Spot-Size converter

Schematic of the spot-size converter (left) and expanded field at the input of the PIC (right).


The spot-size converter (SSC) couples light from a source (free-space or fiberized) to a photonic integrated circuit (PIC) which lies in the same plane of the source (horizontal coupling). This configuration is generally called end-fire coupling or butt-coupling.

The working principle consists in mode-matching between the source output and the SSC input to maximize the coupling efficiency. In the configurations proposed, the spot-size converter is based on a slab waveguide (WG) which transitions adiabatically to a fully etched single mode WG. For deployment in applications requiring large bandwidth, low insertion loss or the need of coupling directly to the laser output.


  • Broadband
  • Low insertion loss
  • Compatible with free-space coupled light sources with modal area ~ 8 µm2 (4.7 x 1.7 µm2) near 3.4 µm

On going

  • Improving insertion loss performance