Study Of Single-Mode And Polarization-stable Vertical-Cavity Surface-Emitting Laters

Vertical-Cavity Surface-Emitting Laser (VCSEL) has been widely used inshort-distance parallel fiber-optic interconnects due to its attractive properties such assurface emission, low cost, a circular and low divergent output beam, high speedmodulation. New applications required high beam qualities are continuously arising,such as spectroscopy, gas sensing and atomic clock. Many of these applicationsrequire stable polarization and single mode output. However, traditional VCSEL withcylindrical symmetry have instable polarization. VCSEL grown on (100)-orientedGaAs substrates tend to polarized along the [011] and [01-1] crystal axis. Polarizationof VCSEL will change with the increasing current and heat. Meanwhile, VCSEL isalways multimode operation due to the large transverse dimension. The mode andpolarization issue decrease the degree of coherence, which cannot be tolerated inapplications need high beam quality.The aim of this paper is to achieve single-mode and polarization-stablesimultaneously. To carry out further research about mode and polarization propertiesof VCSEL, a spatiotemporal VCSEL model based on rate equation is build to analysisdynamic transverse mode competition. Also, a theoretical explanation for thepolarization-controlled effect of noncircular aperture is present. And then we presentfor the first time a VCSEL with diamond shaped oxide aperture, which can obtainsingle-mode and polarization-stable operating at drive current range with OPSR over11dB. The main work can be summarized as following:1. According to VCSEL effective index model and wave guide theory, modeintensity distribution and critical size of each transverse mode is calculated.Dynamic transverse mode competition is calculated by the VCSEL model basedon rate equation. The theoretical calculation about noncircular aperture indicatedthat VCSEL with larger axial ratio of the asymmetric oxide aperture will showbetter polarization control.2. Anisotropic rate wet etching and wet nitrogen oxidation processes is concluded.We proposal a small size diamond shaped oxide aperture structure, which can befabricated by combining the traditional wet etching and wet nitrogen oxidationprocesses. High order mode will be cut off and polarization will be controlled dueto the anisotropic scattering loss.3. Single-mode and polarization-stable980nm VCSELs with3μm diamond-shapedoxide aperture, which was obtained by using the traditional wet etching and wetnitrogen oxidation processes, were fabricated with the threshold current of0.15mA and maximum optical output power of0.45mW under the continuous-wave current injection. The difference of scattering loss of twopolarized light was induced by diamond-shaped oxide aperture, which stabilizedthe polarization state of output beam. The OPSR was over11dB at thetemperature range from15℃to55℃. Measurement of VCSELs with differentoxide aperture shows that the device with larger axial ratio of the asymmetricoxide aperture has higher OPSR, which agree well with the theoretical analysis.