High-intensity nano-aperture lasers for near-field optics

A high-intensity coherent light source with a sub-100nm near-field spot is desirable in many applications such as ultrahigh-density near-field optical data storage, high-resolution near-field imaging, nanolithography, analysis and manipulation of single-molecules etc. Vertical-cavity surface-emitting lasers (VCSEL), in which a nano-aperture is opened in the metal-coated emission facet, are ideal candidates for this purpose due to their low cost and easy 2D-array fabrication and characterization. Previous work utilizes conventional circular or square apertures, which suffer from extremely low power transmission efficiency when the aperture size becomes much smaller than the wavelength. Here we demonstrate record-high-intensity nano-aperture VCSELs with sub-100nm near-field spots using unconventional shapes of aperture, such as bowtie-shaped, C-shaped, H-shaped and I-shaped apertures.; The mechanism for high transmission through these unconventional apertures are explained via simulation and waveguide theory and attributed to the existence of a propagation mode TE10 and the induced surface plasmons over the ridges of these apertures. The high transmission through these apertures occurs only for a specific polarization direction, which requires the control of polarization in VCSELs. We developed a novel integrated method to control the polarization of VCSELs by opening nano-slits in the metal-coated emission facets of VCSELs.; These unconventional apertures show significantly higher power transmission efficiency than conventional square apertures of the same open area. In particular, we measured a net far-field power of 188muW from VCSELs using an 180nm bowtie aperture at a wavelength of 970nm, which is 16 times higher than that from a 130nm square aperture with the same area as the bowtie aperture. From simulation, the near-field intensity spot size 20nm away from the 180nm bowtie aperture is 64x66nm2, compared to the much larger spot size of 174x100nm2 from the 130nm square aperture. Based on the measured far-field power and simulated near-field spot size, the near-field intensity from the bowtie-aperture VCSEL is estimated to be as record-high as 47mW/mum2. This intensity should be high enough to realize near-field optical recording. And the small spot size from the bowtie aperture VCSEL can lead to storage densities up to 150 Gbits/in2, which is 100 times higher than that in DVD.; In addition to VCSELs, a C-shaped aperture has also been applied to edge emitting lasers. Resonant transmission through the C-aperture on edge emitting lasers was observed by scaling the aperture dimensions for a fixed lasing wavelength. The C-aperture shows twenty times higher power transmission efficiency than a square aperture of the same area. Although not explored in this thesis, the other unconventional apertures such as bowtie, H and I-shaped apertures can also be applied onto edge emitting lasers to obtain high-intensity nano-aperture lasers.