基于时变功率谱的激光器调谐瞬时线宽测量方法研究

半导体激光器的线宽通常采用激光外差测量技术,通过差拍信号的功率谱密度函数来确定,受傅里叶变换方法的限制,得到的均是在一定时间段内的静态平均线宽。为了获得半导体激光器在电流调谐过程中的瞬时线宽特性,提出了利用时变功率谱获知调谐瞬时线宽的相干和非相干测量方法,并分别进行了理论分析和实验验证。首先对半导体激光器输出光信号及差拍信号进行了时间-频率域下的数学描述,确定了时变功率谱与调谐瞬时线宽的关系;其次,针对差拍信号的趋向性特征,提出了趋势局部均值分解方法,并研究了利用分解出的乘积函数建立差拍信号及激光器输出光信号的时变功率谱的方法;最后利用非相干和相干测量法分别获得了分布反馈式半导体激光器在50~51及50~100 mA锯齿波电流调谐过程中的瞬时线宽。     

超短时延测量DFB激光器的动态线宽

激光器调谐过程中的动态线宽是非常重要的参数, 然而, 当前各种测量方法得到的都是激光器稳定状态下的静态线宽. 本文提出一种对干涉拍信号进行基于局部均值分解的时频分析进而获取激光动态线宽的方法, 通过仿真信号验证了这种时频分析方法提取瞬时相位噪声的有效性; 构建实验系统, 利用10cm路径差产生约0.5ns的超短时延, 提取相位噪声的时频分布, 首次得到了分布反馈半导体激光器在脉冲工作模式下的动态线宽. 关键词： 超短时延 动态线宽 局部均值分解 时频分布     

减反膜外腔半导体激光器特性的研究

研究了镀减反膜GaAs半导体激光器在Littrow 式外腔结构中的输出特性.采用电流补偿技术,得到了约30 GHz的连续无跳模调谐范围.利用外差拍探测技术获得激光器输出线宽约为120 kHz.还研究了激光器的强度噪声分别随着电流与波长变化的特点并对此进行了分析.该类激光器可以广泛应用在冷原子物理、激光光谱以及量子光学等许多领域. 关键词： 减反膜 半导体激光器 线宽 强度噪声     

基于MI自零差法的窄线宽激光器线宽测量

提出了基于迈克尔逊干涉仪的延时自零差法,讨论了该方法测量激光线宽的原理.搭建了线宽测量系统,对窄线宽激光器的线宽进行了测量.测量系统运用数据采集卡获取拍频信号,通过软件算法分析拍频信号自功率谱半峰值宽度实现激光线宽测量.实验测得RIO公司某型窄线宽激光器的线宽为2.7kHz,与该激光器的标称线宽相符合.同时对另一台激光器不同输出光功率下的线宽进行测量,结果表明其线宽和功率成反比关系,进一步验证了基于迈克尔逊干涉仪的延时自零差法测试的准确性.     

宽带可调谐单频窄线宽光纤激光器

设计出一种集可调谐带通滤波器、高精度环形滤波器和光纤环形镜于一体的全光纤复合腔结构可调谐单频窄线宽光纤激光器。采用980 nm半导体激光器作为抽运源,掺镱光纤在谐振腔内分别作为增益介质和可饱和吸收体,成功实现波长为1030～1090 nm稳定的宽谱可调谐单频窄线宽激光输出。当抽运光的抽运功率为300 mW时,在波长为1070 nm处得到的输出功率最大,为18.5 mW,斜率效率达到7.95%,持续1 h内没有出现跳模现象,功率不稳定性小于1%;当抽运功率为200 mW时,利用延迟自外差法测量线宽,得到波长调谐范围内的平均线宽为8.7 kHz,弛豫振荡频率为64 kHz。     

回音壁微腔激光器噪声特性数值模拟研究(特邀)EI北大核心CSCD

通过建立包含朗之万噪声源的三模速率方程模型,模拟研究了回音壁模式微腔激光器的噪声特性和线宽特性,特别是注入电流热效应引起的跳模及其对光功率和实现窄线宽的影响。回音壁微腔激光器单模工作时,在大偏置电流下可由低频处的频率噪声得到百kHz以下的激光器线宽;在微腔双模激射状态下,由于模式竞争作用,微腔激光器的相对强度噪声和频率噪声在低频处都有明显的升高,使得激光器的线宽展宽。此外,还采用快速傅里叶变换的方法由时域信号计算获得激光模式光谱线型,由此得到的激光模式线宽与通过频率噪声谱获得的线宽基本一致。     

激光自外差相干测量中分布反馈半导体激光器电流调谐非线性的补偿方法

半导体激光器的电流调谐非线性对自外差相干测量的精度影响很大.研究了分布反馈半导体(DFB) 激光器的电流调谐特性,据此提出一种数学模型补偿方法.利用已知光程差下的差拍频率,建立了动态调频 系数的数学模型.以此模型对DFB激光器的电流调谐非线性进行补偿,可以将差拍信号频率预测值的相对误差 减小约3%,提高了系统的测量精度.数学模型补偿方法简化了测量系统的结构,适用于高精度的电流调谐 激光在线测量系统.     

单纵模布里渊掺铒光纤激光器的实验研究

提出了一种具有多环形腔(MRC)和光纤布拉格光栅可调谐滤波器(FBG-TF)相结合的单纵模布里渊掺铒光纤激光器(BEDFL).实验中通过观察激光器输出光的拍频信号分析其光谱精细结构,分别讨论了布里渊增益、FBG-TF、MRC对BEDFL单模输出的贡献,给出了激光器的功率特性曲线和波长稳定性测试图.实验得到了在1550 nm处功率为4 dBm,信噪比(SNR)>60 dB,线宽小于1.5 kHz的稳定单纵模输出光.     

970 nm高功率光栅外腔可调谐半导体激光器

宽条形半导体激光器广泛应用于激光泵浦、激光加工等领域。针对宽条型半导体激光器输出光谱宽、调谐范围小的问题,采用衍射效率分别为28%和55%的反射式衍射光栅作为反馈元件构建了宽条形970 nm波长光栅外腔半导体激光器。研究了Littrow结构激光器参数对其性能（调谐范围、功率、阈值电流、线宽）的影响。实验结果表明,通过结构优化可得到窄线宽可调谐激光输出,适当地提高温度和使用较高衍射效率的光栅可增加激光器调谐范围,并且较高衍射效率的光栅可降低激光器的阈值电流。基于S偏振入射方式的光栅外腔激光器最大可实现27.87 nm的波长调谐范围,光谱线宽压窄至0.2 nm,输出功率可达1.11 W。     

三硼酸锂晶体Ⅰ类非临界相位匹配下近红外波段的差频产生

利用差频发生器产生波长范围为1.1~2.2μm的可调谐近红外激光.实验搭建了差频光路系统,以0.56~0.71μm染料激光器作为泵浦光、1.064μm的半导体激光器作为信号光,经过三硼酸锂晶体在Ⅰ类相位匹配方式条件下通过温度调谐非临界相位匹配方式差频产生较高功率的近红外激光,在近红外波段测得其平均输出功率在30mW以上.泵浦光功率为1.2 W、信号光功率为0.31 W时,测得差频波长为1.54μm的输出功率为35mW,转化效率达11.7%.该近红外差频发生器具有宽调谐、窄线宽的特点.     

DFB半导体激光器调谐动态波长特性研究

为了测量半导体激光器在电流调谐下的动态波长,提出了基于光纤延时自外差法的测量方案,阐述了测量原理,研究了拍频与动态波长的递推关系。应用该实验系统测量了分布反馈式半导体激光器调谐的动态波长特性,与由光谱仪测量的稳态波长特性比较。结果表明,动态波长与稳态波长随电流变化特性有着类似的非线性规律,在20~100 mA调谐范围内二者差异小于0.002 nm。此外,通过气体CO₂的两条吸收谱线与HITRAN谱库中标准吸收线位置比对,辨识出半导体激光器调谐的动态波长,该辨识出的动态波长值与由延时自外差法推算出的动态波长值比较,二者误差为1 pm,进而验证了该测量系统的可靠性。     

High-speed wavelength-swept semiconductor laser with a polygon-scanner-based wavelength filter

Ultrahigh-speed tuning of an extended-cavity semiconductor laser is demonstrated. The laser resonator comprises a unidirectional fiber-optic ring, a semiconductor optical amplifier as the gain medium, and a novel scanning filter based on a polygonal scanner. Variable tuning rates up to 1150 nm/ms (15.7-kHz repetition frequency) are demonstrated over a 70-nm wavelength span centered at 1.32 microm. This tuning rate is more than an order of magnitude faster than previously demonstrated and is facilitated in part by self-frequency shifting in the semiconductor optical amplifier. The instantaneous linewidth of the source is <0.1 nm for 9-mW cw output power and a low spontaneous-emission background of -80 dB.     

Frequency-tunable semiconductor lasers

Recent advances in frequency-tunable semiconductor lasers are reviewed. They are classified into hybrid and monolithic tunable lasers. Monolithic tunable lasers based on distributed Bragg reflector or distributed feedback laser structures are most attractive for practical applications. The device structures and the tuning characteristics are described, with emphasis on the tuning range, spectral linewidth and frequency-switching time. Recent system experiments using monolithic tunable lasers in an optical communication area are also described.An Invited Paper     

Tunable single-longitudinal-mode SOA-based fiber laser based on the spectral narrowing effect in a dispersion-shifted fiber

A tunable single-longitudinal-mode(SLM) semiconductor optical amplifier(SOA)-based fiber laser based on a dispersion-shifted fiber(DSF) is proposed and successfully demonstrated. SLM operation is obtained due to the spectral narrowing effect resulting from inverse four-wave mixing in a DSF. A tunable optical filter performs wavelength selection function. By inserting a length of DSF in the laser cavity, SLM lasing can possibly be obtained when laser oscillation is stably established after traveling through the DSF many roundtrips. Stable tunable SLM oscillation with a signal-to-noise ratio as high as 65 dB over a wavelength range of about 35 nm is achieved experimentally, and each spectral linewidth is less than 6.5 kHz.     

窄线宽高信噪比可调谐掺Er3+光纤激光器

基于偏振态调谐原理，利用多个偏振控制器在环形腔掺Er3+光纤激光器中实现了连续可调谐、窄线宽、高信噪比的单频激光输出.连续调谐宽度达22 nm (1538～1560 nm)，3 dB谱线宽度小于0.1 nm，光信号-自发辐射噪音比大于45 dB，最大输出功率约1 mW.在10～50 mW泵浦功率范围内，输出功率波动幅度小于1 dB.在室温下，工作数十个小时，中心波长漂移小于0.05nm.     

Frequency drift and instantaneous linewidth broadening of phase-section tuned SG-DBR laser

We experimentally investigate the spectral dynamics of a phase-section tuned sampled-grating distributed Bragg reflector (SG-DBR) laser by using optical heterodyne method. The measured time-resolved spectra of the beat signal illustrate that the beat signal suffers from both frequency drift and instantaneous spectrum broadening, which indicates that the wavelengths of the lightwaves experience drift and jitter. We study the variation of frequency drift and instantaneous linewidth broadening with applied voltages. It is helpful in selection of optimum operating conditions and design of experimental setup. Experimental results demonstrate that the pulse-waveform can be used to reduce the frequency drift by shorting the beating time.     

Novel discretely tunable narrow linewidth fiber laser with uniform wavelength spacing

A novel configuration of the tunable fiber laser with uniform wavelength spacing in dense wavelength division multiplexing (DWDM) application is proposed. The ring type tunable fiber laser consists of an all-fiber comb filter which determines the wavelength spacing, and a piece of adjustable fiber grating to select the discrete lasing wavelength for WDM application. The proposed all-fiber ring type tunable laser has potential application in the DWDM and other optical systems due to its advantages such as narrow linewidth, easy tuning, uniform wavelength interval, etc..