Monolithically Integrated High Speed Directly Modulated Distributed Feedback Lasers Array

The update and iteration of optical fiber communication technology have directly promoted the development of semiconductor optoelectronics.High-performance,low-cost semiconductor optoelectronic devices are the key for next-generation fiber-optic communications.The main research object of this paper is the monolithic integrated highspeed directly modulated laser array chip for the Ethernet network,which is dedicated to solving the high-speed growing network demand in the data center,network operators and other high-performance computer environments with the requirement of intensive traffic.A 1.3 ?m band directly modulated distributed feedback laser array for 100 Gb Ethernet communication systems is developed,including high-speed directly modulated lasers,activepassive transitions and passive waveguide combiner devices.The main work includes the following aspects:First,we analyzed the high-speed characteristics of the lasers theoretically.The intrinsic bandwidth of the lasers is obtained through the derivation of the high-speed modulation model.The effect of the structure parameters for the high-speed modulated laser is discussed.A laser simulation model based on the time-domain traveling wave(TDTW)method is developed.Through this TDTW model,the reflection spectrum and normalized optical spectrum of the laser can be calculated and further he dynamic characteristics of the laser can be simulated.A novel scheme of two section DFB laser with an active distributed reflector(ADRDFB)is proposed.The ADR-DFB laser has an active reflection section integrated after the active section to obtain additional reflection.The proposed laser scheme has stable single mode operation with high slope efficiency,wide direct modulation bandwidth and high yield,thus is suitable to realize the high speed directly modulated lasers array.The ADR-DFB laser is analyzed by the TDTW model with two kinds of grating structures designed for single mode operation.The ADR-DFB laser scheme has been experimentally verified.The fabrication process of the laser is optimized.The gratings with different wavelengths are fabricated by electron beam lithography(EBL).The ADR-DFB laser waveguide is fabricated by dry etching to avoid the defects in the second epitaxial.The measured results show that the proposed laser has advantages of low threshold,high slope efficiency and high side mode suppression ratio.The measurements of the lasers array show that the lasers have very high yield and thus are very suitable for monolithic integration.The extracted intrinsic bandwidth of the laser can reach 24 GHz agreed well with our theoretical simulation.Finally,the parameters of the lasers are extracted through test structures.The commercial software for passive devices is used to analyze the optical confinement factors in the active waveguide and optical loss in the passive waveguide.Based on the analysis we designed the epitaxial wafer of vertical twin waveguide structure.By optimization of the twin guide structure,we proposed a novel active-passive transition—vertical coupler of large tolerance and easy fabrication.We optimize the structure parameters of the proposed vertical coupler and simulation results shows that the device has the characteristics of wavelength insensitivity thus suitable for the coupling of different wavelengths.We analyzed the loss of the shallow-deep transition and bending waveguide in detail.Based on the simulation we designed their structures suitable for monolithic integration.The principle and design of multi-mode interferometer(MMI)are studied.By optimization of the MMI structure we designed the four-channel interferometer devices based.To explore the fabrication process of the integrated chip including the laser,vertical coupler and combiner,a variety of methods were adopted to optimize the fabrication process parameters according to different requirements.The low loss active waveguide is obtained by wet etching.The shallow-deep transition from active to passive is optimized.The core layer size of the vertical coupler waveguide is precisely controlled by the combination of dry etching and wet etching.The technology of precise exposure of the thick photoresist was developed to fabricate MMI devices.Finally,an integrated optical emission chip was successfully fabricated with ADR-DFB laser,vertical coupler and MMI combiner based on Indium Phosphide(InP).The fabricated integrated chip was measured.Results show that the threshold is about 15 mA and the output power can reach 1mw for the integrated chip.The optical spectrum spacing between the four channels is 400 GHz as designed for the efficient use of bandwidth,and the side mode suppression ratio can reach more than 50 dB.The electro-optical response curve of the lasers shows that the bandwidth could reach 14 GHz for the four channels at room temperature.A transmission experiment of 10 km for the integrated chip was also carried out.The eye pattern under 28 Gbit/s modulation is clear and the bit error ratio after transmission is measured.The power penalty after 10 km SMF transmission is approximately 0.5 dB.