Two Wave Coupling Using Phase Chirped Resonators

Technology #15486

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FIG. 1 shows a side view of a single resonator (here a dipole) driven by a plane wavefront.  FIG. 2 shows a set of chirped resonators design for right-angle wave coupling driven with the same source as shown in FIG. 1.FIGS. 3A and 3B shows side and top views, respectively, of a vertical coupling structure, spanning a length less than λ/2neff, that couples radiation out of a dielectric waveguide with a refractive index of neff.FIG. 4A shows a vertical coupling structure that includes a set of nano-rods electromagnetically coupled to a dielectric waveguide.  FIG. 4B includes plots of the amplitude R (top) and phase Δφ (bottom) of the wave emitted by the coupling structure shown in FIG. 4A versus nano-rod length for different numbers of nano-rods and an excitation wavelength of 1550 nm.FIG. 5A shows a vertical coupling structure with blue-shifted, chirped nano-rods electromagnetically coupled to a dielectric waveguide.  FIG. 5B is a plot of the free-space, far-field pattern emitted by the vertical coupling structure in FIG. 5A at a wavelength of λ=1550 nm.  FIG. 5C is a plot of the simulated vertical emission for the blue-shifted, chirped nano-rod structure of FIG. 5A; for an unshifted, chirped nano-rod structure; and for an unchirped nano-rod structure.FIG. 6 shows a top view of an array of periodically spaced sets of chirped resonators, each of which is less than λ/2neff long, that couple radiation out of a dielectric waveguide.FIG. 7A shows a diffractive optical element that collimates light emitted from a vertical coupler into an optical fiber.  FIG. 7B shows a negative diffractive optical element that expands a beam emitted from a vertical coupler and a positive diffractive optical element that couples the expanded beam into an optical fiber.FIG. 8A is a plot of the mode emitted by a short grating vertical coupler.  FIG. 8B is a plot of an optical fiber mode.  FIGS. 8C and 8D are plots of the phase profile of the wave emitted by a short grating vertical coupler before and after collimation, respectively, with a diffractive optical element.
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Inventors
Michael Watts
Research Laboratory of Electronics (RLE)
External Link (www.rle.mit.edu)
Ami Yaacobi
Research Laboratory of Electronics (RLE)
External Link (www.rle.mit.edu)
Brad Cordova
Research Laboratory of Electronics (RLE)
External Link (www.rle.mit.edu)
Jie Sun
Research Laboratory of Electronics (RLE)
External Link (www.rle.mit.edu)
Managed By
Jack Turner
MIT Technology Licensing Officer
Patent Protection

Methods and apparatus for vertical coupling from dielectric waveguides

US Patent 8,755,647

Applications

This invention is suited for applications in communications, radar, broadcasting and astronomy.

Problem Addressed

Conventional vertical couplers are designed to be large to maximize coupling efficiency. This size limits the coupler bandwidth and usefulness for other application, such as Optical Phased Arrays (OPAs). Therefore, there is a need for compact couplers that have high coupling efficiency.

Technology

This invention is a frequency-chirped nano-antenna that provides efficient sub-wavelength vertical emission from a dielectric waveguide. This nano-antenna consists of a set of plasmonic dipoles (resonators) on the opposite side of a Si3N4 waveguide from a ground plane. The resulting structure, which is less than half a wavelength long, emits a broadband beam that can be coupled into an optical fiber. Because this coupling structure is short, it is suitable for vertical coupling in Silicon On Insulator (SOI) based Optical Phased Arrays (OPAs).

Advantages

  • Better coupling efficiency than traditional vertical couplers
  • Reduced element size