列阵半导体激光器的噪声

重点报道列阵GaAs-AlGaAs激光器相对强度噪声的测量结果,并和单元器件作了比较.实验测量包括相对强度噪声和驱动电流、调制频率以及温度的关系,并验证了在这些情况下相对强度噪声在激光器处于阈值时具有最大值的理论予言.     

Excess noise in intracavity laser frequency modulation

The response to perturbations and to stochastic noise of a laser below threshold subjected to an intracavity periodic frequency modulation is theoretically studied. It is shown that, when the modulation frequency is close to the cavity axial mode separation but yet detuned from exact resonance, the laser exhibits a strongly enhanced sensitivity to external noise, which includes large transient energy amplification of perturbations in the deterministic case and enhancement of field fluctuations in presence of a continuous stochastic noise. This large excess noise is due to the nonorthogonality of Floquet laser modes which makes it possible continuous energy transfer from the forcing noise to transient growing perturbations.     

基于B样条迭代法的激光光条噪声去除技术研究

在基于线结构光的视觉测量系统中,激光光条中心的提取精度是影响系统最后精度的关键因素。目前常用的光条中心提取方法都没有去除光条上的干扰噪声,在分析现有方法的基础上提出了一种利用B样条迭代去除光条噪声的方法。以光条上的点作为控制顶点拟合B样条曲线,在同一位置下用B样条曲线上的点取代噪声点,这样反复修改噪声点的位置使其逐渐逼近实际曲线,从而达到去除噪声的目的。利用重心法提取去噪后光条的中心,着重分析了参与运算的像素的取值范围。通过对比实验证明该方法的提取精度远高于其它方法,从而验证了去除噪声的有效性。     

Experimental Investigation of the Spectrum Characteristics of Laser Diodes Under Low Frequency Modulation

１ＩｎｔｒｏｄｕｃｔｉｏｎＴｈｅｃｈａｒａｃｔｅｒｉｓｔｉｃｓｏｆｌａｓｅｒｄｉｏｄｅｓｗｈｏｓｅｉｎｊｅｃｔｉｏｎｃｕｒｅｎｔｉｓｍｏｄｕｌａｔｅｄｄｉｒｅｃｔｌｙｂｙｈｉｇｈｆｒｅｑｕｅｎｃｙｓｉｇｎａｌｈａｖｅｂｅｅｎｉｎｔｅｎｓｉｖｅｌｙｒｅ...     

Optically Injection‐Locked Mid‐IR Quantum‐Cascade Lasers: The Output‐Power–Modulation‐Bandwidth–Noise Trilogy

A comprehensive study on the output power, the modulation response, and the relative intensity noise (RIN) behavior of an optically injection‐locked mid‐infrared quantum‐cascade laser reveals that the modulation bandwidth and the output power are enhanced in the stable locking range, while the RIN of the slave laser is a superposition of the master and slave noise sources. Since the RIN level of the master laser can even take the lead, a design procedure is introduced to improve the main characteristics of a free‐running laser, including the RIN, the photon lifetime, the modulation bandwidth, and the bias current, using facet reflectivity tailoring. A figure of merit is defined and the RIN reduction of about 20 dB Hz^?1 is obtained for very low injection powers compared with the injection‐locked system before the design of master laser.     

Speckle contrast evaluation of multi-emitter broad area 638-nm red laser diodes

Speckle contrast of single, dual, and triple emitter broad area laser diodes (BA-LDs) with a wavelength of 638 nm was experimentally investigated. Speckle noise was relatively small near the threshold current probably due to the longitudinal mode competition. Higher output power led to smaller speckle noise owing to the spectrum widening. A wide stripe presented an advantage in terms of speckle reduction in the single emitter LDs. It is also found that wider emitter width leads to the smaller the speckle noise. A larger number of emitters decreased speckle noise due to the beam superposition effect, even for multi-emitter LDs in which the emitters are built into one chipa.

     

金属表面非相干线结构光条纹中心提取方法

采用线结构光法测量金属表面形貌时,由于受到金属表面光学特性和散斑噪声的影响,条纹中心的提取误差往往较大。为此,提出了一种非相干线结构光形貌测量方法,避免了散斑噪声的影响。通过分析该方法测量金属表面形貌时的条纹图像特点,提出一种适合非相干线结构光条纹的中心提取方法。该方法首先采用结合积分图像原理的自适应阈值分割算法,对原条纹图像进行分割。采用灰度重心法粗提取原条纹中心坐标,以该坐标为基准向条纹宽度方向延伸,从而确定阈值分割后条纹图的感兴趣区和背景区,并去除背景区的噪声。经中值滤波后,采用几何中心法提取条纹中心。实验结果表明：采用该方法提取粗糙度样块表面非相干光条纹中心的平均误差为1.5μm,提取齿轮渐开线样板表面非相干光条纹中心的平均误差为0.9μm,均比其线激光条纹中心的提取误差小。所提方法能实现金属表面非相干线结构光条纹中心的精确提取。     

Phase Noise of Optically Generated Microwave Using Sideband Injection Locking

Optically generated 20-GHz microwave carriers with phase noise lower than -75 dBc/Hz at 10 kHz offset and lower than -90 dBc/Hz at 100 kHz offset are obtained using single- and double-sideband injection locking. Within the locking range, the effect of sideband injection locking can be regarded as narrow-band amplification of the modulation sidebands. Increasing the current of slave laser will increase the power of beat signal and reduce the phase noise to a certain extent. Double-sideband injection locking can increase the power of the generated microwave carrier while keeping the phase noise at a low level. It is also revealed that partially destruction of coherence between the two beating lights in the course of sideband injection locking would impair the phase noise performance.     

Narrow stripe semiconductor laser for improved performance of optical communication systems

A narrow stripe (GaAl) As/GaAs laser is described, which has low source noise, high linearity and an expected life in excess of 20,000 hours. It has a short coherence length compared with a self-focused or refractive index guided laser giving very good modal noise performance. It is suitable for all digital systems and all but the most demanding amplitude modulated analogue systems.     

Evidence of stochastic resonance in a laser with saturable absorber: Experiment and theory

A laser with intracavity saturable absorber showing optical bistability is investigated through the simultaneous injection of modulation and noise on the pumping parameter; stochastic resonance is exhibited in the measured signal-to-noise ratio of the laser intensity.     

The statistical fluctuation of a single-mode laser system driven by coloured pump noise with signal modulation and the quantum noise with cross-correlation between its real and imaginary parts

Using the linear approximation method, this paper studies the statistical property of a single-mode laser driven by both coloured pump noise with signal modulation and the quantum noise with cross-correlation between its real and imaginary parts, and calculates the steady-state mean normalized intensity fluctuation and intensity correlation time. It analyses the influences of the modulation signal, the net gain coefficient, the noise and its correlation form on the statistical fluctuation of the laser system respectively. It is found that the coloured pump noise modulated by the signal has a great suppressing action on the statistical fluctuation of the laser system; the pump noise self-correlation time and the specific frequency of modulation signal have the result that the statistical fluctuation tends to zero. Furthermore, the `colour' correlation of pump noise has much influences on the statistical fluctuation of the laser system. Increasing the intensity of pump noise will augment the statistical fluctuation of the laser system, but the intensity of quantum noise and the coefficient of cross-correlation between its real and imaginary parts have less influence on the statistical fluctuation of the laser system. Therefore, from the conclusions of this paper the statistical property can be known and a theoretical basis for steady operation and output of the laser system can be provided.     

Stochastic Resonance in Linear Region of a Single-Mode Laser： Effects of Amplitude Modulation of Signal

A single-mode laser noise model driven by quadratic colored pump noise and amplitude modulation signal is proposed. The real and imaginary parts of the pump noise are assumed to be cross-correlation. The effect of cross-correlation of noise and amplitude modulation of signal on laser statistical properties is studied by using the linearized approximation. The analytic expression of signal-to-noise ratio (SNR) is calculated. It is found that the phenomena of stochastic resonance (SR) respectively exist in the curves of the SNR versus the noise cross-correlation coefficient λ and the SNR versus the pump parameter a, as well as the SNR versus the signal frequency ω in our model. It is shown that there are three different typies of SR in the model: the conventional form of SR, the SR in the broad sense, and the bona fide SR.     

Effect of spontaneous frequency fluctuations on the emission line of a semiconductor laser with pseudorandom modulation of the pump current

The effect of random frequency fluctuations due to spontaneous emission and generation-recombination noise on the shape of the emission line of a semiconductor laser with pseudorandom modulation of the pump current is studied numerically. The roles of spontaneous emission and chirp modulation in forming the lasing spectrum are separated out. The dependence of the output spectral characteristics of the laser on the parameters and type of modulation is analyzed.     

高噪声背景下激光条纹亚像素中心的提取

针对线结构光三维形貌测量中大量噪声易干扰激光条纹中心提取准确度的问题,提出了一种条纹亚像素中心提取方法。分析条纹图像中的噪声,采用平均法和中值滤波预处理图像;利用迭代阈值分割及形态学方法,获取条纹目标,引入距离变换提取条纹的像素级中心;根据像素级中心、二值信息及光强灰度,结合曲线拟合及重心法精确提取条纹的亚像素中心。仿真分析和实验验证下,相邻行条纹中心列坐标最大偏差值像素小于2 ,平均偏差像素值约为0.3,与传统方法相比,2项指标值更小。实验结果表明,算法有效利用条纹灰度分布规律,可降低噪声对中心定位精度的影响,更逼近条纹真实中心位置,抗噪能力极强。     

高斯白噪声相位调制的激光光谱展宽

激光器是现代光学中一种常用的光源,分析其谱宽特性对于激光的研究具有重要意义.由于高性能窄线宽激光的半高全宽通常在几十M Hz以内,难以直接满足宽光谱领域的应用需求,因而无法发挥其在成本和性能方面的优势,这在一定程度上限制了激光的发展.如果在激光内部直接进行调制实现线宽展宽,又会导致频率的严重漂移,破坏稳频特性.为了在激...     

Photonic microwave generation and transmission using direct modulation of stably injection-locked semiconductor lasers

Direct modulation of a semiconductor laser subject to stable injection locking is capable of generating microwave subcarriers that are broadly frequency-tunable, more than 4 times its free-running relaxation resonance frequency, and are highly sideband-asymmetric, more than 22 dB. The latter characteristic makes the laser system particularly attractive for radio-over-fiber applications. Therefore, such modulation sideband asymmetry, its underlying mechanism, and its effect on chromatic dispersion-induced microwave power variation are extensively studied, in particular, over a broad range of injection conditions. Mappings showing integrated and global understandings of the modulation sideband asymmetry together with the modulation frequency enhancement are obtained accordingly. Interestingly, it is found that the microwave frequency can be tuned over a broad range while keeping a similar level of modulation sideband asymmetry and vice versa, either of which is achieved by simply changing the injection condition. This, therefore, considerably adds the flexibility and re-configurability to the laser system. The cavity resonance shift due to injection locking is responsible for not only the enhanced modulation frequency but also the modulation sideband asymmetry, where a modification in its previous interpretation is obtained for explanation. The modified modulation characteristics are strong functions of the linewidth enhancement factor, making it possible to choose lasers with proper values of the factor for different photonic microwave characteristics.     

Experimental observation of noise precursors for virtual Hopf phenomena near period-doubling bifurcations in modulated diode lasers

We present an experimental analysis of the effect of a rf amplitude modulation of the injection current in a distributed-feedback diode laser at 1.55 mum near the first period-doubling bifurcation. First experimental results of a virtual Hopf phenomenon were observed when two moving bumps with Lorentzian shapes appeared in the spectrum before the onset of the first period-doubling bifurcation occurred. We characterized this observation by increasing the amplitude of the current modulation of the diode laser until period-doubling bifurcation took place. The shape and position in the spectrum of these Lorentzian bumps were studied by the noise precursors theory, which predicts that the presence of noise will act as a virtual Hopf precursor in systems undergoing a period-doubling bifurcation.     

Theory of intensity noise in semiconductor laser emission

The intensity fluctuations expected in the output of cw semiconductor lasers are studied analytically using linearized multimode rate equations. Spontaneous emission causes intrinsic fluctuations of the laser wave. A power-independent contribution to the intensity fluctuations may occur due to inversion-induced modulation noise. The correlation of the low-frequency noise of different laser modes is investigated. The results are in agreement with experimental data reported in the literature.     

基于注入半导体激光器的微波副载波相位调制信号产生

光载无线技术是解决终端超宽带无线通信的重要方法,光信号与微波/毫米波信号的融合处理技术在光-无线的数据格式转换中至关重要.提出了一种基于相位调制信号光注入Fabry-Perot型半导体激光器实现微波副载波相位调制信号产生的方法.光学注入半导体激光器的输出光场会产生一周期(P1)振荡效应, P1振荡产生的边带实现了相位调制信号光的调制分量的放大,被放大的调制分量与注入光载波在激光器腔内拍频形成微波副载波.注入光相位的变化导致新产生的微波副载波相位变化, 实现了注入信号光相位信息转化为微波副载波相位信息.本系统完成1.3 Gb/s, 2.7 Gb/s, 2 Gb/s光相位调制信号到微波副载波相位调制信号的转换,并测量了微波的单边带相位噪声. 通过光电转换和电域混频将还原出的光基带信号与原信号进行逻辑对比,证明了数据信息转换的正确性.     

Harmonic and intermodulation distortions and noise associated with two-tone modulation of high-speed semiconductor lasers

We present results of modeling and simulation of the harmonic and intermodulation distortions as well as the intensity noise of high-speed semiconductor lasers under two-tone modulation. Multiple quantum-well lasers are considered, which are characterized by large differential gain and a modulation bandwidth of about 25GHz. The study is based on the rate equation model of semiconductor lasers excited by injection current with two sinusoidal tones separated by a radio frequency. The modulated laser signal is modeled in both the time and frequency domains. The time domain characteristics include the fluctuating waveform, while the frequency domain characteristics include the frequency spectrum of the relative intensity noise (RIN), carrier-to-noise ratio, modulation response, harmonic distortion, and the second- and third-order intermodulation distortions (IMD2 and IMD3). The analysis is performed for three frequencies of 5, 15, and 24 GHz, which are, respectively, lower, comparable, and higher than the laser relaxation frequency. The range of the modulation depth covers the regimes of small and large-signal modulation. We show that both RIN and IMD3 of two-modulated laser are minimum when the modulation frequency is 5GHz, and maximum when the modulation frequency is 24 GHz. The second-order harmonic distortion, IMD2, and IMD3 values are larger in the vicinity of relaxation oscillations and increase with the modulation index, especially under large-signal modulation.