Optical Directional Couplers
The optical directional coupler, analogous to the microwave element1 of the same name, consists of parallel channel optical waveguides sufficiently closely spaced that energy is transferred from one to another. For this coupling to take place cumulatively over a substantial length, the light must propagate with the same phase velocity in each channel. The fraction of the power coupled per unit length is determined by the overlap of the modes in the separate channels. Thus, it depends on the separation of the guides, the mode penetration into the substrate, and the interaction length. Figure 1 is an example of a multichannel directional coupler. It shows a diagram of a large number of coupled waveguides (produced by proton implantation) and typical intensity profiles of the guided light. The incident light is focused into a single channel at z = 0, but is coupled into the adjacent guides as it propagates.
KeywordsCoupling Coefficient Directional Coupler Mode Profile Planar Guide Couple Mode Equation
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