测量证实了腔面的改善可以降低阈值电流,增加斜率效率.利用二维光波导模型计算了脊形高度对限制因子和远场分布的影响.计算结果说明,增加脊形高度可以增加限制因子,降低远场纵横比.通过测量具有不同脊形高度的器件,证实了脊形高度增加,阈值电流降低、远场纵横比减小.     

Characteristics of a Raman laser excited by an ordinary ruby laser

The stimulated Raman effect of benzene has been observed using an ordinary (nongiant) ruby laser. The build-up of oscillation at the v2, 2v2, 3v2and 4v2Stokes lines and also at the first v1Stokes line have been observed. The threshold exciting power for laser action in the v2Stokes line has been measured to be 9.5 kW. A rate equation for the Raman laser has been given, and the total scattering cross section for the v2Raman line of benzene has been determined as σ = 0.46×10^-28cm². The estimation based on the results of this investigation indicates that it is possible to construct a Raman laser of benzene using an Ar gas laser.     

Characteristics of a multimode laser diode in a dual-interferometerconfiguration

The results of an experimental investigation of an interferometric sensor scheme using a Michelson interferometer in conjunction with a Fabry-Perot reference cavity, illuminated by light from a multimode compact disk (CD)-type laser diode, are reported. The results are compared with the results of calculations using a simple theoretical model and good agreement is seen. Potential applications to interferometric-based sensors are discussed     

真空环境下脉冲激光烧蚀等离子体羽流特性分析

激光清除空间碎片利用的是高能脉冲激光烧蚀固体靶材的冲量耦合效应,对于空间碎片来说,激光辐照下的反冲冲量取决于碎片等离子体羽流的喷射过程,并且会随着激光辐照方向的变化而变化。因此,有必要研究空间碎片激光辐照下的等离子体羽流特性。针对等离子体羽流的流场超高速、瞬态、强自发光背景、小尺度的技术难点,采用纳秒级曝光、多幅照片精确拼接技术,采用高速相机和激光器同步时序控制技术,实现纳秒级时间分辨率、亚微米级空间分辨率的流场演化信息定量测量,实验获得典型碎片材料等离子体羽流演化特性,以及不同激光入射角度下的等离子体羽流演化过程,实验结果可揭示反喷冲量形成规律。     

Nonlinearity in power-current Characteristics of narrow-pulse-driven AlGaInP laser diodes

In this paper, a simple yet effective model is developed to analyze the nonlinearity in power-current characteristics, also known as "kinks", observed in AlGaInP selectively-buried-ridge (SBR) laser diodes driven by narrow pulses (/spl sim/10/sup -7/s). The model takes the temperature-induced waveguide as well as the carrier distribution into account, and the simulation results show good agreement with the experiments. The main factors influencing the kink behavior of SBR lasers are investigated based on this model, and it is believed to be of great help for the optimization AlGaInP laser structure for high-power applications.     

非链式电激励脉冲HF激光器

介绍了利用紫外预电离和横向放电结构建立的非链式电激励脉冲HF激光装置,对激光工作介质SF6/C2H6混合气体的放电特性以及不同气体总压和气体分数比条件下的激光能量变化进行了研究,并对激光脉冲信号和近场光斑的空间分布进行了实验测量.实验结果表明:混合气体的放电过程具有辉光放电、电压维持和电弧放电的阶段性特点.为获得最佳的激光输出,混合气体中的C2H6含量应控制在6%～8%之间,并且不同混合气体总压对应着不同的最佳充电电压.在充电电压为28kV、总气压为12 kPa、C2H6含量为8%时获得最大单脉冲能量为0.6 J,比能量输出达到8.5 J/l,激光器的电光转换效率约为2.5%.