Research On High Speed Directly Modulated Distributed Feedback Laser

With the development of Mobile Internet,Big Data and Cloud Computing,the communication quality and cost for networking users has become critical,which brings up new challenges for the short-range optical fiber communication network supporting metropolitan area network(MAN)and local area network(LAN).High-speed directly modulated semiconductor laser that is the core device used for short-range optical fiber communication network,needs further breakthrough on high-speed and low-cost to meet the requirements of short-range optical interconnection network.Focusing on low-cost,lowpower,and high-performance directly modulated semiconductor lasers,the thesis has carried out research on low-cost high-speed directly modulated distributed feedback(DFB)lasers,and has studied wide temperature range(-40?-85?)operation of directly modulated DFB lasers,directly modulated DFB lasers with multi-level amplitude modulation and directly modulated DFB lasers with negative chirp for long-distance transmission.Detailed aspects of the work carried out in the thesis are as follows:The main physical processes involved in the physical model of a DFB laser are discussed,and the corresponding theoretical model and analysis method for each physical process are described separately.Based on these theoretical analyses,the thesis discusses the structural design of standard DFB lasers,summarizes the main limiting factors for the modulation bandwidth of direct modulation DFB lasers,and discusses the characteristics of existing solutions to expand the modulation bandwidth.In order to solve the problems in the existing solutions,the thesis proposes a short-cavity DFB laser integrated with active Bragg reflector(ADR-DFB)for high-speed direct modulation,which has the characteristics of low cost and high single-mode yield.The feasibility of ADR-DFB laser is discussed in terms of device principle,structure and fabrication process.According to the structural characteristics of the ADR-DFB laser,the time-domain traveling wave method has been introduced as the basis for the numerical simulation of the ADR-DFB laser.This article discusses the crucial structural parameters of the ADR-DFB laser based on the time-domain traveling wave method,and analyzes the direct modulation characteristics of the device with the best structure design.According to the optimal device structure discussed in the numerical simulation,the fabrication of the ADR-DFB laser has been accomplished after the development and verification of the fabrication process.The feasibility of the ADR-DFB laser has been verified experimentally with excellent singlemode yield and high-speed modulation characteristics being demonstrated.The fabricated ADR-DFB laser has a modulation bandwidth of 24 GHz and has achieved error-free transmission of 10 kilometers at a modulation rate of 28 Gb/s.The thesis further analyzes the influence of temperature on the crucial parameters of DFB laser.The corresponding parameters to describe the temperature influence have been extracted based on experimental results.The complete temperature parameters are introduced into the time-domain traveling wave model.The design of the direct modulation ADR-DFB laser with wide temperature range(-40? to 85?)operation has been accomplished.The ADR-DFB laser has been fabricated with optimized manufacturing process and device structure,and has demonstrated stable operation within the industrial temperature range(-40? to 85?).Error-free transmission over 10 km single-mode fiber has been achieved at25 Gb/s modulation rate over wide temperature range(-40? to 85?).The main causes for thermal saturation in ADR-DFB lasers are analyzed,and different solutions to relieve the thermal saturation are discussed.Chirped grating ADR-DFB laser is proposed.Linearly chirped grating and segmented chirped grating have been compared through simulation.The effect of chirped grating on relieving thermal saturation has been demonstrated as well as the application of the chirped grating ADR-DFB laser in multi-level amplitude modulation.The modulation rate of 56 Gb/s has been achieved through the PAM4 modulation format.Direct modulation DFB lasers with negative chirp is proposed to provide a potential low-cost solution for long-distance optical fiber communication applications.The negative chirp characteristic of the directly modulated DFB laser has been verified by numerical simulation and experimental measurement.The modulation bandwidth of 20 GHz has been achieved at 20? as well as the frequency chirp of-40 GHz at the modulation rate of 10 Gb/s.The power penalty after 10 km standard single-mode fiber transmission with 10 Gb/s modulation rate is negative.