Backward Second Harmonic Generation in Silicon Waveguide

The first report on backward second harmonic generation (SHG) in silicon waveguides is presented in this paper. Second-order nonlinearlty,
$\chi^{(2)}$
, in silicon is realized by using large
$\chi^{(3)}$
of silicon and large DC electric field obtained in an embedded reverse-biased pin diode via four-wave mixing, an effect which is known as electric filed induced SHG. The considered pin diode has periodic structure along the waveguide to achieve quasi-phase matching technique. An efficiency up to
$\pmb{P_{2\omega}/P_{\omega}=40}$
% is predicted which is 20-fold of all previously reported values, based on the best of our knowledge. Besides, the generated power of the second harmonic frequency can be controlled by applying voltage and even be more efficient with upper limit of ~53%.