Research On Surface Emitting Distributed Feedback Semiconductor Laser And Its Coupled Array

Semiconductor lasers are widely used in national defense,biology,medical treatment,industry,communications and other important fields.Surface emitting distributed feedback laser is a kind of device whose laser mode resonates horizontally along the cavity length direction and output perpendicular to the substrate with the help of second-order grating.The special device structure endows it with excellent working performance(high power,narrow linewidth,low temperature drift,low beam divergence angle,high degree of polarization,simple fabrication process,low cost,etc),which makes it have broad application prospects in emerging fields such as 3D sensing,laser radar,sweeping robot,etc.In this paper,the theoretical design and key fabrication techniques of surface emitting distributed feedback semiconductor lasers are studied.(1)Two structural schemes to enhance the surface radiation directionality of surface emitting distributed feedback lasers are proposed.Dielectric film reflector and high contrast gratings are introduced to reflect the light radiated upward by second-order gratings.Precise control of the thickness of the intermediate layer is the key to obtain high directionality.The directionality of the two is 98%and 92.5% respectively,which is beneficial to improve the mode characteristics and differential external quantum efficiency of the device.(2)High quality fabrication of second order grating is the key to realize high performance surface emitting lasers.The grating is fabricated based on L-edit software,electron beam lithography and inductive coupled plasma(ICP).The grating morphology obtained is ideal and can meet the application requirements of the device.(3)A design scheme of surface emitting distributed feedback laser array based on carrier lateral injection is proposed.Compared with the traditional incoherent laser array,it has higher light source density.The setting of the distributed Bragg reflector in the device is conducive to the efficient output of the laser.(4)An anti-resonance reflection waveguide laser array using periodic narrow slots to define the region of anti-guide core is studied.The near and far field distributions of the fundamental mode and the adjacent modes of the array are compared and analyzed,and the influence of the width of the anti-guide core on the far field distribution of the device is studied.Waveguide Bragg grating is the key structure to improve the mode characteristics of lasers.The theoretical and experimental studies of surface gratings and related devices are carried out in this paper.(1)Aiming at the problems of carrier lateral leakage and poor mode stability in laterally coupled distributed feedback lasers,a scheme was proposed to enhance carrier lateral confinement and mode discrimination by setting narrow slots between ridge and gratings.The simulation results show that the scheme is feasible,and it is found that changing the lateral width of the grating is a simple and effective way to adjust the coupling coefficient.(2)A laterally-coupled grating with low aspect ratio is studied.The low aspect ratio makes it much easier to fabricate than the traditional laterally-coupled grating.It is found that the accurate fabrication of the bottom structure of the grating is the key to obtain the accurate coupling coefficient.(3)The relationship between the coupling and loss characteristics of ridge waveguide high-order surface grating and its order,duty cycle and groove morphology is analyzed.The maximum value of coupling coefficient of high duty cycle grating will not decrease monotonously with the increase of order.The opening width and shape of the groove should be comprehensively taken into account in the optimization of grating characteristics.(4)A novel distributed feedback laser has been developed.The use of a wide ridge and an unstable cavity composed of curved gratings and a high reflectivity rear facet simultaneously enhances output power and mode selection abilitiy.Current injection region and asymmetric waveguide are designed to suppress high-order transverse modes.When the device injection current is 1A,the spectral width and side mode suppression ratio are 0.138 nm and 33 dB,respectively.Kinks-free power reaches915 mW.