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Near field scanning optical microscope having a tapered waveguide

  • US 5,272,330 A
  • Filed: 08/04/1992
  • Issued: 12/21/1993
  • Est. Priority Date: 11/19/1990
  • Status: Expired due to Term
First Claim
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1. An optical system, comprising:

  • a probe, at least a portion of which is optically transmissive at least at a given wavelength, the probe having a longitudinal axis and a distal end;

    an optical aperture defined in the distal end, the aperture having at least one dimension smaller than the given wavelength;

    means for optically coupling a light source to the probe such that at least some electromagnetic radiation emitted by the source, at least at the given wavelength, enters or exits the probe through the aperture; and

    means for displacing the probe relative to an object,CHARACTERIZED IN THATa) the probe comprises a portion of an optical waveguide having a core and a cladding, the cladding having an outer surface, there being associated with the waveguide at least one guided dielectric mode for radiation of the given wavelength;

    b) the waveguide has a taper region that is adiabatically tapered, at least a portion of the taper region being capable of guiding radiation of at least the given wavelength, the taper region having a taper length and a taper angle;

    c) the taper region terminates in a substantially flat end face oriented in a plane substantially perpendicular to the longitudinal axis, the aperture being defined in or adjacent the end face;

    d) the cladding outer surface in the taper region is substantially smooth;

    e) at least a portion of the waveguide in the taper region is coated with an opaque material which has a relatively small penetration depth for electromagnetic radiation of the given wavelength, defining a metallic waveguide portion capable of guiding a metallic mode of radiation of the given wavelength; and

    f) the taper angle and taper length are adapted such that radiation propagating in the taper region is substantially interconverted between the dielectric and metallic modes.

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