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Proceedings Paper

Sub-diffraction optical imaging by high-spatial-resolution photodetectors and Fourier signal processing
Author(s): Milad Hashemi; Michael Hegg; Babak A. Parviz; Lih Y. Lin
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Paper Abstract

With the advance of nano-lithography and nano-fabrication, individual sizes of electronic, photonic, and mechanical components, as well as their integration densities, have progressed steadily towards the sub-100 nm regime. Therefore, being able to image such feature sizes becomes imperative. Many conventional high-resolution imaging tools such as SEM, STM, AFM, and NSOM either require operation under high vacuum or slow scanning across the sample. A far-field optical imaging instrument would thus be highly desirable. Optical imaging, however, is subject to the diffraction limit, which limits the size of the smallest resolvable feature to be ~ λ/2, where λ is the wavelength of the imaging light. Recently, negative-index materials and super lens have been proposed to overcome this limit and achieve high-resolution optical imaging [1-4]. In this paper, we propose a different approach to achieve sub-diffraction optical imaging with far-field microscopy. The technology builds on a high-spatial resolution quantum-dot (QD) photodetector with high sensitivity that we have demonstrated [5]. The photodetector consists of several nanocrystal QDs between a pair of electrodes with 50-nm width spaced ~ 25 nm apart. An optically effective area of 13515 nm2 was determined by modeling the electric field distribution in-between and around the electrodes using FEMLab. High-sensitivity photodetection has been demonstrated by measuring the tunneling photocurrent through the QDs, with a detection limit of 62 pW of the input optical power. The proposed sub-diffraction optical imaging system consists of an array of such photodetectors. We performed theoretical simulations assuming a two slit source and then pixilated the far-field diffraction pattern to simulate the photodetector array. A Fourier transform of the detector signal is then performed to determine how much of the original aperture information remains. Using a wavelength of 500 nm and a screen distance of 10 cm, we found that, as expected, the quality of the resultant image generally degraded with larger pixilation size. With 50-nm one-dimensional spatial resolution at the detection plane, it appears that the original slit image with 100-nm width and 300-nm spacing can still be restored.

Paper Details

Date Published: 1 February 2008
PDF: 7 pages
Proc. SPIE 6900, Quantum Sensing and Nanophotonic Devices V, 690017 (1 February 2008); doi: 10.1117/12.762119
Show Author Affiliations
Milad Hashemi, Univ. of Washington (United States)
Michael Hegg, Univ. of Washington (United States)
Babak A. Parviz, Univ. of Washington (United States)
Lih Y. Lin, Univ. of Washington (United States)

Published in SPIE Proceedings Vol. 6900:
Quantum Sensing and Nanophotonic Devices V
Rengarajan Sudharsanan; Christopher Jelen, Editor(s)

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