850 Nm Distributed Feedback Single-Mode Surface-Emitting Lasers

With the optical communication and optical sensing technology being developed towards small-scale integration in recent years,the application of semiconductor lasers has been realized in a much wider scope.Among them,surface emitting lasers,with advantages of lower power consumption and lower cost,have been widely deployed in data centers and three-dimensional sensing.Currently,however,most of surface emitting lasers are multi transverse mode.To this end,single-mode surface-emitting lasers are highly desired in systems of optical communication,sensing and atomic clock pumping to provide long-reach optical communication systems,high detection resolution sensing systems and high pumping efficiency,respectively.In order to meet this demand,this dissertation mainly focuses on the low-power single-mode 850 nm surface emitting Distributed Feedback(DFB)laser.The main research innovation achievement is as mainly as the following:In order to achieve single-mode surface emitting laser,we propose a novel single-mode surface emitting laser--surface emitting DFB laser based on the surface grating.The surface grating is used to increase the coupling coefficient of the grating,which has the same advantage(single-mode)as a DFB laser.On the other hand,the laser uses the second-order grating diffraction field and the oxide aperture to reduce the carrier injection volume,which has the same low threshold and surface emission characteristics as the vertical cavity surface emitting laser(VCSEL).Firstly,we analyze the influence of the number,the strain and the thickness of InGaAs quantum wells.Based on this,the active region of the laser is designed.The peak material gain and the corresponding wavelength,carried out by simulation,are 886cm^-1 and 843 nm,respectively.Then the effects of the structure parameters of the surface gratings on the coupling coefficient of the gratings are studied.The longitudinal mode selection mechanism of horizontal cavity DFB laser is further studied.By inserting?/4 phase shift into the second order grating,a single longitudinal mode resonator is realized.For the purpose of realizing the laser with low resistance and low threshold current,the effects of laser doping and oxidation aperture on current injection are analyzed.In the aspect of the development of the single mode surface emitting laser,we developed the fabrication process of surface emission DFB laser,including:selective wet etching of GaAs/AlGaAs with citric acid and hydrogen peroxide,slow dry etching of surface grating using reactive ion etching(RIE)with a gas mixture of Cl₂/BCl₃/CH₄,and wet oxidation of Al_0.96Ga_0.04As.Finally,the surface emitting DFB laser was fabricated.The test results show that the threshold current of the surface emitting DFB laser is 9 mA,the side-mode suppression ratio(SMSR)reaches 44 dB,achieving single mode lasing.In order to reduce the power consumption of the single-mode surface emitting laser,we optimized the structure and fabrication process of the surface-emitting DFB laser:the epitaxial structure was improved,and the Distributed Bragg Reflector(DBR)+active DFB+passive DBR three-section structure was proposed.With the rectangular oxidation structure,the laser has the advantages of large area and small resistance.The effect of the length of active and passive regions on the threshold current and slope efficiency of a three-section surface emitting laser was analyzed by using a time-domain traveling wave model.The optimized surface grating surface emission DFB laser was fabricated experimentally.Test results showed that the coupling coefficient of the surface grating is 300 cm^-1.For the surface emission DFB laser with 50?m active region length,the threshold current is as low as 1.8m A,indicating that a low threshold current horizontal cavity surface emitting laser is realized.Under the bias of 6.5 m A,a high SMSR of 47 dB has also been achieved.This shows that the surface emitting laser has very attractive single mode performance.At the same time,the laser has a relaxation oscillation frequency of 17 GHz at bias current of 9 mA(5 times that of the threshold current).In summary,this dissertation has investigated on how to realize single-mode surface emitting laser.We proposed and developed a surface emitting DFB laser based on surface grating.The surface emitting DFB laser consists of three innovations:1)surface grating with large coupling coefficient;2)second order grating with?/4 phase shift;3)a large-area rectangle-shaped oxide aperture.Finally,a surface emitting DFB laser with remarkable single-mode performance and low threshold current has been successfully realized in this dissertation work,paving the way for wide promising application of the laser in the optical communication and optical sensing.