An optical device including an optical bench and an optical chip, the optical bench having multiple optical waveguides formed on its first side and the optical chip has multiple optical waveguides formed on its first side. The optical chip is flip-chip bonded onto the optical bench with its first side facing the first side of the optical bench. The distance between adjacent waveguides on the optical bench are designed to be slightly different from the distance between adjacent waveguides on the optical chip, where the latter usually is a pre-designed value under certain conventions. The difference amount is properly designed such that under reasonable misalignment between the optical chip and the optical bench in the in-plane direction perpendicular to waveguide propagation one can always find that one of the multiple waveguides is aligned sufficiently well with the corresponding waveguide on the optical chip.