  A novel design of large bandwidth, fabrication tolerant, CMOS-compatible
compact tapers (15 um) have been proposed and experimentally demonstrated in
silicon-on-insulator. The proposed taper along with linear grating couplers for
spot-size conversion exhibits no degradation in the coupling efficiency
compared to a standard focusing grating in 1550 nm band. A single taper design
has a broadband operation over 600 nm that can be used in O, C and L-band. The
proposed compact taper is highly tolerant to fabrication variations; 80 nm
change in the taper width and 200 nm in end waveguide width varies the taper
transmission by <0.4 dB. The footprint of the device i.e. taper along with the
linear gratings is ~ 250 {\mu}m2; this is 20X smaller than the adiabatic taper
and 2X smaller than the focusing grating coupler.
