共查询到20条相似文献,搜索用时 31 毫秒
1.
Tao Zhang Ning Hua Zhu Bang Hong Zhang Xin Zhang 《Photonics Technology Letters, IEEE》2007,19(4):227-229
A novel and simple method for measuring the chirp parameter, frequency, and intensity modulation indexes of directly modulated lasers is proposed in a small-signal modulation scheme. A graphical approach is presented. An analytical solution to the measurement of low chirp parameters is also given. The measured results agree well with those obtained using the conventional methods 相似文献
2.
负折射介质中高阶非线性效应所致啁啾的研究 总被引:1,自引:1,他引:0
利用分步傅里叶法对负折射介质中的广义非线性薛定谔方程进行数值模拟,进而分别得到自相位调制、赝五阶非线性、自陡峭、二阶非线性色散所致啁啾及各项非线性所致总啁啾的演变图.从啁啾上分析了负折射介质中各项非线性效应在脉冲传输时的作用,结果表明,负折射介质中,自陡系数取值的正负可控使脉冲中心位置可向前后沿偏移;在正常色散区,赝五阶非线性系数为负时加速脉冲的展宽,二阶非线性色散项系数取正时使脉冲展宽,取负时使脉冲变窄. 相似文献
3.
Wavelength converters based on cross-phase modulation in semiconductor optical amplifiers (SOAs) in the arms of a Mach-Zehnder interferometer (MZI) provide a key network element for reconfigurable optical networks that incorporate wavelength routing. For system design purposes, the properties of the intensity and phase (chirp) modulation of the wavelength-converted signal for an SOA-MZI wavelength converter are important. In this paper, the small-signal α parameter, which characterizes the converter chirp, and the conversion frequency response are characterized experimentally for an integrated all-active SOA-MZI wavelength converter. For both co- and counterpropagating signals, the variation of the a parameter along the interference and conversion curves is considered in detail. Three optical modulators with quite different chirp properties are used to generate the modulated input signal to the wavelength converter. The results demonstrate that the chirp of the wavelength-converted signal is primarily determined by the device properties and the intensity of the modulated input signal. The a parameter of the wavelength-converted signal is negative for noninverting operation and positive for inverting operation. An important contribution of the paper is the detailed assessment of this key device characteristic. The experimental characterization of the wavelength converter is incorporated into a device model that can be used to obtain the pulse response. Calculated and measured results for the time dependence of the intensity and chirp of the wavelength-converted signal are in good agreement. The conversion frequency response for the intensity modulation is also measured along the conversion curve. The 3-dB bandwidth is found to be generally about 8-10 GHz 相似文献
4.
Martin M. Strasser Peter J. Winzer 《AEUE-International Journal of Electronics and Communications》2002,56(4)
We analyze the impact of modulation induced chirp on optically preamplified direct-detection communication systems transmitting over dispersion-free channels, as found in optical free-space communication links. We show that commonly used quantitative measures of chirp (the small-signal chirp parameter and the effective chirp parameter) can fail to describe changing chirp characteristics under large-signal modulation in a satisfactory manner. We present an extended chirp model that lends itself both to measurement and simulation in a straightforward way. Regardingreceiver performance, we show thatreturn-to-zero (RZ) coded data signals can experience receiver sensitivity degradations of several dB due to spectral broadening of the chirped signal. By optimizing optical and electrical receiver bandwidths the penalty can be kept considerably lower than for receivers optimized for chirp-free signals. For non return-to-zero (NRZ) coding, chirpcan even improve receiver sensitivity by means of a pulse compression effect in the presence of narrow-band optical filters, leading to reduced inter-symbol interference (ISI). In our simulations and for the measurements, we exploit the variable chirp characteristics of a dual-drive electro-optic Mach-Zehnder modulator. 相似文献
5.
A.H. Gnauck S.K. Korotky J.J. Veselka J. Nagel C.T. Kemmerer W.J. Minford D.T. Moser 《Photonics Technology Letters, IEEE》1991,3(10):916-918
Using a unique Ti:LiNbO/sub 3/ modulator, the value of the modulation chirp parameter that minimizes the transmission power penalty caused by fiber chromatic dispersion was experimentally identified. System experiments at 5 Gb/s using nonreturn-to-zero (NRZ) amplitude-shift-keyed (ASK) transmission with direct detection reception are discussed, and the optimum values of the modulation chirp parameter versus distance for transmission at 1.5 mu m wavelength over fibre having zero dispersion at 1.3 mu m are identified. 5 Gb/s NRZ transmission was achieved through distances of 128, 192, and 256 km of conventional fiber while incurring dispersion penalties of -0.5, 0.1, and 1.1 dB respectively, by operating at the quantum chirp value.<> 相似文献
6.
The authors report on measurements of the chirp factor versus modulation frequency and bias for 1.55 μm distributed feedback lasers. A scanning Michelson interferometer is used to measure the phase response of the optical field under small-signal modulation of the injection current. The magnitude of the phase response is then quantified in terms of an effective chirp factor corresponding to the well known α-parameter. The authors find this factor to increase monotonically and nearly double as the modulation frequency increases from below to above the resonance frequency of the relaxation oscillation. The results contradict the commonly held view of α as a constant parameter for a given laser structure 相似文献
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A low chirp characteristic was observed in a high-speed GaInAsP/InP BH optical intensity modulator with a bandwidth of 14 GHz. The maximum chirp was about 0.8 Å under large-signal pulse modulation. This value agrees well with the calculated result using the αE parameter which was directly evaluated by a change in the complex refractive index 相似文献
9.
雷达通信一体化是减少电子平台体积与电磁干扰的一种有效途径,而共享信号的研究是实现雷达通信一体化的关键技术。该文提出了一种基于Chirp信号的多载波雷达通信共享信号,其主载波采用唯一Chirp信号实现雷达功能,副载波通过改变调频率和初始频率参数组合的Chirp信号调制通信信息。分析了共享信号的模糊函数以及参数设计方法,并对其处理过程及系统性能进行了研究。仿真结果表明,该信号具有较低误码率和高稳健性特性,使用该共享信号可在微量降低雷达性能的前提下实现通信数据的传输。 相似文献
10.
The electrorefractive effect in a GaAs/AlGaAs superlattice was measured by using a monolithic Fabry-Perot structure, where the superlattice active region is embedded inside a cavity, formed by two quarter-wave stacks, all grown by molecular beam epitaxy. At the wavelength approximately 7675 AA, there is a large absorption change ( approximately 5400/cm) and an accompanying index change ( approximately 0.015) when the applied field change is approximately 100 kV/cm. In addition, the chirp parameter at this wavelength is less than 1. This result shows that superlattice electroabsorption optical modulation can offer relatively very low chirp.<> 相似文献
11.
Tuan Guo Bo Liu Hao Zhang Qida Zhao Xiaoyi Dong 《Photonics Technology Letters, IEEE》2007,19(14):1096-1098
A novel technique for continuous chirp control of a fiber Bragg grating (FBG) based on a double-hole cantilever beam (DHCB) is proposed and experimentally demonstrated. The specifically designed DHCB provides a pressure-position-dependent strain-gradient along an originally uniform FBG and allows a tunable linear and Gaussian chirp modulation over the grating spectrum. Bandwidth and wavelength-independent tuning, under center-applied-pressure effect, is achieved by linear chirp modulation with a symmetrical broadening profile and a temperature-controlled wavelength shift. And intensity-referenced temperature-immune pressure measurement, under side-applied-pressure effect, is accomplished by Gaussian chirp modulation with a single-side-broadening profile and a linear-increasing reflection optical power. 相似文献
12.
A class of chirp modulation called partial response continuous phase chirp modulation is introduced by extending the length of the baseband pulse for more than one interval. Partial response chirp signals are constructed at finite numbers of states. Numerical results show that partial response chirp signals perform significantly better and they also have better spectral variations than the known chirp signals 相似文献
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On the transmission performances and the chirp parameter of amultiple-quantum-well electroabsorption modulator 总被引:1,自引:0,他引:1
The chirp parameter of a multiple-quantum-well (MQW) electroabsorption modulator was measured with accuracy for several operating wavelengths in the 1.5 μm window. It varied strongly with applied bias. Effective chirp parameter, defined as the ratio of phase change to transmission change between modulator on and off states, is about zero, or even negative. However, experimental transmission length on standard fiber at 10 Gb/s NRZ is much smaller than what is expected for such a low chirp parameter. It is demonstrated that the effective chirp parameter should not be computed from changes between on and off states, but from the average of the chirp parameter values in a 3 dB region of the most transparent states of the modulator. This simple rule allows us to predict transmission performances based on measurements of the chirp parameter, and can be used to optimize optical components without actually experimenting on a transmission system. The effective chirp parameter of the MQW electroabsorption modulator is found positive. This should be intrinsic to red-shift electroabsorption effects, such as the quantum confined Stark effect 相似文献
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基于双折射光纤中光脉冲传输方程,详细分析了二阶色散、自相位调制以及交叉相位调制在光脉冲传输过程中引起的啁啾。分析结果显示:通过合理选取入射功率,二阶色散引起的啁啾与自相位调制引起的啁啾在脉冲中心附近可以相互抵消,从而使脉冲展宽最小;交叉相位调制产生的两偏振分量的啁啾引起的频移,可使两偏振分量间产生互束缚,利用这种现象可以抑制偏振模色散。 相似文献
17.
We present a numerical model for the analysis of the chirp dynamics of quantum-dot (QD) semiconductor laser under large signal current modulation. The model is based on the multipopulation rate equation formalism, and it includes all the peculiar characteristics of the active QD material such as the inhomogeneous broadening of the gain spectrum, the presence of an excited state confined in the QDs and the presence of nonconfined states due to the wetting layer and the barrier. In this paper the model is applied to the analysis of the chirp of two QD single-mode lasers emitting from the ground state and from the excited state, respectively. In order to make comparisons of the chirp in various operating conditions, we define some equivalent parameters for quantifying the adiabatic and transient contributions to the chirp. These parameters are then used to analyze the chirp as function of the bias current, of the modulation depth and of the modulation frequency. All the various simulation results show that the carrier accumulation in the QD states, poorly involved in the stimulated emission process and the carrier dynamics in these states, can cause a nonzero chirp under current modulation even for the ideal condition of zero linewidth enhancement factor (or -parameter) at the laser threshold. 相似文献
18.
An efficient and accurate model of a distributed feedback laser integrated with an electroabsorption modulator (integrated laser modulator) is presented. The model is based on an experimental characterization of the absorption, adiabatic chirp, transient chirp, and intensity modulation (IM) frequency response. Agreement between calculated and measured results for the large-signal modulation dynamics (intensity and chirp) is obtained. By implementing the model in a system simulation tool, it is shown that the adiabatic chirp due to reflection from the modulator facet must be considered to accurately assess the performance of systems with dispersive fiber and tight optical filtering. 相似文献
19.
Numerical analysis of the dispersion-compensating properties of fiber Bragg gratings (FBGs) in both reflective and transmissive modes is presented. First, the sensitivity of chirped, reflective gratings to the grating chirp parameter, index modulation, and grating length is examined, showing that apodization provides lower sensitivity to variations in these parameters. Second, we introduce a new transmissive geometry for grating-based dispersion compensation that utilizes the dispersive properties of a uniform Bragg grating in transmission 相似文献