Analytical method for band structure calculation of photonic bandgap fibers with depressed index cladding rods

An approximate analytical approach for revealing bandgap information for photonic band gap fibers with depressed index cladding rods is presented. The method considers isolated rods in cladding, with three layers structure: higher index in the core, lower-index depressed layer and silica cladding. Good consistency is found between the results of the approximate analytical method and those from accurate numerical simulations.