Lightwave Engineering

8	Basic Optical Waveguide Circuit

8.1  COUPLING BY CASCADE CONNECTION OF OPTICAL WAVEGUIDES

8.1.1  GENERAL FORMULA FOR COUPLING EFFICIENCY

When a beam with an arbitrary electromagnetic field distribution is incident on an optical waveguide, the optical power is expanded into each eigenmode as shown in Figure 5.7 and the propagation starts. Then, the coupling coefficient for each mode is given by Equations (5.62a) and b. Using the same approach when two optical waveguides are connected, the electromagnetic field of each of the outgoing modes of the waveguide at the exit side may be expanded to each of the eigenmodes of the waveguide at the incident side. Then, the optical power coupled to the radiation mode will be the coupling loss.

In the ...