半导体激光器稳频技术研究

具有窄线宽和较高频率稳定性的半导体激光器,在高分辨率激光光谱、原子频率标准、大气和环境监测、光通信等众多领域中具有极其重要的应用。因此半导体激光器的稳频研究具有十分重要的意义和应用价值。较为全面的总结了目前国内外广泛应用的各种半导体激光器稳频技术,简要介绍了各稳频技术的实验方案及基本原理;对各方案的特点、能够达到的频率稳定水平、优缺点等进行了全面的分析。对半导体激光器稳频发展趋势做了预测。     

采用温控和碘吸收池技术的发射激光稳频技术

多普勒测风激光雷达通过分析系统回波信号的多普勒频移反演出风速，为提高风场探测精度，从稳频技术方面展开研究。在稳频过程中，分别采取措施消除激光频率的长期漂移和短期抖动。针对激光频率的长期漂移，设计并研制了种子激光器温控箱，通过水浴的控温方式大大减小了激光频率的长期漂移，将激光频率稳定在±50 MHz以内；针对激光频率的短期抖动，采用以碘分子吸收池为核心器件的稳频系统，通过半导体控温方式对碘分子吸收池精确控温，控温精度达0.03 ℃，提高了稳频精度，将激光频率进一步稳定在±8 MHz以内，满足±10 MHz以内的设计精度要求。通过搭建多普勒测风激光雷达系统，对发射激光稳频装置进行系统验证，连续4组风场观测结果表明:系统探测高度为17 km，绝大部分方差在4 m/s以下，满足测风激光雷达测量指标的要求。     

利用锁相飞秒激光对碘分子R(59)8-4超精细跃迁的绝对频率测量

介绍了633 nm半导体激光频标系统,高重复频率锁相飞秒激光器系统和绝对频率测量系统的建立以及测量碘分子超精细跃迁绝对频率的系统方案.633 nm半导体激光频标采用三次微分稳频方法,将激光频率锁定在碘分子谱线上,获得0.5 mW的稳频激光输出.飞秒激光稳频系统通过锁相电路将飞秒激光的高重复频率(760 MHz)和初始频率稳定在微波频率标准上,从而得到稳定的飞秒光梳,其稳定度优于6.44×10-13.在此基础上建立了绝对频率的直接测量系统,即利用波长计直接测量光梳的齿数n,并通过拍频法,测出633 nm半导体激光频标与飞秒光梳的差频,从而计算出相应谱线的绝对频率.这样,通过锁相飞秒激光器,建立了微波频率标准到光学频率标准的传递,为进一步的基础研究工作奠定了基础.     

单频脉冲激光器的分子吸收光谱频率稳定技术研究

单频脉冲激光器的频率稳定性显著地影响直接探测多普勒激光雷达的风速测量准确性,工作在半导体抽运Nd…YAG激光器倍频532nm的种子注入脉冲激光器的典型自由频率漂移可达15MHz/min,相当于4m/s风速误差。基于碘分子吸收光谱稳频原理,采用Labview虚拟仪器控制技术,对种子注入脉冲放大式的半导体抽运Nd…YAG激光器进行稳频,实现了脉冲激光器的频率扫描、碘分子1109光谱吸收线的自动匹配和频率锁定。长时间(大于2h)频率漂移标准偏差为0.8MHz,等效风速误差为0.2m/s,达到直接探测多普勒测风激光雷达长时间测量对脉冲激光器的频率稳定要求。     

基于温度闭环反馈的He-Ne激光器热稳频系统

为了提升激光回馈测量系统中He-Ne激光器的性能, 解决激光回馈镜不断移动时频率无法使用传统方法稳定的技术问题, 采用基于温度反馈控制激光器管体温度的闭环被动稳频的方法, 进行了理论分析和实验验证, 研究了不同管体温度与环境温度差值下频率稳定性。结果表明, 系统最佳温差为25.6℃; 在此温差条件下稳频后, He-Ne激光器波长波动范围达10-4, 即频率稳定性达到1.61×10-7, 功率漂移量低于3.20%。该系统可以根据环境温度的变化调节稳频温度点, 并且稳频结构简单, 满足激光回馈一般应用系统稳定性的要求。     

He-Ne激光稳频技术现状与发展

;激光波长在测量方面的广泛应用决定了激光器输出频率的重要程度.文中分析了各种影响He-Ne激光光源频率稳定性的因素,如温度变化、机械振动以及磁场影响等.还介绍了目前常见的三种稳频技术:蓝姆凹陷稳频法、饱和吸收稳频法和塞曼效应稳频原理.并分析了这些技术各自的优缺点.着重介绍了热稳频法.较之前三种方法,热稳频法的系统结构简单、抗干扰能力强,因此得到了更广泛的应用.最后展望了稳频技术的新发展,即通过检测频率获得误差信号的拍频稳频技术.     

用于原子重力仪的外腔半导体激光器的两种稳频方法比较

在铷原子气室中实现了饱和吸收谱稳频法和消多普勒的双色谱稳频法,以给在建的原子干涉重力仪系统选择合适的激光稳频方法。介绍了两种稳频方法的基本原理及实验细节。通过调整光路设计、自制低噪声光电探测器以及应用数字锁定模块,获得了良好的鉴频误差信号。每种方法都搭建了两套稳频系统并在3 000 s采集时间内保持锁定。激光器在经饱和吸收法和消多普勒双色谱法锁定后,激光频率波动分别为16.2 kHz和31.4 kHz,相应于在10 s采样时间下分别获得4.2110-11和8.1810-11的频率稳定度;相比之下,激光器自由运转时,频率波动和稳定度分别为629 kHz和1.6410-9。在原子重力仪系统小型化的需求下详述了两种稳频方法的优缺点,比较而得消多普勒的双色谱稳频法在原子干涉重力仪的小型化模块化发展方向不失为具有潜力的一种选择。     

自动稳频半导体激光器研究

实现了一种新的稳频方案。通过对饱和吸收信号进行检测,得到半导体激光器频率的变化量,利用温度粗调、电流细调的方法对半导体激光器进行稳频,根据此思路设计了基于单片机控制的稳频系统的硬件电路及软件辅助锁频程序。经实验验证,该系统实现了开机自动稳频,已经连续稳定工作超过180天,得到秒级稳定度4.57×10-11,千秒级稳定度3×10-12,近万秒级稳定度2.78×10-12的稳定度指标。为实现稳频半导体激光器的小型化和模块化提供了一种途径。     

采用射频调制实现对单频激光器频率噪声的抑制

在使用铷原子饱和吸收谱线作为激光频率参考进行稳频的激光稳频系统中,环路带宽是影响激光输出频率噪声的重要因素之一。对激光稳频系统中限制环路带宽的主要因素进行分析,使用射频调制信号直接调制商用外腔半导体激光器的高速电流调制端来对激光稳频系统的环路带宽进行拓展。根据对稳频环路的分析,合理设置反馈电路,实现激光稳频。使用低频谱分析仪对稳频后的鉴频信号进行分析,发现带宽拓展后,在傅里叶频率为5kHz处对频率噪声的抑制度达到了20dB以上。通过将该稳频激光器输出的激光与锁定在极稳恒温晶振上的飞秒光学频率梳进行拍频,测量了该稳频激光相对光梳的频率噪声,测量结果与直接分析鉴频信号的结果吻合。经过测量,通过拓展带宽抑制频率噪声,稳频激光器的短期频率稳定度得到改善。最后,测量了稳频激光相对于锁定在恒温晶振上的飞秒光学频率梳的频率稳定度,Allan方差在平均时间1s时达到4.52×10~(-12),在平均时间20s时达到1.65×10~(-12)。     

外腔半导体激光器设计与高次谐波稳频

研究了利特罗(Littrow)结构外腔半导体激光器的结构参量对激光连续可调范围的影响。给出了反射镜转轴等处的机械加工误差对激光波长连续可调范围所造成的影响的数值计算结果。介绍了半导体激光器外腔结构设计的具体细节要点。利用该设计制作的外腔只需要配合商用半导体激光管便可以得到优质的780nm激光输出,经测量其线宽小于1MHz,连续可调谐范围大于3GHz。利用腔外Rb饱和吸收谱的三、五次谐波稳频方法对半导体激光器进行了稳频。其中提出了优化激光频率短期稳定度的方法,并对调制深度的选择给出了详细的理论解释。根据该优化方法设计出稳频系统对半导体激光器进行稳频,得到了稳定度达到10-12量级的半导体激光输出。     

Frequency stabilization of a GaAs semiconductor laser by use of theoptical-optical double-resonance effect of the Doppler-free spectrum ofRb D1 line

The frequency of a GaAs semiconductor laser was locked to the hyperfine spectrum of the Rb D₁ line by saturation spectroscopy. A first GaAs laser was locked to one of the Doppler-free hyperfine lines using a source modulation method. The burnt hole modulated by the stabilized laser beam was detected by a second laser beam irradicated from the same or the opposite direction and was used as a frequency discriminator to stabilize the second laser. The characteristics of the double-resonance spectrum were measured. The frequency stability of the second laser, which was free from frequency modulation, was estimated to be on the order of 10^-9     

光学谐振腔增强碘分子调制转移光谱

提出了一种新的高灵敏激光光谱技术——激光双频相位调制环形腔增强调制转移光谱技术。该技术采用单一晶体实现激光双频相位调制，在满足环形腔高精度锁定的同时，又结合了调制转移光谱技术的高灵敏度、高分辨率、无多普勒背景的优点和环形谐振腔增强技术在提高谱线信噪比方面的优势；由此，实验观察到^127I2分子在532nm波段高信噪比的超精细结构光谱。与传统调制转移光谱技术相比，该技术在提高微弱吸收光谱信号的探测灵敏度方面具有明显的优势，在高灵敏、高分辨光谱检测和激光稳频方面将有很好的应用前景。     

High frequency heterodyne spectroscopy with current-modulated diode lasers

The use of current-modulated semiconductor lasers for optical heterodyne spectroscopy has been investigated at modulation frequencies up to 2.6 GHz. The current modulation produces a simultaneous frequency and amplitude modulation of the laser output. A characteristic heterodyne spectrum occurs when the modulated laser probes a narrow absorption line. In order to analyze the measured spectra, a complete line shape theory has been derived for heterodyne spectroscopy with frequency- and amplitude-modulated laser light. The results show how the obtained signals depend on the modulation frequency and the phase difference between the frequency and the amplitude modulation. The measurement technique permits investigation of the FM-AM phase difference of current-modulated semiconductor lasers.     

Frequency stabilization of semiconductor lasers for applications in coherent communication systems

The stabilization of the mean frequency of a single-mode semiconductor laser used under modulation in a FSK heterodyne transmission system is achieved by a novel method. The frequency stabilization scheme locks the laser to one of the resonance frequencies of a Fabry-Perot interferometer (FPI). The laser is weakly modulated at a frequency higher than any signal frequencies. Light reflected from the FPI is detected and synchronously demodulated for feedback and current control of the laser. A laser modulated by a pseudorandom sequence with a rate of 140 Mbit/s and an optical frequency deviation of 280 MHz is stabilized with this method against variations in operating temperature and bias current. The mean optical frequency is maintained within ± 10 MHz for hours. Analysis and experiments confirm that the laser frequency remains stable even when the laser linewidth changes under weak optical feedback.     

Optical-feedback-induced chaos and its control in multimodesemiconductor lasers

The effects of optical feedback in multilongitudinal mode semiconductor lasers are studied through computer simulations. Two separate regimes are found based on the length of the external cavity. For long external cavities (external-cavity mode spacing larger than the relaxation-oscillation frequency), the laser follows a quasi-periodic route to chaos as feedback is increased. For short external cavities, the laser can undergo both quasi-periodic and period doubling routes to chaos. When the laser output becomes chaotic, the relative-intensity noise is greatly increased (by more than 20 dB) from its solitary-laser value. Considerable attention is paid to the effects of optical feedback on the longitudinal-mode spectrum. The stabilization of the mode spectrum and the reduction of the feedback-induced noise through current modulation are studied and compared with experimental results. Current modulation eliminates feedback-induced chaos when the modulation frequency and depth are suitably optimized. This technique of chaos control has applications in optical data recording     

Nondegenerate Phase-Locking of a Semiconductor Laser by Sideband Injection

A semiconductor laser rate equation theory is presented that describes sideband injection locking under both weak optical injection and current modulation. By simultaneous optical injection and current modulation, control of both the phase and the frequency of a semiconductor laser is demonstrated. The phase-locked semiconductor laser operates at a different frequency to the optical injection source, with a frequency-difference given by the current modulation frequency. This method can be used to produce broadband sources, such as those producing ultrashort pulses and those required for coherent control, or to create high-frequency electronic oscillator sources with phase control by interference beating     

激光强回馈系统的动态调制稳频技术

激光强回馈系统与弱回馈系统相比,在无任何电子细分条件下就可获得纳米级的分辨率。但是,由于其回馈水平高,容易发生模式转换或偏振跳变,稳频十分困难。提出了一种激光强回馈系统的动态调制稳频方法,研究了动态调制稳频中的零点定位、清零补偿等关键技术及算法。实验结果表明,通过采用动态调制稳频技术,消除了激光强回馈系统中的模式转移及偏振跳变现象,获得了调制均匀、幅值相等的回馈条纹,有效地解决了激光强回馈系统的稳频问题,大大提高了系统的抗干扰能力,对进一步研究高精度强回馈测量系统具有重要意义。     

S/N and error rate evaluation for an optical FSK-heterodyne detection system using semiconductor lasers

Receiving performance is evaluated for an optical FSK-heterodyne detection system in which semiconductor lasers are used as both an FSK transmitter and an independent local oscillator. Noise and error rate are measured under feedback stabilization of IF signal frequency and electrical equalization of semiconductor laser FM modulation frequency characteristics. The minimum received signal power of -44 dBm, which is about 2 dB better than that in IM direct detection, is achieved at a 10^-9error rate for a 200 Mbit/s signal. Excess errors for FSK signals result from frequency broadening of the laser spectrum. Both AM and FM quantum noises in the lasers are primary factors which determine system performance. Error rate characteristics in an optical FSK direct detection system, in which a Michelson interferometer is employed as an optical frequency discriminator, are compared with the above results.