Absorption line profile recovery based on residual amplitude modulation and first harmonic integration methods in photoacoustic gas sensing

Two methods for recovery of gas absorption line profiles are presented in this paper using photoacoustic spectroscopy and tunable diode laser spectroscopy (TDLS) with wavelength modulation (WM). A theoretical analysis based on Fourier coefficients is given in order to describe the various components that arise under simultaneous intensity and frequency modulation. The first method makes use of the residual amplitude modulation (RAM) signal which is always present in current modulation of distributed feedback (DFB) tunable diode lasers. The second method involves integration of a near-pure first harmonic derivative signal, separated from other distorting components by appropriate choice of the lock-in detection phase in the case of low modulation index. Good agreement is obtained with both methods between the experimental results and the theoretical simulation for the P17 absorption line of acetylene at 1535.39 nm but the second method gives a much improved accuracy and signal-to-noise ratio in lineshape recovery with photoacoustic spectroscopy.     

Injection-locking technique for heterodyne optical phase locking of a diode laser

A novel technique is demonstrated for heterodyne optical phase locking of a diode laser to a single-frequency source by injection seeding. By modulation of the drive current of the diode laser at as much as several gigahertz, FM sidebands are imposed upon the output. We demonstrate that it is possible to phase lock either sideband to an injected beam. The carrier of the diode laser output is therefore locked in phase with the injected light but with a frequency difference given by the modulation of the drive current. The phase fluctuations between the lasers are analyzed, and the variance is found to be (4.4( degrees ))(2) , corresponding to 99.4% of the diode carrier light locked to the injected beam.     

Accurate extraction method for the FM response of tunable diode lasers based on wavelength modulation spectroscopy

An accurate wavelength modulation spectroscopy based method to measure the dynamics of the wavelength modulation behavior of tunable diode lasers is introduced in this paper. This method requires only standard equipment and a simple mechanical setup. Under the condition of a constant laser modulation current, the wavelength modulation amplitude can be determined by analysis of the distance between the two zero crossings of the measured second harmonic spectrum of gas absorption. When measuring at different modulation frequencies, the frequency response of the current-to-wavelength tuning coefficient can be obtained. The use of a frequency analyzer instead of a lock-in amplifier to obtain the second harmonic spectrum has two advantages: it provides a higher bandwidth and allows for very precise detection of the zero crossings because of the logarithmic output. The results exhibit very good agreement with a reference measurement performed with a fast FTIR Spectrometer. PACS 42.60.Fc; 42.62.Fi; 42.55.Fx     

基于光注入Fabry-Perot半导体激光器实现同步全光分路时钟提取与波长转换

提出了一种利用Fabry-Perot（FP）半导体激光器同步提取波长转换的分路光时钟的新方法,并对该方法进行了数值模拟和实验验证.光注入半导体激光器会产生非线性单周期振荡特性,利用交叉增益调制效应及对单周期振荡的微波锁频效应,可从光时分复用信号中提取出波长转换的分路光时钟.采用一个FP半导体激光器作为全光分路时钟提取及波长转换器,数值模拟实现了从波长为1555 nm、速率为2×20 Gb/s的光时分复用信号中提取出波长转换为1550 nm、重复频率为20 GHz的分路光时钟,实验完成了从波长为155024 nm、重复频率为1236 GHz光脉冲信号中提取出相位噪声为-105 dBc/Hz的波长为154591 nm、重复频率618 GHz的分频光时钟.此外还详细研究了注入光功率、波长失谐、FP激光器偏置电流及纵模选择对光时钟提取的影响,实验结果和数值模拟结果符合.该方法在光时分复用混合波分复用通信系统中实现全光解复用及波长路由有着重要的应用价值. 关键词： 波长转换 时钟提取 光注入 非线性动力学     

High frequency wavelength modulation spectroscopy with diode lasers

High frequency wavelength modulation spectroscopy with diode lasers is accomplished by dithering the drive current at RF frequencies as high as 250 MHz. This technique is useful for fast and sensitive detection of absorption lines in the near-and mid-infrared spectral regions. Detection of 300 MHz wide spectral features corresponding to 1% changes in transmission is accomplished in time intervals as short as 500 ns. A potential application is for fast reading of information contained in frequency domain optical memories based upon photochemical hole burning.     

Optical phase locking with a large and tunable frequency difference based on a vertical-cavity surface-emitting laser

We present a novel method to phase lock two lasers with a controllable frequency difference. A microwave frequency-modulated vertical-cavity surface-emitting laser is used to phase connect two diode lasers by a two-step injection locking. The phase fluctuations of the two lasers are measured to be 6.4 x 10(-4) rad2, corresponding to 99.94% phase coherence. The frequency difference of the two lasers is tunable up to tens of gigahertz. The sideband suppression of the slave laser is more than 30 dB at 30 microW seed power. A narrow linewidth spectrum of coherent population trapping in rubidium is achieved using such beams.     

A PbSe laser far-infrared television experiment

This paper describes a television experiment with PbSe semiconductor lasers. Excellent picture definition has been achieved in the laboratory. Because of the limited modulation frequency with high currents of diode lasers, pulse position modulation (PPM) was used. It is believed to be the first time PbSe diode lasers have been used in TV links.     

Fourier domain mode locking pulse fiber laser

A novel pulse fiber laser is proposed based on the modulation of the lasing wavelength. Different from conventional amplitude or phase modulated mode-locking fiber lasers, the proposed fiber laser is with a so-called Fourier domain mode locking (FDML) operation (i.e., the cavity round-trip time of the optical pulse should match the period that the open time window of the tunable filter appears for the lasing wavelength or its harmonics). An FDML pulse fiber laser with a cavity round-trip frequency of 19.46 kHz is demonstrated and optical pulses with repetition rate of 19.46 kHz are achieved when the wavelength modulation frequency is 9.73 kHz.     

Effect of gain switching frequency on ultrashort pulse generation from laser diodes

In this work, the effects of gain switching frequency on ultrashort pulse generation are investigated using a model based on the multi-mode rate equations. In addition to the commonly used laser diode parameters, the key parameters corresponding to the different laser diode materials and structures are included in the model. Effects of some laser diode parameters, and d.c. and RF drive conditions on the full width at half-maximum (FWHM) of gain switched pulses are investigated for the 1–15 GHz gain switching frequency range. Multi-pulse generation and the cut-off frequency of gain switching are also determined for this frequency range. It is found that the FWHM of pulses decrease as the RF current is increased, at a constant frequency. However, the FWHM of pulses either decrease or increase as the d.c. bias is increased, depending especially on the gain compression and gain peak. As the frequency is increased, pulse widths start to decrease or increase depending on the laser diode parameters. The FWHM of pulses for shorter cavity lasers are found to be almost insensitive to the frequency. Among the parameters affecting the multi-pulse generation and cut-off, gain compression, gain constant, and d.c. and RF current amplitudes are found to be the most effective. All calculations are also carried out using single-mode rate equations and results of multi-mode and single-mode solutions are compared. This revised version was published online in June 2006 with corrections to the Cover Date.     

基于线性光放大器的交叉相位调制波长转换啁啾特性研究

建立了基于线性光放大器(LOA)的交叉相位调制波长转换模型,模型考虑了纵向载流子密度变化引起的有源区折射率的改变、端面反射、相位调制、放大的自发辐射噪声和横向垂直光场(VCL)的增益钳制作用。利用分段方法模拟计算了布拉格反射镜的反射率、偏置电流、信号光和探测光的功率和波长、信号速率与转换后信号啁啾的关系。结果表明:LOA具有增益钳制作用,能提高转换后信号的性能;增大布拉格反射镜的反射率可以降低转换后信号的啁啾;合理控制输入信号光和探测光的强度,调整干涉仪两臂LOA偏置电流的强度,可以获得啁啾较小的转换信号。     

Current and frequency modulation characteristics for continuous-wave quantum cascade lasers at 9.06 μm

We report the characteristics of current induced frequency modulation (FM) for two continuous-wave quantum cascade lasers (QCLs) at 9.06 μm. Both the frequency tuning rate and the phase shift between intensity modulation and FM are measured at different modulation frequencies from 10 Hz to 200 kHz. The frequency tuning rate of the QCLs depends on both the modulation frequency and amplitude. The tested QCL has been used to detect ambient water vapor with wavelength modulation spectroscopy for validation with a numerical model.     

基于XGM的SOA波长变换器噪音特性分析及优化设计

利用动态载流子恢复时间可以精确模拟基于交叉增益调制的SOA全光波长变换器的饱和增益效应,本文将SOA分段ASE噪音功率和分段动态模型结合,得到沿长度分布的ASE噪音功率,并讨论了偏置电流、泵浦光和探测光的波长、功率、SOA长度对消光比和信噪比的影响理论计算结果表明,大的偏置电流有利于提高消光比和信噪比;对于一定的输入波长,相对较大的泵浦光和相对较小的探测光变换效果好;SOA的长度存在最佳值.     

Generation of phase-coherent laser beams for Raman spectroscopy and cooling by direct current modulation of a diode laser

A setup for generation of GHz side-bands by direct current modulation of a diode laser is described. The first order side-bands are used to inject two slave power diode lasers, in order to produce phase coherent, controllable frequency shifted, light beams, the mutual phase coherence of which has been verified (beat-note FWHM of 1 Hz, instrumentally limited). Some possible applications in the context of laser Raman cooling of cesium atoms are briefly discussed. Received 9 November 1998 and Received in final form 16 February 1999     

利用非线性光学环路镜实现多个波长的同时变换

利用非线性光不路镜（ＮＯＬＭ）成功地实现了多个波长的同时变换,最大波长变换间距大于２５ｎｍ。实验系统中采用增益开关分布反馈半导体激光器（ＧＳ ＤＦＢ－ＬＤ）产生的超短光脉冲作为控制光,频谱分割法得到多波长激光作为信号光。改变控制光的输入功率或非线性光学环路镜中的偏振控制器的偏振方向能够改变不同变换波长信号的性能。     

Theoretical Study on Wavelength Conversion Based on Cross Phase Modulation Using Semiconductor Optical Amplifiers

Performances of wavelength converted signal by cross phase modulation (XPM) using semiconductor optical amplifiers (SOA's) were studied by the use of the multi-section model. Results show that they are related to both the phase arm bias current of the XPM wavelength converter and its operation. When the conversion is under the in-phase operation, the peak extinction ratio (ER) and the chirp frequency of the converted signal increase according to the decrease of the phase arm bias current, but the input signal power dynamic range decreases. When the converter is under the out-of-phase operation, the chirp frequency decreases with the decrease of the phase arm bias current, while the peak ER and the input power dynamic range keep almost the same when the phase arm bias current changes.     

注入半导体激光器混沌调制性能与内部相位键控编码方法研究

研究注入半导体激光混沌调制解调及其性能特性，提出外部光注入半导体激光器混沌内部相位编码方法. 小信号调制分析了系统混沌调制响应函数和解调响应函数以及解调因子，系统的调制解调响应函数以及解调因子在60MHz有一个峰值，系统在高频调制时，响应函数和解调因子明显下降. 理论推导出混沌调制解调方程，给出了小信号调制时的信息信号的解，数值分析出系统在低频有一个调制解调峰值，高频调制解调效果下降，但系统仍可以进行10⁹Hz频率调制解调. 数值模拟并证明了系统在较大的参数范围内都能实现同步，模拟了混沌调制速率200Mb/s和调制频率1.4GHz的保密通信应用. 还通过键控调制注入光的相位相移对激光混沌态进行了编码，通过同步与非同步进行混沌解码，数值模拟了具有调制速率10Mb/s的混沌相位键控编码通信应用. 关键词： 混沌 同步 激光器 相位     

用于固态功放反射式宽带预失真器设计方法

提出了一种特定增益和相位补偿的反射式宽带线性化器设计方法,并通过此方法设计了一种补偿固态功率放大器失真特性的预失真电路。利用肖特基二极管产生非线性补偿,根据电路拓扑结构,利用matlab优化工具找到单频点处特定增益补偿和相位补偿特性的并联负载值,改变频点,并重复上述步骤,可进一步得到特定增益和相位补偿所需的并联负载随频率的变化关系（即Z_L～f曲线）。利用ADS仿真软件优化设计使二极管后端阻抗随频率的变化逼近Z_L-f曲线。仿真的电路增益补偿和相位补偿分别为6 dB和?40°。最终实测频率范围为9.4～11.4 GHz,增益扩张在3.9～4.4 dB,相位补偿在?32.3°～?41.5°,频带特性良好,并且相对带宽达到了19.2%。通过改变二极管直流偏置电压,还实现了补偿曲线的斜率可调。     

Orthogonal control of the frequency comb dynamics of a mode-locked laser diode

We have performed detailed studies on the dynamics of a frequency comb produced by a mode-locked laser diode (MLLD). Orthogonal control of the pulse repetition rate and the pulse-to-pulse carrier-envelope phase slippage is achieved by appropriate combinations of the respective error signals to actuate the diode injection current and the saturable absorber bias voltage. Phase coherence is established between the MLLD at 1550 nm and a 775-nm mode-locked Ti:sapphire laser working as part of an optical atomic clock.     

Fast interrogation using sinusoidally current modulated laser diodes for fiber Fabry–Perot interferometric sensor consisting of fiber Bragg gratings

A fast interrogation method using a sinusoidal modulated laser diode for a fiber Fabry–Perot interferometric sensor consisting of Bragg gratings (FBG–FPI) is proposed.. The FBG–FPI has sharp transmittance peaks in the reflection band of the FBGs. Wavelength sweep produced by current modulation of a laser diode can be used to detect the peak position. This enables high-resolution strain or temperature measurement. To precisely control the current, the current modulation is realized using a laser diode controller (LDC) with external modulation function. In the modulation by a sawtooth wave, the possible speed of wavelength sweeping is limited to 100 kHz or less due to the bandwidth limitation of an LDC and thermal effect in a laser diodeUsing a sinusoidal wave as a modulation waveform enables wavelength sweeping at speeds exceeding 100 kHz. The modulation characteristics of the laser wavelength is evaluated experimentally and the operating wavelength is monitored using an asymmetric Mach–Zehnder interferometer. The resolution of 0.2 fm/\(\sqrt{\mathrm{Hz}}\) and measurement time of 1 \(\upmu\)s were experimentally demonstrated in the present sensor.