Ultracompact Lateral Beam Expander for Mode Size Conversion

Efficiency comparison of segmented beam expander (BE) comparted to beam expanders with rapidly varying tapers (20:1 waveguide width ratio, 1550 nm wavelength)


Invention Summary:

In silicon photonic integrated circuits, the mode-size and refractive index mismatch between a cleaved standard optical fiber and the silicon photonic waveguide leads to high coupling loss. Mode size converters with a compact footprint are needed to avoid this coupling loss. It is difficult to achieve a short length because of rapid tapers lead to high scattering and coupling.

This invention addresses this challenge using a beam expander with composite structure with adiabatic and non-adiabatic segments. This structure reduces wavefront deformation and thereby increase coupling at the end of the waveguide. The beam expander corrects the wavefront and minimizes coupling to higher order modes within a distance on the order of a few wavelengths. This invention enables compact integration of optical fibers and photonic waveguides.

Marketing Applications:

  • Integrated photonic circuits
  • High-speed on/off-chip optical interconnects
  • Wavelength multiplexing/de-multiplexing
  • Optical phased array
  • Waveguide intersections
  • Grating couplers
  • Spatial light modulator
  • Interface for Si/III-V hybrid high-power lasers


  • Ultra-Short taper length (6λ)
  • Low coupling loss (-0.85 dB)
  • High width ratio (20:1)
  • Single-step fabrication process (patterning and etching)

Intellectual Property & Development Status:

Patent pending. Available for licensing and/or research collaboration.

Rutgers ID: 2016-177
Physical Sciences
Kholud Dardir
Wei Jiang
Siamak Abbaslou
Robert Gatdula