Improvement of extinction ratios of polarization independent very short vertical directional couplers

초록

We show that the extinction ratio is improved using slight asymmetry in two core refractive indices of polarization independent very short vertical directional couplers with the double-sided deep-ridge waveguide structure. The optimum asymmetry with the maximum extinction ratio increases as the thicknesses of the inner cladding layer and the two core layers decrease. Also, the device length and the tolerance of the device length with the extinction ratio more than 30 dB decrease as the thicknesses of the inner cladding layer and the two core layers decrease.