  We propose a method for generating Fano resonance in a standalone silicon
nanobeam cavity which eliminates the inconvenience from the unexpected
side-coupled bus waveguide and unlocks new opportunities to develop
ultra-compact and ultra-fast electro-optical modulators.. Taking advantage from
a spatial-division multiplexing principle of operation between transverse
electric modes, a sharp resonant mode and an efficient flat background mode are
simultaneously generated in the same silicon channel for the realization of
efficient Fano resonances. Unambiguous asymmetric spectrum lineshapes are
thoroughly investigated using numerical and analytical methods and
experimentally demonstrated in the near infra-red around lambda=1.55{\mu}m,
presenting an extinction ratio of about 17dB for a delta lambda =56 pm
wavelength detuning for the 1st cavity mode (Q-factor Q=34000), and higher than
23 dB extinction ratio for a delta lambda=366 pm detuning for the 2nd cavity
mode (Q=5600). These extinction ratios are 10~15 dB larger than their
Lorentzian counterparts exhibiting similar Q factors. Silicon Fano modulation
based on plasma dispersion effect is proposed, for which an energy consumption
as low as few fJ/bit is estimated. Fano cavity scheme addressed in this paper
presents a great potential for low power consumption silicon optical modulators
and provides anew insight to the advantages of Fano resonances for optical
modulation schemes.
