Research On 1.3 ?m High Speed Photonic-crystal Surface-emitting Lasers And Topological Surface-emitting Lasers

With the rapid development of new-generation information technology such as smart cities,5G networks,artificial intelligence,cloud computing and big data centers,the data traffic of networks has shown an exponential growth trend in recent years,prompting the development of optical interconnection technology toward higher speed,higher capacity and lower power consumption.As a key core device in this field,high-speed surface-emitting lasers have important research value and broad application prospects.Vertical cavity surface emitting lasers(VCSELs)are still difficult to meet the application requirements due to the difficulty of epitaxial growth of long wavelength DBR and the large loss and series resistance.In contrast,photonic crystal surface emitting lasers(PCSELs)also feature flexible functionalities such as large area single-mode lasing,the arbitrary shaping of beam patterns and polarizations by the appropriate design of the air-hole patterns,and on-chip 2D beam steering and easy wavelength expansion,and are therefore more advantageous in achieving two low-loss transmission windows(1.31?m,1.55?m)in optical fibres.In recent years,inspired by topological phases and phase transitions in condensed matter,a new research field based on topological band theory,topological photonics,has emerged,in which topological cavity surface emitting lasers(TCSELs)with robustness not only have the advantage of high beam quality,but also can produce vortex beams carrying orbital angular momentum(OAM).OAM multiplexing can greatly increase the channel capacity of optical communication systems and is an important development direction for future communication technology.Based on the modulation of photonic states by photonic crystals,In this thesis designs a heterogeneous photonic crystal cavity structure based on the principle of photonic crystal microcavity and photonic crystal band-edge lasing,which provides a feasible solution for realizing high-speed PCSELs,and introduces the photonic crystal with topological properties into the surface-emitting laser with reasonable optimized design to achieve high-speed,high-power,low-threshold,narrow linewidth and improved edge-mode rejection ratio.The aim is to potentially replace the existing VCSELs.The main research contents and innovations of this thesis are as follows.1.The band-edge lasing principle and threshold gain of PCSELs are theoretically analysed,and the optical power equation of PCSELs is derived in conjunction with the rate equation of semiconductor lasers,and the edge states and topological phase transition mechanism in two-dimensional photonic topological insulators are analysed,which provides a theoretical basis for the development of high-speed PCSELs and TCSELs.2.A theoretical study of a high-speed double-lattice photonic crystal surface-emitting lasers(PCSELs)is carried out.To investigate the applicability of PCSELs for high-speed operation,we design PCSELs with enhanced in-plane optical feedback,the resonant cavity is an in-plane heterostructure composed of two photonic crystals with different photonic bandgaps and utilize reflection at the boundary of the two photonic crystals in addition to the optical feedback at the band-edge of each photonic crystal,To realize a strong in-plane confinement of the lasing mode,we increase the one-dimensional coupling coefficients between counter-propagating waves by adjusting the distance between the two air holes of the double-lattice photonic crystal.By using three-dimensional Finite-Difference Time-Domain method(3D-FDTD),we confirm that the proposed hetero-PCSELs can achieve 1.3?m single-mode lasing operation inside a small square region and possibly realize a 3-d B modulation bandwidth larger than 30 GHz.3.A theoretical study of high-speed PCSELs based on Dirac point was carried out.PCSELs with enhanced in-plane feedback at the Dirac point are designed by tuning the photonic crystal parameters to obtain double Dirac cone dispersion,and since the density of states can be reduced to zero at the Dirac point,and the spontaneous radiation coupling coefficient?is inversely proportional to the density of states,the modulation rate of PCSELs can be effectively increased by using the Dirac point as a band-edge lasing,which is confirmed by 3D-FDTD with quadrupole mode lasing,which may have potential applications in less-mode based Space Division Multiplexing Systems.4.A theoretical study of a high-speed topological bulk surface emitting lasers based on the energy band reversal optical field confinement effect is carried out.The topological resonant cavity is composed of the topological photonic crystal(R₂=1.05R₀)completely spliced with the trivial photonic crystal(R₁=0.94R₀)at the periphery of its comparable band gap,and the reflection and confinement effects of the optical field are generated at the boundary of the splice.The 3D-FDTD demonstrates that it can achieve single-mode lasing with a low divergence angle of1.3?m in a small ortho-hexagonal region.In addition,this topological bulk surface-emitting laser is more favorable to realize single-mode surface emission because the reflection caused the band inversion occurs only in a small range of wave vectors around the center of the Brillouin zone,thus limiting the number of modes that can obtain effective feedback,and the mode selection mechanism is completely different from that of band-edge modes PCSELs,which will be more advantageous for the application in high-speed optics communications.5.A theoretical study of high-speed Dirac vortex cavity surface-emitting lasers was carried out.By applying the generalized Kekulémodulation and shrinkage operation to the normal honeycomb photonic crystal supercell,and then splicing them completely to obtain a heterogeneous Dirac vortex cavity(with a single robust mid-gap mode),the size of the sublattices in the cavity are appropriately tuned so that the mid-gap mode converges to the Dirac-point frequency and is in the Photonic Band Gap of the peripheral photonic crystal,in order to achieve enhanced in-plane optical feedback of the mid-gap mode,thus this is conducive to the realization of high-speed modulation.The results show that the mid-gap mode of the heterogeneous Dirac vortex cavity can be used as the band edge lasing to achieve 1.3?m single-mode vector beam output in a small region,which offers the possibility of developing new high-speed topological PCSELs with excellent performance.