Nonlinear dynamics of a laser diode with optical feedback systemssubject to modulation

The nonlinear dynamic behavior of a direct frequency-modulated diode laser with strong optical feedback is examined and compared to a laser diode subject to electro-optically modulated, strong optical feedback. Direct modulation is achieved by sinusoidal modulation of the diode laser injection current. Electro-optic modulation is achieved by applying a sinusoidal voltage to an intracavity phase modulating element. The output state (characterized by the output power versus time, the intensity noise spectrum and the optical frequency spectrum) for both types of modulation is dependent on the ratio of the modulation frequency to the external cavity resonant frequency, and the modulation power. A number of distinct states are observed: conventional amplitude modulation (with FM spectra); multimode, low-noise amplitude modulation; multimode, high-noise amplitude modulation; periodic limit-cycle operation; quasi-periodicity; chaos; low-frequency fluctuations; and mode-locking. There are significant differences between the direct and electro-optic frequency-modulation cases. The onset of the dynamic instability is characterized as a noisy period-one oscillation for direct modulation and a low-frequency fluctuation for intracavity electro-optic modulation. Phase portraits produced experimentally with the use of a digital phosphor oscilloscope are shown to agree well with those constructed from output power versus time data. This represents an experimental method for examining the dynamics phase portraits in real-time     

利用腔内位相调制改善固体激光器的光束质量

提出一种新的利用腔内位相调制的方法来改善激光器输出的光束质量。位相调制用铌酸锂 (LiNbO3 )电光晶体实现 ,所用激光器为连续氪灯抽运的Nd∶YAG激光器。实验结果表明 ,利用腔内位相调制的方法 ,可以有效地使多模激光变为具有均匀光强分布的近基模光束     

High-power 1320-nm wafer-bonded VCSELs with tunnel junctions

A new long-wavelength vertical-cavity surface-emitting laser structure is described that utilizes AlGaAs-GaAs mirrors bonded to AlInGaAs-InP quantum wells with an intracavity buried tunnel junction. This structure offers complete wavelength flexibility in the 1250-1650 nm fiber communication bands and reduces the high free-carrier losses and bonded junction voltage drops in previous devices. The intracavity contacts electrically bypass the bonded junctions to reduce threshold voltage. N-type current spreading layers and undoped AlGaAs mirrors minimize optical losses. This has enabled 134/spl deg/C maximum continuous-wave lasing temperature, 2-mW room-temperature continuous-wave single-mode power, and 1-mW single-mode power at 80/spl deg/C, in various devices in the 1310-1340 nm wavelength range.     

Three-terminal bistable low-threshold strained InGaAs/GaAs lasergrown on structured substrates for digital modulation

Strained InGaAs/GaAs quantum-well three-terminal lasers with monolithically integrated intracavity modulators were fabricated using low threshold current structures formed by the temperature engineered growth (TEG) technique. An on-off switching ratio of 556 was obtained for a 30-mV change in absorber voltage. An optical power contrast ratio of 7.5 was measured with a total DC power consumption of 25.3 mW. These results show a great improvement in the digital (on-off) switching performance of three-terminal lasers with intracavity modulators     

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-speed large-signal digital modulation of three-terminallow-threshold strained InGaAs/GaAs lasers

We present large-signal digital modulation of very low-threshold strained InGaAs/GaAs single quantum well (SQW) lasers with monolithically integrated intracavity modulators. The voltage controlled intracavity modulator was driven from a simple emitter-follower using a single NPN transistor. Modulation response mas obtained from dc to 1 Gbit/s with a modulation efficiency of 27% and modulation depth of nearly 100%. A bit-error-rate (BER) lower than 10^-11 was measured at 1 Gbit/s with an input signal swing of only 110 mV. We demonstrate the suitability of these devices for ultrabroad-band optical interconnection applications     

Q-switching cleaved-coupled-cavity laser with an integrated intracavity modulator

We describe fabrication and performance of a Q-switching cleaved-coupled-cavity laser with an integrated intracavity modulator. The pulse repetition frequency of this 3-section device was tunable between 320 and 450 MHz with an external microwave injected signal, the modulation depth of the pulsations was 80?100% with a nearly single-longitudinal-mode output spectrum, and the Q-switched light pulses were modulated by a pseudorandom PCM signal at 322 Mbit/s.     

A model for optimization of the performance of frequency-Modulated DFB semiconductor laser

We have developed a model of frequency modulated distributed feedback laser with intracavity phase modulator and have shown that it can operate in two different regimes, only one of which has good frequency-modulated (FM) response. We have identified the combination of the laser parameters that forces laser to operate in high FM efficiency regime. The results of our initial experiments support these conclusions.     

An 18-channel multifrequency laser

A multifrequency laser (MFL) is demonstrated that runs simultaneously CW on 18 channels spaced by 103 GHz. The laser emits -14.6-dBm power per wavelength channel into single-mode fiber. Each wavelength channel can be modulated at 1.24 Gb/s. The MFL exhibits a stable and reproducible optical channel spacing owing to the reproducibility of the waveguide grating router that serves as the intracavity filter element.     

Broadly tunable InGaAsP/InP vertical-coupler filtered laser with low tuning current

A tuning range of 48 nm has been achieved with a tuning current of only 40 mA in a 1.55 mu m InGaAsP/InP multiquantum-well laser based on a grating-assisted vertical coupler intracavity filter. Using a combination of current and voltage tuning a 55 nm tuning range was demonstrated.<>     

n型GaAs MESFET沟道特性的研究

报道了ｎ型ＧａＡｓ ＭＥＳＦＥＴ漏源电流Ｉｄｓ和栅源电压Ｖｇｓ间的关系,发现在负栅压状态下,沟道特性分四个区域：过调制区、线性调制区、过渡区和夹断区,并且零栅压饱和漏源电流大的器件线性调制区的范围较大,过渡区的范围较小。     

Dual-polarization frequency-modulated laser source

Diode-pumped 1.3-/spl mu/m as well as 1.06-/spl mu/m Nd:YAG lasers have been operated with two orthogonally polarized modes at slightly different frequencies. The frequency difference, controlled by an intracavity electrooptic crystal, may be modulated. Thus, two polarized-outputs are obtained; one at a constant frequency, and the other frequency-modulated. This is a novel source for frequency-modulated heterodyne detection systems where the reference (local oscillator) frequency originates from the signal laser itself and is automatically locked to it.     

内腔泵浦的BaWO4反斯托克斯拉曼激光器实验研究

实验研究了内腔BaWO4反斯托克斯拉曼激光器的激光特性。通过在调Q的基频谐振腔中插入一倾斜的BaWO4拉曼谐振腔,实现基频光、一阶斯托克斯光和一阶反斯托克斯光的非共线相位匹配,进而实现了内腔反斯托克斯拉曼激光器在968nm的运转。测量了不同泵浦电压下输出的一阶反斯托克斯光的单脉冲能量,当泵浦电压为750V时,获得的最大输出能量为0.79mJ,相应的基频光到一阶反斯托克斯光的转化效率为1.5%。一阶反斯托克斯光的典型脉冲宽度为4.9ns。     

用腔内自注入技术和铁氧体线技术产生脉宽连续可调的毫微秒激光脉冲

对腔内自注入再生放大运转时多种谐振腔结构下的输出脉冲宽度作了系统的分析.借助铁氧体传输线技术,用连续改变电脉冲宽度而不改变谐振腔结构的方法,在磷酸盐钕玻璃器件上实现了脉冲宽度在1.3～6ns内方便地连续可调.用较简单的雪崩管电路在同一个普克尔盒上完成了调Q与腔倒空两个动作,得到了功率3MW的单脉冲输出.     

基于旋磁非线性传输线的小型化强电磁脉冲源的仿真研究

与传统基于电真空器件的窄谱高功率微波源相比,基于旋磁非线性传输线(GNLTL)的宽谱强电磁脉冲源无须驱动电子束、导引磁场和真空条件,具有能量效率高、工作频率可调以及可重频运行等优势,是一种结构简单、适合小型化和固态化的技术方案。该文通过理论分析其产生射频振荡和脉冲陡化的工作机制,并利用商业软件建立一套可视化的2-D GNLTL仿真模型进行验证。通过仿真分别研究不同注入电压和不同轴向偏置磁场下的旋磁输出脉冲的时域和频域特性。模拟结果表明：随着注入电压增大,经调制的振荡电压峰值升高,而调制深度则是先增加后减小到几乎不变,输出电压上升沿减小后趋于稳定,而中心频率则随着注入电压增大而增加;随着偏置磁场增加,输出振荡峰值电压和调制深度均是先增大后减小,输出电压上升沿先减小后增大,而中心频率先减小后增大。     

Optical bistability in a two-section InAs quantum-dot laser

Room temperature,continuous-wave bistable operation is achieved in two-section 1.24μm InAs quantum-dot (QD) lasers with integrated intracavity QD saturable absorbers(SA).It is found that the hysteresis width is narrowed with increasing reverse bias voltage,and broadened with increasing length of saturable absorber.This can be explained by the competition between QD absorption and electroabsorption in the SA section.In addition,a larger hysteresis width is realized than other reports so far,which can be a...     

扰动对非稳腔模式的影响和腔内倾斜像差校正

采用哈特曼-夏克(Hartmann-Shack)波前传感器分析了腔内扰动对无源正支共焦腔调腔光模式的影响,用模式法进行了波前复原计算。引入等量扰动,腔内凹镜对于腔模的影响大于凸镜;且对于大菲涅耳数非稳腔,腔内倾斜扰动量与输出光束中查涅克(Zernike)倾斜像差系数具有较好线性关系。建立了基于哈特曼-夏克波前传感器进行腔外探测,控制腔内凹镜的低阶像差校正系统,比较了在不同腔内扰动状态下对倾斜像差的控制结果。实验表明,对于腔内扰动频率较低或者准静态的情况,控制系统对腔内倾斜像差的校正具有较好的效果。     

Single frequency electrooptical tuning of an extended cavity diodelaser at 1500 nm wavelength

A wavelength-tunable, single-frequency GaInAsP-InP laser diode using an intracavity electrooptic LiNbO₃ crystal as the wavelength selective component is discussed. Wavelength tuning is achieved by applying a driving voltage on the crystal electrodes. First results indicate a tuning rate of 1 GHz/V over a tuning range of about 4 nm. This performance was obtained using a nonoptimized X-cut, Z-propagating LiNbO₃ crystal. A potential tuning rate of 6.5 GHz/V is possible with reasonable improvements     

扭曲向列相液晶在复合消色差延迟器件中的应用

借助琼斯矩阵对扭曲向列相(TN)液晶的光学性能进行了分析,发现在外加电压调制下的TN液晶盒,在选取的液晶厚度合适时,可等效为对应液晶厚度的特定波长λ/2波片,通过合理的设计搭配,与两个λ/4波片进行组合,使其整体作为一个偏振调制元件。经计算可知,当所加电压大于TN液晶盒转向的阈值电压时,其作用相当于一个消色差的λ/4波片或λ/2波片;当撤掉外加电压时可作为一般的90°旋光器。     

光伏锑化铟红外探测器的电容效应

在调制信号下工作的光伏锑化铟红外探测器的探测率和响应率受探测器的交流特性的影响，减小探测器的电容有利于提高其电压响应率和探测率。