Abstract
Optical frequency conversion in semiconductor nanophotonic devices usually imposes stringent requirements on fabrication accuracy and etch surface roughness. Here, we adopt the concept of bound-state-in-continuum (BIC) for waveguide frequency converter design, which obviates the limitations in nonlinear material nano-fabrication and requires to pattern only a low-refractive-index strip on the nonlinear slab. Taking gallium phosphide (GaP) as an example, we study second-harmonic generation using horizontally polarized pump light at 1.55 pm phase matc hing to vertically polarized BIC modes. A theoretical normalized frequency conversion efficiency of 1.1 x 10(4) % W(-1)cm(-2) is obtained using the fundamental BIC mode, which is comparable to that of conventional GaP waveguides. (C) 2021 Optical Society of America