通信激光器及其调制技术研究进展

Research Progress of Communication Laser and Its Modulation Technology

在光通信领域,激光器及其调制带宽、调制速率对无线光通信至关重要。对半导体激光器信号的调制方式主要有内调制和外调制两种。这两种调制技术具有各自的特点,适用于光纤通信中的不同领域,都是当前重要的研究热点。内调制激光器又称为直接调制激光器,因其具有高速传输以及低成本的特点,成为目前应用在第五代移动通信技术(5G)前传和数据中心中的高性价比光源。而外调制激光器不存在光源附加的Chirp,所以可以有效地克服光纤色散造成的复合二次差拍(CSB)失真。文章在回顾通信激光器及其调制技术发展历程的基础上,介绍了西安理工大学在该领域所做的工作以及取得的主要进展。针对半导体激光器发生非线性失真的内外因素进行讨论,仿真响应特性各参数、线性化补偿方法以及功率控制系统对光发射器件输出光源的作用,并分析了温度的起伏对激光器和调制器件输出功率产生的影响。采用折射率椭球基本理论和数值分析,分别在纵向和横向调制下,讨论出射光强随温度的变化趋势。结果表明,纵向调制下出射光光强随温度的变化趋势只与铌酸锂(LN)晶体折射率的变化有关;横向调制下出射光光强随温度的变化趋势不仅要受到晶体折射率的影响,还要受到晶体尺寸及其膨胀系数的影响,因此可以利用特殊尺寸的晶体来提高电光调制器的温度稳定性。

In the field of optical communication,laser and its modulation bandwidth and modulation rate are very important for optical wireless communication.There are two main modulation modes for semiconductor laser signal:internal modulation and external modulation.These two modulation technologies have their own characteristics and are suitable for different fields of optical fiber communication.Internal modulation laser,also known as direct modulation laser,has become a cost-effective light source for the Fifth Generation Mobile Communication Technology(5G)fronthaul and data center because of its high-speed transmission and low cost.There is no additional Chirp of light source in external modulation laser,so the Composite Second Beat(CSB)distortion caused by fiber dispersion can be effectively overcomed.On the basis of reviewing the development history of communication laser and its modulation technology,this paper introduces the work and main progress made by Xi’an University of Technology in this field.This paper discusses the internal and external factors of nonlinear distortion of semiconductor laser,simulates the effects of various parameters of response characteristics,linearization compensation method and power control system on the output light source of light emitting device,and analyzes the influence of temperature fluctuation on the output power of laser and modulation device.Based on the basic theory of refractive index ellipsoid and numerical analysis,the variation trend of emitted light intensity with temperature is discussed under the longitudinal and transverse modulation,respectively.The results show that the variation trend of outgoing light intensity with temperature under longitudinal modulation is only related to the refractive index of Lithium Niobate(LN)crystal.Under transverse modulation,the variation trend of outgoing light intensity with temperature is affected not only by the refractive index of the crystal,but also by the crystal size and its expansion coefficient.Therefore,the special size crystal can be used to improve the temperature stability of the electro-optic modulator.