Research Of A Cascaded Distributed Bragg Reflector Tunable Semiconductor Laser

With the rapid development of Internet and wireless communication,people put forward high requirements of speed,capacity and distance of information transmission.At present,optical fiber communication has become the most important mode of information transmission because of its high transmission capacity.With the further increase of the capacity of optical fiber communication network,the dense wavelength division multiplexing(DWDM)technology is widely used.However,the volume,energy consumption and cost of the communication system and the complexity of the network will both increase dramatically,if separate lasers are still used to build optical networks.Wavelength tunable semiconductor lasers can change the wavelength,which can effectively simplify the system and reduce costs.This dissertation focuses on cascade tunable distributed Bragg reflector semiconductor lasers(DBR).Firstly,the waveguide gratings for mode selection in lasers are introduced,and the optical characteristics of various gratings are analyzed.Then,the coupled mode theory and transfer matrix method are introduced.Based on this,the simulation models of semiconductor lasers are established and modified.The steady-state and dynamic-state simulation models of semiconductor lasers in frequency domain and time domain are established respectively.In this paper,a novel tunable laser based on cascaded passive grating region and active region structure is proposed.By tuning the current of passive grating regions,the wavelength tunability of the laser can be achieved.Specifically,each laser section(LS)consists of two passive adjacent grating sections(GS)with slightly different Bragg wavelengths and active sections(AS)between them.In order to achieve a large tuning range,a step-wise grating structure is designed in the tunable laser cavity.Since two LSs share a common GS,the total cavity length of the tunable laser decreases significantly.Besides,the proposed laser has a fast switching speed due to the DBR structure.In this dissertation,an example is given to design and analyze a tunable laser with four GSs and three ASs,which can achieve a continuous tuning range of 13.2 nm,a wavelength switching speed of 9 ns,a small signal modulation frequency greater than 10 GHz and a digital direct modulation rate greater than 10 Gbit/s.These performance indicators show the technical advantages of the proposed laser scheme,expected to be applied in future high-speed optical communication systems.In addition,the fabrication of the tunable laser with sampling grating is discussed in this paper,which can simplify the fabrication and reduce the cost.