| The revolution of each generation of communication technology is accompanied by the explosive growth of the number of users and speed requirements,and brings huge social and economic benefit.In this situation,the development of optical communication industry is also growing,while putting forward the demand for optical communication devices with high speed,low cost,high capacity and flexibility.The wavelength tunable and high speed directly modulated semiconductor laser is a kind of communication light source which may meet such requirements.Its wavelength tunability helps to adapt to wavelength division multiplexing systems and multi-wavelength transmission systems.Meanwhile,as a directly modulated optical source,it can satisfy demand of short-distance and high-speed communication systems,such as access network and data center.Therefore,this kind of light source with relatively low cost but higher flexibility is getting more attentions.Based on the theory of wavelength tunable semiconductor lasers,characteristics of wavelength tunable three sections distributed Bragg reflection(DBR)lasers are studied in this dissertation.High speed directly modulated tunable semiconductor lasers are studied and proposed by using the asymmetric nonlinear gain(ANG)and the photon-photon resonance(PPR)effect,respectively.And as the key element,equivalent phase shift(EPS)grating,is experimentally studied.The main research contents of this dissertation are as follows:1)The physical process and wavelength tuning principle of semiconductor lasers are studied in this dissertation.Simulation model for three-section DBR lasers is built with static transmission line model,rate equation model and time dimension travelling wave model.Based on this model,static and dynamic characteristics of DBR lasers are theorically studied,and restrictions of direct modulation bandwidth of the devices are discussed.2)Based on the multi-mode rate equations model,the expression of the asymmetric nonlinear gain term is derived without ignoring the weak second lasing mode.A novel DBR laser,name as ANG-DBR laser,is designed by optimizing tranditional DBR laser to introduce the asymmetric nonlinear gain.Static and dynamic characteristics of the ANGDBR laser are analyzed and discussed with numerical simulation method.Simulation results show that direct modulation bandwidth of the ANG-DBR laser is enhanced to 27 GHz while9 nm wavelength tuning range is kept with help of the asymmetric nonlinear gain.3)The PPR effect in normal three sections DBR lasers are studied theoretically to investigate its enhancement on the direct modulation bandwidth and its restrictions.In order to better introduce and maintance the PPR effect,a controllable equivalent phase shift grating is proposed and adopted.Based on the EPS grating,a novel tunable EPS-PPR-DBR laser is designed and its charicteristics are simulated and analyzed with the time dimension travelling wave model.Results show that,the PPR effect could be successfully introduced and kept stable via the noth formed on the main lobe of reflection spectrum of the EPS grating,so that modulation bandwidth of the EPS-PPR-DBR laser could be boosted to 40 GHz,and 40 Gbps eye diagram with good quality as well as low bit error rate after 10 km standard single mode fiber tansmission is obtained.Meanwile,the EPS-PPR-DBR laser has7 nm wavelength tuning range.4)The controllable equivalent phase shift grating,as a key element of the EPS-PPRDBR laser,is experimentally demonstrated.Combined with laterally supported suspended waveguide structure,the EPS gratings are simulated,desined and fabricated.Experiment results show that,the EPS grating could be fabricated with conventional mirco/nano processing,and provide the required special reflection spectrum and phase shift range for the PPR effect,while thermal wavelength tuning efficiency could be greatly improved with help of the laterally supported suspended waveguide structure.The experiment results provide preliminary feasibility verification for fabrication of the EPS-PPR-DBR laser. |
