半导体激光器速率方程的参数提取(特邀)

Extraction of Semiconductor Laser Rate Equations Parameters(Invited)

重新评估了常见半导体激光器参数提取方法中近似条件的适用性,提出更加通用的方程进行半导体激光器速率方程的参数提取。以分布式反馈激光器芯片为例,利用小信号频率响应曲线(S21)准确提取了半导体激光器谐振频率fr与阻尼因子γ,结合激光器的光功率-电流(P-I)响应曲线,即可计算出半导体激光器速率方程的各个参数。对比之前的参数提取近似计算方法,本方法适用的激光器驱动电流范围更宽,大电流下谐振频率fr等参数的提取更精确,对宽工作电流工作的激光器如模拟激光器等的优化改进有借鉴意义。

Semiconductor laser is one of the core light sources of optical fiber communication systems.Better semiconductor laser performance helps to increase the capacity and quality of the entire fiber optic communication system.In order to design better semiconductor lasers,it is often necessary to simulate various performances through rate equations.However,some parameters need to be obtained through experimental results,so it is necessary to fabricate semiconductor laser chip to extract the parameters.Through multiple rounds of iterative experiments and theoretical calculation,chip optimization is continuously carried out to achieve the final goal.In the process of optimization analysis,in order to better analyze the performance of laser chips,laser parameters are usually divided into eigen parameters and parasitic parameters.Parasitic parameters mainly include capacitance,resistance and other properties.They can be obtained by means of a fitting method by combining a reflection curve of the small-signal frequency response(S11)with an equivalent circuit model.These parameters are basically not affected by the lasercurrent change.However,the extraction of the eigenmetric parameters is related to the selected lasercurrent range,and the parameter extraction results themselves have a variety of possible answers.How to obtain more accurate and suitable for a wide operating current range of eigen parameters is the focus of this paper.In recent years,with the development of emerging applications such as 5G optical communication and Radio On Fiber(ROF)analog communication,semiconductor lasers are required to operate at larger drive currents to improve high-speed performance and are required to have better linearity.In such ROF analog communication systems,semiconductor lasers need to work at a lager bias laser-current and in the linear region to obtain excellent microwave performance.Besides,it is need to test and evaluate many microwave performance indicators,such as third-order intermodulation,second harmonic,relative intensity noise,etc.The acquisition of these indicators requires complex test systems,expensive equipment and difficult testing.Therefore,how to accurately and conveniently obtain the microwave performance of the laser at a large drive current is particularly important.By testing some basic performance of the laser,the eigenvalue and parasitic parameters of the semiconductor laser can be extracted.These extracted parameters,combined with system characteristics,can be used to quickly calculate and evaluate most of the microwave performance of the system.This method greatly reduces the test requirements and the costs of test equipment,greatly speeding up the performance evaluation of semiconductor lasers and the entire design process.The traditional parameter extraction method can obtain the parameter values of semiconductor lasers operating at low bias currents(10~40 mA).But the parameter extraction at large currents is not very accurate,and more complicated tests such as measuring chirps are required.This paper re-evaluates the applicability of approximate conditions in common semiconductor laser parameter extraction methods and finds that approximate conditions fail at large currents.To this end,it is proposed to use a more general formula for the parameter extraction of the semiconductor laser rate equation.Taking the DFB laser chip as an example,the small-signal frequency response curve(S21)is used to accurately extract the resonant frequency frand the damping factorγof the semiconductor laser,and combined with the laser power-current(P-I)response curve of the laser,the various parameters of the semiconductor laser rate equation can be calculated.Compared with the previous parameter extraction approximation calculation method,the present method has three advantages.First,the range of laser drive currents that can be analyzed is wider.Second,there are fewer items to test.The third is that the extraction of parameters such as the resonant frequency frat large currents is more accurate.This method is an important reference for the optimization and improvement of semiconductor laser with wide operating currents such as analog laser.