COUPLED-MODE ANALYSIS OF HIGHLY ASYMMETRIC DIRECTIONAL-COUPLERS WITH PERIODIC PERTURBATION

This paper presents an in-depth analysis of highly asymmetric grating assisted directional couplers, The directional coupler consists of a p olymer waveguide with dimensions and refractive indices closely matchi ng a single-mode fiber fabricated atop a Ga0.6Al0.4As/GaAs/Ga0.4Al0.6A s waveguide, The structure is investigated analytically by means of a new orthogonal coupled-mode theory formulated in terms of the Lorentz reciprocity theorem, For the first time, the analysis includes three d istinct loss mechanisms, namely, the leakage of power toward the semic onductor substrate, the power lost to radiation modes (mode mismatchin g), and the grating radiation loss.