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Shadow Optics System

IP.com Disclosure Number: IPCOM000079321D
Original Publication Date: 1973-Jun-01
Included in the Prior Art Database: 2005-Feb-26
Document File: 2 page(s) / 13K

Publishing Venue

IBM

Related People

Fan, GJ: AUTHOR [+2]

Abstract

The resolution of an optical system is one of the fundamental limits of an optical storage system. A lens that covers a large field with a good resolution is expensive, hence there is stringent practical limits on the numerical aperture (N.A.) for a practical optical system. In this publication, a shadow optical system is described which circumvents the above optics problem. The described system provides quantitative design parameters and clearly demonstrates the ability of shadow optics to achieve superresolution.

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Shadow Optics System

The resolution of an optical system is one of the fundamental limits of an optical storage system. A lens that covers a large field with a good resolution is expensive, hence there is stringent practical limits on the numerical aperture (N.A.) for a practical optical system. In this publication, a shadow optical system is described which circumvents the above optics problem. The described system provides quantitative design parameters and clearly demonstrates the ability of shadow optics to achieve superresolution.

To illustrate the advantages of the shadow optics, some computed data are tabulated:
W(lambda) z(lambda) Intensity Half-power 1 over I dIover Width/(lambda)/ dx x = HPW/2 0.75 0.0 2.57 0.41 7.19 0.75 0.1 2.36 0.40 7.03 0.75 0.2 2.01 0.44 6.27 0.75 0.3 1.68 0.50 4.93 0.75 0.4 1.41 0.58 4.53 0.75 0.5 1.20 0.67 3.78 1.3 0.0 1.41 1.17 12.5 1.3 0.1 2.09 0.6 2.39 1.3 0.2 2.49 0.48 5.55 1.3 0.3 2.637 0.468 6.00 1.3 0.35 2.639 0.474 6.00 1.3 0.4 2.61 0.48 5.92 1.3 0.5 2.55 0.50 5.81 1.3 0.6 2.32 0.55 5.14 2.35 0.0 1.42 0.77 -1.54 2.35 0.5 0.51 1.61 5.14 2.35 1.0 1.79 1.63 1.67 2.35 1.2 2.07 0.75 2.72 2.35 1.3 2.15 0.74 3.08 2.35 1.4 2.21 0.74 3.28 2.35 1.5 2.237 0.756 3.42 2.35 1.55 2.244 0.764 3.44 2.35 1.60 2.247 0.772 3.46 2.35 1.70 2.242 0.792 3.47 2.35 1.80 2.225 0.816 3.26 2.35 1.90 2.20 0.84 3.26 2.35 2.0 2.17 0.87 3.22 where W = Slit width z = Distance from the slit

Intensity = Amplitude square of the transverse electric field

field referring to the unit-intensity of a

plane-wave, normally-incident, beam.

Half-Power Width = The distance between the points which

intensity are half of the peak

intensity at the same z.

1/I dI/dx x = HPW/2 is a measure of the slope of the

diffraction curves at the half-power

1

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point to indicate whether a good

definition of the image can be obtained

with reasonable tolerance in exposure

accuracy. Though a critical value has

to be determined for each recording

material, it is safe to assume good

image definition when the value is

above 2.

From the table, it is clear that a 0.4 lambda image can be obtained with a
0.75 lambda slit at 0.1 lambda distance, or a 0.44 lambda image at 0.2 lambda distance. A more practical case would be a 1.3 lambda slit which gives higher intensity, longer focal point, and larger depth-of-focus with slight sacrifice in resolution, i.e., a 0.48 lambda image can be obtained at 0.2 to 0.4 lambda from the slit with a peak intensity of 2.64. In all these cases, the spot size is smaller tha...