Polarization Characteristics Of High-power Vertical-Cavity Surface-Emitting Lasers

At present, most laser sources involved in laser display research are fromall-solid lasers which have been pumped by high-power edge-emittingsemiconductor lasers array, and then red, green and blue tricolor light sources aremade through transforming the frequency. However, when comparing with theedge-emitting semiconductor lasers array, high-power Vertical-CavitySurface-Emitting Lasers (VCSEL) have many advantages, such as smaller volume,better beam quality, higher efficiency and so on. Especially based on the structure ofVCSEL, the output of tricolor lights (red, green, and blue) can be achieved throughefficiently laser frequency doubling inside the external cavity formed by the outcavity output mirror. As the light source, VCSEL has smaller volume, lower cost,and high integration which can make itself very competitive light source technologyin the future laser display area. When frequency doubling is put up to realize blueand green light output, the efficiency of frequency doubling can be highly affectedby the polarization characteristics of the basic frequency light, so the crucial problemthat must be solved is controlling the polarization of the output light in VCSEL.Encircling the research on the polarization characteristics of large-aperture VCSEL,several aspect works expanded by this thesis are as follows:As first, the actualized blue prints for polarization control of VCSEL have beeninvestigated and researched at home and abroad. According to the actual situation of our laboratory, the proper actualized blue prints of polarization control have beenproposed for large-aperture devices, which are introducing rectangular post structurein bottom-emitting and top-emitting VCSEL and shallow surface relief structure intop-emitting VCSEL.Secondly, from the theory point, the transverse mode behaviors and polarizationmodes of circular-shaped VCSEL have been analyzed; the polarization power andlasing spectrum have been calculated in bottom-emitting and top-emittingrectangular-shaped large-aperture VCSEL; the output performances have beensimulated in rectangular-shaped VCSEL; and then a few output parameters havebeen theoretically analyzed and simulated in VCSEL with shallow surface reliefstructure, including the reflectivity of Distributed Bragg Reflector (DBR), thethreshold gain, threshold current and output power.Furthermore, the key technologies have been investigated for fabricatingVCSEL devices with polarization structures, such as material epitaxial grown,cleanout, photolithograph, wet eroding, wet oxidation and metal ohm contactedelectrodes. The process flows have been properly arranged for fabricatingbottom-emitting and top-emitting VCSEL with large-aperture rectangular-shapedstructures and top-emitting VCSEL with shallow surface relief structure. Then thefabrications of device process for VCSEL with polarization structures have beencompleted.Finally, the output performances have been measured and analyzed forbottom-emitting and top-emitting VCSEL with rectangular post structure andVCSEL with shallow surface relief structure, and the lasing wavelength is980nmfor all involved devices. From the experimental results, it is found that inrectangular-shaped VCSEL both the horizontal polarization light aligned with thelonger side and vertical polarization light parallel to the shorter side demonstratecoexistence over the entire range of operation current; the horizontal polarizationlight always dominate over the vertical polarization light; the lasing spectrumblue-shift of the horizontal polarization light occur with respect to the vertical polarization light. These measured results basically accord with the theoreticallysimulated results of rectangular-shaped VCSEL. When the power polarization ofrectangular-shaped bottom-emitting VCSEL with550×300μm2output aperture arecompared with circular-shaped VCSEL with300μm diameter, it can be found thatusing the rectangular post structure can stabilize and control the polarizationdirection of VCSEL. High-power polarized laser have been achieved inrectangular-shaped VCSEL: the maximum output polarized laser is342mW inbottom-emitting VCSEL, and the highest polarization ratio is2.1:1; the maximumpolarized laser is31mW in top-emitting device, and the highest polarization ratio is3:1. The shallow surface relief structure has been etched on the P-side outputwindow in top-emitting rectangular-shaped VCSEL. The total output power ofVCSEL attains360mW in the wafer testing, the threshold current of VCSEL havebeen increased at the same time, and the polarization selectivity ofrectangular-shaped VCSEL has been improved.The rectangular post structure and the shallow surface relief structure have beenutilized for investigating the polarization characteristics of large-aperture VCSEL.The polarization characteristics of large-aperture VCSEL have been simulated intheory, and high-power polarized lasers have been achieved. Therefore, the nicertheoretical and experimental groundwork haven been carried out for the polarizationcontrol investigation of array devices and frequency doubling inside laser cavity inthe future.