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.     

High-quality optical pulse train generation at 80 Gb/s using a modified regenerative-type mode-locked fiber laser

In this paper, we present an experimental demonstration of a high-quality optical pulse train generation at 80 Gb/s. The successful operation was achieved via two steps. In the first step, an ultrastable 2-ps (FWHM), 40-Gb/s pulse train was generated using the technique of fourth-order rational harmonic mode locking. The mode-locked laser was stabilized using a regenerative-type base-line extraction feedback technique. In the second step, an external fiber loop mirror consisting of several meters of polarization-maintaining fiber was used to double the repetition rate from 40 to 80 Gb/s. The output of the 80-Gb/s pulse train shows very small pulse-to-pulse amplitude fluctuation with good long-term stability.     

被动锁模光纤激光器中双波长脉冲的产生

报道了从一个典型的基于非线性偏振旋转被动锁模光纤激光器中产生双波长锁模脉冲的研究。双折射诱导的波长相关腔传输使得激光器能同时在2个或多个波长上振荡,本文设计的激光器中最多有3个波长同时产生。由于偏振相关隔离器(PDI)引入的另外偏振相关腔损,通过调节偏振控制器(PC),3个波长中的任意2个能同时共振,并同时锁模。此外,双波长脉冲中2个不同波长的脉冲会相互作用,并通过交叉相位调制形成各种各样的调制格式。     

Reproducible optical second-harmonic generation using a mode-locked laser

Experiments have shown a one-to-one correspondence between the intensity of a fundamental pulse of light and its second harmonic. This correspondence is observed when the fundamental is each pulse of light in one train of pulses generated by a mode-locked laser. Such fundamental light shows no variation in the spatial distribution of intensity from pulse to pulse in one train of pulses and no randomness in the phases and amplitudes of the locked modes. As a result of these conditions, the ratio of harmonic intensity to the square of the fundamental shows little or no deviation from the mean. To contrast this, the wide fluctuations in this ratio observed when the laser is not mode-locked are also presented. In addition, the deviation from a square law in the relatianship between harmonic and fundamental intensities in one burst laser pulse is demonstrated. These deviations are found less often when the laser cavity is short (40 cm) than when it is long (3 meters). They may be attributed to the appearance or disappearance of different modes of oscillation during the pulse and possible variations in the mode amplitudes.     

Dual-wavelength picosecond optical pulse generation using anactively mode-locked multichannel grating cavity laser

Picosecond pulse generation by active mode locking has been achieved simultaneously at two wavelengths using a multichannel grating cavity Laser. For a spectral channel separation of 2.2 nm, pulses of duration of 60 ps and with a spectral width of 11 GHz have been obtained. The pulse widths are limited by the spectral dispersion of the grating used     

Multiwavelength picosecond optical pulse generation using anactively mode-locked multichannel grating cavity laser

A multichannel grating cavity (MGC) InGaAsP-InP ridge diode laser is found to be suitable for multiwavelength ultrashort optical pulse generation using active mode-locking techniques. By using different configurations of the MGC laser, dual wavelength picosecond pulses are successfully produced with good spectral quality, either simultaneously or with a programmable relative delay between the channels. For a channel separation of 2.2 nm, pulses with a duration of 60 ps and a spectral width of 11.6 GHz have been obtained. The experimental results are compared with those from a theoretical analysis of the multiwavelength mode-locking process using a set of modified coupled-cavity rate equations. The minimum achievable pulsewidths generated by the actively mode-locked MGC laser are shown to be limited by the resolution bandwidth of grating used. The dependence of pulsewidth on RF drive frequency detuning is examined and it is found that the ultrashort pulses can be obtained over a wide range of frequency detuning. The interchannel cross-talk originating from gain saturation and carrier depletion is also discussed     

Picosecond optical pulse generation from mode-locked phased laser diode array

Actively mode-locked 26 ps optical pulses are generated from a gain-guided, 10-stripe, phased laser GaAs diode array with an external cavity consisting of two cylindrical lenses and a corner reflector. To our knowledge, this is the shortest pulse width yet demonstrated from a mode-locked phased laser diode array. The detuning bandwidth of the mode-locking is measured as 2.5 MHz.<>     

基于光纤环镜的被动锁模飞秒脉冲光纤激光器

在当前的高速光通信系统中,光源的选择至关重要。文章分析了光纤环镜的非线性传输特性,论述了利用光纤环激光器锁模产生超短脉冲的原理。     

Bandwidth limited picosecond optical pulse generation from actively mode-locked AlGaAs diode laser

A simple configuration made of a conventional AlGaAs diode laser without antireflection coating combined with an external reflector and an optical etalon was proved to be practically feasible to generate bandwidth limited mode-locked optical pulses of 30 ps duration by synchronous modulation at the external cavity mode interval. Generated optical pulse shape was found to be Lorentzian rather than Gaussian for the first time, based on the measurements of both the s.h.g. correlation method and the ultrafast streak camera.     

Multiwavelength pulse generation using an actively mode-locked erbium-doped fiber ring laser based on distributed dispersion cavity

A simple design of a stable multiwavelength pulse generator was demonstrated using a dispersion-tuned actively mode-locked erbium-doped fiber (EDF) ring laser with distributed dispersion cavity. The distributed dispersion cavity in the fiber laser successfully reduced the cross-gain saturation in EDF, and thus, enabled multiwavelength operation. Simultaneous generation of wavelength-tunable 10-GHz pulses up to four different wavelengths was achieved with the same wavelength space of 2.94 nm. The extinction ratio of all wavelengths was above 30 dB. In addition, smooth wavelength tuning was achieved over more than 41 nm when the laser was working at dual-wavelength mode. The super mode noise was /spl sim/60 dB below the signal level at both wavelengths. The laser state was found to be very stable.     

Supercontinuum generation pumped by a regeneratively mode-locked fiber laser

Supercontinuum（SC） generation in a dispersion-shifted fiber（DSF） pumped by a 10 GHz regeneratively mode-locked fiber laser（RMLFL） is presented. Optimization of pump wavelength leads to a 20 dB bandwidth of 58.73 nm,which covers the whole C band and part of L band. Using an angle-tuning thin film filter, multi-wavelength and pico-second pulse trains of low chirp could be chosen from the SC spectrum. Amplified spontaneous emission（ASE） induced degeneration of the achieved pulse trains is observed and discussed.     

光纤环形激光器中锁模脉冲均匀性的理论分析和实验研究

从描述双折射光纤环形激光器动力学模型出发，模拟并分析了脉冲序列在非线性偏振旋转锁模光纤激光器环形腔内的演化过程，得出光纤快慢轴与起偏器之间的角度、以及双折射强度是影响锁模脉冲序列均匀性的重要因素，通过将普通单模光纤绕制成环产生应力双折射的方法进行了验证，并获得了中心波长1566．8nm、脉宽为1．5ps的稳定短脉冲序列。     

双SESAM被动锁模超短脉冲光纤激光器

针对基于半导体可饱和吸收体（Semiconductor Saturable Absorber Mirror,SESAM）被动锁模光纤激光器脉冲底座宽和脉冲能量小的问题展开研究,设计了一种线型腔结构的双SESAM锁模超短脉冲光纤激光器。首先,通过增加SESAM个数的方式使得光脉冲在谐振腔中的一个振荡周期内多次经过可饱和吸收体,有效增加了可饱和吸收体对光脉冲前后沿的吸收,抑制了因泵浦功率过大而产生的调Q锁模效应,有助于压缩脉冲宽度、提高单脉冲能量,摆脱了因SESAM调制深度较低而对压缩脉冲宽度和提高单脉冲能量造成的限制。其次,通过在系统中引入一段正色散光纤,降低了因峰值功率过高而引起的非线性效应,进一步提高了脉冲能量。最后,在相同调制深度及饱和通量条件下,与单SESAM锁模相比,双SESAM锁模光纤激光器输出脉冲宽度由693 fs降低到449 fs,缩短了35.2%,脉冲能量由2.92 nJ提高到5.31 nJ,上升45%。     

Short pulse generation using multisegment mode-locked semiconductorlasers

Mode-locked semiconductor lasers which incorporate multiple contacting segments are found to give improved performance over single-segment designs. The functions of gain, saturable absorption, gain modulation, repetition rate tuning, wavelength tuning, and electrical pulse generation can be integrated on a single semiconductor chip. The optimization of the performance of mode-locked lasers in terms of material parameters, waveguiding parameters, electrical parasitics, and segment length is discussed experimentally and theoretically     

80-160-GHz mode-locked fiber ring laser synchronized to external optical pulse stream

The authors present a novel scheme to generate ultrahigh repetition rate picosecond pulses synchronized to an optical pulse stream in an actively mode-locked fiber ring laser. A monolithic Mach-Zehnder interferometer with integrated semiconductor optical amplifiers serves as an 80-GHz optically controlled modulator. 80-GHz transform-limited 2.1-ps Gaussian pulse with low timing jitter, extinction ratios up to 25 dB, and 5 mW of average output power are demonstrated. The laser is wavelength tunable over more than 15 nm around 1555 nm. At 160 GHz, 2.5-ps pulse trains with 3-mW output power are generated by rational harmonic mode locking.     

Ultrashort optical pulse generation with a mode-locked long-wavelength (1075-1085 nm) InGaAs-GaAs semiconductor laser

Optical pulses are generated by passive and hybrid mode-locking of a long wavelength (1075-1085 nm) InGaAs-GaAs ridge waveguide laser grown by gas source molecular beam epitaxy. The devices are fabricated with two sections, one of which contains a bend in the waveguide for coupling to an external linear cavity. Pulses 2-5 ps in duration have been generated with average powers ranging from 750 /spl mu/W to 1.8 mW. Pulse compression yields durations as short as 570 fs. Post amplification with a narrow stripe InGaAs-GaAs semiconductor optical amplifier increases the average output power up to 13 mW.     

A harmonic colliding-pulse mode-locked semiconductor laser forstable subterahertz pulse generation

A 192-GHz, sixth-harmonic colliding-pulse mode-locked InGaAsP-InP strained QW semiconductor laser that has a monolithic periodic saturable-absorber configuration is presented. The generation of nearly transform-limited, 0.75-ps pulses with a side-mode suppression ratio of about 27 dB at the central mode is demonstrated. The temporal repetition rate of the pulses was measured for the first time with the accuracy of the synthesizer by photonic downconversion using optical modulation sidebands. The rate for the pulses under a higher saturable-absorber voltage of -2.33 V had a 10-dB reduction RF-spectrum width of 1.1 MHz with a resolution of 300 kHz. The repetition rate versus reverse voltage was linear in a range from -750 to -900 mV     

Colliding pulse mode-locked laser

The fabrication and performance of a colliding pulse-mode locked laser with an intracavity saturable absorber is described. The laser has a threshold current of 65 mA and differential efficiency of 0.04 mW/mA when coupled into a single-mode fiber. Mode-locked pulses with ~1 ps pulse width at ~10 GHz has been obtained     

全光纤结构锁模脉冲光纤放大器

随着光纤技术的不断发展,光纤激光器以其体积小、结构紧凑、高效率、光束质量好、高稳定性等优点逐渐受到重视。近些年,具有高峰值功率、高重复频率和高单脉冲能量的脉冲光纤激光器越来越成为研究和应用领域的热点。利用自行搭建的环形腔光纤激光器,获得了稳定的自启动锁模脉冲种子源,以掺Yb双包层光纤为增益介质,采用包层泵浦的方式和主振荡功率放大结构(MOPA),通过两级放大,使平均功率为70 mW的信号光得到25.2 dB的增益,获得了平均功率23.07 W,中心波长1 064 nm、重复频率41.3 MHz,脉冲宽度50 ps,单脉冲能量0.56μJ,峰值功率11.2 kW的锁模脉冲激光,光光转换效率为42.4%,实现了全光纤结构的锁模脉冲放大器。     

Output characteristics of optical solitons in a passively mode-locked Yb-doped fiber laser

In this paper, we studied the output characteristics of optical soliton in a passively mode-locked ytterbium (Yb)-doped fiber laser by numerical simulation. The structure of the passively mode-locked Yb-doped fiber laser was studied by modeling and analysis. The influence of the inter-cavity average group velocity dispersion on pulse width, pulse peak power and single pulse energy of optical soliton and self-similar pulse was investigated. Simulation results were very instructive for the practical application of the passiavely mode-locked Yb-doped fiber lasers.