Bandpass spectra of evanescent couplers with long period gratings

The authors propose a novel optical bandpass filter with strong sidelobe ex tinction but without the reflected light associated with Bragg grating filt ers. Long period index gratings written in the cores of an evanescent singl emode coupler suppress cross-coupling at the desired transmission wavelengt h, while strong optical loss in the secondary core rejects out-of-band wave lengths. Transmission spectra are calculated using coupled mode theory.