Abstract

Narrowband (<10Å) optical multiplexer/demultiplexers are important components for densely spaced wavelength division multiplexed systems. Waveguide grating reflectors provide an excellent basis for such devices.¹,² This contradirectional interaction provides narrowband response even for relatively short interaction lengths (< 1 mm). However, the wavelength dependent Bragg reflection within a waveguide is, by itself, not sufficient to act as a multiplexer/demultiplexer component. Spatial, not just directional, separation, of the filtered light is also required. Two techniques to efficiently provide such spatial separation in grating-based devices have been suggested. One approach, which employs a grating to achieve phase matched contradirectional coupling between mismatched waveguides has been achieved, with relatively low efficiency, in fiber couplers³ and with vertical couplers based on ARROW waveguides.⁴ Another possibility, well-known in the microwave domain, combines the bandpass reflectors on both output arms of a broadband 3 dB splitter.⁵,⁶ Here we report the first demonstration of this optical waveguide grating-folded coupler to achieve narrowband, spatially isolated wavelength demultiplexing. This approach has the advantage of not placing severe demands upon either the waveguides or grating.

© 1988 Optical Society of America