Compact integrated optical directional coupler with large cross section silicon waveguides

Compact integrated optical directional couplers with symmetrically- and asymmetrically etched S-bend waveguides on SOI platform have been designed, fabricated and characterized. We have found that the directional couplers with asymmetrically etched waveguide structures can increase the device compactness to about 4 to 5 times that of the conventional symmetrically etched bend waveguide structures without compromising much on the optical loss budgets. The over all waveguide loss and loss per S-bend have been measured to be ~ 0.5 dB/cm and ~ 1 dB, respectively. The directional couplers are found to be polarization dependent (up to ~ 2 dB) and nearly wavelength independent (1510 nm < λ < 1600 nm).