A study of very small aperture lasers (VSAL) for near field optical recording

A practical approach for producing very small aperture lasers (VSAL) from low-cost, commercial index guided edge-emitting diode lasers was developed. Detailed fabrication procedures are provided and rationales behind the design choices were explained. For the trickiest issue in the fabrication processes, three solutions were provided to locate the active layer for aperturing. Between 100200 units of VSALs were successfully fabricated and used for a number of studies.; Focused Ion Beam (FIB) operating parameters for best nano-structure etching resolution are discussed. In practice, apertures as small as 30nm in size were achieved. Size dependent etching rate for nano-apertures was observed experimentally and re-deposition was hypothesized as the explanation.; A VSAL far-field power measurement method was established. It was used as a calibration tool for VSAL power throughput optimization. Using this system, three fabrication parameters were studied: the metal layer thickness, dielectric layer thickness and the aperture size. It was found that the ideal Al thickness is 50nm∼60nm and that the aperture power decays in proportion to the sixth power of aperture size when it is below 150nm. This is consistent with the near-field theory. Aperture shape and geometry were also investigated. The most important result was to apply the waveguide theory to the VSAL aperture. By using overlap integral approximation and a lossy waveguide model, the throughput of rectangular apertures with a linearly polarized incident field was simulated. By comparing experimental and simulation results, it was proved that near-field nano-apertures behave like waveguides in cutoff. High throughput geometries were fabricated and higher powers were obtained. A cutoff waveguide approach was also applied to obtain the minimum aperture size limit for recording and explain near-field scanning optical microscopy (NSOM) probe's low throughput.; On the device level, the threshold current changes during the fabrication processes were observed, explained and quantified. The tiny increase of threshold current due to aperturing could have great significance for phase change media readback or aperture near-field power estimation. The polarization property of the aperture emission was compared with that of the original laser. An improved polarization ratio of the aperture emission indicates polarization selective nature of nano-aperture, which further strengthens the waveguide argument. The angular distribution of the aperture power was measured. (Abstract shortened by UMI.)...