356
E. Khan and E. Narimanov
intensity. In the hyperbolic medium, light from the point sources propagates in highly
directional beams. When they emerge from the outer boundary of device, they are
now separated by the distance that is substantially above the standard diffraction
limit, thereby allowing for subsequent processing by conventional optics, in full
agreement with (14.12).
14.5.2 Hyperlens: The Experimental Demonstration
The actual fabrication of the hyperlens can take full advantage of the methods originally developed in the context of planar hyperbolic metamaterials, e.g., using a
hollow core (half-)cylinder that consists of alternating sectors or concentric layers
of metal and dielectric. This straightforward design allowed the first experimental
demonstration of the hyperlens [28] within a single year from the original theoretical
proposal of [26, 27].
Over the next 10 years that followed [26, 27], applications of the hyperlens were
extended to a broad range of frequencies—from MHz [49] and GHz [50] all the
way to visible [47, 51] and UV light, [28] and even to ultrasound imaging [46]—see
Fig. 14.9. The original hyperlens design [26, 27] was adapted from the cylinder to
spherical geometry, [45] which allowed for subwavelength imaging in both directions
of the object plane. Furthermore, hyperlens arrays (see Fig. 14.10) were shown to
offer a practical approach to dramatically extend the field of view of these imaging
systems [52].
More recently, the concept of the hyperlens operating in “reverse” (i.e., in the
demagnification regime) was applied to optical lithography, [48] offering the fabrication of subwavelength patterns with a diffraction-limited optical mask.
14.5.3 Hyperlens: The Limitations
While offering a unique capability of label-free optical imaging with the magnified
image formation in the far field, the hyperlens suffers from three major drawbacks
that severely limit its application to biological imaging.
First, to take advantage of the full resolving power of the hyperlens, the object
must be placed in the near-field zone of its “inner” interface. While one can still image
the target at a further distance from the hyperlens, with its increase the corresponding
resolution rapidly deteriorates to the value typical for a diffraction-limited system.
Second, substantial material losses in the hyperbolic medium lead to a noticeable
reduction of the signal intensity, with the resulting loss of the signal-to-noise ratio.
While not a serious issue for nonbiological structures (such as semiconductor circuits)
with their large index contrast and high tolerance for large incident intensity, this
represents a major challenge for imaging non-labeled biological structures that can
E. Khan and E. Narimanov
intensity. In the hyperbolic medium, light from the point sources propagates in highly
directional beams. When they emerge from the outer boundary of device, they are
now separated by the distance that is substantially above the standard diffraction
limit, thereby allowing for subsequent processing by conventional optics, in full
agreement with (14.12).
14.5.2 Hyperlens: The Experimental Demonstration
The actual fabrication of the hyperlens can take full advantage of the methods originally developed in the context of planar hyperbolic metamaterials, e.g., using a
hollow core (half-)cylinder that consists of alternating sectors or concentric layers
of metal and dielectric. This straightforward design allowed the first experimental
demonstration of the hyperlens [28] within a single year from the original theoretical
proposal of [26, 27].
Over the next 10 years that followed [26, 27], applications of the hyperlens were
extended to a broad range of frequencies—from MHz [49] and GHz [50] all the
way to visible [47, 51] and UV light, [28] and even to ultrasound imaging [46]—see
Fig. 14.9. The original hyperlens design [26, 27] was adapted from the cylinder to
spherical geometry, [45] which allowed for subwavelength imaging in both directions
of the object plane. Furthermore, hyperlens arrays (see Fig. 14.10) were shown to
offer a practical approach to dramatically extend the field of view of these imaging
systems [52].
More recently, the concept of the hyperlens operating in “reverse” (i.e., in the
demagnification regime) was applied to optical lithography, [48] offering the fabrication of subwavelength patterns with a diffraction-limited optical mask.
14.5.3 Hyperlens: The Limitations
While offering a unique capability of label-free optical imaging with the magnified
image formation in the far field, the hyperlens suffers from three major drawbacks
that severely limit its application to biological imaging.
First, to take advantage of the full resolving power of the hyperlens, the object
must be placed in the near-field zone of its “inner” interface. While one can still image
the target at a further distance from the hyperlens, with its increase the corresponding
resolution rapidly deteriorates to the value typical for a diffraction-limited system.
Second, substantial material losses in the hyperbolic medium lead to a noticeable
reduction of the signal intensity, with the resulting loss of the signal-to-noise ratio.
While not a serious issue for nonbiological structures (such as semiconductor circuits)
with their large index contrast and high tolerance for large incident intensity, this
represents a major challenge for imaging non-labeled biological structures that can