半导体光放大器引起的串扰及其抑制技术

由于半导体光放大器(SOA)的增益饱和效应,在波分复用系统中.每个信道的增益受到复用的其它信道的影响.SOA引起的各信道之间的串扰严重限制了其应用.理论研究了SOA增益饱和效应引起的信道间串扰.数值模拟了多路信道复用时系统的误码率随复用信道数和光功率的变化情况,发现随着复用信道数的增加SOA增益饱和引起的信道间串扰越来越严重.对SOA中串扰的抑制方法进行了理论和实验研究.数值模拟发现连续光注入可以抑制输出功率的波动,从而减小误码率,当复用10个信道时,连续光注入可以使功率代价减小2 dB;实验验证了两信道的40 Gb/s系统中,注入连续光可以减少SOA引起的信道间串扰.     

包含两个半导体光放大器的锁模光纤环形激光器数值研究

采用自再现理论,对一种包含两个半导体光放大器的锁模光纤环形激光器进行了数值研究.研究结果表明：为了提高谐波锁模输出脉冲的质量,调制半导体光放大器应当保持高直流偏置,对自发辐射信号进行调制并提供锁模脉冲克服腔损耗所需的增益,而此时的增益半导体光放大器则被低直流偏置充当增益补偿器维持较窄的净增益窗口;与之相反,为了获得振幅均衡的有理数谐波锁模输出脉冲,调制半导体光放大器则应当偏置在较低的电流上,而增益半导体光放大器应当保持较高的偏置电流以提供足够的常量增益克服腔损耗.此外,还必须提高注入光信号的峰值功率.     

强流目标的DC-SRF-II光阴极驱动激光系统设计

为推动北京大学超导加速器实验装置不断向强流目标迈进,提出100 W红外高重频光阴极驱动激光的设计方案,主放大器采用先进的光子晶体增益光纤,保证输出光束的质量。对激光系统中的关键问题,如各部分功率指标、脉冲展宽和压缩、激光耦合等进行了设计,并且考虑了激光的非线性影响。为实现强流加速器开机运行所必备的诊断模式,也提出了对于高重频激光进行两级选频的独特设计方案。将高速的SOA光开关和低速的声光调制器相结合,产生宏脉冲结构的输出激光,从而实现加速器在诊断模式下的运行。     

56 MHz重复频率端泵SESAM连续波锁模Nd∶YVO4激光器

为了增大皮秒注入种子激光的能量,获得较高的激光放大效率和信噪比,关键是要在保持较高的平均锁模激光功率下实现连续波锁模激光器的低重复频率运转。通过选取五镜折叠激光谐振腔腔型和参数设计,克服了随着腔长增加损耗加大而导致的激光锁模不稳定的困难。分析了较长腔长条件下工作物质和SESAM光斑尺寸的大小和变化,及其对激光器稳定性的影响。由于SESAM饱和工作和稳态条件的能量要求,在激光谐振腔调整过程中,对应臂长的光程互补变化。实验中采取腔长和晶体热控制方式,优化了激光谐振腔的工作参数,实现了脉冲能量10.7 nJ,重复频率56 MHz,平均功率1.2 W的SESAM连续波锁模激光输出。     

High repetition rate laser pulses amplified by Nd/Cr:YAG ceramic amplifier under CW arc-lamp-light pumping

Laser pulses with high repetitive rate generated from a Q-switch microchip Nd:YAG oscillator were amplified by Active mirror composed of Nd/Cr:YAG ceramic pumped by CW arc-lamp. The laser pulses were amplified, and saturation of averaged output laser power was observed. Repetitive ratio of injected laser pulses was changed from 20 to 100 kHz. Averaged output laser power and gain were measured, and gain coefficient and power-extraction efficiency were evaluated. Output laser power was calculated and compared to experimentally measured one, and the calculated results are consistent with the experimental ones. For amplification of laser pulses with high repetitive ratio, this laser material can realize very high laser gain with low pumping power density and high optical-optical conversion efficiency under CW-lamp-light pumping.     

高功率超短脉冲激光系统中光谱增益窄化补偿的调制函数

 设计了一种与高功率超短脉冲激光放大过程中获得的总增益、增益介质的带宽、激光带宽、脉冲中心波长等参数相关的调制函数,对激光放大过程中的光谱增益窄化进行补偿。此调制函数的优越性在于,对不同性能的激光系统,无需改变调制函数的形式就能适用。通过数值模拟的方法,讨论了在不同增益介质带宽、激光带宽、脉冲中心波长下的补偿效果。此调制函数在高功率超短脉冲激光系统中有良好的应用前景。     

增益半导体光放大器的特性

为满足半导体光放大器（SOA）在光纤到户FTTH系统接入网中的广泛应用,提出了基于光纤光栅外腔反馈型GC-SOA结构的全光增益机制,窄线宽激光光源经可变衰减器、隔离器和光纤光栅注入到SOA中,SOA的输出光经隔离器和光纤光栅送至光谱分析仪,通过光纤光栅反馈输入SOA形成钳制激光。对GC-SOA的阈值特性、增益特性及开关特性进行分析,结果表明:当注入电流小于GC-SOA的阈值电流时,增益随注入电流的增加而增加;当注入电流大于GC-SOA的阈值电流后,其增益不再随注入电流的变化而变化,实现了SOA的增益稳定,使SOA的饱和输出功率得到了提高。     

Research on a middle infrared and long infrared dual-band laser

We propose a continuous-wave(CW)middle infrared(MIR)and long infrared(LIR)dual-band laser for the calibration and effect research of infrared detecting and imaging systems.A total output power of 18 W is achieved by the proposed dual-band laser through one DF gain medium module and one parallel placed CO2 gain medium module using a common stable resonator and output mirror with nominal transmissivities of ～5%in the MIR band and～10%in the LIR band.Spectra of dual-band laser are acquired.The power extracting efficiency of this dual-band laser can be significantly improved,as validated by a single-band test of optimized parameters.     

Small signal gain and loss measurement of a CW Nd:YAG laser using an antiresonant ring interferometer

An antiresonant ring (ARR) interferometer configuration is introduced for the characterization of a continuous wave (CW) Nd:YAG laser output. The output of the ARR device is precisely characterized todetermine the gain and loss of a laboratory CW Nd:YAG laser by using the Findlay-Clay approach. TheARR arm is then experimentally arranged inside the cavity of an arranged high power side-pumped CWNd:YAG laser. A coated beam splitter with 50–50% reflectivity at normal incidence is placed inside thecavity to provide a wide range of reflectivity from 0 to 100%. This is performed by a rotatable stage and tilting the beam splitter by 10°with the steps of 0.05. By changing the input electrical power of the laser pump the variation of the output laser power is monitored for 20 individual reflectivity of ARR arm.Average pump threshold power of about 180 W is obtained. With the help of the derived equations and obtained threshold power, small signal gain and loss associated with the emerging beam is estimated. It is verified that the former is very dependent to the input parameters. Laser efficiency is also measures 5.6% which is quite comparable with the reported values.     

High-power transverse flow CW CO2 laser for material processing applications

A transverse flow transversely excited (TFTE) CW CO₂ with a maximum output power about 15 kW has been developed. This is excited by pulser sustained DC discharge applied between a pair of multi-pins anodes and a common tubular cathode. Though the laser power in convective cooled CO₂ laser scales proportionally with the volumetric gas flow, it did not increase in this laser when the volumetric gas flow was increased by increasing the electrode separation keeping the flow velocity constant. The discharge voltage too remained almost unchanged with increase of the electrode separation. These observations are explained considering the electrical discharge being controlled by ionization instability. Laser materials processing applications often demand programming facilities for laser power modulation. A four-stage cascaded multilevel DC–DC converter-based high-frequency switch mode power supply has been developed to modulate the output power of the laser. Laser was operated up to 15 kW output power in four different modes viz. continuous wave mode, pulse periodic mode, single shot mode and processing velocity-dependent power mode with 1.2 kHz modulation bandwidth. We describe briefly the laser system, the SMPS, and the temporal behavior of laser beam.     

基于半导体光放大器的环路型全光缓存器中功率均衡的新方法

全光缓存器能够在光域内对数据包进行存储而不需经过光电光的变换,成为全光网的重要组成部分,其性能的优劣将直接影响到网络的丢包率等。但在半导体光放大器中交叉增益调制和交叉相位调制效应并存,导致基于半导体光放大器的环路型全光缓存器中缓存后输出的数据包与未缓存数据包的输出功率间存在不均衡,使得网络误码率增加。在详细分析全光缓存器工作原理的基础上,利用半导体光放大器中交叉增益调制和交叉相位调制并存的现象,巧妙地提出了将控制脉冲反相并配合电可调衰减器的新方法。该方法简单易行,有效解决了此类全光缓存器中数据包输出功率不均衡的难题,缓存器性能得到了极大改善。此方法适用于所有基于半导体光放大器的环路型全光缓存器。     

All-solid-state 543 nm green laser generated by frequency doubling of a diode pumped Nd:YVO<Subscript>4</Subscript> laser at 1086 nm

An efficient and compact green laser at 543 nm is generated by intracavity frequency doubling of a continuous wave (CW) laser operation of a diode pumped Nd:YVO₄ laser at 1086 nm under the condition of suppression the higher gain transition near 1064 nm. With 10 W diode pump power and a frequency doubling crystal LBO, as high as 2.13 W of CW output power at 543 nm is achieved, corresponding to an optical-to-optical conversion efficiency of 21.3% and the output power stability in 3 h is better than 2.27%.     

Multiwavelength fiber ring lasing by use of a semiconductor optical amplifier

A multiwavelength fiber ring laser obtained by use of a semiconductor optical amplifier (SOA) with a simple laser cavity configuration is reported. A Fabry-Perot filter was used in the fiber laser ring cavity to achieve more than 50 simultaneous wavelength lasing oscillations with a frequency separation of 50 GHz. The resulting stable broadband multiwavelength lasing operation was attributed to broadband and flat gain of the SOA, which has a gain flatness of 0.8 dB for more than 20 nm. The laser has a total output power of -3 dBm and a signal-to-spontaneous-noise ratio of 30 dB.     

Ultrawideband monocycle generation using cross-phase modulation in a semiconductor optical amplifier

We propose a novel scheme to generate ultrawideband (UWB) monocycle pulses based on cross-phase modulation (XPM) of a semiconductor optical amplifier (SOA). The proposed system consists of a SOA and an optical bandpass filter (OBF). Due to the XPM, a continuous wave (CW) probe signal is phase modulated by another optical Gauss pulse in the SOA. The OBF will convert the phase modulation to intensity modulation. A pair of polarity-reversed UWB monocycle pulses is achieved by locating the probe carrier at the positive and negative linear slopes of the OBF. Both cases conform to the UWB definition of the Federal Communications Commission.     

All-solid-state CW frequency-doubling Nd:LuVO<Subscript>4</Subscript>/KTP laser with 2.3 W output power at 545 nm

Efficient and compact green-yellow laser output at 545 nm is generated by intracavity frequency doubling of a continuous-wave (CW) diode-pumped Nd:LuVO₄ laser at 1089 nm under the condition of suppressing the higher gain transition near 1066 nm. With 18.7 W of diode pump power and the frequency-doubling crystal KTiOPO₄(KTP), as high as 2.3 W of CW output power at 545 nm is achieved, corresponding to an optical-to-optical conversion efficiency of 12.3%; the output power stability over 4 h is better than 5.4%.     

Multi-wavelength fiber ring laser based on a sampled chirped fiber Bragg grating with a hybrid gain medium

The novel multi-wavelength fiber ring laser based on a sampled chirped fiber Bragg grating with a single SOA or a hybrid gain medium is demonstrated, respectively. In case of a hybrid gain medium, the SMSR improvement of ~ 5 dB was obtained when compared with the system with a single SOA. The proposed fiber laser offers advantages such as simple structure, low loss, multi-wavelength lasing lines with moderate output power.     

Performance analysis and improvement of semiconductor optical amplifier direct modulation with assistance of microring resonator notch filter

We demonstrate through numerical simulations that a passive single-bus microring resonator (MRR) employed as notch filter enables to directly modulate an ordinary semiconductor optical amplifier (SOA) at 10 Gb/s. This data rate constitutes a fourfold increase in the speed that it is possible to modulate the SOA due to its finite differential carrier lifetime. The theoretical analysis unveils how the MRR radius and detuning must be selected so that the MRR-based filtering scheme efficiently overcomes the pattern-dependent impairments incurred by the SOA narrow electrical bandwidth. Moreover, the small-signal analysis conducted to correlate the perturbations in power of the modulated optical signal inserted in the MRR with those at the MRR output confirms the enhancement in the electrical bandwidth of the SOA–MRR combination. Provided that the MRR response is tailored as suggested, which is technologically feasible, the MRR action permits the encoded signal to exhibit at extended data rate a pulse and eye diagram profile of acceptable quality, tolerable amplitude difference indices, an error probability below the forward error correction limit, and a sufficient system net gain for medium-haul transmission in standard single-mode fiber with dispersion compensation. These performance improvements can be beneficial for the direct modulation of standard SOAs. Together with SOAs inherent amplification capability, they can open new perspectives in using these active elements as external modulators in various target applications.     

YAG激光同步泵浦染料激光器产生38fs光脉冲

研究表明,不用碰撞脉冲锁模技术,而由一台简单的线型腔染料激光器,就可成功地产生短达38飞秒的光脉冲。这种激光器用六镜折叠腔,其中有Rh6G和DOPCI两个喷流和一个棱镜对色散补偿器,用连续锁模Nd:YAG激光器的倍频输出同步泵浦。染料激光脉冲的平均功率为20mW,脉冲重复频率近100MHz。     

High-power single-wavelength SOA-based fiber-ring laser with an optical modulator

A semiconductor optical amplifier (SOA) fiber-ring laser (SOAFRL) utilizing a fiber-Bragg grating (FBG) and lithium niobate (LiNbO₃) modulator is demonstrated. The laser operates at a wavelength of 1547.64 nm, which is equal to the Bragg wavelength in the saturation region. By removing the LiNbO₃ modulator in the ring, the laser shows a single-wavelength output, which has a lower peak power. The experimental results show that when reaching the saturation level, the system with the LiNbO₃ modulator shows a higher saturation current and peak power compared to that of the system without the modulator. The effect of varying the modulation frequency on the laser output power is investigated. By incorporating the LiNbO₃ modulator in the laser cavity, the side-mode suppression ratio (SMSR) of the laser is significantly improved and a higher peak power can be obtained at a higher current.     

All-solid-state continuous-wave frequency doubling Nd:YAG/LBO laser with 8.2 W output power at 660 nm

An efficient and compact red laser at 660 nm is generated by intracavity frequency doubling of continuous wave (CW) laser operation of a diode pumped Nd:YAG laser at 1319 nm under the condition of suppression the higher gain transition near 1064 and 1319 nm under the condition of suppression the higher gain transition near 1064 and 1338 nm. With 40 W diode pump power and a frequency doubling crystal LBO, as high as 8.6 W of CW output power at 660 nm is achieved, corresponding to an optical-to-optical conversion efficiency of 21.5% and the output power stability in 8 h is better than 2.73%. To the best of our knowledge, this it the highest conversion efficiency of watt-level laser at 660 nm generated by intracavity frequency doubling of a diode end pumped Nd:YAG laser at 1319 nm.