Simplified coupled-wave equations for cylindrical waves in circular grating planar waveguides

A simplified form of the coupled-wave equations for cylindrical waves in circular grating distributed feedback (DFB) planar waveguides is presented. The coupling coefficients can be expressed as the product of a cylindrical-wave factor and the corresponding coupling coefficient between planar waveguide modes. Under the large radius approximation ( beta r>>1), which covers most practical cases, the interpolarization coupling between TE and TM cylindrical waves approaches zero. The coupled-wave equations can then be reduced to two independent families, one for TE- and the other for TM-cylindrical waves.<
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