Study On High-Speed Directly Modulated DFB Laser Chips Based On Detuned Loading Effect And Photon-Photon Resonance Effect

The explosive growth of data traffic has led to an increasing communication pressure and energy consumption in data centers.Directly modulated lasers(DML)have the advantages of costeffectiveness,small footprint,and low power consumption compared to externally modulated lasers,making them suitable for short distance transmission and have great commercial value.To break the limitation of the intrinsic bandwidth of semiconductor lasers and the RC bandwidth roll-off,DML often uses detuned loading effect and photon-photon resonance(PPR)effect to realize high-speed direct modulation.But the active and passive integration technology results in complicated manufacturing processes and high costs.Target at the problems above,a monolithic integrated multisection distributed feedback(DFB)laser scheme is adopted in this thesis.By designing the period of gratings in each section to control the Bragg wavelength accurately,detuned gratings can be formed.This thesis utilizes reconstruction equivalent chirp technique to equivalently achieve the detuned grating structures.The fabrication of sampled gratings only requires conventional holographic exposure and photolithography technology with micrometer-level control accuracy.The main work of this thesis is as follows:1.A monolithic integrated two-section DFB laser and its array based on the detuned loading effect are proposed.The device consists of a DFB laser and a detuned grating reflector,both facets are antireflection(AR)coated to eliminate the random phase of gratings.The results show that each laser in the array has excellent single mode performance.The side mode suppression ratio can exceed 59 d B.It can maintain good single-longitudinal-mode output over a large current and temperature range,and the average lasing wavelength error of adjacent channel is only 0.004 nm.The detuned loading effect increases the 3-d B bandwidth from 13 GHz to 17.6 GHz,and reduces the chirp parameter from 4.69 to 2.24.The eye diagram can still maintain large opening extent after 5 km standard single mode fiber transmission under 10 Gb/s non-return-to-zero signal modulation.2.A monolithic integrated two-section DFB laser based on the PPR effect is proposed.The DFB laser is high-reflection(HR)coated,and the light is reflected by the HR coating and outputs after through a detuned grating reflector.The two sections form a coupled cavity to generate PPR effect.This structure combines the detuned loading effect and PPR effect together.Compared to one-section DFB lasers,the carrier-photon resonance frequency is enhanced from 8 GHz to 14 GHz,and the 3-d B bandwidth can reach 37 GHz.Research shows that the gap between PPR mode and the main mode is related to the length of the coupled cavity and the detuning of the gratings within the two sections.In addition,the random phase of grating at the HR facet will deteriorate the modulation bandwidth under some conditions,while under certain phase,the 3-d B bandwidth can reach 73 GHz.3.A monolithic integrated optical injection locked(MOIL)DFB laser is studied,which consists of two sections of DFB lasers and a tuning section.Both facets are AR coated,and the lasing wavelengths of the two lasers DFB1 and DFB2 are precisely controlled through detuned gratings and introducing equivalent π phase shift.The tuning section is located between DFB1 and DFB2,to tune the intensity of optical injection.When the MOIL DFB laser is in stable locked state,the device shares the same lasing wavelength and PPR effect is generated.The results of the theoretical analysis show that by increasing the current in the tuning section,the frequency difference between the main mode and PPR mode can be increased,and response curve can be smoothed and enhanced.The 3-d B bandwidth of the device can be enhanced to approximately 42.5 GHz,which is 2.5 times that of DFB1 in free-running state.Besides,the optical injection locking can reduce the frequency chirp and modulation nonlinear distortion.The second harmonic distortion at different optical modulation depths can be improved by more than 5 d B.