| The vertical-cavity surface-emitting laser (VCSEL) has been proved to be alow-cost light source with attractive properties such as easy fabrication oftwo-dimensional arrays, high-efficiency, easy integration of two-dimensional array,uniformity and small migration rate of the wavelength of light emergent. Thesefeatures, together with its circular beam, easier for beam shaping and thecharacteristics of integration, have given it a wide range of applications in recentyears, for example, integrated circuit, optical coupling, laser pump, microfluidic chipand etc. However, due to the short cavity length of the vertical cavity surface emittingsemiconductor laser, the divergence angle of the emergent light is relatively large. Themicro-optical elements need to be fabricated for the beam shaping to reduce itsdivergence angle. The three-dimensional micro-optical element, in particularnon-spherical morphology cannot be achieved by the conventional fabricationmethods. To our surprise, the appearance of femtosecond laser direct writingtechnology solves the difficulty on the manufacture of three-dimensionalmicro-optical components.Femtosecond laser has three main characteristics:"thin, strong, fast"."fine" meansthat femtosecond laser could break through the diffraction limit of ultra-high precisionmicro-nano processing;"Strong" means magnitude and high peak power because ofits interval for femtosecond pulse;"Fast" means that femtosecond laser could doresearch into electron transfer of ultrafast spectroscopy referring to the duration of asingle pulse as order of femtosecond. Attributing to its micro-and nano-scale-highaccuracy breaking through the diffraction limit, the femtosecond laser direct writingtechnology provides the possibility for fabricating arbitrary complicated shape in thethree-dimensional space. The micro-optics element aspherical microlens has beenfabricated for the beam shaping of the VCSELs to reduce the divergence anglethrough femtosecond laser direct writing technology in our experiment. This paperintroduced the principle and application of femtosecond laser direct writing, andimplemented the fabrication of different sizes of aspherical microlenses, solved theprocessing error problem caused by using low numerical aperture lens processing tofabricate the large size microlens, and achieved in any opaque substrate of thefemtosecond laser direct writing. Besides, we had built two kinds of femtosecondlaser direct writing systems: upright and inversion processing systems.In order to get the better effort of beam shaping, this thesis adopted low numericalaperture lens fabricating large-size microlens integrated semiconductor laser separatedand directly integrated aspherical microlens on Vertical-Cavity Surface EmittingLaser Emitting Surface, respectively. In the process of separately integrated asphericalmicrolens, we made two different kinds of large-size microlenses with long and shortfocal lengths. Because of numerical aperture of the long focal length microlens iscloser to the numerical aperture of semiconductor laser beam, so the beam shapingresult of long focal length microlens is better than the result of the short focal length microlens. The beam shaping result of long focal length microlens is the divergenceAngle reduces from the original18.16。Reduced to2.6。, and the beam shaping result ofshort focal length microlens is the divergence Angle reduces from the original18.16。Reduced to5.25。.Considering the complex of separately integrated microlens, such as difficultdebugging equipment, the existence of refraction and diffraction on glass substrate,we put forward the aspherical microlens was directly integrated on Vertical-CavitySurface Emitting Laser Emitting Surface. This method combined the microlens withthe laser as a whole, and had some advantages, for example, easy integration,decreasing the complexity and difficulty of measure and eliminating the refractionand diffraction on glass substrate. In theory, we simulated the direct integration ofaspherical microlens on Vertical-Cavity Surface Emitting Laser Emitting Surface andthe result of the theoretical results proved that this method could effectively reducethe divergence Angle of VCSEL. The beam shaping result of direct integration ofaspherical microlens is from the original18.16。reduced to0.86。, the result is farbetter than the result of separately integrated aspherical microlens. |
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