PhD oral defense (Zhilong Rao): High-intensity nano-aperture laser (12:15PM, June 11th)
zlrao at stanford.edu
Mon Jun 4 15:54:20 PDT 2007
Ph.D. Oral Examination
High-intensity Nano-aperture Laser for Near-field Optics
Department of Physics
Advisor: Prof. James S. Harris
Date: June 11th (Monday), 2007
Time: 12:15 PM (refreshments at 12:00)
Location: Center for Integrated Systems Extension (CIS-X), Auditorium
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, 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 demonstrated 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 achieve a record-high intensity of 47mW/mm2 with a near-field spot size of 64*66nm2 from VCSELs using an 180nm bowtie aperture at a wavelength of 970nm. This intensity is 60 times higher than that from VCSELs using a 130nm square aperture which has the same area as the bowtie aperture but produces an even larger near-field spot of 174*100nm2. For the first time, this intensity is 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.
With the high-intensity and small near-field spot size, nano-aperture VCSELs using these unconventional apertures are very promising means to realize applications such as ultrahigh-density near-field optical data storage, ultrahigh-resolution near-field imaging, nanolithography, analysis and manipulation of single-molecules etc.
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