Broadband Polarization-Independent Directional Coupler Using Asymmetric-Waveguides

A high-performance broadband polarization-independent directional coupler is designed by using asymmetric-waveguides configuration on a silicon-on-insulator platform. Through the design of cascaded directional couplers, the coupling characteristics of the light with the orthogonally polarized transverse electric (TE) and transverse magnetic (TM) can be manipulated, so that the coupling strength could be equivalent between TE and TM polarizations within an ultra-broadband. Couplers with 50 splitting ratio are designed and simulated for operating in the wavelength range from 1450nm to 1650nm for both polarizations. Within the 100nm wavelength range from 1500nm to 1600nm, the deviations of splitting ratio for TE polarization and TM polarization are $\pm$3.3 and $\pm$6.2, respectively. And within the 200nm wavelength range from 1450nm to 1650nm, the deviations for TE polarization and TM polarization are $\pm$9.0 and $\pm$7.8, respectively. The footprint of this polarization-independent directional coupler is only 21$\mu$m × 1.6$\mu$m.