Injection locking of diode lasers

We present a theoretical analysis of the forward and reflected amplitudes in a diode laser oscillator cavity for both a single resonant mode and an injected signal. The analysis includes gain saturation and allows the gain coefficient at the injected frequency to be different from that at the resonant frequency. Analytic solutions for the axially dependent amplitudes are presented for the case of equal gain coefficients. For the more general case, a formula is presented for the intensity necessary for locking, which is shown to reduce in various limits to other expressions previously published. One immediate consequence of the present formalism is that the use of antireflection coatings on the diode end facets should act to reduce the injected signal intensity necessary for locking. In fact, reduction of the reflectivities to values of a few percent should enable locking over the entire gain curve with incident intensities which are small compared to the slave oscillator's normal output.     

自聚焦型自锁模固体激光器谐振腔的最优化研究

提出了对自聚焦型自锁模固体激光器谐振腔最优化的方法 ,讨论了 2个、3个和 4个反射镜组成的谐振腔的使用可能性 ,并对它们之间的数学关系服从ABCD矩阵法的客观规律进行了描述     

压电式微固体模态陀螺谐振频率自动跟踪电路

压电式微固体模态陀螺振子通过交变电压激振、传感电极感应出电荷。当激励电压频率为某阶振动模态谐振频率时,感应电荷达到最大值。设计了谐振频率自动跟踪电路,使陀螺稳定工作在谐振模态。使用现场可编程门阵列(FPGA)控制直接数字频率合成器(DDS)产生频率精确可调的激励电压,驱动陀螺振子振动。检测谐振点对应的激励电压和感应信号间的相位差,作为反馈信号调节激励电压频率。实验结果表明,当相位差锁定区域处在98.48°~100.27°时,振子感应电极输出信号最大,振子处于谐振状态,实现了振子谐振频率的跟踪锁定。该系统可用于以谐振器为核心器件的振子工作模态锁定与跟踪。     

Resonant passive mode-locked Nd:YLF laser

The authors review the theory of resonant passive mode locking (RPM) lasers and present experimental results for an improved Nd:YLF RPM laser that produced stable pulses as short as 3.7 ps at a repetition rate of 250 MHz. The average output power was 550 mW with 1.3-W average pump power from a Ti:sapphire laser. It was possible to couple 85% out of the nonlinear coupled cavity and still maintain stable mode locking. In RPM and amplitude nonlinearity such as absorption bleaching in a semiconductor reflector introduces an intensity-dependent reflectivity which strongly mode locks the laser. The reduced carrier lifetime in a low-temperature MBE-grown (LT) InGaAs-GaAs quantum-well reflector produces a sufficiently fast saturable absorber in the coupled cavity     

Diodes as pseudo-active elements in high-frequency DC/DC converters

A novel approach to realizing zero-voltage switching in high-frequency DC/DC converters is presented. Utilizing the parasitic associated with the diode stored charge, it is shown that the diode reverse current established for charge removal can be used advantageously to accomplish soft switching. The entire family of single-transistor DC/DC converters can be realized using the technique. The converter topologies are seen to differ from their hard-switched counterparts only by the presence of a resonant capacitor. It is also shown that device and component stresses are moderate as compared to existing quasi-resonant and resonant techniques. Converter analysis is rather complex as a result of the dominant diode nonlinearities, and no closed-form expressions are possible. Converter transfer characteristics are obtained through simulation, and operating limits are analytically obtained. The concept is validated by experimental results using buck-type converters rated at approximately 100 W and operating at frequencies around 1 MHz     

High speed nano-scale positioning using a piezoelectric tube actuator with active shunt control

Piezoelectric tube scanners are the actuators of choice in scanning probe microscopy. These nanopositioners exhibit a dominant first resonant mode that is excited due to harmonics of the input scan signal. This introduces errors in the scan obtained. The presence of this resonant mode limits the upper bound of a triangular scan rate to around 1/100th of the first mechanical resonance frequency. Passive and active shunts have shown to damp this resonant mode substantially and improve scan performance. Sensorless active shunts optimised using H₂ and H_infin techniques, is designed. These shunts reduce the amplitude of the first resonant peak of a prototype tube nanopositioner by 24 dB. A triangle wave input is used to test the improvement in scan performance due to the damping achieved by these active shunts. Analysis shows that damping the resonant mode in such fashion reduces the scan error by five times     

中心金属原子对萘酞菁化合物激发态的光学非线性增强效应

应用Z-扫描技术对比研究了萘酞菁铅和萘酞菁钯化合物在波长为532 nm纳秒激光脉冲作用下的三阶非线光学特性。实验结果表明,两种萘酞菁化合物均显现出较强的非线性吸收特性(反饱和吸收)和非线性折射特性(自聚焦)。理论拟合得出萘酞菁铅和萘酞菁钯的非线性吸收系数分别为6.5410-10 m/W和3.9010-10 m/W;非线性折射系数率n2分别为1.6810-10 esu和8.0410-11 esu;二阶分子超极化率系数分别为3.4410-28 esu和2.5710-28 esu,CS2二阶分子超极化率系数为4.3210-33 esu;两种萘酞菁化合物的二阶分子超极化率强于CS2近5个数量级。实验结果表明,萘酞菁铅化合物具有较强的非线性吸收和非线性折射特性,且大于萘酞菁钯化合物的光学非线性特性是由于萘酞菁铅化合物的重原子效应提高了其光学非线性特性。     

Slow amplitude modulation in the pulse train of a self-mode-lockedTi:sapphire laser

Periodic pulse-train amplitude modulations have been observed in a Kerr-lens self-mode-locked Ti:sapphire laser when the size of an intracavity slit is reduced below its optimal value for stable mode locking. These transient processes are dominated by 100-500 kHz periodic pulse-energy modulations and are inherent to the Kerr-lens mode-locking mechanism based on the intensity dependent transverse-beam profile of the laser and the long gain relaxation lifetime (3.2 ps) of the Ti:sapphire rod. We observe that when the slit width is decreased from 2 mm to 1.4 mm the modulation period increases from 2 ps to 10 μs and amplitude modulation deepens to almost 100%. An explanation similar to repetitive self-Q-switching and undamped relaxation oscillation is presented, which is consistent with the experimental results. A large low-frequency timing jitter on the order of submicroseconds, associated with the periodic pulse-train modulations, is also observed. The timing jitter is analyzed by incorporating the pulse energy modulation into the phase variation through the Kerr effect and consistent results are obtained. We have determined the cavity parameters to control these detrimental processes for stable mode-locked output. The observation of the amplitude modulation further confirms the Kerr-lens self-focusing model of self-mode locking in Ti:sapphire lasers     

Mode locking by cascading of second-order nonlinearities

We present a comprehensive theoretical and experimental study on a new passive mode-locking technique, called cascaded second-order nonlinearity mode locking (CSM), which exploits cascaded second-order nonlinearities to obtain large third-order susceptibilities from an intracavity second harmonic crystal. The nonlinear phase shift that originates in the nonlinear crystal is converted into a nonlinear amplitude modulation by a suitable intracavity aperture. A numerical model, based on a perturbative approach, allows the nonlinear loss modulation of resonators used for CSM to be calculated as a function of the resonator parameters and of the phase mismatch. The predictions of the model are confirmed by experiments performed on a CW Nd:YAG laser. The effects of group velocity mismatch and the limitations which it poses on the minimum achievable pulsewidth are analyzed both experimentally and theoretically     

DFB半导体激光器自注入锁定失稳因素分析

分布反馈(Distributed Feedback, DFB)半导体激光器具有体积小、成本低和工艺成熟等优势,但兆赫兹量级的线宽使其应用范围受限。采用环形谐振器对其进行自注入锁定,可将线宽压窄到千赫兹量级,但仍存在锁定不稳定的问题。文章采用四只不同的环形谐振器对DFB半导体激光器进行自注入锁定,通过实验监测自注入锁定时多个端口的光功率、偏振态和光波长的变化,揭示影响DFB半导体激光器自注入锁定稳定性的因素有谐振模式跳变、偏振态跳变,以及外界温度和振动引起的锁定环路的相位变化,且使用不同类型的环形谐振器进行锁定时,主导的影响因素不同。控制这些影响因素可以改善DFB半导体激光器自注入锁定的稳定性,使DFB半导体激光器自注入锁定技术有更好的应用效果。     

Polarization-dependent ultrafast optical nonlinearities of N,N-dimethylformamide at 400 nm

Ultrafast optical nonlinearities of N,N-dimethylformamide(DMF) are studied by using polarized light at 400 nm. Both nonlinear refraction(NLR) and stimulated Rayleigh-wing scattering(SRWS) depend on the polarization state of incident beam, while two-photon absorption(TPA) changes negligibly with polarization state. The polarization dependence of SRWS originates from that of NLR via self-focusing effect. Third-order susceptibility elements of DMF were determined, and a method to distinguish the mu...     

Comparison of Indirect Optical Injection-Locking Techniques of Multiple X-Band Oscillators

Experimental results of indirect optical injection-locking of two X-band FET oscillators are presented. An S-band master source is used to synchronize both oscillators simultaneously, with 18-MHz locking range using the fiber-optic link nonlinearity. The source of the optical link nonlinearity is traced to the laser diode by interferometric measurement. Both the laser diode and the FET oscillator nonlinearities can be exploited to achieve frequency multiplication of the master oscillator signal. The merits of these different methods are evaluated based on the locking range and the FM noise level of the injection-locked oscillator.     

受控非线性自聚焦

在高功率密度激光作用下，某些线性介质中会产生非线性自聚焦现象。非线性自聚焦的产生过程具有丰富的内涵。在一定条件下它是可控的．受控成模后在线性介质中传播保持其模不变。     

基于多模谐振的低剖面宽带贴片天线

为了增加贴片天线的工作带宽和改善其辐射特性,提出了一种基于多模谐振的低剖面贴片天线。通过在矩形贴片的非辐射边加载短路壁降低H面的高交叉极化,在贴片下方加载短路销钉提高TM_1/2,0模式的谐振频率（f_1/2,0）;然后在TM_3/2,0模式的零电流位置处切割一个矩形缝隙来激发辐射缝隙模式（TM_RS）,得到低剖面、宽频带和低交叉极化的三模谐振贴片天线;最后通过增加贴片宽度和调整天线结构,降低TM_1/2,2模式的频率（f _1/2,2）,实现了四模谐振。仿真和实测结果表明该四模谐振贴片天线在0.03λ₀的厚度下可将带宽增加到21.7% (2.67～3.32 GHz).     

Resonant Frequency of Open-Ended Cylindrical Cavity

The TE/sub 011/ mode of oscillation in an open-ended circular cylindrical microwave cavity is analyzed. The cavity consists of a circular waveguide that is terminated at each end with a thin cylindrical partition coaxial with the circular waveguide. The resonant frequency of the cavity is computed by using Laplace transform and Wiener-Hopf techniques. Numerical values for the resonant frequency are presented.     

渐变折射率多模光纤中的多模干涉应用研究

论述了SMS(单模-多模-单模)光纤结构的多模干涉基本理论,利用FD-BPM(有限差分光束传播法)对渐变折射率多模光纤和阶跃折射率多模光纤进行数值模拟,将自聚焦位置、激发模式等特征进行对比,给出渐变折射率多模光纤的优点。利用自聚焦效应,对渐变折射率多模光纤的聚焦和发散作用进行了理论分析,以较短的长度充当透镜的功能,并总结了现阶段的主要应用。     

DBR单纵模光纤激光器波长温度调谐

报道了采用DBR方式,利用8 mm的高浓度掺Yb3+单模光纤,实现了波长为1 064 nm的单纵模调谐激光稳定输出的实验结果。该DBR谐振腔有效腔长为16 mm,输出最大功率为7.4 mW,通过半导体制冷器温控改变谐振腔的温度,实现了0.824 nm的单纵模无跳模调谐。采用光纤外差法,并利用低损耗环形器和光纤反射镜倍增延迟线长度提升测量精度的方式,测量得到激光最大线宽为4.4 kHz。单纵模激光的弛豫震荡峰位于900 kHz处,其相对强度噪声为-110 dB/Hz,当频率大于1.5 MHz时相对强度噪声为-145 dB/Hz。     

小型TEACO2激光器的锁定技术研究

对小型ＴＥＡＣＯ２激光器的注入锁定技术和混事式锁技术进行了理论分析，指出了这两处锁定 缺点，提出了一种新型的用复合腔注入锁定方法来锁定小型ＴＥＡＣＯ２激光器，给出了复合腔注入锁定的实验结果。     

Ni(mpo)_2的近双光子共振光学非线性特性的研究

采用脉冲宽度为7ns、波长为532nm的激光束,首次利用Z-扫描技术测量了新型功能配合物材料Ni(mpo)2[分子式C10H8N2NiO2S2]的非线性吸收系数和非线性折射系数。用粒子数重新布居模型,合理地解释了非线性吸收和非线性折射的产生机理:非线性吸收来自于近共振双光子吸收,而非线性折射是由于近共振双光子吸收造成的折射加强。非线性吸收系数和非线性折射系数随光强的增大而线性减少是近共振双光子吸收引起粒子数重新布居的结果。